sr20det rebuild. low compression?

[kylekinnamon1989]

so im in the middle of a rebuild on an s13 redtop.. the compression test came up bad, 90psi on cyls 1& 4 and 110psi on 2 & 3. i bought it off a guy who said it also had a low end knock.. i never actually heard the knock but i got a hell of a good deal on it so i went ahead and bought it.. so i took it all apart and this engine is SOOOO clean! i went ahead and ordered all new bearings, piston rings, complete gasket set, stage 2 bc cams and some other s***.. "currently just waiting for the parts to come it" but up until today, i totally forgot that the compression was horrible.. what would cause that? i dont want to put everything back together and still have bad compression you know?!

[Shadow Drifter]

if yoru replacing all the rings and HG you shoudl be fine then. Just make sure you break everything in like you would with a new motor

[compactfean]

Don't forget to check the head and block for warpage. Could have been overheated and popped a head gasket. Also make sure you hand lap your valves because that could also have been an issue. If your doing a full rebuild and are fallowing the steps than you should be fine. Did you mic out the crank and cylinder bore? If your cylinders are out of round and/or crank is out of spec than bigger pistons and or oversized bearings and machine work will be involved.

[kylekinnamon1989]

This is my first rebuild so I honestly don't really know what I'm doing but everything thing is pretty straight forward. I figured a basic hone would do the job? How would i tell if the head is warped?

[JDizzle]

Check it with a straight edge and feeler gauge. I would (and did) just take it to a machine shop so they pressure test for cracks and straightness. As mentioned before, also have the machine shop check the cylinder bore and crank journals.

[compactfean]

I honestly think that rebuilding the motor yourself is a better option. Alot (almost all) of machine shops are very laid back about certain clearances because there job is to push work quickly. I can't even count how many times I've checked clearances that were not acceptable by me.(I'm very picky and do not skip any steps though) its a big difference from a race motor and and plain stock motor. If you do find a speed shop that will build a decent motor usually costs you. My best suggestion do it yourself and don't skip ANYTHING. if anything needs machined check what work needs to be done ...get it fixed and double check it before moving on. An fsm will become your best friend in a build and there is no such thing. As being to precise.