Discussion in 'Early CJ5 and CJ6 Tech' started by Scott Sherraden, Sep 30, 2020.
That was my thought too and it seems a more logical scenario.
Pretty easy to check...and a heck of a lot easier to remedy if it happens to be
He says he has new wires and plugs but we all know new doesn't guarantee good.
I'm really struggling to imagine a tappet sticking.
Yep. And no noise associated with it.
Hi all I do have new plugs and wires but I'll verify spark on that cylinder. Good thing to verify.
Understand that I've driven it several times lately, put about 30-40 miles on it, and twice after driving I have checked the compression on #3, no compression and I can visually see the exhaust valve sticking up. Then I took the time to remove the exhaust manifold, and valve cover on the exhaust side. Then I can wiggle the tappet with a wrench and I can loosen it and get it to go down like it should but in the process it is very obvious that the tappet is sticky. I can tell it isn't the spring, it isn't the valve itself, it is the tappet.
The tappet on the other three cylinders are very free, the difference is quite obvious.
Giving all of this information so that you can see how I come to the conclusion that the tappet is sticking. If you could see it you'd agree but I know it is difficult without seeing.
With the tappet stuck down, sure I agree it would hammer and make a lot of noise. But the tappet sticks in the up position. So it just stays up there, the spring stays compressed and the valve is stuck up in the cylinder. So there isn't any mechanical noise because there is no contact. Of course there is a different exhaust sound. Glenn does that make sense? What noise do you expect?
Bad or broken valve spring? I would bet you have a partially burnt exhaust valve or the guide is faulty. Could be foreign material along side the tappet? If you can't free it up, the engine is going to require some disassembly to figure out your issue and repair it.
I expect a metallic noise, either from the tappet and cam lobe or the adjustment end. That .018 gap you set is enough to have a distinct noise from a perfectly running engine, especially noticeable at idle.
As I mentioned before the cam lobe would be just at a minimum contact if the tappet is stuck up so you probably wouldn't hear any noise there. It's just weird there's no contact noise when it frees up and moves.
It wouldn't be possible for the tappet to stick down of course, unless there was no cam lobe. You have visually verified that the tappet sticks up and holds the valve open, but it doesn't take a significant amount of effort to free it. That's the weird part which makes us question whether the cylinder is firing consistently. In other words what makes it free on it's own when it does release?
First question is what does the plug look like? Clean or carboned up?
Have you got another plug wire you can at least temporarily use?
If you determine and are confident it always fires then some disassembly is no doubt going to be needed.
When you removed the cover was everything in there oily as expected?
Good ideas thank you!
Yes when I remove the valve cover everything looks normal (oily, and full of oil where it holds oil in the little recesses).
Regarding the spark plug that is kind of a catch-22 problem. Because usually when I check the compression after running for a while, the valve has been stuck open, so then of course with no compression the plug gets wet and oily. So every time I have checked, the plug is sort of wet either from gas as expected or a light oil/gas mix. It doesn't mean the plug is not firing necessarily or doesn't have spark, to me it means there is no compression and with the valve stuck open oil can get in the chamber. And unburned fuel of course. So the plug gets wet either way. Without compression and a proper explosion the plug is not going to look normal. So to me that is a bit inconclusive to determine that a wet plug means a bad/non-firing wire.
However easy enough to check I can put the old wire back on and see what happens! Of course it is possible a new wire can be bad.
Oh more info - the plug does look good, it isn't carboned up. It is a relatively new plug. It just gets wet (gas/oil). So each time I checked compression, I cleaned it off before replacing it.
Wet from gas tells me the plug isn't firing. If it was carboned up it would mean incomplete burning.
OK thanks based on that, I'll try with a fresh new plug and put the old plug wire back on. That's easy enough to test.
Proper timing about 10 degrees advanced, good distributor, relatively new Pertronix ignition, new Pertronix coil, new distributor cap, so spark leaving the distributor should be good.
Shouldn't timing be 5 degrees? I don't think that would cause the problem you're having though.
5 degrees is factory spec, but the consensus on this forum and others seems to be that with a Pertronix setup, you can cheat it to 10 degrees and most have better results there.
I'd say the exhaust valve is sticking open, allowing the tappet to stay "up" in it bore. It is very unlikely the tappet is the source of the problem. A sticking valve is very likely due to iron guides.
I would consider pulling the pushrod on the offending valve just to make sure its straight. A stuck valve could have bent the pushrod, possibly causing the symptoms you have.
No exhaust push rod on a f4.
Pull the head, pull the valve, inspect the bore & stem, verify the rotator is working.
I agree with this. I do believe you have an issue with the valve and or guide.
The guide being the problem seems logical to me also but his earlier comments tend to dispute this though.
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