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Ring gear shrink

To: mg-mmm@autox.team.net
Subject: Ring gear shrink
From: "Bill Traill" <bill@clovermachine.com>
Date: Thu, 8 Jun 2000 16:09:03 -0700
In-reply-to: <66.45434ea.266eb152@aol.com>
Reply-to: "Bill Traill" <bill@clovermachine.com>
Sender: owner-mg-mmm@autox.team.net
Hi Brian,

About 20 years ago I machined off my J2's very warn ring gear and 
shrunk on a new one.  The gear was purchased thru Barry Walker 
or Mike Dowley and had an instruction tag attached. I never throw 
anything away so knew that tag was around somewhere...found it.  
Unfortunately, I don't remember the inner diameter of the ring, but 
the tag says to turn to 9.359".  If luck is with us your PA gear may 
be the same as the J2. replacement.

The J2 ring gear is about 10.55" OD with 83 teeth. The tag say's... 
" "Shrunk-on" ring gear. Size C83, Turn 9.359, Chamfer 9/16".
The back say's... "To expand the gear before fitting DO NOT 
EXCEED 290deg C. you may destroy the gear if you do."  (Note: 
there is no 9/16 chamfer on the gear, but it is 9/16" wide).

290 degC. is about 550 deg F. or within kitchen oven limits. I 
calculate the ring will grow .028" in diameter at this temperature.  I 
will guess the flywheel should be .010 to .012" larger than the ring 
at room temperature, but that is a guess.


When machining the flywheel, leave a radius on the inside corner 
to avoid a stress riser and possible future crack. The ring gear 
should have a chamfer to allow a small radius. 

An old time automotive machinist heated mine by "eye" with an 
acetylene torch and it went on with no problem. 

Before heating make sure you have the gear in proper orientation 
so it does not go on down side up!  A pair of gloves and two pliars 
to grab it would be helpfull too. 

Have an accomplice ready with a hammer in case it jams, you 
have about one second to tap it down.

It should slip on easily, and when it does, tap gently on the 
flywheel a little to set up a vibration to help it seat evenly.

If it jams you will have to hack saw it partially thru and split it with a 
cold chisel to remove.

For what it is worth:
I machined mine flush to the flywheel. My old time  automotive 
machinist friend who had apprenticed in the 1920's, said I should 
have machined in another .03" and left a small wall a few 
thousands high to keep the gear from being knocked off by the 
bendix.  Said he had seen a few do that in the old days.  Naturally 
the gear would have to slip over the wall when hot.   I have not put 
mine to the test, but  I am not too worried.

Good luck

Bill Traill
Santa Clara, Calif. 


Re:PA  
> Finally, on a new flywheel ring gear installation what would be the
> correct measurement for shrink fit?  Any comments appreciated. Thanks,
> 
> Brian.
> 



Bill

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