The Stovebolt Site Forums The Shop Area Engine Shop front engine mount washers

Does anyone know if the thick outer washers on a 51 3100 front engine mount with a 235 are above or below the crossmember? Imprints seem to indicate they go between the crossmember and the retainer serving as a spacer. They appear to be too beefy to be just a washer under the nut. Thanks

I do not have any documentation of this, but from the several dozen trucks I have swapped engines on, the thick washers are shims.
They go between the mount and the top of the crossmember on the outer bolts, not under the crossmember.

Thanks. That helps.

Now you guys are making me question the installation of the front motor mount on my '54 3104.

The FAM illustration < CLICK > of the mount is not very clear regarding the placement of the thick outer washers - GM #365685 3/8" ID, 1-1/4" OD, 0.187 thick. Only one washer is shown on the outer bolts. So if it goes between the retainer and the crossmember, then there is no washer between the nut and the bottom of the cross member.

I always wondered why a thick washer was specified for the outer bolts. I don't understand why a spacer is needed. But to add fuel to the fire, I found this pic < CLICK > of the bottom of a retainer in a Stovebolt Tech Tip. You can see the indention from the edge of a washer on the left side of the retainer as you described. The washer would be between the retainer and the top of the crossmember.

If other Bolters will supply documentation of this placement of the washers, then I'll add an update to my old post that details the installation of motor mounts on my '54.

Lonnie,
The way I see that drawing if you look closely,is the arrow pointing to the washer on TOP of the crossmember,not under it,as Dave Has said above.
steve sr.

Steve -

That's kinda what I saw today, too. That placement didn't even occur to me when I was replacing the mounts in my '54. Any idea of the purpose of the spacers?

Wouldn't it be nice to talk to the engineers on some of this stuff.

Denny -

Did you install washers on the outer bolts between the retainer and the crossmember on your '50? Looks like I see one in this pic from your photo album ...
> CLICK - Denny Graham's 1950 Front Mount

If so, did you put a washer between the outer nut and the bottom of the crossmember?

The thick washer is a ‘standoff’ and sits between the frame cross member and the cushion
retainer. The rubber cushion is supported between the (cover) plate and the retainer. The
bolt is tightened till you have the clearance between the two as instructed in the service
manual. The replacement cushions in my opinion are not as thick as the original ones or
as hard and do not allow for the proper amount of crush, that makes it difficult to
maintain the proper clearance between the plate and retainer:
http://www.pbase.com/dennygraham/image/149005338
http://www.pbase.com/dennygraham/image/149005339
The outer bolts would have originally been adjusted by crushing the cushion for the
correct clearance between the retainer and plate then the castle nut was locked with a
cotter pin and the original castle nut did not have a washer under it. I chose to use a
elastic stop nut rather than a cotter pin and put a thin washer under the nut.
http://www.pbase.com/dennygraham/image/149005340

I talked with the people that maintained this truck from the time it was new and they had
never changed the motor mounts, which were completely oil soaked and turned to mush
front and rear when I got the truck in ‘05. So I’m about 95% certain that this was the way
it was assembled at the factory in 1950.
Denny Graham
Sandwich, IL

RATS!

I wish that I had wandered through your album when I was researching and installing the front motor mount in my '54. The pictures and notations are perfect.

I thought that I had educated myself enough to become the "motor mount professor." I had the right parts, but just not in the right location. It goes to prove that you can't take a life-long liquor salesman and woodworker and make a mechanic out of him overnight.

I still don't understand how the retainer and cushion sitting on the washers perform any differently than sitting directly on the crossmember.

Thanks for the pics and info.

My guess would be that the cushion retainer and the crossmember
are not consistently flat so they used the two large area flat
washers as standoffs, something like spanning a rocky river bed
with a bridge. Two bridge abutments work better than one big
flat bridge laying on the rocks.

Denny G

I like that explanation Denny!
I have never come up with anything.

Tks Dave, means a lot comming from you. That's the only thing
that makes sense to me since all of them I've seen had the
thick washer, including the '54 that I have in the barn, which
I bought from the original owner and was never replaced according
to him.
The illustration in the FAM leaves a lot to be desired. When
they scanned it for the reproduction they lost a lot of the
detail which I'm sure was quite clear in the original
publication.

Denny Graham
Sandwich, IL

Why do u need the washers between the retainer and the cross member ? I'm confused

Does anyone know why u need that washer between the retainer and the crossmember ??

Did you read Denny's and PreDaves's statements above?


I believe mine are missing,without ill effect

Ok thxs..

What manual is this out of??? The shop manuals I have state that the spacing is CHECKED BEFORE any weight is applied to the mount. And if it is out of spec (not enough) you are to grind the retainer. If its to large, to replace the retainer. Nothing in the manual (48-51 Truck shop manual) states to compress the cushion with torque.

Also, once the shield is in place, you cannot even see the gap anymore.

And the assembly drawing does not show any retainer to cross member spacers (or they are not clear... but the parts call out do not mention any spacers.

What manual is this out of??? The shop manuals I have state that the spacing is CHECKED BEFORE any weight is applied to the mount. And if it is out of spec (not enough) you are to grind the retainer. If its to large, to replace the retainer. Nothing in the manual (48-51 Truck shop manual) states to compress the cushion with torque.

Also, once the shield is in place, you cannot even see the gap anymore.

And the assembly drawing does not show any retainer to cross member spacers (or they are not clear... but the parts call out do not mention any spacers.

What manual is this out of??? The shop manuals I have state that the spacing is CHECKED BEFORE any weight is applied to the mount. And if it is out of spec (not enough) you are to grind the retainer. If its to large, to replace the retainer. Nothing in the manual (48-51 Truck shop manual) states to compress the cushion with torque.

Also, once the shield is in place, you cannot even see the gap anymore.

And the assembly drawing does not show any retainer to cross member spacers (or they are not clear... but the parts call out do not mention any spacers.

steps 1-4
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0613.htm

lower right side

That's the same thing I read... but the post said:

" The bolt is tightened till you have the clearance between the two as instructed in the service
manual."

It doesn't say that at all. It says to check the clearance BEFORE TIGHTENING BOLTS and APPLYING ENGINE WEIGHT.

He then states:

The outer bolts would have originally been adjusted by crushing the cushion for the correct clearance between the retainer and plate then the castle nut was locked with a cotter pin and the original castle nut did not have a washer under it.

ABSOLUTELY NOT. If the clearance is to small, you grind the lip of the retainer. If its to large, you REPLACE IT.

Nowhere does it mention clearance washers (even in the official GM assembly drawing). Plus, as I already noted, as soon as you put on the shield, the gap is cover.. so you cannot see it.

I don't think that post could be any wronger if it tried.

I believe he is referring to the reproduction rubber mounts in his post,
they are not as thick. The top plate touches the retainer with no weight on some of the repos.


The factory assembly manual shows the special washers under the retainer
See Lonnies photobucket link on the first page

I just bought a repro rubber cushion from Chevys of the 40's. It fit exactly and was in spec. The only difference was the old rubber was 'squeezed' out around the two metal bolt bushings... most likely from improper assembly.

In my search for motor mount parts I have not read about any wildly varying cushion issues,

Mounts ready to paint

As for the washer (365895?) In the assembly drawing it appears to be the washer on the mount to cross member bolt... but the image I have is kinda hard to read due to low resolution.

Looking at the 29-57 Master Parts manual:

Mount parts book page

Does not show that part number.

Just curious... none of the other threads I have read about the mount ever mention any spacer.