Bad compression in cylinder number three help!!!

[konigtalon]

Hey there guys I just purchased Two Turbo DSM's a 90 GSX and a 91 TSI. We'll the gsx is mine and I did a compression check and come up with the following results 160 in every cylinder but the third one which was 40 . We'll my question is this if what do u all think would cause this I'm leaning towards the rings being bad haven't done a wet test yet. Also when I attempt to do this I just want to make sure I got everything correct. To begin I remove the timing belt, take the head off, remove the pan and unbolt the rods from the crankshaft then check the cylinder to see if it's hurt bad if not then I can do a rehone put the piston and rings in bolt everything back up and be done right? Also how do I line the piston ring's up? They are already on the piston any help would be greatly appreciated IM attemptinmg this this weekend. Thanks, Dewayne

 

[91 Turbo Mitsu]

Before you get to exited about it you need to do a cylinder leak down test to see what is going on. I had the same problem with my gst and cylinder 3 turned out to have a hole in the piston. As to just doing a rering and hone on one cylinder I dont know but I am sure one of the others will chime in with some more advice for you. Travis

 

[95blackGsTurbo]

x2 do a leakdown test. It is probably the rings buy could be a piston. Your accurate on how to take it apart but it's a little more difficult that just unbolting stuff. You will wanna get the head checked for straightness while it's off to make sure no damage was done. Line the pistons rings up 120* from each other. Don't forget to check end gap in the cylinder.

 

[domestic hater]

I've had this problem too and it turned out to be the piston.A piece broke inbetween the 1st and second pitston ring. I think its pretty common with 1g pistons because i've had it happen several times

 

[wont_luz]

After I built my new motor I had something similar happen...3 cylinders had 180psi and one had 20...turns out I had a bent intake valve, damn used head. A cylinder leak-down test like mentioned above will give you a good idea.

 

[duwackerTSi69]

This is to the OP, I had the same thing with my 95 tsi awd and in cylinder 2 I had 40psi. I took it all apart and it was a 1/8th inch hole in the exhaust valve. This happened to me about 4-5 months ago.. Im leaning towards the valves in your engine...

 

[My1GLaser]

Like stated above^^ I'm thinking a valvetrain issue. I had 3 pistons with cracked ringlands and cracked rings give good results in a compression test...150. (I mean cracked where a 1-2" piece of ringland fell out when I tore apart the motor and the rings were in 3 pieces. )I would think a valve is bent or something major like a hole in a piston.