Vibration Problems
 

Hello Everybody,

I am working on a 30' coupe and I have a vibration problem. Here is the history of the work on the car. I had the engine rebuilt at a well known builder in So Cal. The transmission, I rebuilt with new parts from Mac's. I had the flywheel balanced, but they couldn't balance the flywheel and pressure plate assembly together (for some reason?).
I have a vibration that is noticeable at idle, really noticeable at cruising speed. It is at its worst when you lift your foot off the gas and coast. As in approaching a stop sign.
I have used a long screwdriver and listened to the engine at idle and I don't hear any knocks. I have to believe that it is coming from somewhere between the flywheel and the u-joint.
If you have any advise, thoughts, or wisdom, I'd love to hear it.

Thanks for your time,
Chris

Re: Vibration Problems
 

I would really want to know why the flywheel and PP could not be balanced together and start there. Were they too far out of balance to bring into unified balance? That is hard to imagine. Were they "balanced" at all? Was the crankshaft balanced?

Re: Vibration Problems
 

Is the vibration the same when its in neutral and sitting still ?? Was the engine or any part of it balanced.. Was the crank balanced with the flywheel ?? This may seem like a dumb question but was the flywheel installed correctly ??

Re: Vibration Problems
 

Could be the U/J .Try decelerating with the clutch pedal down,just stopping on the brakes.Then try leaving clutch pedal up and use engine braking to see if any marked difference . Worth a shot,worn U/Js when back driven on overun do cause vibration.

John in heavy rain shower afternoon England

Re: Vibration Problems
 

Thanks for the responses. Yes the engine was balanced, however not with the flywheel on. The flywheel was balanced alone because the machine shop here in town said that their machine could not accept the whole assembly. I don't know if they couldn't or just didn't want to. As for installing the flywheel correctly, I believe I did it correctly however I will be checking it out.
The vibration occurs at idle with the clutch both in and out.
I'll go out and try coming to a stop with the clutch in and again with it out.

I'll report back later.

Thanks again,
Chris

Re: Vibration Problems
 

Re: Vibration Problems
 

What Marco and I are trying to do is determine on which side of the flywheel the vibration is coming from and Marco is even eliminating the disk and transmission.. It seems as though its coming from the flywheel forward,,but,, its nice to know before taking anything back apart..

Re: Vibration Problems
 

Thanks again for your help with my vibration problem. I have taken Marco's advise and the vibration is present when I have the trans in gear, clutch pedal in, sitting still, and reving to various levels then lifting my foot off the gas. So would you say the problem is in the flywheel forward? I wanted to eliminate all other sources before I yank the engine and transmission. However, that seems to be the way this train is heading. What do you think?

Thanks for your time,
Chris

Re: Vibration Problems
 

My guess is that the crankshaft was ground off-center. This would put the flywheel off center as well. I could not find the right drawing, but I think that you might be able to get a dial gauge on the outside of the flywheel either from the top or from the bottom where the large cotter pin is in the flywheel housing.

Re: Vibration Problems
 

You can pull the starter and use the gauge on the flywheel there. Just need to crank it over by hand.

Re: Vibration Problems
 

Before doing anything major, be sure to try running the engine without the fan belt to rule out the fan being out of balance.

Re: Vibration Problems
 

I don't know whether it's relevant to your larger problem or not, but this aspect is common to car motors and especially noticeable in the Model A. The greatest stress on the rod bearings is normally when the piston is at the top of the exhaust stroke, where the piston has to reverse direction instantaneously and there's little springy cushioning from combustion chamber gases to help it out. If the car is coasting, there is even less cushioning since only idle-level amount of gas is being burned.

It's not so much a problem at the other end of the stroke because the direction reversal occurs leisurely over the time it takes for a rod crank bearing is swinging around in a big arc.

Also, by the way, this explains why high compression heads are actually easier on the bearings--greater cushioning to help the piston reverse direction at the tops of the strokes. Of course, at high enough rpms, this benefit is overwhelmed by other issues, and all bets are off if you've got detonation or preignition.

You can reason through which side of the rod bearings should wear out first; you would get the opposite answer if compression/combustion force were the main problem.

Let me be clear, I am not claiming that this explains your excessive vibration.

Steve

Re: Vibration Problems
 

Is your flywheel stock or has it been lightened ? If stock, it should be balanced as Ford was very perticular about that portion of the engine. Back in the early 60's I had a flywheel cut down to 39 lbs. I took the flywheel and a rebuilt A pressure plate to a balance shop. When I picked them up a few days later the owner said he didn't have to do anything to the flywheel that it was in balance but he said the pressure plate was terrible, like it had a 80 lb glob on one side at 1800 RPM.
A good balance shop will check the flywheel first, then bolt up the pressure plate and check the balance and if out will make the corrections on the pressure plate. They will then mark the flywheel and pressure plate and when installing you match the marks.

Re: Vibration Problems
 

I would pull JUST the engine and leave the tranny in place. Also be sure to dial in the flywheel housing. A dab of grease will hold the shims in place while bolting the engine back in.

Vibration Problems: Check the fan first....
 

Good point on the fan being out of balance...
This past spring a car with an engine I rebuilt showed up at my shop to help find a source of a severe vibration. Before delivery of the engine, I ran the engine on my break-in stand over 3 hours and had not noted any vibration. I had my waterpump and fan on for the break-in.
The observed vibration was ever present but most noticeable at higher RPM and upon quick let off of the gas pedal. Suspecting the fan, it was removed and checked. The cast aluminum fan was way out of balance. Replacing the fan with a balanced one solved the problem.
Tom Wessenberg and Brent Terry have posted info on the device used to balance fans. Search their posts for more info.
The source of vibration in this thread may well be something else but checking the fan is so little work....
Good Day!
Dave in MN

Re: Vibration Problems
 

yes it was a dumb question no way can you install one any other way

Re: Vibration Problems
 

Huummmm, so you can't install a flywheel incorrectly.. Huh.. I'm not much of a betting man,, but,, I'll surely take this one.. In all the years I've been doing this type of work, when its said that something is foolproof and can only go one way, trust me, someone will find a different way..

Re: Vibration Problems
 

Yeh, nothings foolproof because we fools are very clever. To add to Marco's thoughts on isolatiing the engine as the cause, you can drive it and when the vibration is at its worst, put it in neutral and turn off the engine and coast a ways. If you are going to take the engine out, dial gauge the flywheel both side to side and fore and aft before you remove it from the crank. It could be warped, or not square on the crank, and gives you info for the machinist. I would really want to get the flywheel and PP balanced together. Balancing the wheel is not going to help much if the PP is off very much. Balancing them all with the crank is better. Also, there is some vibration "noticeable" on any A and you might check with other cars to see if yours is excessive. It is hard to describe in words on a post when "some" or "noticeable" become "too much."

Re: Vibration Problems
 

My 28 float a motor kit had a piece that connected to the u joint cover and rested on the cross member behind the transmission. Removed it and my vibration issues disapeared.