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Old 11-14-05, 01:12 PM   #1 (permalink)
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norvalwilhelm is offline
 
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Join Date: Apr 2004
Location: Waterloo, ontario
Posts: 396
My Corvette(s):
75 blown bigblock
Default Customizing motor mounts

I decided to do away with the poly mounts because the motor was really torking over and with the blower so high it really emphasized how much. I decided to go with solid mounts. I also wanted the rigidity the solid mounts would give the steering box frame rail.
When we install mounts we usually put both motor mounts on first and then install the transmission mount last. We usually find the tailstock off to one side so we pry it over to fit the transmission crossmember. What we are doing is putting a large load on the motor mounts. Given the distance back from the motor mounts to the transmission mount and the force we exert with a bar to align things the motor mounts are taking a lot of bending stress. They are rubber or poly so they hopefully survive.
I have my tailstock centered roughly in the tunnel and put the first solid mount on the passengers side.
It basically fell into place. With a jack under the oilpan with a large board and felt protecting the pan and raised the motor slightly, unbolted the passengers side, slid the new solid mount into place and started all bolts before tightening them down.
Did the same for the drivers side but found nothing lined up.
Not a hope that the mounting holes on the block and the arms for the frame for the through bolt would line up. Not even close. Out by more then the size of the 3/8th bolt hole.
I could remove the tranny mount and then install the mount, pry it over and reinstall the trany mount but what about the stress on the mounts?
Poly mounts come with a backing plate, solid mounts do not.
I cut the mounting ears and the one mounting hole off the solid mount leaving only a base plate with the 2 wings that go over the frame for the through bolt.
I then took the poly mount backing plate and bolted it to the engine.
I then lowered the engine into place.
Using a sharp scribe I traced the outline of the frame mount onto the backing plate bolted to the motor. Scribed it hard and deep.
I then jacked the motor up, pulled the mount , held the 2 together with a clamp and lined up the scribed lines. I then welded up a new mount.
After cooling a grinding I painted in the original gold color and when I went to install all holes lined up perfectly, no need to pry the motor over, no side loading on the mounts and the transmission mount lays more in the center of the tunnel.
While it would be more tricky to do with a poly mount you would have to weld slowly to keep the heat out of the mount but it could be done.
All three mounts should go into place, sit neutral, no side loading and no forced side loads.
This shows how much the bolt needs to be moved over from center

This shows how the one bolt is moved right over under the mount

This shows how the other bolt is moved out from the mount
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