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tadd's Avatar
 
Join Date: Dec 2005
Location: Mount Airy, MD
Posts: 1,658
Intermediate shaft thrust

Question for the board... I have an early 68 aluminum case that will be run with the early IS shaft with straight cut gears. The early shaft rides directly on the Al case and is located to a shimmed steel plate by the thrust from the stock helical gears.

Since there is no thrust generated from the straight cut gears, I was thinking of inserting a spring of the correct length and OD (so its not slopping around) into the splined tube that mates the IS and oil pump to provide that force so that the stock shimmed plate can be used for location.

I have seen somewhere on this board where the splined tube has had a pin inserted as well. The spring would not need drilling or welding and provide the missing thrust pressure.

Any thoughts on this would be greatly appreciated!
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Old 08-02-2016, 07:25 AM
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Walt Fricke's Avatar
 
Join Date: May 2004
Location: Boulder, Colorado
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I'm thinking you may be overthinking. I have run straight cut gears in this case with no problems. The oil under pressure on the iron IS cover plate keeps the end of the shaft from scoring or otherwise rubbing too much on the plate. I can't say I ever gave any thought to what keeps the shaft from moving toward the oil pump, though the circlips on the shaft ends appear to be up to that light task.

Seems to me that allowing the IS shaft to float a bit, with restrictions which prevent enough movement for any interference or misalignment of the chains (which, themselves, should exert a sort of centering force. When you are measuring chain wheel parallelism, you push the shaft into the engine to take that measurement.
Old 08-02-2016, 09:50 PM
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Walt:
I have been accused of that by many good people... over designing too :-).

You make really good points. I actually hadn't considered the chains as a locating device, probably cause they aren't supposed (designed) to do that, despite doing just that.

I was just thinking a spring in the splined tube would be trivial to add, allow a bit of movement (as you pointed out), yet provide a resistance to gross movement.

I think my biggest concern was maintaining full tooth engagement... but like you said, the chains wont let it walk too much.

Thanks for the reply! More to think about...
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Building molecues or building cars... you do get more of first in every batch. A mol of porsches anyone?
Old 08-03-2016, 05:47 AM
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