Bad engine vibration -- HELP

[Kohnke Rebabbitting]

Re: Update

As I stated earlier I removed the new reproduction original style front motor mount springs and flat metal plate. I put the old "home made" setup back in. I also loosened the rear motor mount bolts which resulted in the front of the motor dropping about 1/16". Then I re-tightened the rear motor mount bolts.

I drove the pickup about 30 miles on the highway. The vibration problem did calm down but it is still more than before I rebuilt the engine. As before the vibration is the worst when I decelerate. I increased the speed to 65 mph as I approached the off ramp. I took my foot off the gas and left the transmission in 3rd gear (overdrive engaged). At 65 mph the vibration was very slight. As the car slowed down the vibration increased and reached a maximum at about 55 mph at about 45 mph the vibration was very slight again.

As I was going down a fairly steep hill at 55 mph there was considerable shaking (less than before). I pushed in the clutch and as the engine speed decreased the vibration when away. However if I reved the engine up to approximately the same engine speed as it was when the clutch was engaged the vibration returned but was just a little bit less than when the clutch was engaged.

I do have a Mitchell Overdrive so 55 mph is about 1800 rpms.

With the car parked and the transmission in neutral as I reved the engine and the vibration increased up to a certain rpm then calmed down as the rpms got above that speed. I guess that the maximum vibration in this test is the same 1800 rpm that I found in the other tests.

The frequency of the vibration is engine speed dependent and not road speed dependent.

I feel better that the vibration is not as bad as before. But I still think there is something not quite right. It looks like there are 2 issues. First the engine is vibrating too much at a certain rpm. Second that vibration is amplified when the car is decelerating.

What now? Remove engine and recheck all balancing. Remove rear end and check u-joint. Do some more testing ??? Leave it alone and live with the vibration.

Bob

Bob. I have read all your Information again, but this post, TO ME, is of the most intrest. I could be wrong, and I would like to find out, but I do not think it is the drive train. I have missed the part where you have said if you have had the over drive before, or if it was a new addition. But you described the vibration at 45 M.P.H., that will fit most of the Model A's in the world. It sounds like the 55 M.P.H. mark would be when in over drive, that would be about right on the speedometer. A Model A, and other engines when balanced well, will still transfer vibration to the frame, and the mirror will still give you a funny out look on life. Model A motor mounts leave alot to be desired, I would regardless, put on float-A- Motor, like what was suggested. Just for the heck of it, take a compression test. You will always have less vibration on on acceleration, then deacceleration. The rods showing no signs of metal removal still makes me wonder, or some one was real lucky. When you balance an engine, it still vibrates, but all the parts last longer, with less wear, and a higher engine R.P.M.'s, before it levels off. Let us know what you find out. thanks Bob, Herm.

 

[newshirt]

I also ruled out the drive train after hearing this statement:

Yes I feel a similar vibration in 2nd gear at around 25 mph. Also in 1st and reverse at much lower speeds.

If horrendous vibration occurs in 1st gear, it's probably not the ujoint, right? Because it's turning at low speeds in 1st.

But if the vibration is actually much more intense at 55 mph, perhaps there are multiple causes. E.g. engine, ******, ujoint.

Bob?

 

[James Rogers]

I suspected from the beginning the vibration Bob is experiencing is the kind that is inherently common in 4 cylinder engines with opposing crank throws. Without riding in the car and experiencing it first hand it is difficult or impossible to define and diagnose. All the Model A's I have ever driven have a vibration at about 45 MPH and it lessens at about 48-50 MPH, some worse than others. I agree with Herm and don't think you will ever get rid of this vibration completely. I suggested the u-joint because it is a viable possibility. I have been wrong before even when I could have hands on the problem.

 

[d.j. moordigian]

I have followed this thread from last week, the thing that " spook's " me is,
in #23, no metal was removed from the rods. In another, " no new holes ", I think
in either the crank or flywheel (can't remember which ), I've done engines for almost
40 years, both balancing and building, and that bothers me.

Dudley

 

[Kahuna]

I agree with Dudley. It is definitely in the engine.

 

[Bob Johnson]

I understand that vibration is inherent in a Model B engine. However my point is that there is a stronger vibration now than before the rebuild. Before I put the old front motor mount springs back the vibration amplitude was much more than what I would consider acceptable. Currently the vibration strength is on the high side of acceptable. I have been in Model As which have stronger vibrations and ones that have less vibrations than what I am currently experiencing. I had hoped that with the rebuild the vibration strength would have gone down.


Bob

 

[Mike Mc]

Nothing silly like a intermittent misfire under load?

 

[Bob Johnson]

Mike Mc,

I am fairly certain that it is an engine balance problem and not a misfire. But thank you for the suggestion.

Bob

 

[Louis]

Bob,
You might be expecting to much. Have you driven any other "A's" to compair?
My 31 coupe vib's all the time , but it allways start's and idles and pull's good for an 80 year ole car. Good luck .

 

[Milton]

Bob,
I've been following this thread since it started an held back on a reply since so many are more knowledgable about this than I am. There are a couple of things that cause me to think about it by what has been said by you and others.

What, exactly, do you mean by this, "(exchange rods and main caps)"? Are you saying that the original rods were replaced with a set of rods that were rebabbitted? Also please explain what you mean by exchanging main caps. Do that mean the caps were prepoured and the block was poured and align bored with the new caps? I am quite illiterate when it comes to babbit.

When you say "Rod checked for straightness and weight." My first thought is, this is not how rods are balanced. Rods have both rotational and linear motion. When balancing rods the weight at the crank ends must be equal and the weight at the pin ends must be equal also. This point was brought up by Brent early on, "were the reciprocating parts of the engine balanced during the recent rebuild?"

Another thing that I find puzzling is, "There were 3 new holes drilled in the counterweights of the crankshaft." Now why would that be since, I assume, cranks are straightened and balanced when counterweights are added. "The flywheel showed no new holes." This part bothers me also. When you say there are no "new" holes do you have "old" holes that indicate a previous balance i.e. factory? Way back when I had a 15 lbs removed from a wheel and was too stupid to balance it I was lucky that it worked OK.

The experience that I have had with deceleration vibration has usually been main bearing related along with that extremely heavy flywheel. During deceleration the load is removed from the crank and it is free to wobble. If the tolerances are incorrect the flywheel will certainly let you know it.

I don't know the cause of the vibrations but I would suspect the "balance" that was done, especially in relation to the rods and the flywheel.

 

[Bob Johnson]

Milton,

Yes the rods were exchanged with ones that were already babbitted. They were poured undersize then bored to fit my crank. Yes the main caps were also exchanged with ones that were pre-babbitted.

My crank is a 1934 Model B chank and the counterweights are part of the crank forging. The flywheel at sometime before I owned th car was lightned. At that time it was balanced, holes drilled. When I had it balanced this time I saw not new balance holes which suggests that it was still in balance.

I had the rods balanced but I did not notice that any material was removed. I did not watch the balancing so I can not say exactly how it was done.


Bob

 

[1931 flamingo]

Have you gone back to the engine "builder" and ask how e/thing was balanced??
Paul in CT

 

[Milton]

When the exchanged main caps were installed did the block have the babbitt repoured and was the assembly align bored?

 

[Bob Johnson]

Milton,

Yes the block was re-poured and then caps and block were line bored.

 

[Milton]

Well nuts, I had hoped to be of help but, you answered all of the stupid and not so stupid questions correctly. So, unfortunately, the only thing I can imagine would be the rods not being balanced at both ends? Not knowing the qualifications of the rebuilder is a hinderance also because about all that is left would possibly be a twisted crank, which I haven't heard of, or a combination of small things that just happen to combine into some thing big. Such as the case of uneven compression in the rebuilt engine due to not having seated rings along with a gram or so of bottom rod weight difference causing torsional twisting in the crank especially with uneven piston acceleration and add to that a bad pilot bearing. At some point these things could reach a point where they harmonize and presto harmonic vibration.

This is a tough thing to diagnose but, some simple overlooked testing may lead to the source of the problem. I hope so because this vibration thing has been a longstanding dilema which, in many cases, has just been accepted. Whatever the cause, when the solution is found, please post your findings here as they will be invaluable.

Again, I'm sorry I couldn't do better for you.

P.S. If you haven't done so already, here is some info on why rods need both ends balanced and other possible answers toward a solution.

http://www.fordgarage.com/pages/etbaebalancing.htm

 

[newshirt]

Could you put the motor on an engine stand and diagnose the vibration there?

Maybe you could observe the vibration at each rpm interval. At the very least, it would eliminate the motor mounts and drive train as possibilities. I'm just fishing for ideas...

 

[George Miller]

Milton,

Yes the rods were exchanged with ones that were already babbitted. They were poured undersize then bored to fit my crank. Yes the main caps were also exchanged with ones that were pre-babbitted.

My crank is a 1934 Model B chank and the counterweights are part of the crank forging. The flywheel at sometime before I owned th car was lightned. At that time it was balanced, holes drilled. When I had it balanced this time I saw not new balance holes which suggests that it was still in balance.

I had the rods balanced but I did not notice that any material was removed. I did not watch the balancing so I can not say exactly how it was done.


Bob

Bob I have seen many cranks on the A that have been ground off the center line. I know you said the flywheel did not wobble but did it run out up and down. I have seen them .007 out because the grinder did not indicate where the flywheel seats.

 

[J and M Machine]

I have been following this link and clearly the machine shop by not checking the rods nor flywheel did a dis service for not checking the weights.
Enclosed are a few pictures of the associated problem so you can see how much the flywheel could be off. This flywheel is cut down as was sent to us. You can see how much it was off 24 grams. Which would make quite a thump in the engine as it rotated.
The rods are weighed end for end and then total weight.
Since there is no way of knowing the rods you received are out of the exact same engine and no way of know how much babbitt gets poured in the best way to solve the problem unfortunately is to disassemble the engine and rebalance everything.

http://www.jandm-machine.com

 

[Bob Johnson]

I think I should clarify some things.

The flywheel was checked for balance as was the pressure plate. The flywheel did not have any new balance hole drilled in it. The pressure plate did have extra weight added in 2 spots. Since the pressure plate can only be balanced while on the flywheel and the pressure plate was adjusted the flywheel would have to had been balanced first. The shop that did the balancing told me that they balanced the flywheel first then the pressure plate on the flywheel. So IMHO the flywheel was still in balance from a previous rebuild.

As I said before I did not notice any metal removal from the rods. However I did not spend much time examining them. My instructions (which the shop wrote down on the order) were to install the bushings, straighten and balance the rods. I do not know how they were balanced.

Bob

 

[J and M Machine]

Hello Bob:
Typically if the clutch and flywheel are balanced it makes a big difference how it was first spun and then the orientation of the clutch and the flywheel have to stay the same whent hey are spun together.
Since you said they put metal on the clutch. If the clutch is reassembled one hole off then you have an out of balance again.
That's why I posted the two pictures of before and after so you can see the amount it was off.

George Miller has a point also that occasionally the crank grinder when grinding aggravates an out of center position of the crank and the balance will be worse because of that fact.

In regard to the rods. I've never seen a set that was perfect, either total weight was off or big end or small that just doesn't happen.
I believe Herman Kohnke had mentioned this also.