Bad compression on 2.5RS - anyone got an idea?

Kevin Hoff · **Posted:** Sun Feb 04, 2007 10:31 pm

I've been trying to diagnose a low compression problem on #4. It's about 60 on #4 and 190 on the other 3 cylinders... A leakdown test showed about 30% leakdown. It's burning oil about a quart every 200 miles.

So I pulled the motor this morning and pulled off the driver side head, fully expecting to see the rings scoring the hell out of the cylinder walls. Instead what I saw was a really nasty oil soaked combustion chamber and piston with virtually perfect cylinder walls. There is one tiny scratch on the cylinder wall but otherwise the scoring looks no worse than the other cylinders that have such great compression. Unfortunately I did the work at a friend's house and don't have pictures.

I'm going to take the head in to a shop on Tuesday or Wednesday to be checked for cracks and bad seats/seals. Until then, anyone had a similar issue? How big of a scratch in the cylinder wall is enough to cause significant oil problems? Is it possible for a broken ring to lose compression without destroying the cylinder wall?

Also, any suggestions on a good shop to use? I've heard good things again about T-Hoff. Any other choices?

--Kevin H.

Carl Fisher · **Posted:** Sun Feb 04, 2007 11:12 pm

Bret Luter wrote:

I have been using Cylinder Head Specialties (CHS) in Wake Forest, right off the US1 service road (Star Rd?) on the right before you get to the Wakefield/US1 Business intersection. They're tucked in behind a used car dealer- I think it's called Hollingsworth. George and the guys there do a great job at a great price. They do all sorts of race motors so they won't look at you funny if you ask about something that's not stock. They also do full engines, not just cylinder heads as their name implies. Highly recommended.

I used them too when the Neon was having probs and they fixed me up quick and easy.

Cylinder Head Specialties
(919) 556-0775

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

Good looking cylinder walls, oil soaked combustion chamber, right?

How did the head look? Degrease the heck out of the combustion chamber and look for bad/bent/not seating valves, and for cracks.

How does the head gasket look, and how does the oil look? There is a *small* chance of a head gasket oil leak on the "top" of the gasket from the directly from the cylinder to the oil passages.

I just had my EJ22 heads freshened at CHS, they did a great job. I believe a few years back they said they could magnaflux heads to look for cracks.

It's an interesting problem -- where are your parts? Can I come take a look?

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

Two other thoughts --

1 - bolt the head back on and do a leakdown, look for bubbles in the valvetrain area.

2 - bolt the *other* head on and do a leakdown. If the leakdown is bad, the problem's in the block.

BretLuter · **Posted:** Mon Feb 05, 2007 10:30 am

Sorry, can't help much with specifics- but I'll repeat what Carl and Mike said about CHS- take your head to them!!!

No sense in trying to figure it out until they confirm whether or not the head is good- THEN you can start looking elsewhere. Talk to George- he is very soft spoken but knows his stuff when it comes to heads and engines.

I took a Kawasaki 4 wheeler head up to him last Friday that had a bent valve, he swapped out the bent valve for the new one I supplied (at his suggestion) and tested both valves for leakeage WHILE I WAITED!!!

Bret

Kevin Hoff · **Posted:** Mon Feb 05, 2007 6:55 pm

Thanks for the leads everyone.

Mike - good idea on swapping the heads l-r and trying the leakdown to see if it follows the head or stays with the piston. I might try that this evening. (BTW the stuff is way out at Eric's house, probably farther than you are willing to drive just to look at them)

No oil leaks or head gasket problems evident at all unfortunately.

I might pop the piston out this evening to look at the rings. Luckily this is easy (supposedly) on a Subaru. We'll see...

<edit> I didn't take the piston off but did pull the other head. Here's a link to a bunch of photos: http://forums.nasioc.com/forums/showthread.php?t=1194980</edit>

BTW, Subarus ROCK. The design is incredibly easy to service. The manifold comes off with 8 bolts and ALL the fuel/emissions lines +engine wiring comes along.

--Kevin H.

Kevin Hoff · **Posted:** Mon Mar 05, 2007 3:34 pm

It runs! WooHoo!

I got the car together, cams timed, valves adjusted, and bolts tightened last night. It started first try after cranking for about 30 sec with the coil unplugged to build up the oil pressure!

I ended up replacing the rings in the bad cylinder, having the heads rebuilt, and doing a lot of preventative maintenance while things were apart. The problem was apparently 100% the rings as the machine shop found nothing wrong with the heads that would have led to the poor compression in that cyl. Thanks to messing up one of the CV's wrestling with the motor putting it back in (D'oh!) it drives pretty rough so I really can't tell how well the rings are seating. No smoke though.

Thanks a million Eric Adams for the extended use of your garage. I couldn't have done this without your help.

--Kevin H.

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Bad compression on 2.5RS - anyone got an idea?

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