Small Cracks in The Bottom Of the Pistons

What is the skirt clearance when they were first installed? Most of the time, it's caused by too much clearance. When we ran the Arias stuff, we used to swap the pistons to the other bank to get a few more runs out of them. When we went to the JE's, because I was working there, we tightened up the clearance and the problem disappeared. Two steps are hard on parts also. I haven't experienced it myself, but I know of a couple of people who have had the 2 step come on during the run and the oil pan wasn't big enough to hold all the pieces.

 

Cracks

Hi Mike,
with the proximity of the cracks to the pin boss, is it possible that the wrist pin is flexing and working the piston in that area ? Checking the pins between V-blocks with a DTI would indicate if they are bent.
Cheers Jim

 

That doesn't tell me what the clearance was. Detonation will show up in the pin bosses. If the clearance is too loose, then they bang around inside the bore causing the skirts to crack. They should be .006" to .007" at .500" up from the bottom of the skirt.

 

Mike, I have found that no matter what I do, the Arias pistons will crack in that area within about 10 runs. We run J&E pistons now, and haven't had much trouble. I always assumed that detonation would cause the cracks.

 

If I remember correctly our fix for that was to take the die-grinder with a small sandpaper bit and massage that sharp corner to a nice radius then they stopped cracking. I believe we did this with new pistons, and also with cracked ones and never had a problem afterwards. Haven't had any issues with the JE pistons though as my Dad said.

 

This is known as oil pan failure.
Yes, I'm quoting myself. The voices keep talking to me, make them go away.

 

sitko....they are rite , that is the fix..we do the same.Dave
www.myspace.com/daveloweswr

 

Well, beyond what we've already discussed, the only way to figure it out is to Rockwell test the pistons and do a visual check. A trained eye can tell alot about the tune up by looking at pistons. Pistons tell no lies. Something else is going on then.

 

Mike;

This is here say, but I'll repeat it.

I have heard that quite a few good people went to www.CPPistons.com from JE.

You might want to inquire with CP about this issue and see if they know anything.

 

Mike, fortunately I don't work at JE anymore. But the guy to talk to is at CP now. Call CP Pistons and ask for Ed Urcis. Like me, he used to be at JE. He's a pretty busy guy. If you have to leave a message, tell him I told you to call him. If it's a TAD, AFUEL or TAFC, and their fast, chances are Ed had a hand in designing their pistons.

 

I had the same thing happen to BBC TRWs (after 24 runs) 28 years ago, but I don't think the pistons were really designed to be used in a TAD. We trimmed the "skirt ear" but they still got small cracks in the same area you mentioned. Being in South Carolina and not able to wait 4-6 weeks for Arias (or any other custom piston), we tried the repair method. We had the Div 2 points lead and did not want to skip the next race. At least it waited until the ~1100 ft mark in the final before coming apart (lucky the rod and wrist pin w/ buttons ran the last 200 ft w/o going through the side of the Rodeck. The solid cast RayNick heads survived too. I have to admit that was a funny sight when we removed the heads and seeing just a rod and wrist pin in #1 cylinder. If we would used snap rings, it may have become a V-6 after that run. We had to use another set for the 3rd points race. We prepped them similar to the above post, backed the tune up down a little, but the cracks appeared after 3 more events (~15 runs), but the pistons stayed in one piece. We also checked (and re-checked) the clearances and just concluded that the pistons were not up to the task for that application. Several years before we had a set of arias (for a 4 in stroke) used in a BB/FC (Rodeck) and the a cast iron combo for IHRA TAD (50+ runs total) w/o any issues.

 

I know im digging up an old post but I'm wondering if there are any new ideas here. I'm having this issue with two completely different engine combinations. My big 4.500 x 4.500 Mopar wedge is showing these cracks at roughly the same rate as our little 4.165 x 3.500 SBC.

 

Have a self full of airas piston with exact same cracks. Best reason to switch to another manufacture.

 

Mike I had this recently on my blown small block.
Pull the rack out after every meeting - never seen a crack in ten years.
I got double bulbed one meeting - and the green would not activate as I timed out. I came back off the limiter - realised what had happened - and left from idle.
Pulled the rack out and all eight were cracked like you said. I sent Ed the sample at CP, and they beefed them up for me in the area.
High load and low rpm is my guess - either on the launch, or short shifting and the motor getting pulled down too much.
PC