Has anyone ever seen a failure (with motors) due to using shims that have less than a full foot pattern? I have a 700HP, 4507 frame motor, 1200 rpm that has about eight inch square foot pads. The contractor used shims that are about 3.5 inches square in his alignment job (I think "C" size). Thanks.

Sid,

I have never seen a failure from one, but have found big time soft (or I guess sprung is more accurate) foot, corrected it with the anticipated results in spectrum change.

I guess your meaning 2xLF. Like you Danny, I'm thinking possible distortion of the motor casing and maybe eventual stress cracking at the foot. Time will tell... Thanks

Sid,

You are right time will tell. It can be a long slow death, too.

Have seen cracked feet but don't know what caused it, unless there are some clues in the picture.

An alignment of a refurbished a pump required it to be shimmed (cant bring motor down any further). The largest shim we had only covered ~ 80% of footprint. Subsequent vibration testing revealed high 1R in axial direction. Alignment Sat.
Did quick modal testing and found sharp resonance at (you guessed it) running speed. Testing of a similar pump revealed damped Fx several Hz higher.
My suspicion is the shim reduced stiffness term and brought down the Fx to running. We purchased correct size shims and will soon change out to confirm.
Has anyone experienced similar ??

Regards Jim P

Good points. Also, check your OEM warrantee; it may require full footprint shim. I really do like the color coded shim material and have used it since 1967. Of course there's sofshoe shims for wedge foot conditions. Naturally, changes make changes and what was the reason the OEM made the foot the size they did?

Great thoughts! I especially like the warranty advice. Thanks.

Unless it has changed, when we replaced one of our papermachines we installed Reliance DC drive motors. At that time, Reliance would void the warranty if we did not use full foot shims. Their foot print was almost 2x the size of a D size shim. It would be nice if someone made shims that fit a manufacturers foot.

Gary B

If the shim size is shorter than motor feet size, a part of motor feet become unsupposrted and the vibrations are not damped out properly & hence vibration level in vertical direction may be high. It will certaily reduced if full size shim is used.

Gary, I have such a shim that is basically that easy. They are color-coded and economical coming in various sized. What makes these shims great is the hi-density plastic (poly) good at 10,000 psi, ~400F, and will hold up to some chemicals that SS won't. They are easy to cut to size from a 10" X 20" sheet (& 5" X 20") or custom. You can cut a shim that looks like a stamped-out shim w/sissors.

I have set or aligned large machines with these and gone back 3 yrs later to check and the alignment is still sitting right exactly where I left it and all intact. I love 'em. See Granger or McMaster Carr or I have 'em. They also come pre-cut in sizes A, B, C & D. Don't have to mic them and they are correct.

I tried to attach a picture but for some reason wasn't able. Thought possibly that I could pull from the photo album, but the album posted as the next topic, huh? Oh well, there is a picture of the shimming job in my next post ("Low Hanging Fruit") on the forum... Sam, I heard a number of people praise the plastic shims. I suppose the material is similar to bearing housing shimming material (sometimes plastic).

Electricpete: That crack could have been caused by a pry bar or wedge........

That's right Sid, used in bearing shimming on gearboxes and, and,.......... It is wonderful stuff and I'm always surprised how many don't know of it's uses and availability. It's much cheaper than SS and often withstands harsher chemicals than SS. And some acids that will eat SS, won't touch this stuff.