(this grew out of my thread about crank snout threads)

BLUF: What needs to be balanced when building an engine?

I was going to take the crank, rods, pistons, and rings to the machine shop to be balanced.

This is a '65 327 (bored out .030, so technically a 331 CID) building to roughly L76 specs. So it's an internally balanced engine.

Do the 8" harmonic dampener, flywheel, and clutch assembly need to be balanced WITH the engine internals?

Some of the on line resources are conflicting.

 

They are not necessary. But you would want them balanced. I wouldn't worry about the damper as long as it's in good shape. I would want the flywheel and pressure plate checked and they should stamp the pressure plate in relation to the flywheel.

 

The Wikipedia engine balance reference is comprehensive, except for naming what needs to be balanced by itself, or as an assembly.

The harmonic dampener, flywheel, pulleys, and clutch disc have no moving parts that change balance with rotation, and on an internally balanced assembly like a 327 they can be balanced separately and are expected to remain balanced in an assembly. This does not mean they are always balanced out of the box, or that the assembly hardware is matched for balance. It's always good to check, and becomes more important as rpm increases.

The reciprocating mass need to be balanced individually, and as an assembly. The rods, pistons, and rings should be balanced separately with separate procedures for each. Big and small end rod rest weight, piston bob weight and wrist pin balance, and ring weight after end gap optimization, and even bearing shell weight can all be static balanced before assembly. Engine builders try to match everything as rpm increases and the risk/reward of reliability and power increase.

The crank counterweights need to be balanced to the bob weight of the piston/rod/ring assembly weight, after all crank machining is complete to improve oil separation and aerodynamics of the rotating edges.

External balance assemblies like a SBC 400 or 454 BBC should have the crankshaft balanced with the flywheel and harmonic balancer assembled.

Detailed builders will match weight of flywheel bolts, the water pump impeller, and fan bolts, and some even match valve and push rod weight, and try to match rocker arm rest weight (yes, some people have time to play, or get paid to play with what we might term as excessive perfection).

There are also historical dirty tricks to upset the balance of an assembly like gluing weight inside pulleys during a car's engine inspection to take out a water pump or hydraulic pump shaft seal from the resulting vibration (validating the benefit of good balancing in accessories as well as the engine).

Talk to your machinist for advice for your usage and rpm needs.

 

That's a lot, but makes a lot of sense.

Like was said in the thread that triggered this one - one would replace a clutch set without rebalancing the engine.

While some of the excessive (obsessive?) detail discussed in the wiki - like balancing rockers - seems over the top, building a high-stress, high-power engine like a racing engine might dictate some extra balancing.

But as was said above, an internally balanced engine should be able to be balanced without its external rotating parts. I would expect to balance the flywheel and clutch pressure plate as a unit, and possibly the harmonic dampener (but it appears intact, and has evidence of having been balanced when new - lightening bores on the back side).

 

I would have the flywheel and clutch balanced at the same time as the engine assembly but stress that you want them zero balanced and match-marked to each other. The reason is I could not find anyone in my immediate part of the country last summer who could match balance a flywheel and clutch by themselves any longer. No problem 20 years ago but now those guys are gone and the equipment is gone. The only shops who would tackle it said they would need my entire engine rotating assembly to balance my flywheel/clutch. I was going to have to go to Memphis or Tulsa from here in Little Rock to expand my search and I finally just put all new parts in and kept my fingers crossed that the manufacturers got them close enough.

Your experience may be different where you live.

 

If the pressure plate has any weights welded to it, it has already been neutral balanced. The flywheel should also have some holes drilled into it for balance. That means they are each neutral balanced, so they can be bolted together with any rotation and not upset the balance.
If you have a pressure plate with no weights on it, I'd have to assume it was not balanced and then your only choice would be to have it and the flywheel done together and indexed (given that the tooling to balance a pressure plate alone is not available as stated).

Imagine you have two tire & wheel assemblies that have been balanced on a bubble balancer. Put the first wheel on the balancer, then put the second one on top of the first one. No matter what rotation you place the second one on top, the bubble should stay in the center.

Verne

 

I managed a shop where we did about 10-12 balanced assemblies a day and later had my own shop with balancing equipment. Most of what you are reading is correct. If the engine is externally balanced you have to have the flywheel and or balancer attached to spin the crank or it would vibrate extremely and try to jump off of the machine. You calculate a bob weight from the rod weights, piston, pin (and locks if used), rings, rod bearing, and a small amount for oil. If the engine is internally balanced first you would balance the assembly, then add each component one at a time, flywheel then clutch plate, then damper if you wanted. This way it's all balanced and if you need to replace the flywheel or clutch you could do so without affecting the engine. When you do this you place a mark for indexing the clutch to the flywheel. I have seen many times where lazy people will use the flywheel to balance an externally balanced engine by drilling on the flywheel. The problem then is if you have to replace it you've got a real problem. When we shipped our engines out if they were externally balanced they came with a flywheel and damper. As opposed to a thread I just read where the engines don't come with either. We/I never used a damper on and internally balanced motor for balancing.

 

Cruciform cranks V-8s can be balanced for rotating mass by adding appropriate weight to each crank check. This balances the assembly statically, but not dynamically because there is a residual first order rocking couple from the reciprocating mass. This can be balanced by moving some of the crank cheek weight from the center to the ends. This is why most V-8 cranks have large weights on the end checks, but none on the center cheeks.

This is the equivalent of dynamically balancing a wheel/tire assembly by adding weights, usually of differing values, to both side of the wheel/tire assembly, and the final assembly is balanced both statically and dynamically.

So you have to provide the balancing shop the crank, all rods, all pistons/pins and one set of rings and rod bearings. The latter two items are relatively light and precision manufactured, so weight variation is noise level and all are assumed to be the same.

It's also a good idea to check and correct, as necessary, static balance of the flywheel and front damper. Once the flywheel is balanced, install the clutch and recheck adding any necessary weight to the clutch assembly, then stamp clear marks on both to document proper assembly orientation.

OE clutches and flywheels are stamped with an "X", but rather than balancing each assembly, they matched up the light/heavy side of the flywheel/clutch yielding the least residual balance, but not as good as balancing each specific set.

The above type precision balancing can reduce or eliminate the annoying "shifter buzz" that is common on vintage Corvettes.

BTW, the first design 327conn. rods used through '65 are inherently weak at the bolt seat and subject to fatigue failure, especially on high revving SHP/FI systems. They should not be reused. The Eagle SIR5700 is a good choice and moderately priced at $250 a set, and it's the best insurance policy you will ever buy.

There are many to choose from, but most are significantly heavier than OE, which can complicate and increase the cost of balancing by having to add "Mallory metal" to the crankshaft.

Duke

 

Thanks, Duke.

And the Eagle SIR5700s are exactly what I bought. Maybe I could have gotten by without them, but I don't expect to ever rebuild this engine, the good Lord willing.

The cost of the new rods was only marginally more than the costs or reworking the 50+ year old rods that came out of my engine, if that by the time you upgrade the rod bolts.

 

Easy Rhino,
Would appreciate hearing about your experience with the machine shop you choose. I'm considering having my L79 rebalanced and I'm not too far from your area.

Thanks,
Ralph

 

Ralph;

Glad to. I did shop around and sought out several people's price experience with machine shops in the tidewater, VA area.

I almost went with a guy who is maybe 2 miles from my house, but he was impossible to communicate with and a cranky old SOB. So am I, but I can listen and communicate.

The guy I went with, although he is a long-time MoPar guy at heart, has owned his own privately owned shop for decades, is super busy, is really good to work with on details, and knows small block Chevys. You might have to wait in line to get work to him, but I'm not in a hurry so that works for me. He has no problem discussing options and giving technical advice.

Last fall I dropped off my 327 block for him to clean, mag, measure and evaluate boring it. He spent a lot of time looking at it closely before he took it in, and discussed the plan with me. He pulled the freeze plugs and oil gallery plugs, dipped the block, magged it, measured it and determined that it was .011 over 4.000 bore, so I went ahead and had him bore it .030 over. Afterwords, he cleaned out all the oil passageways, and installed brass freeze plugs and all the oil gallery plugs and installed fresh cam bearings. He wanted to see the piston rings I intended to use before he put the final hone on the cylinders. Very conscientious, and seems to be very knowledgeable. All for $300 and change, and it was all on the honor system - no contracts or paperwork, just cash between two men.

He builds lots of engines for local racers, as well as doing old classic stuff - like a straight eight (I think it was a Pontiac). Since then, every one I have run in to that knows him only have good things to say about him.

I see no reason to go anywhere else.

 

Many thanks, sounds like he's one of a vanishing breed...

 

I went with SCAT brand rods in my 327 .040 over rebuild. Eyeballing these rods out of the box, they looked to be on the heavy side compared to the stock rods they replaced. The side beam flash was removed to smooth down a tiny bit of rod weight.

The machinist at the engine shop balancing the rotating assembly MIG welded metal material back into the original factory drilled crank cheeks to get the assembly to balance out. He said it was close but was able to get the rotating assembly balanced. .. Don't know if the Eagle SIR 5700 rods are lighter, by comparison.
John

 

I think so. He's not an old man, but many (most) are young as compared to me, I think.

But he does business in the traditional way.

 

I started with Chevy "pink" rods (40 years ago)...Then
Crower "Sportsman" Rods $920...Now
Carrillo "Pro H" Rods "$2500!
There is NO comparison between a drag race motor turning 7500RPM for a few seconds, and a ROAD RACE motor turning 7200+ for, um...8 to 10 laps on the Indy Oval.

 

My set of Eagle SIR 5700 rods weigh 580 grams +/- 1 gram each.

As it turns out the OEM 4.000 flat pistons (with valve reliefs), stock rods, and rings that came out of the short block I'm building were only 10 grams heavier than the forged 4.030 L2166N pistons, Eagle 5700 rods, and rings that I'm putting in it. So, my total change in reciprocating mass is only -80 grams. If I knew anything about the shape of this used crank, I would be tempted to just bolt it up without the expenditure of balancing costs.

 

The same for the Crower Sportsman rods in my original RE block assembly, and the Oliver Ultra Light rods in my fun 357 currently in the car. I played with Pontiac engines and their sketchy rods at extended periods of high rpm to learn the damage from rod failure is far worse than wallet damage from spending the money for quality connecting rods.

With the expense already invested in good parts, the balancing is worth the small incremental cost. Depending on what windage tray and rod & crank counter weight finish that you have to move oil away from the crankshaft you may want to talk to the balancing expert about his thoughts to address the potential for excess friction and weight from the oil clinging to the reciprocating mass.

 

Yeah, I see no rationale for skipping the balancing, most certainly because I have no history knowledge of this crankshaft.

I'm going with the L76 factory stock windage tray, as well as the SHP deep trap door oil pan, absent any additional info the precludes it.

 

Yes the aftermarket rods just look so much better it's difficult to use the stock rods for nearly the same price. Machine shop didn't even want my old rods.

I think you really got some good help here and will have a much better than stock motor when it's ready.

 

Quite right.

I would be lost without all of the knowledgable and insightful help provided by so many here. Not to mention frustrated and overspent, if not for people's willingness to offer skilled advice!