EJ25 broken ring land

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bentvalves
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EJ25 broken ring land

Post by bentvalves » Mon Feb 11, 2019 5:28 pm

subaru ej255 engines (DOHC) seem to suffer a similar common problem.... broken ring lands in cylinder 4 when they are lightly modified.

they don't have to be making anything north of 300whp for this to happen.

anyone familiar with these engines have any insight as to what is causing the broken pistons?


I'll be taking one apart this week and the first thing I will be looking for is the ends of the rings butting together in that cylinder, but I doubt that is the issue here.


fire away fellas, nice to have the board back up.


CONDOLENCES to Don's family, RIP Don.

mekilljoydammit
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Re: EJ25 broken ring land

Post by mekilljoydammit » Mon Feb 11, 2019 7:30 pm

It's all consequences of trying to get an old design to pass emissions. Hypereutectic pistons are brittle but seal better, moving the top ring up reduces crevice volume but means the top land is weaker, tune that stays closed loop longer helps emissions tests but means it's closer to the border of detonation... also #4 is the hottest cylinder, also closest to the turbo, and the knock sensor is on the other bank.

KnightEngines
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Re: EJ25 broken ring land

Post by KnightEngines » Mon Feb 11, 2019 7:55 pm

Glass pistons, 1st thing you do with a Subi is open up the bearing clearances & fit a set of drop in forged pistons.

mekilljoydammit
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Re: EJ25 broken ring land

Post by mekilljoydammit » Mon Feb 11, 2019 9:29 pm

I know some Aussie Subaru guys who claim it's our gas too. Dunno. There's a lot of stuff piled on the things over here though.

Geoff2
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Re: EJ25 broken ring land

Post by Geoff2 » Tue Feb 12, 2019 3:23 am

Ring ends butting?

Aussie Dave
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Re: EJ25 broken ring land

Post by Aussie Dave » Tue Feb 12, 2019 6:43 am

Yep like Tony said glass pistons and the are the for the reason mekilljoydammit said.
When I worked at MMAL we went from 3.5 V6 with an ACL piston. To a 3.8 V6 with a Japanese piston to meet euro3 emissions. MMAL intended to build the 3.8 locally and consulted ACL about piston production and there reply was they don't make pistons out of such a brittle material.
The manufacturer needs that brittle material and that top ring high to meet emissions, by getting that crevice volume really small . If you want to push up the power level up,change the pistons, simple. Don't blame the piston for failing when you asked it to do something it wasn't designed to do.
I don't thinks our fuel, I think we expect to much. I have broken those 3.8 piston N/A they just don't handle knock at all. I really feel for those stock turbo pistons.

mag2555
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Re: EJ25 broken ring land

Post by mag2555 » Tue Feb 12, 2019 6:46 am

In looking at the spark plug from that cyclinder where does the color change over point on the plugs electrode take place, more towards the plugs body then in the middle?

jed
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Re: EJ25 broken ring land

Post by jed » Tue Feb 12, 2019 7:32 am

KnightEngines wrote:
Mon Feb 11, 2019 7:55 pm
Glass pistons, 1st thing you do with a Subi is open up the bearing clearances & fit a set of drop in forged pistons.
Tony what kind of bearing clearances are you talking about??

BLSTIC
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Re: EJ25 broken ring land

Post by BLSTIC » Tue Feb 12, 2019 7:33 am

It's the fuel delivery system. Because of the two fuel rails joined by a narrow pipe, the last injector to get fuel has notably lower fuel pressure compared to the first. You'll find the regulator is by cylinder #4 and the feed is on the opposite bank.

You need to swap one fuel rail so you can run a split feed into either two factory regulators rails with a joined return or two non regulator rails t'd into a single aftermarket regulator. This will even out fuel pressure across all four cylinders.

"Split fuel rail mod" is the google term

Doubtless there are other factors as well, but this is s known problem and if you have uneven fuel delivery by an amount you can't tune for because you don't have individual lambda, it's easier to fix this and improve the situation a lot.

KnightEngines
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Re: EJ25 broken ring land

Post by KnightEngines » Tue Feb 12, 2019 7:42 am

For a basic motor up to about 500hp you want .0018" minimum on big ends, up to .0022" is fine.
Mains minimum .002" & up to .0026"
Tighter than that & it'll hurt bearings.

I've pulled down brand new sti short motors & measured big end clearance at .0008" :shock:

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