Piston ID Help

Ok, I good news and bad news for you, a mixed bag really. The good news is those are most likely Arias pistons, a well known piston manufacturer of performance pistons. There still in business and here is there web site: http://www.ariaspistons.com/index.html . The bad news they don't list AMC pistons any more. The good news is they make custom pistons , so making a replacement should not be all that big a problem. The bad news is I believe your pistons have already been reused once before. The piston skirts should be smooth, and yours are not. This is general refereed to Knurling a piston. It's cheap way of reusing a piston again , generally done by a cheap mass market engine rebuilder. So, your piston probably have got a 100,000 miles on it plus however many 1,000s of miles the cheap rebuild lasted. Not only do to I believe the pistons were knurled , but they did a poor job of it to boot. The idea of knurling a piston is the compensate for piston wear by cutting the piston skirt to expand it a bit and make up for any wear. You should have a good machine shop check the pistons and cylinder bores for wear and taper. you may need a complete set of new piston and bore job any way, but only a good machine shop with the equipment to measure to 1/10,000 of an inch can tell you.  LRDaum

I bought a similar 401 last year. Mine has a little better cylinders , but still a mystery Jeep motor. Cork gaskets are another dead give away that some one did not know AMC engine. No ,AMCer would ever use cork valve cover gaskets ,as they are very prone to leaking on any AMC. Good luck, sound like you got the right idea. See if the shop has the same low opinion on the knurl job I do. BullTear.com has a lot of trick AMC and Jeep parts , espically for engines, and Wiseco has recently come out with some new very nice looking 401 pistons. LRdaum

The picture of the piston does not show a knurled skirt.  It shows a pattern of shallow radial grooves designed to help retain oil on the piston skirt during sever usage.  Lots of aftermarket custom piston manufacturers have done that over the years, though modern technology has shown that the grooves really do not work that well.  If you have ever seen old TRW or Speed Pro performance pistons, their skirts are finished with continuous radial grooves to accomplish the same thing. Knurling creates a harsh crosshatch and the piston in the picture has not been knurled.  BTDT.  I would guess the piston was manufactured in the 70s or 80s.

Ok, the Buick comment is not that far off the mark. The AMC and Buick are pretty similar and Jeep used Buick engines before AMC bought Jeep and in fact AMC looked at Buick as it's main competition most of time. RE: The piston skirts, that why I called a BAD  knurling job piston, what ever it's purpose. Not surprised it's old pistons. I figured it been used more then once .

Machine Shop in Las Vegas: Universal Automotive & Engine , 212 W. Utah Avenue it's no far off Charleston, Main and Las Vegas Blvd(where they split) in an industrial area in the shadow of the Strat Tower, phone # 702 . 384.5858 . They do have a small web page from City-Data.com. The guy I talked to claimed to have been a mechanic on a Local Javelin Trans-Am car run from one of the old local casinos back in the day. Also every one I've talked to Street Rodder, Performance guys , every one has recommended this place. Oh, by the way I live out in Pahrump,NV close to LV. We do have an AMC club in LV that does welcome AMC powered Jeeps. But for the next meeting on Aug 13th at the Blue Ox on Sahara at 6 PM I'm going to be in Detroit for the AMO National meet that weekend though. LRDaum

Cool, that's the shop I'm using... I feel much better about it now. It sucks to move to a new place and not know anything about the local businesses. The machine shop I used on my first 401 closed down shortly after they completed my work last year and I never got my .030 pistons back from them after they bored out to .040.  Mramc..Thanks for the inside scoop!

Edited by motiv8ya - Jul/30/2010 at 7:40pm