Dead Hole
 

Finally ran a compression test last night and found out that #2 is totally dead... zero compression. The other 5 are all sitting right at 160. So, here is my plan and please feel free to weigh-in.

Step 1: Pull the manifolds so I can see the back side of the valves. Stick a flashlight in the spark plug hole so I can see which valve is not closing. Roll the engine over and compare movement of the valves on #2 with the rest of the cylinders. If one is not closing, go to step 2.

Step 2: Pull the cam cover and see if that valve closes. (Hopefully this is the case) Identify the offending HLA and either replace or re-bleed and try again.

I'm really hoping that it's just an HLA that's pumped up too far and not something more serious. I've already been able to look into the cylinder and am pretty confident that there's not a hole in the piston... the plug was not damaged and the engine has run now for a total of about 40 minutes. If there was a problem with the piston, I should have seen evidence on the plug or in the chamber (I hope). Anyway, please let me know if I'm on the right track.

Thanks again guys!

Pretty common for a re finished valve to protrude a little too high. V8s do not seem to have this problem...
Find the offending valve & give the tip a little "haircut"
Just blow a little air through the Cyl at TDC to find the leaker.

If you have a hole in the piston the blowby out the breathers is massive, you know when you have a hole in the piston, and I speak from experience.

Most likely you have a valve that either isn't closing because of valvetrain mis-adjustment, or possibly a bent valve due to something solid going through the combustion chamber bending the head of the valve. A bent or broken pushrod another possibility. Another possibility is a flat cam lobe, but that would be with a flat tappet cam, not a roller.

A leakdown tester can be used at this point to find whether it's, intake or exhaust that's leaking the compression. Backing off both intake and exhaust rockers to do the leakdown test may also give you a clue whether it's adjustment, or a mechanical problem.

Now all you have to determine is which scenario you have...................:confused:

The valve job was done at the same time as the rest of the rebuild and there was plenty of Prussian Blue on the seats. I know the guy that did the job well and he knows these engines, so I'm pretty confident he did the job correctly. He did have to touch up a couple of the stems afterward to make sure they were all the same and correct height.

I appreciate the feedback Sirrotica, but this is an overhead cam engine so there are no pushrods or rocker arms to contend with...

Sirrotica: he has an OHC6.

george

I was looking at new posts, and neglected to notice that it was from the OHC 6 tech....................:sorry:

The basics still apply though on finding out where the problem lies.

I assume the oil restrictor tube is in place and has the correct sized hole. What oil pressure does the engine have? Too much will cause problems at the top end of the engine.

Yes, the restrictor is in place and the engine runs at 30 pounds cold, 25 or so warm.

Sounds like the oil pressure is within spec. Did you measure the hole size in the restrictor tube before install? Should be ~.080”. Some tubes came from the factory with a hole size of .125”. Way too big and too much oil! Will cause the valves to hang open. (Pumped up lash adjusters) Good luck in correcting the problem.

I haven’t measured it yet, but when the cam cover comes off again I will. I do know the engine was built in late ‘66 and installed in a 67 Tempest with a manual trans. If it is one of the larger ones, wouldn’t it effect more than just one cylinder? And where could I find the smaller size?

Not necessarily. You can either braze or weld it shut and redrill it, or contact Jerry Woodland for a drop in replacement. woodlandsports@gmail.com

Okay, after disassembling and reassembling twice, I found the issue. The cylinder would hold air pressure until the cam cover was bolted down... even with the HLA’s on number two totally bled down. Finally figured out that two of the cam followers that I bought are made wrong. The groove that sits on top of the valve is nearly a 1/16th too shallow! It’s just funny that out of a bag of 12 I ended up putting the only bad two on the same cylinder! What are the odds?? Anyway, I’m going to call the unnamed manufacturer on Monday and see what they say.

Good catch. I have seen valves a little to high but never a rocker a little too low!

Good to hear you found it. Too bad the quality control is lacking in the aftermarket followers.

My thoughts exactly.

Good Catch!
Please advise us of Mfg so we can all beware!

I got the cam and followers from Kanter. I am going to give them a chance to rectify the situation. I’ll let y’all know how they handle it.

Great catch, that had to feel good. Those followers are pretty rough looking. Nothing says "China" like parts that look like that. If you get in a jam and can't get replacements, they can be easily modified in a mill. Not sure about heat treat in that area, if any. Best of luck the rest of the way.

1/16th"(.0625") at the valve stem would be right at .042" at the lash adjuster.

That was enough to bottom the lash adjuster out and hold a valve open.

Makes me think the whole project is right on the verge of running like a solid lift engine.

I've heard cam followers clatter on OHC engines when oil pressure was too low. Seems like this one wouldn't have enough slack to clatter with no oil pressure to the lash adjusters.

This how they came factory? Or is valve stem height just a little too tall? Did deck of cam carrier get trued and move the cam closer to the head?

IDK, just feel like there's some little things adding up here. Is there a factory procedure for checking lash adjustor pre-load?

just thinking out loud
Clay