Compression

[Amokster]

I've looked through the handy Subaru Book on what the compression is suppose to be for an older Brat, 138-168 psi I believe. Is having the compression on the middle to lower end of things ever a problem. The Brat I'm looking at ( still for crying out loud ) has 150 psi in all 4 cylinders. Is there a difference between the lower middle end and the higher end?

[GeneralDisorder]

You will get an answer if you post in the older generation forum - this is not the place for specific questions.

 

GD

[nipper]

On engine compression you need to do a dry test, followed by a wet test. All the pluygs need to be out and you need a strong battery. A wet test lets you know if your rings are leaking or not..

 

The numbers matter in two ways, both of wichc are just as impotant, Firs is peak compression, which can be in the 170-190 psi range depending upon engine. The second, which is more improatnat, is the cylinder balance. Engines loose compression sometimes with age, but they should be balanced between cylinders, usually 10%. So a 170 psi compression number can be 170- 153 and be considered healthy.

 

An even 150 really isnt that bad for an older engine. That tells me the valves are ok, and the rings may be a little worn. A wet test would be great.

 

nipper

[GeneralDisorder]

Wet tests don't work well on boxer engines - the oil seals the valve seats just about as well as it seals the rings. Rings are rarely the problem with these engines - the valve seats are usually the biggest compression issue. Stem seals will cause oil burning - usually the EA's need one or two valve jobs in their lifetime to stay in top running order.

 

GD

[Amokster]

Thanks for the answers. Sorry about the wrong Thread.