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88 stock L98 4+3. Been dealing with a vibration around 2800 rpm since I bought it a little of a year ago. I have zero history of the car, and I have been chasing this issue for a year now. The vibration is present even in neutral and I have taken the accessory belt off too. I even replaced the harmonic balancer with a Fluid Master and it made zero difference. I replaced the clutch and flywheel with a LUK weighted flywheel and the vibration is still there. I’m in the process of replacing the valve seals and when I removed the rockers and pushrods I could see the valley was pristine, which is making me think this engine has been rebuilt. Our thinking is that the engine might have been internally balanced and the weighted flywheel is causing the vibration. Or maybe the engine was replaced with a 89 and later engine that’s internally balanced ?
I’m think of getting an aluminum flywheel, but can’t seem to find one for a 88 C4 ? Would a neutral balanced flywheel from a 89 and later SBC fit my L98 ?
I’m desperate to fix this issue, and I am willing to throw some money and labor at.
You said you replaced the balancer and no difference. There are 2 different ones. External and internal balance. Did you try the opposite of what you have to see if it helps? Like you said you have no idea on the engine as to what it is. Its worth a shot and wont hurt anything temporarily.
FYI, 1989 and later engines are not neutral balanced, all one piece rear main crank engines (1986 and later) are externally balanced at the flywheel with a neutral balanced at the harmonic balancer.
It is possible that someone rebuilt your engine and internally balanced it, if that is the case you will need a neutral balanced flywheel for whatever crankshaft you have in the engine. The stock crankshaft is a one piece rear main crank design but it is possible that a 2 piece crankshaft was installed with a crankshaft adapter.
You really need to understand what parts you have on your engine to solve this problem.
FYI, 1989 and later engines are not neutral balanced, all one piece rear main crank engines (1986 and later) are externally balanced at the flywheel with a neutral balanced at the harmonic balancer.
It is possible that someone rebuilt your engine and internally balanced it, if that is the case you will need a neutral balanced flywheel for whatever crankshaft you have in the engine. The stock crankshaft is a one piece rear main crank design but it is possible that a 2 piece crankshaft was installed with a crankshaft adapter.
You really need to understand what parts you have on your engine to solve this problem.
I definitely need to see if my engine is the stock L98 or maybe it was replaced with another short block, so my next issue is to check the numbers on the block. I’m not sure why I was thinking a 89 and later were neutral balanced, I understand all one piece main seals are externally balanced. I replaced all the valve springs and valve seals today, and the engine has never ran smoother under load and at idle, but the vibration is still there. I’m think if it were a bent crank or rod, wouldn’t the engine start showing more issues as time goes on?
I definitely need to see if my engine is the stock L98 or maybe it was replaced with another short block, so my next issue is to check the numbers on the block. I’m not sure why I was thinking a 89 and later were neutral balanced, I understand all one piece main seals are externally balanced. I replaced all the valve springs and valve seals today, and the engine has never ran smoother under load and at idle, but the vibration is still there. I’m think if it were a bent crank or rod, wouldn’t the engine start showing more issues as time goes on?
A bent rod would probably show up as down on power due to compression loss. So maybe a compression check is in order. Also, a bent rod, if severe enough, you can hear the loss of compression when cranking over without intent to start it (aka, no ignition or fuel). Might have a bit of a gallop to it.
A bent rod would probably show up as down on power due to compression loss. So maybe a compression check is in order. Also, a bent rod, if severe enough, you can hear the loss of compression when cranking over without intent to start it (aka, no ignition or fuel). Might have a bit of a gallop to it.
Compression is good, around 180 and all cylinders are within 5-6 psi of each other.
I replaced the clutch and flywheel some months back, new LUK clutch and flywheel and ARP FW bolts.
This is a pic of the original GM flywheel, and shows some really sketchy work, this is why my thinking is the engine has had some work, and not correctly done. The FW bolts were a mixture of OEM and hardware store grade, and not sure what caused the bolt hole damage, but damn, that’s pretty bad. So this is what I’m dealing with; past crappy repairs and no history. This vibration is driving me nuts.
The part # 14088646 would have been correct for any L98 Corvette '86 - '88
I understand that, and that was never a question, but before I replaced the clutch, I didn’t know if the FW had been replaced, so when I replaced the clutch I bought and installed a new FW. I was hoping to find a neutral balanced FW which would have explained my vibration, but no such luck. Though the original FW has seen some things, which tells me a lot of work has been done.
You said you replaced the balancer and no difference. There are 2 different ones. External and internal balance. Did you try the opposite of what you have to see if it helps? Like you said you have no idea on the engine as to what it is. Its worth a shot and wont hurt anything temporarily.
I found out that my engine is the original numbers matching engine. I have replaced the stock HB with another GM OEM balancer with no difference and then tried using a fluid type HB and have the same results. Are you saying there is an internal balance HB I could try ?
EDIT: the Fluidamper HB I installed on my L98 is a 620101, though their website says it’s for an internal balanced engine, could I have gotten the wrong one ?
88 L98 Viration Issue Revisited
