At wits end with engine vibration
Is my vette stock?? HAHA
Joined: Oct 2015
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From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
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Does it do it while sitting still as you climb slowly past 3300 rpm?
Le Mans Master
Joined: Jun 2006
Posts: 6,393
Likes: 1,225
From: Tampa Florida
I bought my '71 when it was 4 years old and the original owner replaced the 3/4" shaft water pump with a 5/8" shaft water pump.
Since the '71 fan clutch is a 3/4", it caused a weird look at idle, like something was out of round.
I thought is was an illusion until I removed the fan clutch and discovered the mismatch. I installed the correct 3/4" water pump and problem solved.
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,070
Likes: 9,202
From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
I would disconnect the tranny and check the flywheel bolts to see if they are loose. IF that isnt it , after all you have replaced, I would then pull it apart and check the engine balance. You said somethng about the pulleys wobbling, is the front dampner bolt in tight?
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,070
Likes: 9,202
From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
You siad this was a 90s build so I am guessing the caar was fine and this started a few months ago. Is this correct? If so yo ucan pull everything off the front of the motor and start it without any pulleys for a few minutes while cold. It doesnt have to have the water pump spinning for a minute to see if the vibration goes away
Last edited by Rescue Rogers; Nov 30, 2020 at 12:04 PM.
Thread Starter
Racer
Joined: Sep 2019
Posts: 349
Likes: 44
From: Spokane, WA
I'm just throwing this out there, and I'm sure yours is correct. Does your '69 water pump have a 5/8" shaft along with a 5/8" fan clutch?
I bought my '71 when it was 4 years old and the original owner replaced the 3/4" shaft water pump with a 5/8" shaft water pump.
Since the '71 fan clutch is a 3/4", it caused a weird look at idle, like something was out of round.
I thought is was an illusion until I removed the fan clutch and discovered the mismatch. I installed the correct 3/4" water pump and problem solved.
I bought my '71 when it was 4 years old and the original owner replaced the 3/4" shaft water pump with a 5/8" shaft water pump.
Since the '71 fan clutch is a 3/4", it caused a weird look at idle, like something was out of round.
I thought is was an illusion until I removed the fan clutch and discovered the mismatch. I installed the correct 3/4" water pump and problem solved.
Thread Starter
Racer
Joined: Sep 2019
Posts: 349
Likes: 44
From: Spokane, WA
I would disconnect the tranny and check the flywheel bolts to see if they are loose. IF that isnt it , after all you have replaced, I would then pull it apart and check the engine balance. You said somethng about the pulleys wobbling, is the front dampner bolt in tight?
Thread Starter
Racer
Joined: Sep 2019
Posts: 349
Likes: 44
From: Spokane, WA
You siad this was a 90s build so I am guessing the caar was fine and this started a few months ago. Is this correct? If so yo ucan pull everything off the front of the motor and start it without any pulleys for a few minutes while cold. It doesnt have to have the water pump spinning for a minute to see if the vibration goes away
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Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,113
From: Crossville TN
What kind of fan do you have on the engine? (stock, thermal, flex-fan?) I agree that, after the engine has been warmed up and then shut down, you should just remove water pump, power steering and any smog related belts, then fire it and rev it up to see if the vibration is still there. If it is, your problem is in the engine or engine-to-transmission interface somewhere. If the vibration is gone, you have a 'front-end accessory' problem.
Thread Starter
Racer
Joined: Sep 2019
Posts: 349
Likes: 44
From: Spokane, WA
What kind of fan do you have on the engine? (stock, thermal, flex-fan?) I agree that, after the engine has been warmed up and then shut down, you should just remove water pump, power steering and any smog related belts, then fire it and rev it up to see if the vibration is still there. If it is, your problem is in the engine or engine-to-transmission interface somewhere. If the vibration is gone, you have a 'front-end accessory' problem.
I am thinking about ignition...maybe there is one or more cylinders not firing regularly. Just not sure it would cause such a vibration in the upper RPM range. I would think it would get masked by the other cylinders as engine speed increased.
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,070
Likes: 9,202
From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
YOu might be stuck diassembling it and rechecking the internal balance incase something has changed. If the crank had heavy metal added to it then it fell out then it would effect the balance. If this was a new build and it was vibrating since the first start then it wouldnt be an issue but to start vibrating after so many miles have been put on it then it has to be a change in the balance. Internal balanced engines generally dont have weights added except for the crank. on the outside the flywheel may have weights added and the damper may. If it was externally balanced like a big block or a 383 then I could see a weight coming off.
If you do pull it apart it will generally only cost you the price of a new set of seals and gaskets. while its a part oyu can re ring it and give it a fresh hone to rough up the cylinders....maybe a bigger cam...or some nice domed pistons....
If you do pull it apart it will generally only cost you the price of a new set of seals and gaskets. while its a part oyu can re ring it and give it a fresh hone to rough up the cylinders....maybe a bigger cam...or some nice domed pistons....
Race Director
Joined: Dec 1999
Posts: 11,092
Likes: 990
From: Sierra Foothills CA
Have you made sure the bell housing to block bolts are all tight? Many years ago I had freshened up the engine in my ''69 Vette and reinstalled it. One of the folks helping was a friend of a friend. My bad for not checking, but the bolts he was on there did not get tightened. Based on the vibration, I feared that the engine balancing had been badly botched. I found the loose bolts, torqued them properly, and life was wonderful. Best of luck.
Thread Starter
Racer
Joined: Sep 2019
Posts: 349
Likes: 44
From: Spokane, WA
YOu might be stuck diassembling it and rechecking the internal balance incase something has changed. If the crank had heavy metal added to it then it fell out then it would effect the balance. If this was a new build and it was vibrating since the first start then it wouldnt be an issue but to start vibrating after so many miles have been put on it then it has to be a change in the balance. Internal balanced engines generally dont have weights added except for the crank. on the outside the flywheel may have weights added and the damper may. If it was externally balanced like a big block or a 383 then I could see a weight coming off.
If you do pull it apart it will generally only cost you the price of a new set of seals and gaskets. while its a part oyu can re ring it and give it a fresh hone to rough up the cylinders....maybe a bigger cam...or some nice domed pistons....
If you do pull it apart it will generally only cost you the price of a new set of seals and gaskets. while its a part oyu can re ring it and give it a fresh hone to rough up the cylinders....maybe a bigger cam...or some nice domed pistons....
Thread Starter
Racer
Joined: Sep 2019
Posts: 349
Likes: 44
From: Spokane, WA
Have you made sure the bell housing to block bolts are all tight? Many years ago I had freshened up the engine in my ''69 Vette and reinstalled it. One of the folks helping was a friend of a friend. My bad for not checking, but the bolts he was on there did not get tightened. Based on the vibration, I feared that the engine balancing had been badly botched. I found the loose bolts, torqued them properly, and life was wonderful. Best of luck.
Le Mans Master
Joined: May 2007
Posts: 5,007
Likes: 1,114
From: North tonawanda NY
I'm just throwing this out there, and I'm sure yours is correct. Does your '69 water pump have a 5/8" shaft along with a 5/8" fan clutch?
I bought my '71 when it was 4 years old and the original owner replaced the 3/4" shaft water pump with a 5/8" shaft water pump.
Since the '71 fan clutch is a 3/4", it caused a weird look at idle, like something was out of round.
I thought is was an illusion until I removed the fan clutch and discovered the mismatch. I installed the correct 3/4" water pump and problem solved.
I bought my '71 when it was 4 years old and the original owner replaced the 3/4" shaft water pump with a 5/8" shaft water pump.
Since the '71 fan clutch is a 3/4", it caused a weird look at idle, like something was out of round.
I thought is was an illusion until I removed the fan clutch and discovered the mismatch. I installed the correct 3/4" water pump and problem solved.
Last edited by augiedoggy; Nov 30, 2020 at 06:52 PM.
Thread Starter
Racer
Joined: Sep 2019
Posts: 349
Likes: 44
From: Spokane, WA
My Plan:
1. Put a vacuum gauge on the car and rev to the vibration zone to see what the gauge is doing. This may identify an engine related issue I am not considering.
2. Compression test
3. Use a known good distributor to eliminate possible ignition issues (thanks Rescue Rogers)
4. Recheck accessories
5. Replace solid engine mounts with stock rubber mounts (i have them, so why not?)
6. Confirm bell housing and trans mount bolt torques
7. Change the chambered under car exhaust back to stock (very unlikely a resonance issue...but, I have the stuff so again, why not?)
8. Pull the trans and change the new flywheel (25 lbs) back to the stock original and line up the dowel holes...even though aligning it shouldn't make any difference, but the increase FW weight may make a difference
9. Pull oil pan and confirm main cap torque values
10. Pull engine for a rebuild.
Anything else?
Its a shame this issue exists...the car is very nice. No hit body. Beautiful frame. Clean, numbers matching.
1. Put a vacuum gauge on the car and rev to the vibration zone to see what the gauge is doing. This may identify an engine related issue I am not considering.
2. Compression test
3. Use a known good distributor to eliminate possible ignition issues (thanks Rescue Rogers)
4. Recheck accessories
5. Replace solid engine mounts with stock rubber mounts (i have them, so why not?)
6. Confirm bell housing and trans mount bolt torques
7. Change the chambered under car exhaust back to stock (very unlikely a resonance issue...but, I have the stuff so again, why not?)
8. Pull the trans and change the new flywheel (25 lbs) back to the stock original and line up the dowel holes...even though aligning it shouldn't make any difference, but the increase FW weight may make a difference
9. Pull oil pan and confirm main cap torque values
10. Pull engine for a rebuild.
Anything else?
Its a shame this issue exists...the car is very nice. No hit body. Beautiful frame. Clean, numbers matching.
Thread Starter
Racer
Joined: Sep 2019
Posts: 349
Likes: 44
From: Spokane, WA
Fairly common change..."upgrade" is relative to the person. Will generally last forever.
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,070
Likes: 9,202
From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
we used to do it all the time as kids. The old style motor mounts were pretty week and you could easily make you engine dance in the engien compartment. The guys with "High" torque motors used short lengths of chain to keep the engine from really flopping around
Race Director
Joined: Dec 1999
Posts: 11,092
Likes: 990
From: Sierra Foothills CA
My Plan:
1. Put a vacuum gauge on the car and rev to the vibration zone to see what the gauge is doing. This may identify an engine related issue I am not considering.
2. Compression test
3. Use a known good distributor to eliminate possible ignition issues (thanks Rescue Rogers)
4. Recheck accessories
5. Replace solid engine mounts with stock rubber mounts (i have them, so why not?)
6. Confirm bell housing and trans mount bolt torques
7. Change the chambered under car exhaust back to stock (very unlikely a resonance issue...but, I have the stuff so again, why not?)
8. Pull the trans and change the new flywheel (25 lbs) back to the stock original and line up the dowel holes...even though aligning it shouldn't make any difference, but the increase FW weight may make a difference
9. Pull oil pan and confirm main cap torque values
10. Pull engine for a rebuild.
Anything else?
Its a shame this issue exists...the car is very nice. No hit body. Beautiful frame. Clean, numbers matching.
1. Put a vacuum gauge on the car and rev to the vibration zone to see what the gauge is doing. This may identify an engine related issue I am not considering.
2. Compression test
3. Use a known good distributor to eliminate possible ignition issues (thanks Rescue Rogers)
4. Recheck accessories
5. Replace solid engine mounts with stock rubber mounts (i have them, so why not?)
6. Confirm bell housing and trans mount bolt torques
7. Change the chambered under car exhaust back to stock (very unlikely a resonance issue...but, I have the stuff so again, why not?)
8. Pull the trans and change the new flywheel (25 lbs) back to the stock original and line up the dowel holes...even though aligning it shouldn't make any difference, but the increase FW weight may make a difference
9. Pull oil pan and confirm main cap torque values
10. Pull engine for a rebuild.
Anything else?
Its a shame this issue exists...the car is very nice. No hit body. Beautiful frame. Clean, numbers matching.