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Author Topic:   20 thou
the last dive
Gearhead

Posts: 147
From: sydney australia
Registered: Dec 2001

posted 07-27-2002 10:15 AM     Click Here to See the Profile for the last dive     Edit/Delete Message   Reply w/Quote
has anybody ever taken 20thou off the top of a forged piston??

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Buster
Gearhead

Posts: 780
From: Orlando
Registered: May 2002

posted 07-27-2002 11:10 AM     Click Here to See the Profile for Buster   Click Here to Email Buster     Edit/Delete Message   Reply w/Quote
If I remember correctly I have taken more then that.

I built a 351W engine with Aussy rods. The Aussy rods are 6.050" vs 5.956" for the 351W. So, it was about .094" longer rod, less .025 piston to deck. I needed to take 065" off the top of the piston. In the end I was .005" out of the hole.

This was done with a TRW 351W dished, 13cc cup, forged piston. The skirts did crack, but I don't think it had anything to do with machining the top of the piston. The oil ring land was to long and that weakened the skirts.

I had talked to some other engine guys that said they had the identical problem with the same TRW forgings, Ford and Chevy.

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[email protected]
Gearhead

Posts: 422
From: Lakewood, CO, USA
Registered: Jun 2001

posted 07-27-2002 01:15 PM     Click Here to See the Profile for JCQuinn@work   Click Here to Email JCQuinn@work     Edit/Delete Message   Reply w/Quote
Ihave taken more than that off of several different brands of pistons with no ill effects.

It would be good to call the manufacturer and ask them but they are all so afraid of lawsuits these days that they probably can't answer those types of questions anymore.

I used to know a number that I used as a minimum thickness but the number ran away with my youth so I I can't pass it along.

If you talk to some performance machinists they can probably give you good advice.

John

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bluestreek
Gearhead

Posts: 1289
From: Athens,GA
Registered: Jul 2001

posted 07-27-2002 01:54 PM     Click Here to See the Profile for bluestreek   Click Here to Email bluestreek     Edit/Delete Message   Reply w/Quote
I drilled a hole through a bad KB piston once on the thin side away from the valve relief and went through at about .080". The forged pistons are a little thicker. Milling 020" should be OK. The engine machinist will have the tools and knowledge to let you know if it is "relatively" safe, but it's normal if he doesn't recommend it.

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ccode67
Gearhead

Posts: 1605
From: douglasville,ga,usa
Registered: Mar 2001

posted 07-29-2002 07:28 AM     Click Here to See the Profile for ccode67   Click Here to Email ccode67     Edit/Delete Message   Reply w/Quote
I just had .022 cut from a set of TRW forged pistons, L2246 was the part # I think. They were .020 out of the deck. Early block with shorter deck height and pistons for a later block.

------------------
Stuart MCA #48902
M&M #1091
67 stang 5 speed, 351W,
Edelbrock Performer RPM package
Currie 9 Inch
91 f-150 xlt
98 explorer xlt sohc v-6

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Mike Harris
Gearhead

Posts: 122
From: Oakfield, Ga USA
Registered: Jul 2002

posted 07-30-2002 09:47 AM     Click Here to See the Profile for Mike Harris   Click Here to Email Mike Harris     Edit/Delete Message   Reply w/Quote
Just remember, when you are done, take some light grade sand paper and knock off any sharp corners. They build up heat easily and will become both a source of detonation and fatigue.

------------------
Mike Harris
MKZ Racing
home.isoa.net/~mharrisj

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