View Full Version : Bushed Conrods

01-24-2007, 08:49 AM
When converting the small end of an A series rod to a bushing for a floating wrist pin how is the pin retained? Iím assuming a custom piston with provisions for circlips is needed but I would like to know for sure.

Dave Russell
01-24-2007, 12:01 PM
I think Circlips or wire clips are almost universally used. A few folks that are spooked by the possibility of a retainer getting loose use two Truarc clips per side, some ues Spiraloc, a few Teflon buttons.

I personally have never had trouble with wire clips as long as there is a chamfer on the OD of the pins.

01-24-2007, 05:52 PM
Chris, if using the pistons that aren't set up for a retainer, I've had good luck with Teflon buttons.

01-24-2007, 07:29 PM
That's what I thought. Then there really isn't a way to use AE 21253 pistons that have the skirt even with the wrist pin then is there.

01-24-2007, 09:34 PM
Sure, you just use the buttons.

01-25-2007, 07:45 AM
OK, I thought the OD of the button was such that it was located within the piston skirt. I didn't think there would be enough support by simply pushing them inside the wrist pin. Thanks.

01-25-2007, 08:48 AM
Where could they possibly go once in the pins? <insert :devil: icon here!>

sorry... couldn't resist it, Chris. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif

My skepticism over using "~plastic~" wrist pin retainers was quelled after a tear-down of an engine with 'em used. Now I'd have "NO FEAR!".

01-25-2007, 09:47 AM
I haven't seen them first hand so I'm trying to get my mind wrapped around the concept. It's a small mind so it doesn't wrap far or easily. I've had flow problems with teflon in other applications at elevated temperatures and I guess I expected the need for more support. The picture below shows the piston configuration. I understand it now.


01-25-2007, 05:40 PM
Chris, I ran an air cooled Super Vee with buttons for a few years and never had any problems. I would imagine that the cylinder temps on that were higher than we see with our water cooled stuff.

01-25-2007, 06:47 PM
My 1941 airplane engine uses aluminum buttons.

But it is designed for more relaxed running.
2300 RPM redline and compression ratio of about 6:1

Hap Waldrop
01-27-2007, 09:15 AM
Chris on the AE 21253, floating is kinda a waste of time, ask me how I know. The AE 2153 has a fairly large slipper on the side of the piston and and a much shorter piston pin, if you try to just use a teflon button with the suppiled pin, you got way too much distance to get back to the cylinder wall and a risky set up if you ask me, the race pistons (JE, Venolia, etc.) either are full circle pistons are have samller slippers on the side. I floated a AE21253 with longer stock pins and made custom teflon buttons on a LP/HP SCCA engine, but the piston weight increased with the longer pin, it worked fine but was a PITA, in my opinon if you're going to use the AE21253 piston just press fit it and get the advantages of the shorter pin and less weight. By the way, the AE21253 is the same piston as the AE21251 except it has less oiling slots in the oil control ring land area, thus more meat holding the top and bottom of the piston together and a good candidate for racing with a off the shelf piston, it's a tough little piston that doesn't cost that much, you just limited to what you can do with it, as long as you don't go over about 12.0 to 1 and keep the lobe lift at .350-.355" with zero deck, you will have tons of valve clearence and be fine. If you end up going with a floating the stock rods, conatct me, I've got a slick deal for that and it's a ton better than what most are doing.