Engine Mounts & Vibrations

[Bob Bidonde]

I seek your opinions in this matter. My goal is have minimal engine vibrations transferred to the frame.

I decided to experiment with my Victoria which has a balanced Model "B" engine.


Currently it has a Model "B" type front engine mount and stock Model "A" rear engine mounts. Vibrations transferred to the frame are more severe than with the stock front motor mount.


I am considering changing the stock rear mounts to the Float-A-Motor rear mounts and keeping the Model "B" type front mount. Will the vibrations be less or more severe?
Should I return to all stock engine mounts?

[Ray in La Mesa]

I've had the best luck with Float A Motor rear mounts and a stock y front Model A mount.

[chrs1961815]

I am a stock guy. What you have to realize is that you will not be able to do much about vibration since it is inherently part of the design.

[Brokenvette]

Like the previous post. My last build has Float A Motor and stock front. Minimal vibration.

[katy]

Originally Posted by Ray in La Mesa

I've had the best luck with Float A Motor rear mounts and a stock y front Model A mount.

That's what's on my '31 CCPU. It came to me w/F-A-Ms on the rear and some kind of springs w/hard as a rock rubbers at the front, replaced the front w/stock type, works well.

[Big hammer]

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Rear FAMS used the transmission mount stock front ! I probably need to tweak the rear transmission mount next time the floor boards are out. I believe the rear rubber block is to thick for my application. Noise has been reduced greatly, as for vibration you’ll never completely get rid of the vibration from in an A or B motor IMHO . The rear side mounts will need to be adjusted/ fine tuned.

[nkaminar]

As stated above, no Model A or B motor will be completely vibration free because of the fact that the pistons change direction at TDC and BDC but not at the approximately 90 degree positions. So it cannot be 100% counter balanced.

With the stock rear engine mounts, the rubber pads must be in good condition (new) and installed correctly (with the spacers and correct bolts and nuts). This will reduce the vibration but the Float A Motor mounts have less vibration.

When using the Float A Motor mounts in the rear, do not over tighten the two mounting bolts that go through the rubber bushings. Just snug. The stock front engine mount works best for me and for a lot of other Model A/B owners. The front mount must be installed correctly and adjusted correctly.

[johnneilson]

nkaminar,
You are partially correct about the vibration due to the 4 cyl design.
the issue is the offset acceleration of the masses (pistons et all) at TDC and BDC, this causes the harmonics and contributes to the vibration.
Another contributing factor is that, well, 50 cu/in of displacement causes a resistance on compression (up) with a pretty good acceleration on the next stroke down. Remember that one power stroke per 180 degs rotation of the crank, compared to 90 degs on a V8 (normal)
A stock motor is .25 hp per cu/in (40 hp / 200 cid) not much to BMEP (brake mean effective pressure)
As the HP goes up, the BMEP increases and the resultant forces are contributors to the vibration felt.
All of this to say, no, without an engineered counter shaft the felt vibration will never be dampened out. I see genius in the rattler flywheels and harmonic balancers, none of these will be 100% effective until the crankshaft flexing is controlled.

Best, John

[Rob Doe]

Originally Posted by Brokenvette

Like the previous post. My last build has Float A Motor and stock front. Minimal vibration.

Can you be more specific as to the tightness of each side of the Float A Motors. And do you have the transmission mount also?

[Synchro909]

By my experience, less vibration will be transferred to the chassis with the FAMs but handling will be detrimentally affected. Both the front and rear axles rely on the location of the gearbox for their position. With FAMs, the gearbox moves around, allowing the alignments of both axles to change. That makes the car feel "Fuzzy" on the road.
It seems that for every gain, there is a loss somewhere else with these cars. when we make a change.

[31a]

I have the B mount on the front and the regular float a motor on the Rear once I loosened them up it was much better also the rubber seems to get hard quickly and does not work as well

[Bob Bidonde]

Here's my plan. My Victoria currently has the Float-A-Motor front mount and the stock Model "A" rear engine mounts. The vibrations transferred to the frame became more severe when I changed to this arrangement, so:
> Try adjusting the front Float-A-Motor mount to frame bolt clamp-up to improve the vibration transfer;
> If no sweet spot is found, try the rear Float-A-Motor mounts including the transmission support to hold the drive-line 3-degree angle;

> If no sweet spot is found with above, then convert back to the stock Model "A" front & rear engine mounts, and tweak the stiffness of the springs to tune the vibration transfer.

More to follow.

[duke36]

The latest vendprs' rear FAMS are less prone to cracking than the older repro alumin ones and the rubber biscuits are nice and firm. Sometimes the rear yoke mount hard rubber to crossmember pad may need some shaving to get 3 deg. Older instructions suggested to tighten the FAM bolts just until the top round plates can firmly be rotated by hand.

[WHN]

64 years of owning Model A Fords and I am still amazed by the number of car owners that just like to play with improving a car design that has lasted almost 100 years.

I have always felt that “Stock” was the best way to go. Bring it back to “as from the factory”!

With a good engine, one that is not worn or used up, and good stock motor mounts. I have never felt that any of our cars ever had an engine vibration problem.

If it isn’t broken don’t fix it. Unfortunately for our cars and future owners. Some of us just have to try to improve things that we really don’t know much about. Shade tree mechanic’s.

At my age the soap box comes out more often than it did when I was younger. Sorry.

[JayJay]

Thought I had responded last night but I can't see it.

Within recent past I've had three Model A's with stock Y front mounts and essentially stock (unbalanced) engines. Two ('30 pickup and '30 Town Sedan) had standard hard rear engine mounts, and one ('31 Town Sedan) has old (1980's) FAM.

Vibrations and noise were significant in the '30 pickup such that it was painful to drive at anything above about 45 mph. '30 Town Sedan was much better, perhaps as much due to the wood body frame and cloth interior as anything else. The '31 Town Sedan was much less vibration initially, and got even better once I replaced the 40-year old FAM rubbers and tightened down on the bolts (see https://www.fordbarn.com/forum/showt...ighlight=Float). I can now drive and converse with my passenger comfortably at 50 mph+, limited by terrain and engine power. I expect it to get even smoother and quieter when I either counterbalance this engine or install the Burtz I have.

The guy I sold my '30 pickup to has subsequently installed new rear FAM and reports that the vibration is significantly improved.

I frankly can't see any performance downside to installing rear FAM. Obviously would not work for a points car, but for the driver this seems like a no-brainer to me.

JayJay

[Bob Bidonde]

WHN, the issue is that I do not drive my Model A's like they did in the early 1930s. As you know, driving in modern traffic necessitates changes in the Model A as well as driving habits. It would be foolish to drive a stock Model A in modern traffic without adding a right side taillight, LED taillights, turn signals, a leakless water pump, traffic light finder and brighter headlights. In local traffic, a Model A needs to cruise at the posted minimum speed limits.

[WHN]

Originally Posted by Bob Bidonde

WHN, the issue is that I do not drive my Model A's like they did in the early 1930s. As you know, driving in modern traffic necessitates changes in the Model A as well as driving habits. It would be foolish to drive a stock Model A in modern traffic without adding a right side taillight, LED taillights, turn signals, a leakless water pump, traffic light finder and brighter headlights. In local traffic, a Model A needs to cruise at the posted minimum speed limits.

I agree with you 100%. I was referring to the subject, motor mounts and engine vibrations.

The additions you have listed, in my mind, are not engineering changes. They are safety up dates.

Enjoy your car, drive safe.

[Flathead]

Is a "leakless" pump really necessary?

[Richard Knight]

A couple of important points need to be made. It has been suggested that the rear motor mount fams be unequally tightened. Drivers side slightly compressed, passenger side loose enough to turn by hand. The rear most mount on the clamshell the rubber needs to carry some of the weight. I can vouch that these points do make a difference.

[Bob Bidonde]

WHN, peace be with you. Have a great & happy holiday!