The Stovebolt Site Forums The Shop Area Engine Shop Vibration update

Got a vibration between approx. 1800 - 2000 RPM. Same RPM in every gear regardless of speed. I had the crank turned and a threaded hole cut in it for a bolt to hold the harmonic balancer on. Also, can a 216 balancer fit on a 235 crank?Cause that could have happened. Could it also be the flywheel loose? I need to fix this cause its right in my cruise RPM range. I got a T5 behind a 235 with a 12 bolt 3.73 rear. The vibration was worse and at all speeds and RPMs before I installed a trans crossmember and shimmed the pinion angle a little. Now I'm trying to fine tune it. It's a little scary at 75MPH

How about just revving the engine into that range with the trans in neutral, or with the clutch depressed? If either of those situations cause a shake, it's definitely engine-related. It's possible the balancer ring could have slipped, or maybe it's gotten a little crossed up. Use a strobe from a timing light, and see if the balancer is wobbling. By switching to different spark plugs with the trigger lead, you can inspect the damper all the way around. A delay-flash light would serve the same purpose.
Jerry

to answer you question, a 216 balancer will fit a 235 crank. ck pulley diameter and belt width.

OK, everything behind the engine (driveshaft and wheels)is balanced and I still have a vibration around 2100 rpm. No matter how fast I'm going, if I push the clutch in, the vibration goes away. This tells me it's got to be the engine, right? I think its either the balance of the motor itself or the flywheel may be loose. I didn't put the flywheel bolt locking plates back on. I thought red locktite would hold them) Am I wrong on this? Any other suggestions? Is it possible to balance the engine after its put together? I also had the machine shop thread a hole to hold the harmonic balancer on. Could that throw it out of balance? Forgive my ignorance, please. :confused:

The design of the balancer prevents the internia ring from slipping,it's like a heavy plate with the pulley and hub rivited to it with rubber discs in between.They all seem to wobble a little,I got one that wobbles and the engine runs smooth.
Sounds be an out of balance clutch assembly or somethin in the engine,a loose flywheel should make a knocking noise when you get on and off the gas,but............just drop the flywheel pan and see if it's loose..

Thanks Trucked up. I have heard that these engines were externally balanced from the factory. Is this correct? I went to my local old chevy graveyard last weekend and the guy had a bucket full of old balancers. Every one seemed to have a little bit defferent pattern of drilled holes on the outer edge. It looks like thats how they were balanced. If so, how the heck am I ever going to get this thing right now. I'll surely check the flywheel first. Thanks

the drill marks are to balance the balancer itself, not the engine, but I think having the wrong type balancer for that engine can cause problems, as they are the 'external balancing' - the 'harmonic balancer' is to take care of the particular harmonics developed by that design of engine, so they're different for different engines, tho 216 and 235 may be close enuff - that said [I think!], I'd check out the flywheel/clutch assembly, which can also be unbalanced like truckedup sez

Bill

How would one go about balancing a clutch assembly? Could a clutch shop do this? Thanks for the replies.

never ran across a clutch shop, but any automotive machine shop can check it for ya, the flywheel too - like where ever you got the engine done [or crank turned - sure they did a good job?]

Bill

These engines are not externally balanced,the flywheel is neutral ,as is the damper.The alignment dowels insure the flywheel is positioned correctly on the crank,for lining up the timing marks,not a balance issue.Unless the crank was altered during the rebuild,the engine should run as smoothly as before the rebuild.The piston and rod weight is not important on an inline 6 so long as they all weigh the same within reason.
Does the vibration get worse with higher engine speed,or it it worse around 2000 rpm?

I guess it is important to verify that the vibration is there with the truck sitting still and the motor running in neutral. Too many times I have read about a vibration and the cause became obvious when a fan blade flew off, very very dangerous. An easy test for this problem is to remove the fan belt and run it up that way.

This engine had been rebuilt before. When I bought it, it still had the crosshatch pattern in the cyls. and .40 over pistons. I guess it could have been unbalanced before I started. I had the crank turned is all. And my engine guy got all the pistons in the order they came out. I helped him so I know this is fact. I guess I learned something here. It seems the best thing to do is have the entire rotating assembly balanced at a machine shop. Live and learn I guess. I'm gonna check the clutch assembly today. Make sure the flywheel isn't loose. Thanks for the help guys.

Shipwright, If you have a rebuilt pressure plate and most are these are netorious for being out of balance. This information came from my mechinest who has ben messing with these engines for 45 years. Remove it and the fly wheel and take it and have it balenced. I had the same problem in my 53 235 and it fixed the problem. Make sure that they make a witness mark so you can align everything when installing the pressure palte to the fly wheel. Hope this helps

Thanks 235 fat. I had a sneaking hunch that could be the prob. Who should I take it to to have it balanced? Just any machine shop? Thanks again.

Any automotive machine shop can balance a flywheel and pressure plate assembly, it has also been my experience that rebuilt pressure plates are out of balance. Also check your drums.

if it vibrates in neutral with the clutch engaged it is either engine or clutch related.If it vibrates going down the road and stops when you disengage the clutch it is in the drive line.

When I go down the road and disengage the clutch, it stops the vibration. The engine speed goes down to idle and I'm going the same speed. How can this be drivetrain? Dosen't it have to be engine or clutch?

seems most likely - after you've definitely eliminated that possibility, if it's still doin it ... on to the next! the driveshaft and rear end may act differently under power or not

Bill

Just out of curiousity, what kind of fan do you have on it?...
Tony

I had to get one from the bone yard. Don't know what it came off of. I did have to tweak and trim it to get it to clear the balancer. (I had a threaded hole cut in the crank to hold the balancer on). I see where your headed here. Do ya think that could be it? Boy, that would sure save me alot of work if it is.

if you cut on the fan blades that is where your vibration is.i would almost bet money on it.try starting it with the belt off bring the rpms up to around 2100 slowly and see if it still vibrates.

I also suggest that you not have your head under the hood at the time, and I AM SERIOUS!

Is there a way to balance the fan blade? I need it trimmed to clear everything.

Try removing the fan and running down the street and back before it gets too hot. that rotating mass can be a problem especially if its not balanced. I was thinking there were diffrent diameter fans for diffrent year stovebolts. I think mine is a 15" 4 blade, for a 41' 1/2ton 216ci.
Tony

My vibration was in the rear end, only under power, but it was a newer vehicle. With the clutch in, coasting at speed, no vibration. Clutch out at the same speed, vibration, but not constant. It was a rythmic vibration, like you can get out of a U-joint going bad. All new U-joints didn't fix it. New rear bearing in the tranny didn't help. Drive shaft balance didn't help. New pinion bearings in the rear end cleared it right up.

im sure you could find a machine shop that would balance your fan blade but it wouldnt be cheap.you might consider an electric fan that would solve your vibration and clearance problems

Trucked up had a post on here a while ago about the fan. He bought a plastic one, I think from Summit Racing and trimmed it with a pair of scissors.

Even a slightly out-of-balance fan is dangerous. Doing any trimming at all on fan blades is a recipie for disaster. There are several types of aftermarket fans designed to fit a variety of applications, but use then "as is", with no modifications. Spacers between the fan and the pulley are OK, trimming the diameter isn't!
Jerry

Had the same vibration at the same RPM! It was engine RPM, not drivetrain that changed the vibration.

1. Found the flywheel I took off had a series of holes drilled on one side. I did not pay any attention. It came off the 216 that was in the car and installed on a 235.

2. Vibration destroyed the rear main bearings.

3. Found also that the crank end play way out!Thrust surface of the main bearings was shot out or not right! Crank was walking back and forth over 3/16 in.! End play should be .008 or less!

4. This was a fresh rebuilt 235.(Not by me!)

5. New crank, bearings, oil pump, and a different flywheel (from a known 235, no drilled holes!) NEW clutch cover and plate, fixed the problem.

6. 235's are internally balanced. Harmonic balancer and flywheel are netural.

Trimming fans is simple,ya just gotta be smarter than the fan and not just hack away.I would consider a 50 year old fan far more potentialy dangerous than a new one with a slight edge trimming.
The stock 302 GMC and a few other engines have the inner fan blade edges trimmed for damper clearance.When nothing off the shelf fits,make what ya want.

When I trimmed it, I tried hard to trim the exact same amount off of every blade. It was about 1/4" X 1" on each blade. I'm gonna try to drive it in the morning with the fan belt off and see what happens. Haven't had time to mess with it the last 2 days. I'll keep ya'll posted.

Shippy... did you check that it is balanced after you cut it?

I just hacked my blades off with a sawzall, then "balanced" it by laying it on top of something (i forget what i used)..

It doesnt have any noticeable vibration.

I thought 235s weren't supposed to have a bolt holding the damper in place, and that if one is used to pull the damper in, it should be removed before running the engine. I could be misremebering though.

It ain't the fan. I installed an electric fan in the 49 today and it still vibrates. So, I got :mad: and took the tranny out. Sent the pressure plate and flywheel out to have it balanced. Got my fingers crossed cause if that ain't it I'm in deep %#@^$. Have to be internal engine. One more thing to try before that is the harmonic balancer. Can't imagine it being bad. It looks good and does not wobble. Getting the flywheel off was a chore as I used red loctite on the bolts.

Balancing the flywheel and Pressure plate seemed to have helped alot. The guy that did the balancing said it wasn't that bad so I didn't think it was gonna help. But, I got it all back together and seem to be better. Still a little there but not as bad. I have about 4,000 miles on it since I got it together so I hope all is well. Joker, Thanks for the heads up on not following thru and reporting on how our problems were solved. I'll try to remember next time.