Engine Vibration

R

Richard Lorenz

Senior Member
I have an engine that was recently rebuilt by a very good builder. It has a vibration in it that I cannot figure out. The flywheel and crankshaft were balanced together by a competent shop. The vibration feels like it is something caused by an out-of-balance component, but that could not be the case. The vibration is present when we ran the engine with only the flywheel attached, so adding the clutch pressure plate could not be causing the vibration.
I could tolerate the vibration of the engine, but the worst thing is that it results in a loud rumbling noise in the cab. That rumble is present even when the floor-board is removed. We changed the engine mounts to float-a-motors front and back which helped some, but not enough to want to drive for very long.

The crankshaft has counterweights attached. The oil pan looked to be in excellent condition. There was no indication of any parts rubbing that we could see when we took the engine apart to try to find the problem. Could there still be some reaction between the counter-weights and something else, like oil splashing around. The shaking seems like it would take something stronger than that. Your ideas are appreciated. Richard Lorenz
 
You might try shorting out each cylinder to determine if it from one of them. Hold a screwdriver from a head stud over to the top of the spark plug. Is the vibration at low idle or all through the range? Check the gap inside your distributor body from the contacts to the rotor.
 
yep stuff happens. rebuilder and balancing shop didn't get it where it is supposed to be, if it vibrates with just crank and FW attached
Weights may not be properly centered to each other, either

Or they didn't balance rods and pistons.
Some piston sets are off by as much as 10-20 grams
Also, if you used the old school stock type heavy pistons they are harder to get right
 
Good Evening...It seems to me that you have a problem with the re-built engine that you are not going to be able to solve on your own. Before damage is done to the engine, talk to the engine re-builder and see if they would like you to put the car on a trailer and bring it to them as it is. Then they can hear and feel the problem and figure out what the issue is. Hopefully the re-builder is not too far away from you. The safest way to take delivery of a rebuilt engine is to have it completely assembled at the re-builder and run on their test stand as proof of a good rebuild. The flywheel, clutch and pressure plate should be in place. If all is well on the stand, then it will install well. If there is a problem, you have the correct folks assembled to figure it out before it is put in the car. Good Luck...Ernie in Arizona
 
About 10 years ago I had a local, well-known homebuilder help me with a head gasket replacement and valve adjustment. When I picked up the car it vibrated, and he said , oh, it'll smooth out. It didn't, and he refused to take it back in for a further check. We pulled the engine and took it to another homebuilder in another state. Picked up the new rebuild which we specified with a counterweighed crank and lightened flywheel. When we were reinstalling the engine I picked up the fan that was on the engine before it went bad, same fan I had used before the gasket problem, a new alloy two blade one. AT THAT POINT we noticed that a 3/4" chunk was broken off the tip of one end of the blade. The first guy had dropped it and broken it and not investigated the vibration. That chunk cost me a new engine and a lot of education.
Fearless
 
denniskliesen said:
You might try shorting out each cylinder to determine if it from one of them. Hold a screwdriver from a head stud over to the top of the spark plug. Is the vibration at low idle or all through the range? Check the gap inside your distributor body from the contacts to the rotor.
Click to expand...

I am currently getting a rebuilt engine tweaked and broke in. Also had a vibration problem, even though it has counter balanced crank, lightened flywheel matched to V8 clutch. Starting out, had to clean carb--got a little better. Then determined dist rotor was striking dist contacts--fixed that with a file. That helped. Shorted the plugs, number one didn't change so replaced the plug, now running pretty smooth. I think I might have another problem though. I have a Snyder 5.5 head but only 62 psi compression, need to figure that one out next. I think it should be better than that--maybe not. I have retorqued the bolts.
 
we have 100 psi on a Snyder 5.5 on a brand new motor here....I would investigate.
65 is closer to stock 4.2 head.
Sure it is a 5.5?
stock and snyders are not marked.....
 
Thanks for all of the suggestions. We will check compression tomorrow. The flywheel is not on upside-down. We carefully marked it with red paint.

My grandson, who is doing the heavy work(6 foot-eight inches tall), will have a new business work schedule which means that we will have to slow down on this project for awhile.
 
I don't know how severe your vibration upon deceleration is, but don't overlook the fact that model A engines do vibrate considerably more on compression (when not applying power, or slowing down) than when accelerating. That's just the nature of the beast. I won't go into why, since that has been documented here in the past, several times.
 
I built an engine several years ago, a BB crank in a B block. All was balanced professionally. It had 3 vibration points, none of which was in the RPM range I drive in, all of them turned out to be "normal" in some engines. It was more noise than anything, it was not noticeable unless out on the road with it. Yours doesn't seem to be anything near normal! Remove the fan belt to see if that helps. Good luck!
 
gustafson said:
yep stuff happens. rebuilder and balancing shop didn't get it where it is supposed to be, if it vibrates with just crank and FW attached
Weights may not be properly centered to each other, either

Or they didn't balance rods and pistons.
Some piston sets are off by as much as 10-20 grams
Also, if you used the old school stock type heavy pistons they are harder to get right
Click to expand...
Seems to me you jumped to the WORST possible conclusion with very little information. I would recommend going back to the builder first.
 
Universal joint. It got better because it got re-lubed (deep down inside the surfaces, but it will only get marginally better. Put it up on jack stands and star it up. Jar of water on the head, and watch the water. Kick it in gear and watch again. Pull the drive shaft / rear end, and I bet the vibration goes away. If you suspect the fan, slack the belt and drive it abt 1/8 of a mile. It's either a fan, U-joint, flywheel position, or in the worst case a bad rod.
 
I have looked at all of the above suggestions and checked them on my engine.
They are good ideas, but they are not what is causing my vibration.

The good news is that we installed float-a-motors front and back and that took stopped most of the vibration from being transmitted to the frame and from there to the cab. The noise level in the cab is way down, so we can drive it and be comfortable. Not perfect by any means.

Our latest compression test, is 56, 55, 58, and 62 psi. We plan to drive the car 100 miles or so and check the compression again. We did a bleed-down test by blowing air into the cylinders using a gadget that I built. There was a lot of air bypassing the piston rings and coming out the oil filler tube. This might be normal for a room-temperature engine, or it might mean that the piston ring end gaps are unusually large. After a 10-mile drive, there was only a very small amount of oil that came out of the filler tube and got on the engine.

We ran a timing check to see if the dimple on the fiber cam gear might have been put in the wrong place. It checked out to be O.K. With the #1 cylinder at the top, the timing pin detent was felt, and the old timing mark on the pulley was also in the correct place.

As mentioned above, we hope that driving will improve things. Thanks again for your help. Richard Lorenz
 
In my experience, NEVER Balance a Model A, or any 4 cylinder crank with the flywheel!


Balance a rebuilt Flywheel, always with the new pressure Plate, and Mark the position. Pressure Plates are always way out !


A crank with chunks of weight bolted, or welded, or both, on one side of the crank, will never be in as good of balance as the Ford weights, that encircle the crank, not by a long ways.


I can also tell you, there are Guys that Balance, and Guys that know how to balance. There are always a difference in Doctors.!


Herm.
 
Hmmmm.My motor is modified and was scrupulously balanced by a highly respected balancer.
It had vibration periods exaggerated by camshaft gear rattle. After changing to bronze timing gear and matched crankshaft gear also from a highly respected source, nothing changed.
Finally I fitted a harmonic balancer pulley which simply transformed the motor.
Is your vibration continuous or are there vibration periods?
A harmonic balancer pulley could solve your problem?
 
denniskliesen said:
Question Herm, What then is your opinion of Burlington or Scat cranks as far as balance?
Click to expand...


They have balanced out good, as they have more weight between where the weight would be welded on, and smoothed out and filled in to the Rod Pin.


Picture of a scat Model T crank.


Herm.
 

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Kohnke Rebabbitting said:
In my experience, NEVER Balance a Model A, or any 4 cylinder crank with the flywheel!


Balance a rebuilt Flywheel, always with the new pressure Plate, and Mark the position. Pressure Plates are always way out !


A crank with chunks of weight bolted, or welded, or both, on one side of the crank, will never be in as good of balance as the Ford weights, that encircle the crank, not by a long ways.


I can also tell you, there are Guys that Balance, and Guys that know how to balance. There are always a difference in Doctors.!



Herm.
Click to expand...

So, are you saying that the crankshaft should be balanced separately from the flywheel/pressure plate assembly?
 
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