Low Compression question

[busanostra]

My first cylinder has very low compression the rest are acceptable.
Its 2007 engine - I got it sitting in the lot could be a long time. I worked on bringing the compression back to normal by
cleaning spraying the intake/exhaust valves. I also poured each cylinder with "engine restore".

The 3 cylinders went back to 170 - 190 - 165 but the 1st cylinder stayed 100/90 psi. Stuck there.
I'm running out of option to except tear it down and do a rebuild. I will do everything to avoid expensive route.
The original sparkplugs when took it off, seems normal with no oil sludge that's why i was trying to bring the engine back.

Question:
Does un-adjusted valve (intake-exhaust) create low compression?

 

[Tached1300]

My first cylinder has very low compression the rest are acceptable.
Its 2007 engine - I got it sitting in the lot could be a long time. I worked on bringing the compression back to normal by
cleaning spraying the intake/exhaust valves. I also poured each cylinder with "engine restore".

The 3 cylinders went back to 170 - 190 - 165 but the 1st cylinder stayed 100/90 psi. Stuck there.
I'm running out of option to except tear it down and do a rebuild. I will do everything to avoid expensive route.
The original sparkplugs when took it off, seems normal with no oil sludge that's why i was trying to bring the engine back.

Question:
Does un-adjusted valve (intake-exhaust) create low compression?

Yes a misadjusted valve can create low compression if it’s such that the valve is hanging open. A bent valve would as well or a valve seat issue.

Any chance this motor sat outside in freezing temps w/o antifreeze? Could be headgasket related as well...

 

[Kiwi Rider]

You need to perform a leak down test to determine where the compression is leaking from, valves? Rings? Head gasket?

It may be carbon build up on valve seats, there is a product in a spray can that cleans carbon from valves called upper engine cleaner, you can get from a Subaru dealer, it’s a Barr’s product and very effective.
Spray it directly on to the back of the valves while rotating the crankshaft, remove throttle bodies and exhaust to gain access to the the ports. Leave it to soak for an hour, softens the carbon crust and when the motor is started all the carbon material is blown out the exhaust.
Good luck.

 

[Dopey]

What @Kiwi Rider said... do thr leak down test and that'll point u in the direction to go

 

[busanostra]

"Yes a misadjusted valve can create low compression"
Thank you -- If I find the shim is tight, I will replace the shim and try again.
"Any chance this motor sat outside in freezing temps w/o antifreeze? "
Could be sitting without anti-freeze but not too sure.
"Could be headgasket related as well"
When I did the compression test, I put a sparkplug to the nearest cylinder with a low compression
hoping to raise the compression to diagnose if its headgasket issue. But it did not raise the compression.
I'm sure not a headgasket issue.


"upper engine cleaner "

I will try to get it from subaru and try this option ...
Then I will do the leakdown test.
This will be my best option for now.
I appreciate the help very much ---- I thank you

 

[Tached1300]

Yeah I’d do the cleaner that Kiwi mentioned and see what compression is after that, if still not up to par then I’d do the leak down (as I’m assuming you may have to buy or borrow the equipment so save this for if compression doesn’t come back from the cleaning of the valve or valve adjustment) Good luck! Definitely report back your results

 

[busanostra]

Yeah, I will buy the spray first.
By the way, can I spray the "upper engine cleaner" directly inside the piston cylinder?
I was also thinking beside the valves, the ring was also stuck and not compressing.

As I mentioned, the original sparkplug when I took off, looks normal and clean
that is why I believed the engine is good ... & trying to revive it ---- but who knows.

 

[Kiwi Rider]

Subaru Upper Engine Cleaner - Bar's Leaks Australia LP | H.O. Wiles Limited

Subaru Upper Engine Cleaner SA459 is the only upper engine cleaning product that has been tested and approved by the factory to be used in Subaru vehicles, and included as a factory requirement in the maintenance and service schedule. It contains a powerful foaming agent to effectively clean...

www.barsleaks.com.au

I recommend it, I used it when I was a Subaru technician . .

 

[Kiwi Rider]

Yeah, I will buy the spray first.
By the way, can I spray the "upper engine cleaner" directly inside the piston cylinder?
I was also thinking beside the valves, the ring was also stuck and not compressing.

As I mentioned, the original sparkplug when I took off, looks normal and clean
that is why I believed the engine is good ... & trying to revive it ---- but who knows.

Yeah, you can spray it directly in to the cylinder thru the spark plug hole, won’t do any damage. Just remember to let it soak a while.

 

[Dopey]

Yeah, I will buy the spray first.
By the way, can I spray the "upper engine cleaner" directly inside the piston cylinder?
I was also thinking beside the valves, the ring was also stuck and not compressing.

As I mentioned, the original sparkplug when I took off, looks normal and clean
that is why I believed the engine is good ... & trying to revive it ---- but who knows.

I suggest doing the leak down test first it'll tell u if the loss of compression is going past the valves or the rings. Cleaning isn't a bad idea either way but if it's the cylinder and not valves it'll need to be tore down and cleaned anyway

 

[Tached1300]

I suggest doing the leak down test first it'll tell u if the loss of compression is going past the valves or the rings. Cleaning isn't a bad idea either way but if it's the cylinder and not valves it'll need to be tore down and cleaned anyway

I agree with you IF he has the stuff there already to do the leakdown test

My suggestion is based on assumption as well that he doesn’t have leakdown equipment on hand, he can start with what he has there with those quick checks and may not need to go any further if that resolves it. Minimal time or effort invested considering the return it could have

Not being argumentative W/o a doubt leakdown is the way to go just saying sometimes you gotta work with what’s available or within those means.

 

[fallenarch]

I assume it runs? Does it smoke? Does it rev clean?

 

[c10]

FYI your 3 good cylinders are not good at all . Why ? there is more than a 10% difference . You could pop the valve cover , and check clearance of the valves . If # 1 is all tight you might have found the issue there .
Going to guess though with numbers like that all over the place ring / piston damage . Usually a bent valve or blown gasket have a much lower # than 90 or 100 psi . like 0 to 20 psi .