valves partially open?

[thor]

Hi,
I have one question for someone to help me with.

I've done hours of diagnosing my idle problem, and i've come to the conclusion that the valves are parially open when they should be closed (when the cam lobe isn't pushing down on rocker). I have low vacuum at idle which is causing the plugs to 'load up'. A leakdown test confirms that I have air rushing into the intake or exhaust on every cylinder. compression numbers are roughly 70-80-80-90 but car doesn't burn a drop of oil or antifreeze and I just did a head gasket.

i've replaced the lifters with a known good set from an engine that ran fine, but the same thing happens.

could there be oil holes plugged in the head that isn't properly allowing oil out of the lifter? Are my valves bent? I just rebuilt this head, but anything is possible.

help! the car runs great at highway speeds but barely idles at all. Once it loads up it's impossible to start again. btw it's a 93 talon 2.0 non turbo automatic

 

[afastdsm6969]

I would say check your timing. This is what my car was doing and it was off 2 teeth.

 

[thor]

since I have to pull it apart now anyway, i'll check that. But it does run great once over 1000rpm. I was able to set initial timing at -5° though. If it was off a tooth or 2 wouldn't that be impossible to set? I'm just curious.

thanks for the reply!

 

[afastdsm6969]

mine would run like crap till i got it up in the rpms. i would check it it cant hurt and can save you money down the road

 

[GVR4592]

When you rebuilt the head did you set the valve installed height?

 

[thor]

actually, no I didn't. I did keep all parts in order and put them back in the same holes though.

The machine shop re-surfaced the head taking off 10 thousandths. Am I to understand that I should be taking up this difference with spring shims? That little bit isn't compensated for in the lifter?

so what i'm thinking here is that I messed up..

 

[GVR4592]

It sounds like you just put new seals in it and resurfaced it, and didn't do a full rebuild. Resurfacing the head doesn't have any effect on valve height. If you didn't remove material from the face of the valve or the valve seat, then installed height shouldn't have changed.

Some other things that can cause low compression are, improperly bled lifters, slightly bent valves, or cam timing off a couple teeth. I'd check cam timing next.

 

[thor]

well, I think I discovered the problem..

my crankshaft is off by one tooth. According to the manual, the keyway should be at the 9:00 position, however it is in the 8:00 position.

What bothers me is that the wheel behind the sprocket with the timing notch on lines up with the mark on the block. I used that mark to align the belt. So apparently that mark isn't always accurate or someone put it on wrong. I don't know until I pull it apart the rest of the way.

This would explain why it runs like crazy at highway speeds (advanced) but crappy at idle. Plus it gave me inaccurate compression numbers.