Replacing my crankshaft balancer
Race Director
Joined: Sep 2007
Posts: 16,557
Likes: 2,108
From: Peoria/Phoenix AZ
C6 of Year Finalist (performance mods) 2019
Wow. Lots of good conversation's been going on here. 
The tan dot is just a dot, but the green one is a weight. As noted, the SM mentions putting new weights in the same locations as the old. It doesn't say how/if you can get them out. It describes how to determine the weight size by measuring it, but again, unless you can get the old one out, you can't measure it. Most importantly, no parts catalog/diagram appears to have these weights. So I have no idea how to get new ones!
On the other hand, the TSB makes a good observation:
"31. Place the old and new balancers on the bench and orient them the same way (i.e. face up with a weight balance hole at 12 o'clock). Scribe/mark the new balancer in the same location as the old balancer. Do not transfer weight pins on manual transmission equipped vehicles. Most vehicles will be balanced without the use of any additional weight pins. Because some balancers may have spun on the crankshaft, transferring weight pins to the same position would produce a random imbalance. For vehicles that exhibit imbalance (very rare), contact Technical Assistance."
If the pulley is neutral balance, I'm not sure what value reproducing the same orientation gives if you don't reinstall the same weights.
Also, I have an M6.
The tan dot is just a dot, but the green one is a weight. As noted, the SM mentions putting new weights in the same locations as the old. It doesn't say how/if you can get them out. It describes how to determine the weight size by measuring it, but again, unless you can get the old one out, you can't measure it. Most importantly, no parts catalog/diagram appears to have these weights. So I have no idea how to get new ones!
On the other hand, the TSB makes a good observation:
"31. Place the old and new balancers on the bench and orient them the same way (i.e. face up with a weight balance hole at 12 o'clock). Scribe/mark the new balancer in the same location as the old balancer. Do not transfer weight pins on manual transmission equipped vehicles. Most vehicles will be balanced without the use of any additional weight pins. Because some balancers may have spun on the crankshaft, transferring weight pins to the same position would produce a random imbalance. For vehicles that exhibit imbalance (very rare), contact Technical Assistance."
If the pulley is neutral balance, I'm not sure what value reproducing the same orientation gives if you don't reinstall the same weights.
Also, I have an M6.
Safety Car
Joined: May 2011
Posts: 3,807
Likes: 508
From: Oshawa, Ontario
I had to chuckle when you said "I'm not seeing more questions here." in response to my "It seems we have more questions than answers." and then proceeded to post 4 more questions. 
It seems we both see confusion, but from a different perspective.
From a manufacturing standpoint and a further review, drilling balancing holes after the ring to hub assy does make sense. I envision all the rings are drilled with the 12 hole pattern and spaced in 30* intervals prior to assembly. Then after assembly, it's spun to determine the quantity and location of balancing holes needed. A shot of paint (beige on the old one and blue on the new) is put on at the balancing operation as a locating point for the fixture to start the drilling operation. That creates a zero/neutral balance condition. Then for the M6 cars, an extra weight can be added in one of the 12 original holes if necessary. I say one of the 12, because on the old one, that's where the weight is located and on the new one it appears the secondary holes are slightly smaller than the others, probably to avoid a tech from trying to stuff a weight in those.
The remaining question is similar to yours. "..why the GM process to mark the exact location of old HBs and transfer weights (variable, unit to unit) to new HBs on M6 only?"
Since the added weights come in 3 different sizes and would be installed in a location of +/- 15*, the deeper question would be "How does GM originally determine how much weight to add to which hole and how to orient that on the crankshaft at the initial assembly?" Maybe the paint dots play two roles.
I'm currently at a loss for the reason why a M6 balancer wants to be out of balance.
So here's another question for irok. Did you ever notice weights in the bad balancers you removed from A6 cars?
It seems we both see confusion, but from a different perspective.
From a manufacturing standpoint and a further review, drilling balancing holes after the ring to hub assy does make sense. I envision all the rings are drilled with the 12 hole pattern and spaced in 30* intervals prior to assembly. Then after assembly, it's spun to determine the quantity and location of balancing holes needed. A shot of paint (beige on the old one and blue on the new) is put on at the balancing operation as a locating point for the fixture to start the drilling operation. That creates a zero/neutral balance condition. Then for the M6 cars, an extra weight can be added in one of the 12 original holes if necessary. I say one of the 12, because on the old one, that's where the weight is located and on the new one it appears the secondary holes are slightly smaller than the others, probably to avoid a tech from trying to stuff a weight in those.
The remaining question is similar to yours. "..why the GM process to mark the exact location of old HBs and transfer weights (variable, unit to unit) to new HBs on M6 only?"
Since the added weights come in 3 different sizes and would be installed in a location of +/- 15*, the deeper question would be "How does GM originally determine how much weight to add to which hole and how to orient that on the crankshaft at the initial assembly?" Maybe the paint dots play two roles.
I'm currently at a loss for the reason why a M6 balancer wants to be out of balance.
So here's another question for irok. Did you ever notice weights in the bad balancers you removed from A6 cars?
Last edited by irok; Dec 9, 2016 at 04:52 PM.
Race Director
Joined: Sep 2007
Posts: 16,557
Likes: 2,108
From: Peoria/Phoenix AZ
C6 of Year Finalist (performance mods) 2019
So iroc, would I be correct in assuming you put on replacements with no weights on the A6 cars?
Safety Car
Joined: May 2011
Posts: 3,807
Likes: 508
From: Oshawa, Ontario
Maybe we have a bingo here. Anyone else think that if HB's with weights were inadvertently put on engines destined for A6 cars and that the imbalance condition was enough to cause the delamination and eventual failure?
So iroc, would I be correct in assuming you put on replacements with no weights on the A6 cars?
So iroc, would I be correct in assuming you put on replacements with no weights on the A6 cars?
Race Director
Joined: Sep 2007
Posts: 16,557
Likes: 2,108
From: Peoria/Phoenix AZ
C6 of Year Finalist (performance mods) 2019
Thanks. I'm always ready to learn more. Sometimes the age thing has problems retaining information, but I blame that on overstuffing the capacity.
Le Mans Master
Joined: May 2016
Posts: 7,180
Likes: 1,546
From: Florida
I had to chuckle when you said "I'm not seeing more questions here." in response to my "It seems we have more questions than answers." and then proceeded to post 4 more questions.
It seems we both see confusion, but from a different perspective.
From a manufacturing standpoint and a further review, drilling balancing holes after the ring to hub assy does make sense. I envision all the rings are drilled with the 12 hole pattern and spaced in 30* intervals prior to assembly. Then after assembly, it's spun to determine the quantity and location of balancing holes needed. A shot of paint (beige on the old one and blue on the new) is put on at the balancing operation as a locating point for the fixture to start the drilling operation. That creates a zero/neutral balance condition. Then for the M6 cars, an extra weight can be added in one of the 12 original holes if necessary. I say one of the 12, because on the old one, that's where the weight is located and on the new one it appears the secondary holes are slightly smaller than the others, probably to avoid a tech from trying to stuff a weight in those.
The remaining question is similar to yours. "..why the GM process to mark the exact location of old HBs and transfer weights (variable, unit to unit) to new HBs on M6 only?"
Since the added weights come in 3 different sizes and would be installed in a location of +/- 15*, the deeper question would be "How does GM originally determine how much weight to add to which hole and how to orient that on the crankshaft at the initial assembly?" Maybe the paint dots play two roles.
I'm currently at a loss for the reason why a M6 balancer wants to be out of balance.
So here's another question for irok. Did you ever notice weights in the bad balancers you removed from A6 cars?
It seems we both see confusion, but from a different perspective.
From a manufacturing standpoint and a further review, drilling balancing holes after the ring to hub assy does make sense. I envision all the rings are drilled with the 12 hole pattern and spaced in 30* intervals prior to assembly. Then after assembly, it's spun to determine the quantity and location of balancing holes needed. A shot of paint (beige on the old one and blue on the new) is put on at the balancing operation as a locating point for the fixture to start the drilling operation. That creates a zero/neutral balance condition. Then for the M6 cars, an extra weight can be added in one of the 12 original holes if necessary. I say one of the 12, because on the old one, that's where the weight is located and on the new one it appears the secondary holes are slightly smaller than the others, probably to avoid a tech from trying to stuff a weight in those.
The remaining question is similar to yours. "..why the GM process to mark the exact location of old HBs and transfer weights (variable, unit to unit) to new HBs on M6 only?"
Since the added weights come in 3 different sizes and would be installed in a location of +/- 15*, the deeper question would be "How does GM originally determine how much weight to add to which hole and how to orient that on the crankshaft at the initial assembly?" Maybe the paint dots play two roles.
I'm currently at a loss for the reason why a M6 balancer wants to be out of balance.
So here's another question for irok. Did you ever notice weights in the bad balancers you removed from A6 cars?
The A6 flex plate, BTW has none of the rotating mass the clutch assy has and I'm assuming, is insignificant in some process tolerance limits.
BTW, it takes a little thought to consider how a rotating mass might be balanced in a manufacturing process by removing weight. It's more than just arriving at the point of imbalance and removing material. Especially if, in a final assembly scheme, weight might need to be added back the achieve a final balance.
With that in mind, the only real way to manufacture such a part is to "remove" more material than necessary first. This can only be achieved by drilling evenly spaced holes in a pattern that covers 360* of the wheel. THEN, focus is put on the "heavy" end of the part. Here too, a predetermination is probably made based on a simple calculation of how much weight is removed by each hole, and the aggregate weight removal needed to achieve balance. This will "pre-determine" the # of holes drilled to achieve balance. An odd # of holes would start the first hole directly centered on the highest point of imbalance. Then at least two more holes, either side. An even # of holes would require the first TWO holes to be drilled either side of the highest imbalance point. THEN, based on some pre-determined values, a series of concentric holes both before/after the centerpoint, enough to be able to safely add weights back in to reach some manufacturing process upper/lower control limits...simple...easy peasy...
One final point - From a manufacturing cost prespective, when we look at the two parts in the OPs first post, every one of those holes in the unit on the left adds cost to the unit. I'd suggest they're not there for decoration.
Last edited by BlindSpot; Dec 9, 2016 at 07:52 PM.
Race Director
Joined: Sep 2007
Posts: 16,557
Likes: 2,108
From: Peoria/Phoenix AZ
C6 of Year Finalist (performance mods) 2019
Only one reason in my mind. It is the massive external multi-piece sub-assembly on the other end of the CS. Even if individual components, such as Flywheel, pressure plate and disc are individually balanced, a certain amount of imbalance will occur in final assembly. When I consider this, in production, after the FW, PP, CD are installed and before the HB, the only easy and cost effective way to achieve a final "assembled balance" is at the front, the HB.
The A6 flex plate, BTW has none of the rotating mass the clutch assy has and I'm assuming, is insignificant in some process tolerance limits.
BTW, it takes a little thought to consider how a rotating mass might be balanced in a manufacturing process by removing weight. It's more than just arriving at the point of imbalance and removing material. Especially if, in a final assembly scheme, weight might need to be added back the achieve a final balance.
With that in mind, the only real way to manufacture such a part is to "remove" more material than necessary first. This can only be achieved by drilling evenly spaced holes in a pattern that covers 360* of the wheel. THEN, focus is put on the "heavy" end of the part. Here too, a predetermination is probably made based on a simple calculation of how much weight is removed by each hole, and the aggregate weight removal needed to achieve balance. This will "pre-determine" the # of holes drilled to achieve balance. An odd # of holes would start the first hole directly centered on the highest point of imbalance. Then at least two more holes, either side. An even # of holes would require the first TWO holes to be drilled either side of the highest imbalance point. THEN, based on some pre-determined values, a series of concentric holes both before/after the centerpoint, enough to be able to safely add weights back in to reach some manufacturing process upper/lower control limits...simple...easy peasy...
One final point - From a manufacturing cost prespective, when we look at the two parts in the OPs first post, every one of those holes in the unit on the left adds cost to the unit. I'd suggest they're not there for decoration.
The A6 flex plate, BTW has none of the rotating mass the clutch assy has and I'm assuming, is insignificant in some process tolerance limits.
BTW, it takes a little thought to consider how a rotating mass might be balanced in a manufacturing process by removing weight. It's more than just arriving at the point of imbalance and removing material. Especially if, in a final assembly scheme, weight might need to be added back the achieve a final balance.
With that in mind, the only real way to manufacture such a part is to "remove" more material than necessary first. This can only be achieved by drilling evenly spaced holes in a pattern that covers 360* of the wheel. THEN, focus is put on the "heavy" end of the part. Here too, a predetermination is probably made based on a simple calculation of how much weight is removed by each hole, and the aggregate weight removal needed to achieve balance. This will "pre-determine" the # of holes drilled to achieve balance. An odd # of holes would start the first hole directly centered on the highest point of imbalance. Then at least two more holes, either side. An even # of holes would require the first TWO holes to be drilled either side of the highest imbalance point. THEN, based on some pre-determined values, a series of concentric holes both before/after the centerpoint, enough to be able to safely add weights back in to reach some manufacturing process upper/lower control limits...simple...easy peasy...
One final point - From a manufacturing cost prespective, when we look at the two parts in the OPs first post, every one of those holes in the unit on the left adds cost to the unit. I'd suggest they're not there for decoration.
, the one in my car that I've abused as much as you can with an A6, the one in the video in the other current HB thread, nor any other new HB on other websites I've visited, have I seen an added weight. Some of them had the balancing holes on the same diameter circle as the 12 main holes, while some had smaller or larger circles. Additionally, other than the 12 main holes that appeared to be larger, the holes didn't always follow a prescribed pattern or remain in a group.Since the SM only discusses weights to be added for M6 cars, it infers there are none in the replacement units on the parts room shelf.
Everything I've seen contradicts removing more weight than necessary and then adding some back to get a correct balance. Removing the correct amount initially only requires one operation. Drilling even one additional hole and adding a weight requires 3 extra operations and associated costs.
If I assume that the final weight is installed to balance the entire assembly at the time of an engine test run, then that would include the FW, CP, and PP. That theory would also provide the reason to require M6 cars to orient the HB to the crank and add a specific weight when a replacement was needed. However, that conflicts with irok's statements about finding weights in A6 HB's that theoretically never needed them, unless a worker missed the instruction to bypass engines with flex plates.
Maybe I'm making too much of something that doesn't affect me, but my lifetime of identifying and resolving problems still inhabits my mind.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Le Mans Master
Joined: May 2015
Posts: 5,187
Likes: 1,216
From: Las Vegas Nevada
10-15 years????
Safety Car
Joined: May 2011
Posts: 3,807
Likes: 508
From: Oshawa, Ontario
Le Mans Master
Joined: May 2016
Posts: 7,180
Likes: 1,546
From: Florida
While we're creating theories and don't have the luxury of seeing the manufacturing process, I want to throw out a tidbit for you to contemplate. Neither the new HB on the left, which came weightless , the one in my car that I've abused as much as you can with an A6, the one in the video in the other current HB thread, nor any other new HB on other websites I've visited, have I seen an added weight. Some of them had the balancing holes on the same diameter circle as the 12 main holes, while some had smaller or larger circles. Additionally, other than the 12 main holes that appeared to be larger, the holes didn't always follow a prescribed pattern or remain in a group.
Since the SM only discusses weights to be added for M6 cars, it infers there are none in the replacement units on the parts room shelf.
Everything I've seen contradicts removing more weight than necessary and then adding some back to get a correct balance. Removing the correct amount initially only requires one operation. Drilling even one additional hole and adding a weight requires 3 extra operations and associated costs.
If I assume that the final weight is installed to balance the entire assembly at the time of an engine test run, then that would include the FW, CP, and PP. That theory would also provide the reason to require M6 cars to orient the HB to the crank and add a specific weight when a replacement was needed. However, that conflicts with irok's statements about finding weights in A6 HB's that theoretically never needed them, unless a worker missed the instruction to bypass engines with flex plates.
Maybe I'm making too much of something that doesn't affect me, but my lifetime of identifying and resolving problems still inhabits my mind.
, the one in my car that I've abused as much as you can with an A6, the one in the video in the other current HB thread, nor any other new HB on other websites I've visited, have I seen an added weight. Some of them had the balancing holes on the same diameter circle as the 12 main holes, while some had smaller or larger circles. Additionally, other than the 12 main holes that appeared to be larger, the holes didn't always follow a prescribed pattern or remain in a group.Since the SM only discusses weights to be added for M6 cars, it infers there are none in the replacement units on the parts room shelf.
Everything I've seen contradicts removing more weight than necessary and then adding some back to get a correct balance. Removing the correct amount initially only requires one operation. Drilling even one additional hole and adding a weight requires 3 extra operations and associated costs.
If I assume that the final weight is installed to balance the entire assembly at the time of an engine test run, then that would include the FW, CP, and PP. That theory would also provide the reason to require M6 cars to orient the HB to the crank and add a specific weight when a replacement was needed. However, that conflicts with irok's statements about finding weights in A6 HB's that theoretically never needed them, unless a worker missed the instruction to bypass engines with flex plates.
Maybe I'm making too much of something that doesn't affect me, but my lifetime of identifying and resolving problems still inhabits my mind.
Hypothetical - if it took 3 holes at one end of the unit to achieve balance in production but we needed to provide the option of more holes, then we would drill additional holes opposite. That is why I think we see some appearance of a pattern of clocked holes whether it is or isn't an actual pattern.
No new production replacement part would come with weights installed. That would not make sense to just drill holes and fill them back with weights.
BTW, there is a plausible explanation, if we happened to see a replacement part on the shelf with a weight in it. If we made a production error and drilled one too many holes, we could fill it to save scrap. However, if THAT part were installed as a replacement in an M6 and and needed replacement, then that repair could be confused as a transferred weight.....
To the OP - hope you're OK with this and hope we're not too far afield from the original Qs. I know you said you're replaced already. Everything work out OK? Belts align, I'm sure?
Last edited by BlindSpot; Dec 10, 2016 at 08:19 AM.
Instructor
Joined: Jan 2001
Posts: 230
Likes: 10
From: Valencia,Ca,USA CA
A thought.... My engine has 93K on it ( wrecking yard in MI. ) ...
I decided NOT ( right now ) to replace the HB... I was more interested in the fire up & getting the car back in 1 piece. Well I do not have a wobble for now. BUT A stock LS2 has a TON of torque... Assume 2 driving conditions.. Johnny leadfoot vs Grandpa.. I would venture that there is ALOT of mass in the serp belt drive train.. Alt had the " dampner " BIG bell on the water pump, power steering etc etc. So if you leadfoot it ALOT the rubber in the HB is under considerable stress, on accel & decel. I would "GUESS" that if you babied the car the HB would go the distance ~ 100K. Where WAHOOO driving 25K....Thought's ?
Mike
I decided NOT ( right now ) to replace the HB... I was more interested in the fire up & getting the car back in 1 piece. Well I do not have a wobble for now. BUT A stock LS2 has a TON of torque... Assume 2 driving conditions.. Johnny leadfoot vs Grandpa.. I would venture that there is ALOT of mass in the serp belt drive train.. Alt had the " dampner " BIG bell on the water pump, power steering etc etc. So if you leadfoot it ALOT the rubber in the HB is under considerable stress, on accel & decel. I would "GUESS" that if you babied the car the HB would go the distance ~ 100K. Where WAHOOO driving 25K....Thought's ?
Mike
Last edited by vigman; Dec 11, 2016 at 10:50 PM.
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
A thought.... My engine has 93K on it ( wrecking yard in MI. ) ...
I decided NOT ( right now ) to replace the HB... I was more interested in the fire up & getting the car back in 1 piece. Well I do not have a wobble for now. BUT A stock LS2 has a TON of torque... Assume 2 driving conditions.. Johnny leadfoot vs Grandpa.. I would venture that there is ALOT of mass in the serp belt drive train.. Alt had the " dampner " BIG bell on the water pump, power steering etc etc. So if you leadfoot it ALOT the rubber in the HB is under considerable stress, on accel & decel. I would "GUESS" that if you babied the car the HB would go the distance ~ 100K. Where WAHOOO driving 25K....Thought's ?
Mike
I decided NOT ( right now ) to replace the HB... I was more interested in the fire up & getting the car back in 1 piece. Well I do not have a wobble for now. BUT A stock LS2 has a TON of torque... Assume 2 driving conditions.. Johnny leadfoot vs Grandpa.. I would venture that there is ALOT of mass in the serp belt drive train.. Alt had the " dampner " BIG bell on the water pump, power steering etc etc. So if you leadfoot it ALOT the rubber in the HB is under considerable stress, on accel & decel. I would "GUESS" that if you babied the car the HB would go the distance ~ 100K. Where WAHOOO driving 25K....Thought's ?
Mike
.. The answer to the problem is not to change your driving style, but to put on a balancer that won't fail no matter how you drive.... The mistake you made, was not putting on an aftermarket balancer before installing the new engine...It would have been a 30 minute job with the motor on a stand...WW.
.
Last edited by WW7; Dec 13, 2016 at 04:56 AM.
Safety Car
Joined: May 2011
Posts: 3,807
Likes: 508
From: Oshawa, Ontario
A thought.... My engine has 93K on it ( wrecking yard in MI. ) ...
I decided NOT ( right now ) to replace the HB... I was more interested in the fire up & getting the car back in 1 piece. Well I do not have a wobble for now. BUT A stock LS2 has a TON of torque... Assume 2 driving conditions.. Johnny leadfoot vs Grandpa.. I would venture that there is ALOT of mass in the serp belt drive train.. Alt had the " dampner " BIG bell on the water pump, power steering etc etc. So if you leadfoot it ALOT the rubber in the HB is under considerable stress, on accel & decel. I would "GUESS" that if you babied the car the HB would go the distance ~ 100K. Where WAHOOO driving 25K....Thought's ?
Mike
I decided NOT ( right now ) to replace the HB... I was more interested in the fire up & getting the car back in 1 piece. Well I do not have a wobble for now. BUT A stock LS2 has a TON of torque... Assume 2 driving conditions.. Johnny leadfoot vs Grandpa.. I would venture that there is ALOT of mass in the serp belt drive train.. Alt had the " dampner " BIG bell on the water pump, power steering etc etc. So if you leadfoot it ALOT the rubber in the HB is under considerable stress, on accel & decel. I would "GUESS" that if you babied the car the HB would go the distance ~ 100K. Where WAHOOO driving 25K....Thought's ?
Mike
Team Owner
Joined: Mar 2008
Posts: 21,502
Likes: 462
From: Southern Utah
The two are not related...the HB is just poorly implemented. It's sad too because the technology of a harmonic balancer has been around for a very long time and shouldn't be having problems at this point...it would be like Bayer all-of-a-sudden having trouble making decent aspirin.
Racer
Joined: Jan 2010
Posts: 296
Likes: 33
From: Virginia Beach VA
I was just going to let all this go. I really was. But to see so much thoughtful discussion on my “favorite topic”, I just can’t resist. This discussion usually develops from a “vibration with new clutch” type of thread. Interesting to see it develop this much from a HB replacement thread. But of course they are intimately related.
There are lots of really good theories in this thread, so very close, but still not quite correct, since they are after all, theories. There is an actual process that is employed, it has been in use since the first C5’s, 1997, and continues to today. GM developed a post engine assembly “hot balance” procedure to deal with NVH issues in manual transmission corvettes. Everyone can agree that the corvettes have a “different” driveline configuration; engine up front, transmission in the rear, connected with a rigid torque tube. This sets up unique vibration characteristics not seen in traditional engine/transmission setups. Manual transmission vettes have a different vibration transfer path from the automatic transmission vettes. Consequently, only engines designated for the manual transmissions go through the additional “hot balancing”. I researched this extensively back in 2012 actually talking to the GM folks involved in the process. Talked with folks involved with the C5, C6, and current C7 eras to see if the same procedure is being employed consistently. I talked with the then lead NVH engineer, balance stand operator, and several Powertrain head engineers. I’m not going to go in to great detail here, because I have many detailed posts already on this topic. I’ve tried to think of how to summarize the main points as concisely as possible.
- LS engines are an internally balanced design. Engine internals are held to tight manufacturing tolerances such that they are assembled in the engine build process “as delivered” while still resulting in a final engine balance/imbalance that is good for reliable engine operation. They are not “hand balanced” as one would do while building a “one off” engine in a race shop. These are mass produced engines. They are not blueprinted and they are certainly not “perfectly” zero balanced. Due to the unique driveline and vibration transfer path of the manual corvette, it was found that engines with slight imbalances that were fine for operation could still produce unwanted vibrations that could be felt inside the vehicle. They wanted a way to “fine tune balance” these engines even further closer to zero to eliminate these unwanted vibrations. Hence the hot balance procedure. They get these further balanced engines down to within 0.5 oz∙in or better. This is much less imbalance than allowed in the assembled engines going in to other vehicles.
- The hot balance procedure IS NOT done to correct poorly balanced engines. It is only done to further reduce NVH in manual transmission corvettes.
- Engines are built with the internals “as delivered”
- Flywheels and pressure plates are delivered already neutral balanced to within their own balance tolerances. This is important. Each has its own balance tolerance. Consequently, the pressure plates have a “looser” balance tolerance than the flywheels. But they are still considered to be “zero balanced”. Again, nothing is perfectly zero balanced. Only on the computer!” Balancing from the manufacturer on the flywheel is done via drilling blind holes where needed to bring the piece into neutral balance, within its tolerance. Pressure plates often have weights to achieve the same purpose.
- Harmonic Balancers/Dampers are also delivered having been “zero balanced” to its own balance tolerance. It is not perfectly zero. Balancing is done by the manufacturer by drilling blind holes where they are needed to bring it into balance within spec tolerances.
- Flywheels (GM) have 12 equally spaced circumferentially located “balance weight receptacle” holes. These are through holes designed to accept and retain balance weights if needed. (They are not part of the manufacturer’s balancing process. They an equally spaced symmetrical hole pattern, their own weight removal cancels each other out, sooooo………)
- Harmonic Balancers (GM) have similar 12 equally spaced through holes for the same purpose.
- The manufacturers DO NOT install any weights in to the flywheel or HB as part of their own zero balancing process.
- The hot balance procedure is a dual plane dynamic balancing process utilizing BOTH the Flywheel/PP sub assembly AND the HB to add weights (to the flywheel, HB, or both) if necessary to bring the ENTIRE engine assembly down to within the lower balance requirement of 0.5 oz∙in as required by the manual transmission vettes to minimize NVH.
- Hot balance procedure goes as follows:
- The flywheel and pressure plate are installed to the engine. The “fingers” of the pressure plate are depressed so that the friction disc does not spin.
- The HB is installed on the engine.
- The engine is loaded into a balance stand and run for a brief time on natural gas. Yes, natural gas. Sensors and accelerometers read vibrations and tell the balance operator where to install weights if needed. Some engines don’t require any additional weights. Some require weights only in the flywheel, some only in the HB, some in both.
- The hot balance accounts for the stackup imbalance contributions of the internal engine parts, flywheel, pressure plate, and HB. All the components contribute.
- Once this is done, you have a unique HB that matches up to your engine. You also have a unique FW/PP COMBO that matches up to your engine.
- IF you wish to maintain this balance relationship, you need to match balance any parts you replace with the originals (as they are AFTER the hot balance). Do you NEED to do this? No, your engine will be fine, but you MAY have new vibrations you did not feel before. In fact, most aftermarket flywheels and balancers do not have the 12 balance receptacle holes anyway, soooo…….
Lots of people replace their HB without regards to any balance weights from the old one and do not notice any new vibrations. The balance correction capability is much smaller on the HB due to its relatively small radius of the holes' location. The flywheel is a different story. Lots instances of vibrations after not matching the FW/PP combo to the original FW/PP combo. Larger radial location of the holes, and more parts contributing imbalances.
Well so much for keeping it short
If anyone wishes to ask more specific detailed questions, I'll be happy to answer what I have learned. And If I don't know the answer, I'll say I don't know!
There are lots of really good theories in this thread, so very close, but still not quite correct, since they are after all, theories. There is an actual process that is employed, it has been in use since the first C5’s, 1997, and continues to today. GM developed a post engine assembly “hot balance” procedure to deal with NVH issues in manual transmission corvettes. Everyone can agree that the corvettes have a “different” driveline configuration; engine up front, transmission in the rear, connected with a rigid torque tube. This sets up unique vibration characteristics not seen in traditional engine/transmission setups. Manual transmission vettes have a different vibration transfer path from the automatic transmission vettes. Consequently, only engines designated for the manual transmissions go through the additional “hot balancing”. I researched this extensively back in 2012 actually talking to the GM folks involved in the process. Talked with folks involved with the C5, C6, and current C7 eras to see if the same procedure is being employed consistently. I talked with the then lead NVH engineer, balance stand operator, and several Powertrain head engineers. I’m not going to go in to great detail here, because I have many detailed posts already on this topic. I’ve tried to think of how to summarize the main points as concisely as possible.
- LS engines are an internally balanced design. Engine internals are held to tight manufacturing tolerances such that they are assembled in the engine build process “as delivered” while still resulting in a final engine balance/imbalance that is good for reliable engine operation. They are not “hand balanced” as one would do while building a “one off” engine in a race shop. These are mass produced engines. They are not blueprinted and they are certainly not “perfectly” zero balanced. Due to the unique driveline and vibration transfer path of the manual corvette, it was found that engines with slight imbalances that were fine for operation could still produce unwanted vibrations that could be felt inside the vehicle. They wanted a way to “fine tune balance” these engines even further closer to zero to eliminate these unwanted vibrations. Hence the hot balance procedure. They get these further balanced engines down to within 0.5 oz∙in or better. This is much less imbalance than allowed in the assembled engines going in to other vehicles.
- The hot balance procedure IS NOT done to correct poorly balanced engines. It is only done to further reduce NVH in manual transmission corvettes.
- Engines are built with the internals “as delivered”
- Flywheels and pressure plates are delivered already neutral balanced to within their own balance tolerances. This is important. Each has its own balance tolerance. Consequently, the pressure plates have a “looser” balance tolerance than the flywheels. But they are still considered to be “zero balanced”. Again, nothing is perfectly zero balanced. Only on the computer!” Balancing from the manufacturer on the flywheel is done via drilling blind holes where needed to bring the piece into neutral balance, within its tolerance. Pressure plates often have weights to achieve the same purpose.
- Harmonic Balancers/Dampers are also delivered having been “zero balanced” to its own balance tolerance. It is not perfectly zero. Balancing is done by the manufacturer by drilling blind holes where they are needed to bring it into balance within spec tolerances.
- Flywheels (GM) have 12 equally spaced circumferentially located “balance weight receptacle” holes. These are through holes designed to accept and retain balance weights if needed. (They are not part of the manufacturer’s balancing process. They an equally spaced symmetrical hole pattern, their own weight removal cancels each other out, sooooo………)
- Harmonic Balancers (GM) have similar 12 equally spaced through holes for the same purpose.
- The manufacturers DO NOT install any weights in to the flywheel or HB as part of their own zero balancing process.
- The hot balance procedure is a dual plane dynamic balancing process utilizing BOTH the Flywheel/PP sub assembly AND the HB to add weights (to the flywheel, HB, or both) if necessary to bring the ENTIRE engine assembly down to within the lower balance requirement of 0.5 oz∙in as required by the manual transmission vettes to minimize NVH.
- Hot balance procedure goes as follows:
- The flywheel and pressure plate are installed to the engine. The “fingers” of the pressure plate are depressed so that the friction disc does not spin.
- The HB is installed on the engine.
- The engine is loaded into a balance stand and run for a brief time on natural gas. Yes, natural gas. Sensors and accelerometers read vibrations and tell the balance operator where to install weights if needed. Some engines don’t require any additional weights. Some require weights only in the flywheel, some only in the HB, some in both.
- The hot balance accounts for the stackup imbalance contributions of the internal engine parts, flywheel, pressure plate, and HB. All the components contribute.
- Once this is done, you have a unique HB that matches up to your engine. You also have a unique FW/PP COMBO that matches up to your engine.
- IF you wish to maintain this balance relationship, you need to match balance any parts you replace with the originals (as they are AFTER the hot balance). Do you NEED to do this? No, your engine will be fine, but you MAY have new vibrations you did not feel before. In fact, most aftermarket flywheels and balancers do not have the 12 balance receptacle holes anyway, soooo…….
Lots of people replace their HB without regards to any balance weights from the old one and do not notice any new vibrations. The balance correction capability is much smaller on the HB due to its relatively small radius of the holes' location. The flywheel is a different story. Lots instances of vibrations after not matching the FW/PP combo to the original FW/PP combo. Larger radial location of the holes, and more parts contributing imbalances.
Well so much for keeping it short
If anyone wishes to ask more specific detailed questions, I'll be happy to answer what I have learned. And If I don't know the answer, I'll say I don't know!
Le Mans Master
Joined: May 2015
Posts: 5,187
Likes: 1,216
From: Las Vegas Nevada
THBWLZ...thank you for the great write-up. I normally would not read anything that long, but it was interesting right from the start. The conclusion I got was that, if you are replacing your HB, you will likely have no balance issues with a new one due to the fact that so much has been done to get the total balance of the engine to get it as balanced as mass production processes allow, correct? But, if you are replacing a flywheel/pressure plate, there also may be no issues, but the potential is greater due to the greater mass, weight, and forces encountered during operation, correct?
Also, all LS engines go through the same balance processes, regardless of whether they will go into a manual or auto tranny vehicle, correct? Finally, is the attention to correct total balance and closer tolerances the reason why these engines (not including accessories) are relatively trouble-free?
Again, thanks for the great write-up. Really good stuff.
Also, all LS engines go through the same balance processes, regardless of whether they will go into a manual or auto tranny vehicle, correct? Finally, is the attention to correct total balance and closer tolerances the reason why these engines (not including accessories) are relatively trouble-free?
Again, thanks for the great write-up. Really good stuff.
Racer
Joined: Jan 2010
Posts: 296
Likes: 33
From: Virginia Beach VA
THBWLZ...thank you for the great write-up. I normally would not read anything that long, but it was interesting right from the start.
thank you, I don't like reading stuff that long either, but this is kind of involved.
The conclusion I got was that, if you are replacing your HB, you will likely have no balance issues with a new one due to the fact that so much has been done to get the total balance of the engine to get it as balanced as mass production processes allow, correct?
Sort of, but more specifically, the weights in the HB only represent 1/2 of this hot balance process. Plus, the radial location of the holes is so much smaller than the radial location of the holes used on the flywheel. There is much less corrective capability available by using the same weights in the HB as compared to the FW.
But, if you are replacing a flywheel/pressure plate, there also may be no issues, but the potential is greater due to the greater mass, weight, and forces encountered during operation, correct?
Not necessarily due to the greater mass, but due to more parts potentially contributing more (and greater) imbalances from the start. At least back in 2012, the balance tolerances for the PP were 3 times greater than the balance tolerances of the FW, as delivered from the manufacturer. Those tolerances alone could stack up to be greater than the 0.5 oz∙in specified for total engine balance.
Also, all LS engines go through the same balance processes, regardless of whether they will go into a manual or auto tranny vehicle, correct?
No, only the LS engines going into manual transmission vettes get the additional hot balance procedure. Nobody is actively "balancing" the rotating assemblies during engine build. They are installed "as machined". Their build tolerances are held tight enough that direct assembly results in a final balance range that is good for reliable engine operation. But quite a bit larger than 0.5 oz∙in. The engines going in to a manual are further and better balanced to get below that 0.5 threshold.
Finally, is the attention to correct total balance and closer tolerances the reason why these engines (not including accessories) are relatively trouble-free?
The build tolerances on all the parts are pretty darn tight. Those engines going in to manual transmissions are just checked and further balanced down even better. That's why I don't know why anyone would want to "undo it" by not bothering to match their factory stuff (balancewise). Its relatively easy, but mostly if you are replacing with GM parts. So I get why people always think the stock parts are inferior to the aftermarket.
There are so many instances of people doing a clutch change, putting the new stuff in right out of the box with no regard to their stock assembly, then they have vibrations that they never felt before. Of course, some go in like that and have NO problems. Its a crap shoot unless you accurately match your stock setup for balance. GM already did the hard part for you, through the hot balance, to give you a unique matched "set" for your engine.
Again, thanks for the great write-up. Really good stuff.
thank you, I don't like reading stuff that long either, but this is kind of involved.
The conclusion I got was that, if you are replacing your HB, you will likely have no balance issues with a new one due to the fact that so much has been done to get the total balance of the engine to get it as balanced as mass production processes allow, correct?
Sort of, but more specifically, the weights in the HB only represent 1/2 of this hot balance process. Plus, the radial location of the holes is so much smaller than the radial location of the holes used on the flywheel. There is much less corrective capability available by using the same weights in the HB as compared to the FW.
But, if you are replacing a flywheel/pressure plate, there also may be no issues, but the potential is greater due to the greater mass, weight, and forces encountered during operation, correct?
Not necessarily due to the greater mass, but due to more parts potentially contributing more (and greater) imbalances from the start. At least back in 2012, the balance tolerances for the PP were 3 times greater than the balance tolerances of the FW, as delivered from the manufacturer. Those tolerances alone could stack up to be greater than the 0.5 oz∙in specified for total engine balance.
Also, all LS engines go through the same balance processes, regardless of whether they will go into a manual or auto tranny vehicle, correct?
No, only the LS engines going into manual transmission vettes get the additional hot balance procedure. Nobody is actively "balancing" the rotating assemblies during engine build. They are installed "as machined". Their build tolerances are held tight enough that direct assembly results in a final balance range that is good for reliable engine operation. But quite a bit larger than 0.5 oz∙in. The engines going in to a manual are further and better balanced to get below that 0.5 threshold.
Finally, is the attention to correct total balance and closer tolerances the reason why these engines (not including accessories) are relatively trouble-free?
The build tolerances on all the parts are pretty darn tight. Those engines going in to manual transmissions are just checked and further balanced down even better. That's why I don't know why anyone would want to "undo it" by not bothering to match their factory stuff (balancewise). Its relatively easy, but mostly if you are replacing with GM parts. So I get why people always think the stock parts are inferior to the aftermarket.
There are so many instances of people doing a clutch change, putting the new stuff in right out of the box with no regard to their stock assembly, then they have vibrations that they never felt before. Of course, some go in like that and have NO problems. Its a crap shoot unless you accurately match your stock setup for balance. GM already did the hard part for you, through the hot balance, to give you a unique matched "set" for your engine.
Again, thanks for the great write-up. Really good stuff.