Engine Mounts......

Dave Bilyk

Dave Bilyk
Supporter
Malcolm,
I don't have a specific answer for you, but typical industrial AV mounts are generally in the range 40 to 60. 70 might be too hard and below 40 I think would be too soft and allow too much engine movement.

regards
Dave
 

Malcolm

Supporter
That is softer than I thought. My current gearbox mounts "feel" about 10 ie real jelly. My engine mounts are fine but whilst chopping and changing one bit might as well do all! Polyurethane suspension mounts seem to be between 70 to 90. The perfect fit bushes I was going to use are 83. I had wanted to start at 70 ish and am concerned 83 might be just too damnably hard. They are sending me a sample. I was going to work out a compariosn hardness test, possibly using a tyre hardness tester or something similar. Won't give me a formal figure but perhaps a rough indication!
 

Dave Bilyk

Dave Bilyk
Supporter
Malcolm,
in the final analysis, it depends, at the low shore values, how much engine movement you get on and off the throttle, and if it starts knocking on the bulkhead when you brake or blip the throttle etc.
At the higher shore values, general vibration transmission into the chassis increases and can excite chassis resonances at certain speeds. Also the engine mounted natural frequency which would normally be below tickover, might come up to tickover or into the running speed range, in which case there would be a lot of engine vibration at one or two particular speeds.
I agree and would rather start at 70, 83 could be too hard. Nothing wrong with experimentation though.

regards
Dave
 

Malcolm

Supporter
I was playing around with the sample they sent me today and comparing to the mounts I have at present. The 80 sample is way too hard in my view. I think I will try some 70 ish mounts on the gear box end by itself and see if that solves the issue I am working on. The engine mounts are in good order so do one thing at a time and I will properly solve the problem!
 

Malcolm

Supporter
Under hard driving conditions the gearbox is moving about on its mounts so the solid link gearchange is awkward to get gears. Tie the gearbox down and the gearshift should hit its mark.
 

Dave Bilyk

Dave Bilyk
Supporter
Malcolm,
now I see, agree you are doing the right thing, stiffening the gearbox mount only shouldn't have a big effect on vibration, but should anchor the gbox end more effectively re gearchange. Good luck and let us know how you fare.

regards
Dave
 
Just a question, if the gear change is a solid link, are the rod end bearing joints that the shift rod goes through mounted on the engine or the chassis? If they are mounted to the engine there wont be such a problem - only the gear lever end itself which could be cured by having a torque tube from the engine to mount the gearshif selector on. Or perhaps rubber mount the gearshit selector unit ?
 
On Roy's 40, we ended up with 2 braces.

One from the n/s cyl head to suspension turret which stopped the motor rocking with torque.

and

One from the top centre of the gearbox to the cross member above which stopped the up/down movement of the trans when accelerating/braking hard.

Without braces, the shift lever would move side to side during the first condition and back and forth under the second.

It made for a much better shift with than without and the rear linear bearing mount was attached to the trans casing.

I still believe a well setup cable shift with no play is hard to beat. The new FORD GT still uses a cable shift and I've heard rave reviews of the slickness of that mechanism.
 

Malcolm

Supporter
Gearbox mounts now fabricated, engine mounts were left alone ....for now! Using a tripod design has made these mounts very strong, just hope I haven't over done it and get vibration transmitted to the chassis!
 

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