Engine troubles - Valve(s) not sealing

[neill]

Hey Guys,

After some opinions and potential ideas on a problem I have.

I bought a 3.0 that was rebuilt, hadn't been started and was good to go as far as I was aware.

I have finished building the itb intake, wiring it etc and went for a run on the dyno to get a tune. We had a few dramas (as you always do on dyno day) and while diagnosing issues we pulled the spark plugs, only to find cylinder one plug looked brand new, nothing had ignited in that cylinder.

We then pulled out the laptop and did a test on the spark, all ok. Then tested the injector, again ok. Then tested the compression and only have 90psi. The other 5 cylinders all have 190-195psi.

We took it off the dyno and I suspected it may have been the valve adjustment too tight, pushing the valves open ever so slightly. I adjusted the valves on cylinder one to be loose to ensure the rockers weren't going to be holding it open and did a compression test. Still only 90psi.

To ensure it was the valves I put some oil in the cylinder to try and see if that raised the compression and eliminate it being the rings. Still 90psi.

So I am fairly confident it is the valves not seating correctly.

Has anyone else had an issue similar?
Do I have any tricks I can try before pulling the motor and subsequently the head(s)?
Am I way off and its actually something else?

[Alan L]

Leakdown test on #1.
That will tell you where the compression is going. much more definitive than compression.
Alan

[boyt911sc]

Use P7I and P7E tools to test the valves. With these tools, you could remove the valve’s springs from the engine without removing the cylinder head. And install them back after the test. Were the cylinder heads tested for leaks (liquid test) prior to installation? Or a vacuum test done? The problem could be existing from the start (?).

Tony

[neill]

Leak down test was planned next. I will definitely do that.

I can't say if the heads were tested prior to building as it was bought assembled, done by another person. I am of the opinion that this issue was pre-existing but I haven't found it until getting it started.

I like the idea of trying to seat the valves insitu. I am really dreading dropping the engine again.

[boyt911sc]

Originally Posted by neill

Leak down test was planned next. I will definitely do that.

I can't say if the heads were tested prior to building as it was bought assembled, done by another person. I am of the opinion that this issue was pre-existing but I haven't found it until getting it started.

I like the idea of trying to seat the valves insitu. I am really dreading dropping the engine again.

Neill,

A leak down test will tell you which of the valves is the culprit or maybe both. But doing the troubleshooting with the engine install in the car is quite a feat. If I were in your shoes, I would do the following:

1). Do a leak down test. Determine where the leak source is originating.
2). If one of the valves or both is the culprit, remove the valve’s springs and spin the valve against the seat. A very light spring compression (optional) will keep the valve up and against the cylinder head. Spin the valve using a hand drill. There could be some sort of debris or rust caught in between.
3). Test if the valve stem is straight and not binding. Do another leak down test. If the problem still persists.........you know what to do next?
4). I would drop the engine and do the troubleshooting with the motor mounted in an engine test stand similar to this set up.








Keep us posted and good luck.

Tony

[Alan L]

Another thing you can do if the valve shows up suspect is to remove the rocker arm and tap the head of the stem to 'ping' it. I am assuming you can get that rocker out, and you can get enough room to get to the top of the stem for a sharp tap. It may be a bit of crud stuck in the guide. Other than what has been suggested above, it will be an engine out job. But at the end of the day the time you spend mucking around pulling rockers off etc, you could have the engine out.
Regards
Alan

[manbridge 74]

I’m going with the crud theory as it seems you are not running filters. Lots of possibilities though. You might want to find someone with a good borescope. Take a few pics..

Nice car by the way...

[blpetry]

Even with only 90psi compression, I would certainly think it would still be firing. How many miles are on the engine since the rebuild? Is it broken in yet? Triple-check that the plug is actually firing by looking at the spark and double check that the cyl is getting fuel (if its not firing the plug should be wet right?). You can also put a IR thermometer on the exhaust manifold to see if its firing. Running it moderately hard will also wear off any surface rust that may have formed on the valve seat(s).

I wouldn't worry about crap until it has a few hundred miles on it. New motors leak until the rings are broken in.