Compression Problems

[zxdude]

ok so this is the situation.....

Got my block and head back from the machine shop......

block was bored .020 over and new 1g pistons were intallled

the head I broght in .... had 8 bent intake valves....

Head work....

New valve stem seals
8 new intake valves
head was milled (not sure how much)
all new gaskets
standard valve job

when I got the head back the valves were not seated (lifters were holding them open)
- the machinest said to turn over the cams a few times by hand to get them to seat...

so I did exactly what I was told to do

got the engine into the car and fired it up... started almost right away... ideled and died it did this a few times untill it would not start anymore....

I was like WTF and got out the compression tester...

it read 90 0 90 90 psi way below the service limit (could it partically be due to a 0 miles on the rings maybe ideled 30 sec total...

when it stareted it made a loud tapping noise (like a real bad lifter tick) now I think it bent 1 or more intake valves..


Any Ideas I bought the car as a project car now over 1k into the POS and its still isn't running....

Any ideas... I going to the shop tommaro to ask them WTF happened (why valves hit)
we tripled checked the timing and it was perfect everything aligned

 

[SlowSpyder]

Were you the one who put the engine back together? The low compression across the board shows signs of incorrect cam timing, that cylinder that reads zero is the one that is puzzling me. Ask the shop what their "standard valve job" consists of. Did you try a west test during the compression test? (cap full of oil) If the compression goes up then its your rings. If nothing else works then try a cylinder leakage test, this will tell you if its your valves or rings and the nice thing is that cam timing doesnt affect this test, unless your valves are opening during the compression stroke

 

[zxdude]

was just a 3 angle valve job... they reused the 8 exhaust and put in 8 new intake valves... me and a friend ( that has done lots of work on dsm's ) put the engine together the rings are brand new ? how could they be bad? .... after the compression test we hooked up the air compressor to the 0 psi cylinder and poped off the rocker arms so the valves we pulled as tight as possible... and you could hear air leaking on the intake side. so I think its a bent valve but how is that possible. The timing was perfect.

thankx Adam

 

[zxdude]

... I hope this is " techy " enough

 

[SlowSpyder]

Depending on how much your head was milled, this will actually retard cam timing. If the cylinder was set to tdc on the compression stroke and you hear it coming out of the intake then its your intake valves. Positioning the ring gaps on the piston the wrong way can seriously affect compression, but i dont think is a bottom end problem. I think the problem is in the head. I still believe that the engine has incorrect cam timing and that one cylinder with no compression has a problem with the intake valves either not sealing properly or its now bent due to incorrect cam timing due to taking material off of the head.
This is just my opinion, I am by no means an expert. Just keep this info in mind when asking the shop what could possibly went wrong. Anyways, goodluck in finding the problem

 

[Tevenor]

... I hope this is " techy " enough

No, it's not.

And any machine shop worth their salt would have:

A) Bled the lifters to verify the valve seat seal
or
B) turned the cams for you


If the timing belt install is correct and didn't cause a deflection of the valve in the 0 compression cylinder, then the head was faulty when you got it. The low compression I would take with a grain of salt since from your account, you haven't run the engine long enough to actually seat the rings.

 

[zxdude]

when i talked to thwe machinest he said he milled the head 50/1000ths then i told him the valves only clear the pistons by .080 intake and .100 for the exhaust, and he told me you can safely take over 80/1000 off. he wants me do check if something is holding the valve open and if not bring it back... isn't the 50/1000ths to an extreme

Adam

 

[zxdude]

thanks for all your help by the way...