Small Cracks in The Bottom Of the Pistons

Discussion in 'InsideTopAlcohol.com Tech Questions' started by Mike Canter, May 4, 2008.

  1. Mike Canter

    Mike Canter Top Dragster
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    I am talking to racers that are seeing small cracks in the pistons on the bottom where the skirt joins the pin boss area. Some of these guys use Rootes blowers and some use screw blowers. The screw blower car has JE pistons and does not use a Two Step on launch. Then I have another car that is a screw blower car with JE pistons and has had them in the car for over three years and has no cracks. The cracks seem to only be appearing on the thrust side of the pistons. Anybody have any ideas as to what causes this and how to prevent it?
     
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  2. Alkydrag

    Alkydrag Sr. Dragster

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    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.
     
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  3. 560Jim

    560Jim Member

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    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
     
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  4. Mike Canter

    Mike Canter Top Dragster
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    Nope, wrist pins are good. The cracks are right at the junction where the thin skirt wall starts to thicken into the wrist pin boss.

    Alkydrag, as far as I know the clearances between the pistons in all cases is within specs. This is not one motor but has happen on several that I know of. As you said one of the soloutions is to swap the pistons from one cylinder bank to the other and prolong thier life but why does it happen on some motors and not on others. Their is no evidence of detonation.
     
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  5. Alkydrag

    Alkydrag Sr. Dragster

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    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.
     
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  6. Ken Sitko

    Ken Sitko Super Comp

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    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.
     
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  7. Nathan Sitko - 625 TAD/TAFC

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    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.
     
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  8. Alkydrag

    Alkydrag Sr. Dragster

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

    secondwindracing top alcohol

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  10. Mike Canter

    Mike Canter Top Dragster
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    Tony Ramos, the clearances on one motor was .007" at the .500" mark which was exactly what the spec sheet said to put them. The motor that has over three years running the same JE pistons with NO cracks is somewhat beyond that.
     
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  11. Alkydrag

    Alkydrag Sr. Dragster

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    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.
     
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  12. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    cracks

    While I don't know why they happen, those cracks are why I pull the rack out each race to inspect the pistons. We don't run them after they develop that crack. Like many have said, the problem improved with the JE's but we still saw it. Usually around the 20 run mark, but I've seen some cars go a long time without cracking them.
     
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  13. Mike Canter

    Mike Canter Top Dragster
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    So, Will then the big question is WHY? :confused: We all seem to accept that this is happening.:cool: So many racers are seeing these cracks but nobody seems to know if we are doing anything wrong to cause them. This should not be happening.:mad: I really find it hard to believe that we are all screwed up the same.

    Tony Ramos..... are you still working for JE? If not is there somebody you know there that can tell what is really going on. My friend called JE and asked them and all the guy (unknown name) said to do was grind out the cracks and put them back in. Believe or not that will work if you get all the crack out but doesn't fix the problem.
     
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  14. WJ Birmingham

    WJ Birmingham New Member

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    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.
     
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  15. Alkydrag

    Alkydrag Sr. Dragster

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    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.
     
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  16. Mike Canter

    Mike Canter Top Dragster
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    I called Ed at CP Pistons. A great guy and very helpful. We talked about the cracks and this is what he passed on. The probable cause is that the piston skirts are banging the cylinder walls and are flexing because the skirt area is either too thin in that transition area and the pin boss area is thick (something has to give). The problem maybe that the pistons are too light in metal in the area of where the cracks are occurring for your style driving or tuning, or the skirt clearance is too great or the motor is not being warmed up enough so that the piston skirts are slapping the cylinders during burnout until the motor gets heat in it and the clearances close up. The problem with that is the damage has already been done.

    Some ways to prevent it is to put a very slight radius on that sharp edge of the skirt on where the cracks are starting. It doesn’t take much just a Dremel tool with a sandpaper drum and then polish that area with some 400-600 sandpaper. Sharp edges make it easier for cracks to start. The other fix is to get the company that makes your pistons to add some material in that area. The problem is that this makes the piston a little heavier. Ed did state that CP Pistons have a replacement that is thicker in that area but probably close to the same weight as the JE piston. Ed would prefer that you send him a piston so he can see where it is cracking and he can adjust the design of the piston to help prevent this from happening and keep the piston at close to the same weight.

    He also said that when the cracks start they may not get any bigger than what you see when you first notice it. Grinding the crack out will give you extra piston life but it is probably going to happen again until you either try a different design piston or change whatever you are doing that causes it.
     
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  17. TAFC 5 81

    TAFC 5 81 Member

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    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.
     
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    Last edited: May 7, 2008
  18. Moparious Maximus

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    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.
     
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