Found a problem while adjusting my valves, can 1 valve stem be shorter?

[byrd101]

Car: 71T with mystery 2.7 maybe 76 or 77
Recent history:
1st I replaced heat exchangers and can now hear the rest of the engine noise. (Ugh, that sounds like chain dragging.)
2nd I upgrade to Carrera chain tensioners and newer chain wheel supports. The PO had installed cheep retainer clips so that the tensioner would not fail completely. (Got lucky, I hope) After I installed the new tensioners the Z1 marks lined up with the top of the cams.

Currently: I am in the middle of adjusting the valves. I noticed that the adjuster screw for the #4 exhaust valve is screwed almost all of the way into the locking nut. All the other adjuster screws have about 3/8” sticking out of the locking nut. This is not the first time I have adjusted the valves, but I didn’t notice this before. The elephant foot looks ok. The valve stem looks shorter then the rest. I just did a leak down test on that bank and all 3 cylinders are about 20% - 25%. (I did the leak down cold) I can hear air through the oil tank but not through the exhaust or intake. Could I have a problem with a valve seat or could the valve just be shorter?

Last: While I was double checking the valve clearance on the #6 exhaust valve I reached over to wiggle the #5 and #4 rocker arms. The #4 felt loose. Checked it with the feeler gage, yep very loose. After turning the engine to bring #4 to TDC I found that it was just right. Is this normal, or do I have some cam wear? Can my valve timing be off.

Side note: While adjusting the valves, I checked the head studs. Last year they needed a little tightening, this time they all check out fine.

[yelcab1]

your engine has problems. We need more info.
How does it run?

[byrd101]

The engine runs well, I little smoke when started then clears up. No miss firing and the plugs look good. I have what sounds like a valve tap. I will do a compression check and full leak down after work. I can tell that the #5 cylinder was changed at some point in the past, Don’t know if any valve work has been done.

[Grady Clay]

STOP, loosen all the valve adjusters except #1 & #4 intake, check cam timing. It is possible that the cam jumped a tooth while a failed tensioner or replacing the tensioners. Just looking at the ends of the cams is not easy to tell. Once you are certain of the timing, go back and adjust the valves.
Another cylinder leak test is now in order.

If the cam was out of time and a valve hit the piston and was bent, that will open up the valve clearance. Another possibility (unlikely with CIS) is something is between the valve and seat. However, both of those would have shown up with your first leak test, if they were present at that time.

Yes, I suppose someone could have put in a valve with the stem ground a lot shorter or an incorrect seat replacement.

Do the best you can to look at the cam lobes (not easy) for any obvious wear. If suspect, remove that rocker for a better look.

Do some more and report back.

Best,
Grady

[Superman]

Perhaps that cam lobe is worn, or the rocker foot.

[byrd101]

I checked the intake valve overlap and left: 0.47mm, right: 0.54mm. The specs in Wayne’s book list 0.40mm – 0.54mm with the desired value of 0.47mm. I don’t have the nice “Z” block for my dial indicator, and my bracket is a little cumbersome but I am ok with the numbers. Having never set valve timing I don’t know if this ok or bad. I intend to do a full rebuild next year, can I wait or should I just drop the engine and retime the cams?

[Grady Clay]

byrd,

Perhaps another test would be to swap the rocker with an adjacent cylinder. If the problem (adjusting screw down to the nut) followed the rocker, replace the rocker and adjusting screw. If the problem stayed at the same cylinder, you need to look further. Possible valve or cam lobe.

Not too difficult test.

Best,
Grady

[byrd101]

Good idea, I was just getting ready to pull it off to check the cam.

[ChrisBennet]

Originally posted by byrd101
I checked the intake valve overlap and left: 0.47mm, right: 0.54mm. The specs in Wayne’s book list 0.40mm – 0.54mm with the desired value of 0.47mm. I don’t have the nice “Z” block for my dial indicator, and my bracket is a little cumbersome but I am ok with the numbers. Having never set valve timing I don’t know if this ok or bad. I intend to do a full rebuild next year, can I wait or should I just drop the engine and retime the cams?

How did you tension the chain?
Do you perform the measurement multiple times and get the same reading?
-Chris

[byrd101]

On the left side I used the vice grip trick. Checked it 3 times and the number was consistent. 0.47mm. The right side was a pain. I cut a piece of wood and wedged it in with the tensioner. Shade tree, but the best I could do at the moment. The number on the right side came out 0.51mm the first time and 0.54mm the next 2 times.

I pulled out the rocker arm and found what looks like a little wear on the cam. The valve stem is definitely shorter then the other valves. How could that happen?

I put it back together and fired it up. Runs smooth but, with a slight valve tap at #4. It’s too late to startup the compressor tonight for a leak down test. I’ll get a warm leak down and compression check in the morning. Thanks for all your help!!

P.S. I’ll post the results in the am.

[Wayne 962]

Maybe a small piece of carbon is wedged in there, although 20% leakdown is pretty bad...

-Wayne

[byrd101]

I’m hoping for better results when I test it warm. The first time it was cold and I was looking for something catastrophic.

[byrd101]

The verdict is in, and it’s not so good.

Cylinder Compression Leak down
#1 135 PSI 12%
#2 125 PSI 22%
#3 135 PSI 15%
#4 120 PSI 25%
#5 140 PSI 15%
#6 135 PSI 15%

All the cylinders appear to be leaking past the rings. She looses about a quart of oil every 800 – 900 miles and only smokes on startup. Thamks for the help.