C1 vibration

[Ray Hoctor]

Since I have prety much solved the cooling problem on my '61 thanks to everyone who helped out, my next priority is the vibration I have starting about 1800 rpm and gets worse around 2200 rpm and tapers off, but never quits up to 3500 rpm. For some background, I had this problem, but not as severe prior to pulling the engine. The engine is a later model 283(starter mounts in the block). It vibrates in neutral, so it is not the driveshaft. I changed the bellhousing to the orginal and found I had a 153 tooth flywheel. I found a used Hayes 168 tooth flywheel that appeared to be in good shape and installed it. The crank is an automatic with a dowel pin hole which lined up with the one on the flywheel. If my flywheel, pressure plate and engine are all internally balanced, where is the vibration coming from? It really shakes the whole car. I already checked the motor mounts. You can acutally see the rear of the engine shaking. I'm close to pulling the transmission and installing a new flywheel, clutch and pressure plate. I'd appreciate any input before I do this.
thanks.

[Chris S.]

Re: C1 vibration

check the harmonic balancer - I have seen the outer shell/ring - slip
when the rubber ring between them - goes bad.
Did it vibe before the new flywheel ?

[Terry D.]

Re: C1 vibration

You say you found a flywheel, did you have the assembly balanced before you put it in? If not I would pull it out and do that. Did it vibrate before this?
Terry

[Robert Willis]

Re: C1 vibration

Bent or twisted crack ? Or main bearing bores out of align a little. I had a 283 that the cam bores somehow got out alignment and I had to have it bored with oversize bearings installed, the cam wanted to corkscrew forward.

Bob

http://members.kos.net/willisb/vette.html

[Ray Hoctor]

Re: C1 vibration

I purchased the flywheel from a machine shop. I did not balance it as it was supposed to be neutral balanced. Maybe not, but the vibration was there before the flywheel switch, just not as severe, which sort of rules out the flywheel (maybe). I plan to rotate the pressure plate half a turn and see what I get.
I saw a posting in the archives that the 400 cu. in. crank was the only small block crank with a dowel pin hole on the flange. Does this sound correct? Is the 400 crank internally balanced? The flange is round and does look like it is internally balanced.

[Christopher R.]

Re: C1 vibration

I'm not an engine expert, but I believe that the 400 cubic inch engine was the only Chevy small block that was not internally balanced. It was balanced externally - by either the flywheel, harmonic balancer, or both. If that's right, then flywheels and harmonic balancers for 400s are unbalanced.

[Chris S.]

Re: C1 vibration

400 is externally balanced.
I would balance the flywheel and assy (stick) ?
Check the balancer

[John H.]

Re: C1 vibration

All SB cranks have a "dowel hole" in the flange, but it wasn't used for a dowel pin except on the externally-balanced 400; it's the master indexing point during crank machining and grinding. All 283 cranks have a round flange - if yours is a different shape, it's a later 327 or 350 crank.

[Mike McKown]

Re: C1 vibration

You said the crank was an automatic. Does it have a pilot bearing/bushing in it? If you push the clutch pedal in, does it still vibrate?

A long shot: you don't say that your engine has been balanced. I just wonder if someone has put a different crank in your engine than what it was equipped with originally. If they did, that shot your factory balance job. Sometime, in late '64 or early '65 the 283's changed from a steel crank to iron. This required a harmonic balancer be installed to replace the crank hub on the forged crank.

Does your engine vibrate with the fan belt removed?

[Ray Hoctor]

Re: C1 vibration

I have a round flange so it looks like a 283 crank. Since I did not rebuild the engine, I am not sure of the P/N on the crank. However, I discovered it was from a turbo glide transmission since it took a huge pilot bushing. I'll try it without the fan belt. Tomorrow is Corvette day in my garage!