Rear Motor Mount Seat Problem- Update

[ramcr913]

I am doing a chopper build and ran into a little issue. The frame is an aftermarket unit. When I put the motor in I noticed that the motor would rock a bit side-to-side. Traced the problem to the rear motor mount seat, that is the flat plate welded to the seat tube. First I noticed that the weld itself spilled over to where the motor was sitting on it. I ground a bit of the weld off to provide a flat spot for the motor to sit. That helped significantly but there was still some rocking going on. Turns out the rear motor mount is welded on to the seat tube a bit crooked. Using a torpedo level and some shims I was able to determine that (relative to the front mount seat) the rear motor mount seat is higher on one side by approximately .017 to .020". Using a hand grinder and a flat file I managed to take the high side down. Right now the difference is down to about .010". It has been slow going, but and with frequent checking with a machinists straightedge I have been holding the surface pretty flat while I take down the high side. I intend to work it till I get the gap all the way out, but I am curious- Is there a "tolerance" on motor mount seats? I have never ran into this but then again it could be I never noticed. Anyone ever run into this- any insight?
BTW, I have the build thread posted here in the General forum but wanted to split this off and solicit some opinions.
Thanks

[Skin]

I've run into this situation even on stock frames. The service manual will tell you to use a feeler guage and shim accordingly.

[Admiral Akbar]

I've run into this situation even on stock frames. The service manual will tell you to use a feeler guage and shim accordingly.

It's good to drop in the motor and tranny and bolt the primary before checking for shims.. Nice thing about twincams is that they eliminated this issue. Pretty much gone on rubber mounts also..

Max

[ramcr913]

Skin and Max-
I have seen things a little off before, but .020" seemed excessive. The factory service manual says to inspect the front mounting boss relationship to the engine but that's about it. And yes, I do have the tranny in and am using the motor plate (open belt drive) to align things. I think I will continue to flatten things out a bit more and move on with it.
Thanks for the replies and heads-up.

[ramcr913]

Well I got back out there today and finished flattening the motor mount boss. Stayed on it with a hand grinder- light passes checking it with a straightedge. Pictures are kinda deceiving but the seat is now pretty flat.



I set the motor back in and the "rock" was gone. Got the tranny in, then he motor plate. Tightened down the rear mounting bolts and checked the front mount for clearance. I managed to get a .003" feeler gauge in there but it was a tight fit. It was a tedious job, but I guess it was necessary.

[88b]

doing it right now will save a lot of grief later.

[Deye76]

On Pans and Shovels & Evo's I always bolted the rear down, then shimmed the front as necessary, kept the "ears" from cracking.

[ramcr913]

88b- yep, you're right. Hopefully it will be OK now.