2nd. piston pin ?

rod · 05-02-2012, 04:01 PM

sometime back i posted about shortening a pin. this is a forged TRW piston with a 3" Chevy pin.
what i want to do is place 2 .042" Tru-Arc lock rings on each side of the piston. i have now done some serious measuring and i find that there, for whatever reason, is a large amount of end play between the pin and the OEM single lock ring groove, .029" to be exact.
so, if i widen the original groove to the outside by .0275" i can get the 4 lock rings in, and not have to shorten the pin.
this leads to a whole new question. there will be approx. .0875" of material remaining between the outside of the lock ring and the flat face area [on the outside] of the piston.
the question then , is .0875" enough material to hold the ring in place and not be hammered out? currently, in unmodified form there is .111" of material.
.111"-.0275" = .0875"

thanks rod in AZ

Alan Roehrich · 05-02-2012, 06:49 PM

Avoid using Tru-Arc retainers if at all possible. There is a very good reason that people use either round wire retainers or double spiro-locs, and it is not because Tru-Arc retainers are real reliable. Those things are "okay" at best for a stock rebuild, in a restored car that won't be driven a lot. In a modern race or high performance engine, they are a recipe/invitation for disaster.

Marine One · 05-02-2012, 06:58 PM

Is a pressed pin out of the question, or maybe nylon buttons...?

05-02-2012, 04:01 PM	#1
rod Member Join Date: Dec 2009 Location: Kingman, NW AZ. in the middle of the longest stretch of Route 66 Posts: 314 Likes: 0 Liked 20 Times in 15 Posts	2nd. piston pin ? sometime back i posted about shortening a pin. this is a forged TRW piston with a 3" Chevy pin. what i want to do is place 2 .042" Tru-Arc lock rings on each side of the piston. i have now done some serious measuring and i find that there, for whatever reason, is a large amount of end play between the pin and the OEM single lock ring groove, .029" to be exact. so, if i widen the original groove to the outside by .0275" i can get the 4 lock rings in, and not have to shorten the pin. this leads to a whole new question. there will be approx. .0875" of material remaining between the outside of the lock ring and the flat face area [on the outside] of the piston. the question then , is .0875" enough material to hold the ring in place and not be hammered out? currently, in unmodified form there is .111" of material. .111"-.0275" = .0875" thanks rod in AZ

05-02-2012, 06:49 PM	#2
Alan Roehrich Veteran Member Join Date: May 2006 Location: Murfreesboro TN Posts: 5,107 Likes: 1,564 Liked 1,796 Times in 409 Posts	Re: 2nd. piston pin ? Avoid using Tru-Arc retainers if at all possible. There is a very good reason that people use either round wire retainers or double spiro-locs, and it is not because Tru-Arc retainers are real reliable. Those things are "okay" at best for a stock rebuild, in a restored car that won't be driven a lot. In a modern race or high performance engine, they are a recipe/invitation for disaster. __________________ Alan Roehrich 212A G/S

05-02-2012, 06:58 PM	#3
Marine One Junior Member Join Date: Mar 2010 Location: Indiana Posts: 69 Likes: 2 Liked 0 Times in 0 Posts	Re: 2nd. piston pin ? Is a pressed pin out of the question, or maybe nylon buttons...? __________________ Chad Sheets \| STK 319 \| 10.69 \| 1.39