74k20
Registered Member
Hoping someone out there is a really sharp engine guru who might be able to lend some advice and hopefully really good tech.
Here is the situation:
Had a 383 stroker built for my truck when I was in high school. I took the builder the flywheel, harmonic balancer, and pressure plate for the final balance. Got it in the truck and it ran beautifully. Smooth as glass.
Fast forward about 5 years. Clutch was chattering and I was pulling the trans for a swap. Figured on having the flywheel resurfaced and putting in a new clutch. When I took it to a machine shop, the guy said because it was external balance I would need to bring in the crank and all. I figured this could not be true. A call to the original engine builder, mind you they could not bring up any record of me or my specific engine, confirmed what I wanted to believe. "We balance to the off the shelf 400 small block spec for most 383s". So I told the shop doing the resurfacing to clean it up and check it to a stock 400 flywheel. This may have been the fatal error.
Put it all back together and it shook. Starts about 1750 rpm and rattles the dash by 2000, then cleans up a bit up around 2400. Checked EVERYTHING...pugs, wires, tuning, motor mounts, clutch in/out, rolling or not, exhaust hangers, valves, etc, etc. No help. It wasn't a tooth rattling shake, but people riding in the truck notice it for sure.
The trans that went in for the swap was used and a bit tired...so a few months later out it comes for a rebuild. New bearings, bushings, pilot bushing, throwout, etc. While it was out I did a little test. With only the flywheel on the back of the motor (jack under the rear of the pan to hold it up) I revved it up to the right rpm and confirmed it was still shaking. Then I swapped it for a brand spanking new 400 wheel and tried again. Still shaking but I could have sworn it was a little better. Frustrated and needing the vehicle I put it back together with the new wheel.
So here I am with a motor that still shakes. I think I may be on the right track with my next idea, but let me know if I am way off...
Looking closely at the original flywheel (I kept it) and the harmonic balancer, there are four or five half inch deep holes drilled to remove weight from the "intentional" imbalance that exists in each. What if the original balance was not to "400 spec"? Different pistons and rods from stock might affect the necessary weight, no?
Resurfacing of the wheel either threw off the balance or the shop tried to correct it to "400 spec" after resurfacing. My fault for not having them determine the imbalance in the wheel and re-balance to that afterward. This would mean the new wheel on the engine now is also off from the original balance which explains the shake.
So what to do? Take the crank out and have it re-balanced from scratch?
THE BIG QUESTION: Is there a way to determine what the flywheel imbalance should be based on what could be measured on the harmonic balancer?
I thought about maybe trying to bolt some weight to the wheel in different spots (starting opposite the cast in weight to try to "reduce it" as the original wheel had been drilled there). I could use the seat of the pants technique to get back to something reasonable. Anyone ever tried this?
I am working full time now and while I don't want to have to pull the crank out, I realize that ruining a perfectly good engine just means more time later.
Any tips or tricks, advice or told-ya-so's, theory or wild-ass-guessing would be appreciated!
Sorry for the long winded post
Here is the situation:
Had a 383 stroker built for my truck when I was in high school. I took the builder the flywheel, harmonic balancer, and pressure plate for the final balance. Got it in the truck and it ran beautifully. Smooth as glass.
Fast forward about 5 years. Clutch was chattering and I was pulling the trans for a swap. Figured on having the flywheel resurfaced and putting in a new clutch. When I took it to a machine shop, the guy said because it was external balance I would need to bring in the crank and all. I figured this could not be true. A call to the original engine builder, mind you they could not bring up any record of me or my specific engine, confirmed what I wanted to believe. "We balance to the off the shelf 400 small block spec for most 383s". So I told the shop doing the resurfacing to clean it up and check it to a stock 400 flywheel. This may have been the fatal error.
Put it all back together and it shook. Starts about 1750 rpm and rattles the dash by 2000, then cleans up a bit up around 2400. Checked EVERYTHING...pugs, wires, tuning, motor mounts, clutch in/out, rolling or not, exhaust hangers, valves, etc, etc. No help. It wasn't a tooth rattling shake, but people riding in the truck notice it for sure.
The trans that went in for the swap was used and a bit tired...so a few months later out it comes for a rebuild. New bearings, bushings, pilot bushing, throwout, etc. While it was out I did a little test. With only the flywheel on the back of the motor (jack under the rear of the pan to hold it up) I revved it up to the right rpm and confirmed it was still shaking. Then I swapped it for a brand spanking new 400 wheel and tried again. Still shaking but I could have sworn it was a little better. Frustrated and needing the vehicle I put it back together with the new wheel.
So here I am with a motor that still shakes. I think I may be on the right track with my next idea, but let me know if I am way off...
Looking closely at the original flywheel (I kept it) and the harmonic balancer, there are four or five half inch deep holes drilled to remove weight from the "intentional" imbalance that exists in each. What if the original balance was not to "400 spec"? Different pistons and rods from stock might affect the necessary weight, no?
Resurfacing of the wheel either threw off the balance or the shop tried to correct it to "400 spec" after resurfacing. My fault for not having them determine the imbalance in the wheel and re-balance to that afterward. This would mean the new wheel on the engine now is also off from the original balance which explains the shake.
So what to do? Take the crank out and have it re-balanced from scratch?
THE BIG QUESTION: Is there a way to determine what the flywheel imbalance should be based on what could be measured on the harmonic balancer?
I thought about maybe trying to bolt some weight to the wheel in different spots (starting opposite the cast in weight to try to "reduce it" as the original wheel had been drilled there). I could use the seat of the pants technique to get back to something reasonable. Anyone ever tried this?
I am working full time now and while I don't want to have to pull the crank out, I realize that ruining a perfectly good engine just means more time later.
Any tips or tricks, advice or told-ya-so's, theory or wild-ass-guessing would be appreciated!
Sorry for the long winded post
