I just finished putting together an engine for a first gen... The head is not known good, thought it passed a hydro test while on the bench with the cams out of it.

Cylinder 1 has only 30 psi of compression. This was weird to me, as it passed the hydro test and the rings are new (I expected lower compression, as the rings have not seated, but 30 psi is wrong).

I then went to leakdown test it. I could feel significant amounts of air rushing out of the exhaust, as the downpipe is disconnected. I popped the rockers off and the air discontinued and the only air I detected was that which was coming from the oil pan (which is to be expected).

Obviously the valves are not closing completely at TDC. This also makes sense from before I pulled the engine apart, as there was something that sounded like lifter tick, except louder (loud enough that it caused knock count).

What do you suppose my problem could be here? Thanks in advance.

Incorrect timing possibly. Obviously something is wrong if the valves are staying open when the cams are in.

Timing is on. Cyl 3 has 140 psi.

Try bleeding the lifters.

Lifters were all bled prior to installing into the head

Are these stock or aftermarket cams? Clearly something is off somewhere in the valvetrain if they seal when the rockers are off, but not when they are on.

To the best of my knowledge, they're stock cams... I, personally, have never messed with them. However, who knows when it's a DSM with however many miles on it....

So today I replaced the lifters/rockers with known good ones out of an old 1G head. They were my first suspect. Cylinder 1 still has 30 psi of compression; no change. That means that either the springs are too weak to pull the valve closed the whole way vs. the hydraulic lifter (unlikely), the valve stem is too long, or the camshaft lobe is holding the valve open slightly (which would be really weird.....)

This is definitely an odd issue.

no valves are bent?

I had a situation where the valves were still cracked open after installing the cams. I ground a couple thousandths off the bottoms of the lifters. Solved my problem. I'm not advising anyone else do this, just saying that's what I did and the car ran fine for the next 3 years, trapping 130.

Which is exactly what I intend to do at this point... either grind the cam lobes, or grind the lifters; Could also grind the roller on the rocker. All of these options would yield my result... lifters are the cheapest option, though, I believe. We'll see what happens. And no, none of the valves are bent - they were just replaced.

Memphetic said:

Which is exactly what I intend to do at this point... either grind the cam lobes, or grind the lifters; Could also grind the roller on the rocker. All of these options would yield my result... lifters are the cheapest option, though, I believe. We'll see what happens. And no, none of the valves are bent - they were just replaced.

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Edit: Nevermind... read that wrong

I would suspect the valves are the issue at this point. Was a valve job done? If it was, most likely the seats were machined and the valve stems were not, this would make the valves too long, and would cause this issue.

Either that or the seats are installed incorrectly.

I HIGHLY doubt it is the camshaft, rocker, or lifter causing this issue. I would put my money on it being valve itself, or a shitty valve job causing it.

Yeah, pulled the head today... redoing the valves.

was tip height the issue?

Kapok6 said:

was tip height the issue?

Click to expand...

"Just the tiiiiip"

Tip game is strong.

Ahh, to be 18 again.

talontd92tsi said:

Ahh, to be 18 again.

Click to expand...

It's fun to jump back 13yrs occasionally.