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Old 05-11-2007, 07:53 PM   #1
exekious
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Default Ring Failure... what piston rings to get?

Okay, my #4 piston rings failed in my Crawford S3L motor. They are OEM STI rings. Crawford says stick with stock rings, while Subaru dealer thought I should go with CP rings to go with CP pistons. Crawford says the oem rings are better, but more expensive. Subaru dealer is rebuilding my motor since they have a tech that understands high power STIs.

Can I get some opinions. Car has made a max of 616whp on C16+meth on a dynojet.

Thanks for any help.



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Last edited by exekious; 05-12-2007 at 11:25 AM.
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Old 05-11-2007, 08:11 PM   #2
VTsuby
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In what way did the ring fail?
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Old 05-11-2007, 09:23 PM   #3
MJU1983
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I'd go with the CP rings that can be purchased with the CP Pistons.
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Old 05-11-2007, 09:35 PM   #4
VTsuby
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I'd go with mahle pistons and rings that way you still have an arm to steer with and a leg to mash the happy pedal with
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Old 05-11-2007, 10:34 PM   #5
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I would def buy some cp rings we just go tdone rebuilding a block for the same problem and it was because of the oe rings. should be an easy pick.
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Old 05-12-2007, 11:00 AM   #6
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im using new oem rings in my build and im not using the cp rings that came with my cp pistons, i bet both do a good job, its probably more bad luck if they fail or improper install.....but i have heard and my builder said to get the oem ones, he said they are the best...so im going by him
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Old 05-12-2007, 11:25 AM   #7
exekious
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I added a pic of the piston with the failure.
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Old 05-12-2007, 12:57 PM   #8
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I still can't tell what failed, please explain
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Old 05-12-2007, 12:59 PM   #9
MJU1983
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Quote:
Originally Posted by mick_the_ginge View Post
I still can't tell what failed, please explain
I was thinking the same thing.
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Old 05-12-2007, 03:56 PM   #10
Devan M
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Phew, I thought I was becoming blind like my dad
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Old 05-13-2007, 01:01 AM   #11
modaddict
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+3, what failed?

Lots and Lots of builds use the OEM rings......go OEM rings, IMO.
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Old 05-13-2007, 01:29 AM   #12
reddevil
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Thats a used piston as far as I am concerned.
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Old 05-15-2007, 01:13 AM   #13
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I'm afraid I'm in the same boat here - other than some light skirt scuff and carbon build up, there is nothing wrong with the piston or the rings in that picture. Got another picture?
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Old 05-15-2007, 08:29 AM   #14
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The only thing I see is the combustion getting by the first and second combustion rings....not that big of a deal

From all my dealings with different engine builders, I have concluded the stock rings are good, but they will fail over time in high boost applications....that's what happened to my motor....the #4 rings gave up, everything else looked great. So I'm using Wiseco pistons with the new build along with Wiseco rings.

So I'm assuming the high boost you ran (616whp on a Dynojet) caused the rings to finally give up.
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Old 05-15-2007, 08:48 AM   #15
exekious
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I think that might have caused some of it. I have owned this car since October 06 and so far I had only been running that car at around 450whp or 26psi with meth turned on.

Anyway, sorry about the poor pic (I got the wrong angle). Freedom Subaru called CP and THEY RECOMMENDED OEM RINGS! That is over their own rings. So we are going OEM.
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Old 05-15-2007, 12:15 PM   #16
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Quote:
Originally Posted by SloRice View Post
The only thing I see is the combustion getting by the first and second combustion rings....not that big of a deal.
At 600+whp, you know there will be some blow-by. I mean, what are we talking here...35 psi? Even with great leakdown, there is a lot of combustion air sliding by the top rings.

Quote:
Originally Posted by SloRice View Post
...I have concluded the stock rings are good, but they will fail over time in high boost applications...
Educate me here, since I haven't seen this. What do you mean by "fail?" Do they actually break, or collapse, round off, what?
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Old 05-15-2007, 12:52 PM   #17
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I agree, there is going to be some blow by with 30+ psi of boost...its the nature of the beast.

By fail, I don't mean break. I don't really have an answer for this....I think the metal starts to breakdown and the rings start to deform (can't think of a better word) and allow the compression to get by the rings. The rings I got from Wiseco are a lot harder than the stock rings. So I'm assuming they will be able to handle the additional pressure placed on the rings by high boost pressures. So while they will eventually "fail" too, I don't think it will be as quickly as the stock rings.
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Old 05-15-2007, 02:43 PM   #18
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It'd be interesting to look at one under magnification and see what really happened. Unless it's fatigue and it simply looses tension, you'd think the top and bottom edges would round off. Either way, it would glaze and loose seal. You should be able to clearly see it under a scope, no?

I wonder if Mick has any experience with this?
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Old 05-15-2007, 07:30 PM   #19
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My rings are never in the block long enough to fatigue I just looked at my stock rings off my CP's that came out of my failed block, they looked fine. Outside edges seem a little rounded but they are supposed to be like this. None of the pistons have visible burn marks down the piston which would suggest ring failure.

The only time I've seen pistons with blow by is either when the top ring was put in upsidedown or the ring land has cracked and no longer supports the ring correctly. Remember the top ring has a bevel at the top on the back which helps seal the ring onto the cylinder wall using cylinder pressure.

What was the engine symptom that lead you to pull the block and blame the rings? What was the compression and leakdown numbers? What was the ring end gaps? Too big a gap could have lead to this.

What do the cylinders look like, ie can you still see the cross hatch?
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Old 05-15-2007, 07:35 PM   #20
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has anyone here ever used total seal rings? I got a set with my ross pistons but wasnt sure how good they are. I know I've heard of V8 guys using them.
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Old 05-15-2007, 08:48 PM   #21
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Quote:
Originally Posted by mick_the_ginge View Post
...None of the pistons have visible burn marks down the piston which would suggest ring failure...
FWIW, that's what we get in kart motors when a ring is done and it no longer seals: a big, black burn down the skirt. It's really obvious and there is zero doubt about what's happening. And, that's what I don't understand in this case: that piston looks fine, and I just don't see any visual evidence of big time blow-by at all.
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Old 05-17-2007, 08:42 PM   #22
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anyone on total seal rings?
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Old 06-02-2007, 11:31 AM   #23
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I know a guy who is. Everything seems to be okay
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Old 06-04-2007, 01:04 PM   #24
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I've used Total Seal that are 0.010 oversized. If I had to guess, I'd say CP rings are made by total seal based on comparing the two sets. CP's have a thermal coating on the top ring.
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Old 06-04-2007, 01:05 PM   #25
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Not gapless.
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