low compression after valve/head job

[hidingfrogleap]

hey guys,

So I'm struggling with my 97 gst after a valve job. Basically, I had the timing belt go on me due to a faulty auto tensioner and so I had the machine shop replace all the valves. I had the head machined, new bronze valve guides put in and so, after installing some slightly used valves and springs, new stem seals, arp headstuds and a 4 layer metal oem headgasket i fired it back up and now i have compresson as follows: 150-150-150-80. As such I am getting rough running all thoughout the range, and a cel with a misfire on the 4th cylinder.

I just replaced one of the lifers thinking that was it but didn't do any good. I also removed the rocker arm on one of the valves on the exhaust side then tested it and got 150 across the board. I swapped parts all around and nothing really helped the compression any. Any ideas? Thanks in advance.

 

[snox135]

Sounds like the installed valve height is wrong on the one you removed the rocker arm from. I would check that. The lifter you replaced, is that on the same one as the removed rocker arm?

 

[hidingfrogleap]

yeah, it is the same one. so you think the valve guide height from the block isn't at the right clearance on that particular valve?

 

[gpz750]

No, Installed hieght is the distance the valve stem sticks up out of the head as compared to where the spring sits. The machine shop has to set up this since we don't have adjustable rockers. You might want to give them a call and see what they have to say

 

[hidingfrogleap]

doh, whoops. I meant off the head. Good catch, long day i guess. Well, I have it at the shop right now and maybe I'll give a call over to the machine shop later this afternoon if they can't figure it out. They'd have to be pretty slow to do that since I gave them a copy of the specs from the factory service manual.

 

[hidingfrogleap]

ok, so just to finish up the topic: After taking off the head again, I took it back to the machine shop and they found that the one exhaust valve was bent. Thanks for the replies.