Compression Numbers: To rebuild or refresh

[RoughDiamond]

Long time lurker and Subaru owner, finally brought home a rough, but ridiculously solid 91 BC, 4EAT.

Long and short, it has 190K, looks to be untouched (head gaskets, ect) and has running higher than normal operating temps, it's getting pulled for a reseal and top end inspection/refresh.

It runs pretty well (minus the high idle and occasional sputtering under high load), does not smoke and the plugs, while tired, look great. French-Fry gold. Passed E-check today too (sniffer test).

I grabbed some compression numbers today before I pull it to see if I need to hunt down some bearings and ring along with the gaskets and seals.

Cyl Pressure(psi) Dry/Wet (Wet = 1 cap of 5w-20 in cylinder)

1 145 / 170
2 130 / 185
3 155 / 185
4 165 / 185

I haven't pulled the heads to look at cylinder condition or valve condition yet, but from the look of the intake and exhaust, it doesn't seem to have any problems with fouling or spitting back through the exhaust.

Assuming another 50-75K is what I want/need to get out of this motor (and no nasty surprises like a scored wall or cracked ringland), would a simple reseal suffice? Or should I just rebuild the whole damn thing because a catastrophic compression loss is near?

Thanks for the advice!

[Legacy777]

Welcome to the BBS!

When you were doing the compression tests, was the throttle plate fully open?

If so, the factory manual lists 156 - 185 psi as "standard" and 128 psi as "limit" with a 28 psi as the max "diff. between cylinders".

The "dry" numbers you posted are what I believe the factory manual is referencing....which does leave things outside of spec. Does that mean the engine will have catastrophic compression loss....probably not. I guess rebuilding it really depends on what your budget is and I know you mentioned keeping it another 50-70k, which might be a little bit of a stretch more to put on that engine, but it might make it.

There is a member on here (Charles - rallyak) that has several very high mileage Legacies 300+ and might be able to give you some feedback about your situation.

[rallyak]

Personally if its not burning much oil I wouldn't touch it. My wife's is completely stock and never been apart and it at 413k and I have no plans to rebuild it any time soon.

If I was you I would do the normal maintenance plugs, wires (NGK), oil and inspect the timing belt and oil seals.

[RoughDiamond]

Thanks for the replies! I consider myself a Subaru enthusiast, and the BC Lego the crown jewel of Subaru's engineering and KISS mentality.

I did read the FSM before attempting and while it was not at FULL operating temp (after a car wash), it was warm and had been idling for a few mins. Yes, the throttle was WOT and the rest of the plugs removed. Starter and battery are strong.

For the specs, I believe 140-165 is spec for the turbos and 118 the limit... while the one cylinder with its 130 is a bit concerning, I'm not ruling out HG or other non-bottom end sealing issues at play here.. but I'm inclined to leave the short block alone. I've done several Frankenmotors and 25D rebuilds, all of which are still tearing around (knock on wood), but I don't want to risk a closed deck block if I don't have to...

Looks like I'm setting aside Sunday for the pull, and probably the tear-down as I'm anxious to see what it looks like since the 'scope doesn't have that good of resolution.

EDIT: I should mention that it has had SOME maintenance done to it, and I had to put a new TB and water pump since the OE (at 190K) had locked-up. Dry, but seized in the housing. That was a first..

Also, of the higher mileage blocks I've torn down, I haven't seen high-wear problems in the bore and I still can see a nice cross-hatch pattern.. I know these aren't EA motors, but they still do alright.. ;D

[Legacy777]

I guess I missed that it was a turbo engine and not a non-turbo engine. So I am in agreement with Charles to not tear it down and rebuild it. Just do the normal maintenance items and call it good, especially if you plan to keep the boost at stock or near stock levels.

[RoughDiamond]

That sounds like a plan to me. Of course, that's all dependent upon the condition of the cylinders (roundness, bore, surface, ect) but the 'scope looks promising.

I've already started to gather the necessary gaskets and it's coming out Wednesday or Thursday!