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-   -   Compression (http://legacygt.com/forums/showthread.php?t=198961)

jp71ss 01-01-2013 09:04 PM

Compression
 
What would be the normal cranking PSI on a 98 2.5 that was turned over by hand? 2,3 and 4 are at 80-90 and 1 is at 60. I am thinking I may need new rings/pistons. It only has 118,000 on it and I just had the heads resurfaced and new gaskets and timing components. By the way, with six star headgaskets should the logo be placed facing the head?
Yeah I'm a subie noob but I have done a lot of small/big block chevy's.

Tr00b 01-03-2013 08:53 AM

180 Psi ish. Those numbers sound horrible.

jp71ss 01-03-2013 08:00 PM

Thats what I was thinking. Guess I better bore it. Where is a good place buy pistons and rings and such?

Tr00b 01-03-2013 09:58 PM

This is my 2.2.

http://i27.photobucket.com/albums/c1...203828_247.jpg

I used the starter though, and turned it over 10 times like the instructions said on the compression tester. I imagine, if you do it that way instead of with a wrench, you will have a different result. If the engine is out of the car, you could easily jumper to the starter and use it to test the compression.

It would be a shame to spend $2000 for no reason.

jp71ss 01-04-2013 06:18 AM

If I was going to spend $2000 it would be for a reman shortblock from Subaru. I hope I can get by for less than that. I have to. Thanks

Tr00b 01-04-2013 05:18 PM

I'm not saying you need to spend 2000 dollars on your engine just that you should make sure your compression test is accurate before jumping to any conclusions.

it just seems to me the piston rings go bad on 1 or 2 cylinders rather than all of them like have happened to your car. I don't even know how it would have run with that bad of compression.

spooln30 01-05-2013 01:10 AM

You did say by hand cranking the engine? I'm not sure you can get an accurate reading by turning the engine over by hand, you need to crank it via the starter. Like 3-4 sec per cylinder.

jp71ss 01-05-2013 07:54 AM

Kinda difficult to crank it over with the starter when it has a flex plate for a automatic. With that much difference in one cylinder I will put pistons and rings in it anyway. Is this block sleeved from the factory or does it have the nikasil coating?

johnegg 01-05-2013 02:24 PM

Quote:

What would be the normal cranking PSI on a 98 2.5 that was turned over by hand?
there is not going to be a spec for this.

compression test should be done with all plugs removed on a warm engine with the starter cranking the engine.obviously this is not possible.

a few things,
1/ before you assume the rings are bad, check the timing. if the timing has jumped the compression will be off.
2/ hand crank the and stop with the each piston at TDC and listen for escaping noise in the intake or the exhaust. again if the timing is off you may not learn any thing.
3/ bent valves due to a busted timing belt are much more likely cause. or maybe a burnt valve. bad rings are very very very rare.
4/ it is WAY WAY WAY cheaper to find a good used engine than to rebuild one. even a JDM import will be cheaper, but you will have to add the EGR.

but before i spent a dime on an engine or a rebuild, i would check the timing and then pull the head on the low pressure side and see if the valves leak.

what is the history of the engine??


good luck.

johnegg 01-05-2013 02:50 PM

or go to a salvage yard and do a similar compression test on a known good engine.

jp71ss 01-05-2013 10:30 PM

Timing belt and idlers, tensioner was new and dead on. I have the heads at the machine shop now checking the valves. Waiting on that now. I have another engine in the car I am building (97 gt wagon) with the original engine. I guess I could use it as a guinea pig for that. It has 5000 more miles and had the head gaskets replaced but they still leaked when I bought it. I wanted to get this engine out of the 98 outback together to replace the one in the 97 that I think may have a bad block cause the new headgaskets didn't fix it. If it is still good then I will have a spare to build at a later date or sale it if I don't need it.
I sprayed oil in the motor that is in question on the compression to try to get it to raise. They did raise some cause no. 1 didn't have any compression at the start and now I have 60 on it and the other 3 raised some too (30 to 40 lbs.).
I still would like to know if I can bore either block and have good cylinders that will last a long time. So I still need to know it they have liners or nikasil.
What the machine shop finds will answer a lot.

spooln30 01-06-2013 12:08 AM

You know that doing a leak down test is better then a simple compression test. You can rent them from your local auto parts store. With a LDT you can figure out the percentage of leakage, plus when you have compressed air in each cylinder you can figure out if its the rings or either intake or exhaust valves. Simply set the cylinder at TDC and hook up the LDT to the spark plug hole. Fill with air and listen for the leak, if you remove the oil filler cap and you hear air hissing then it's your rings. If you can hear air hissing in the intake manifold then intake valve and same with the exhaust, remove the header and listen for air hissing.

jp71ss 01-06-2013 04:59 PM

I don't know of any cylinder that wouldn't leak some by the rings with compressed air on it. I have used that method to replace valvesprings before and it always blows into the engine.

jp71ss 01-07-2013 06:42 PM

Well I went down there and checked the engine a little more and I can physically rock the no1 piston in it's bore a lot more than I like.

jp71ss 01-08-2013 09:01 PM

No bent valves!


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