Just want to know more about compression. I did a bit of research on the web and said that if you have bad compression in the one cyclinder, then it normally means bad exhaust valve. Is this normally true?

I'm thinking of buying my friends car who has a low compression on one of the cyclinders, its out by 10-15. I was told anymore than that and I am looking at getting new pistons, rings, valves etc which is costly. If that was the case what am I better of doing?

Thanks.

 

rings
headgasket

 

... hole in piston etc.

It can be many things. Do a leakdown test to further narrow the cause.