Im putting my 79 74" shovel back in the frame and was wondering what the deal was for shimming the motors. The book doesnt say anything about it but ive read a few things where they say you should. My motor fits flush on the frame mounts with no gaps between motor and frame. is that good? or should i shim the motor for some reason?? Any help is appriciated . Thanks

 

To determine if ya need them. First mount the engine in the frame. Insert rear mounting bolts and torque to specs. Use a set of feeler gauges to check for gaps in front mount area from frame to engine. If you do need them get some brass shim stock (I ordered on-line from Enco for mine).

If your motor does need shims and it is not done, you are looking at a broken motor mount (on pans it is usually the left front that busts loose); not sure about where the weakest spot would be on a shovel as far as engine mounts.

At any rate you may not even need shims, but since you have a fresh build it is worth checking on the front end.

Last words, if you have had your frame painted, make sure all the mounting points for the engine and tranny are bare clean metal....no paint.

 

Thanks for the help

 

Panz is right! My Pan needed shimed but my Shov. didn't. It's about the tolerances in manufacturing these parts. I have seen some broken front mounts over the years. Also, the paint removed from the mount surface keeps the dimensions proper. I also run a ground wire from a engine bolt to the frame ground, which is one of the reasons for removing the paint. The old school way was shims cut from beer cans.

 

I'll add a bit to that also , after your done shimming and torquing down the motor do the transmission too . loosen the 4 studs and the 4 bolts that hold the plate to the frame . Next put the inner primary on torque the front to the motor then tighten the 4 studs for the trans in the primay , then do the trans to plate studs hand tight and check the plate to frame points . You may just find and air gap on plate to frame points on the rear , I'd say 6 out of 10 bikes I do need significant shimming on the trans rear .020" to .030" is common, had a few over .080" . You won't believe the amount of vibration this knocks down , leaks go down or away . Just a heads up it could worth you time on the older frame you got miles . You basically blueprint the drive train and it does a make difference in vibration big time .

 

My motor shows about .003 of gap so I am not sure if I need to shim.

 

I would shim. Beer cans are the most used item for shim stock. Auto parts stores or industrial supply. Shims can be had from .0005" to .010" in .001" increments. The stress of pulling the engine mount to the frame even that little will, over time, crack the aluminum and maybe break it off. Remember vibration is acting on it also. Better to shim now than weld later.

 

i 've always used the old chevy starter shims, they come in different sizes in a pack.

 

Shim it and while your doing this check the top motor mount too, a lot of times the upper needs a washer or 2 between the mount & frame to sit solidly without pulling when tightened down. Every little bit helps kill transmitted vibration.

 

yes, i've seen top motor mounts and transmissions that needed big time shimming. it's amazing how far off some transmissions are off and people just force the primaries on. no wonder why they end up with the o-ring lip and inner primary case broken.