I'm trying to get to the root of an apparent valve ticking in a mostly stock L-36. For the most part, it runs pretty strong but I have a slight wobble in vacuum at about 13-14 inches at idle. The cam is a bit bigger than stock with 110 LSA and .520 lift in/ex (after rocker ratio of 1.7) while the cam lift itself is ground at .302 which might account for the lower vacuum. I can feel a slight miss at idle and a compression check in #3 reveals 180 psi while the others are around 210-215 psi. I have checked the lifters and pushrods for that cylinder and the lifters are rock solid and will only yield oil when pressed in a vise. The base of the lifters show no wear pattern at about 15,000 miles and the lift as measured at the pushrod tips show about .293 (I used dial calipers to roughly check the wear).
With the intake off, I then applied compressed air to the #3 and hear air coming from the lifter valley and the exhaust crossover port in the head. I can also hear exhaust coming out the side pipe. No sounds appear to be coming out of the intake ports. With a leak down tester, I show 57-58% leak in this cylinder and only 8% in the cylinder next to it.
The interesting part is that the #5 next to it also has a leak in the exhaust crossover port, but about a tenth as much by sound, and the lifter valley sound is just as loud. I've never done a leakdown test before so I am not sure what the sounds should be like. The coolant is out so I can't check for bubbles, but I don't hear any hissing in the mouth of the radiator, but the system is completely open with the hoses off and the block drained.
My question is that if the sounds coming from the lifter valley is about the same from each cylinder and one tests at 180 psi and the other is about 210 psi, is it logical to assume that the compression rings are ok but the exhaust may have leak due to carbon buildup? If so, would that cause the valve ticking and would the old fashion steam method of breaking up carbon be a best way to proceed. I don't want to have to tear off a head or pull the motor if I can help it.
Thanks for any advice or experience anyone may have to offer.

 

The air you hear in the lifter valley is air going past the rings and into the crankcase. Are those compression numbers right? They seem pretty high.

 

The compression readings have actually come down a bit since my rebuild in 1990. When first rebuilt, after a ring land broke on the original cast piston, I replaced with forged TRW's at the same 10.25 CR and the numbers were 225-230 psi, WOT, all plugs out, crank for 6-10 seconds until gage stopped rising. I am not an experienced mechanic but have done much of my own wrenching since I was 18 and know most basics, but with your comment on high psi readings, I did some searching and found that at least on the 1966 and 1967 L-36, the compression pressures are supposed to be at around 160 psi, which I never knew. I assumed my Craftsman gage was giving me accurate readings, if not at least relative to each other; it's the only one I've ever used, but must be time to buy a new one.
I have also read that these big blocks are prone to valve shrouding with carbon, especially on the exhaust, and that de-carbonizing may make matters worse by getting loose pieces caught in between the valve and seat. I can see the carbon build up on the intakes at least with intake off, but I can only guess it's not affecting the intake valves since no air seems to coming out of the intake port opening on the head, just the exhaust (and lifter valley).
With larger piston to bore clearances for forged pistons (.0036-0063) as opposed to cast which run around (.0007-.0015), is it normal to hear a certain amount of blow-by in the lifter valley, or should it be silent? In other words, do compression rings do the same amount of sealing whether for cast or forged pistons?

 

There will always be a small amount of leakage by the rings, 8% is acceptable, but still enough you would hear it escaping into the crankcase.

Hearing air escaping through the crossover would be exhaust valves leaking and something you need to fix. You should never have leakage at a valve.

The clicking sound might not be mechanical. An exhaust leak at the manifold/header gasket to the head can sound like a lifter ticking.

The lift of your cam has nothing to do with idle vacuum. Intake valve closing point and overlap will affect idle vacuum. Intake valve closing point affects cylinder pressure. Your high cranking compression is an effect of high compression with a somewhat early intake valve closing. How early I don't know as you did not post cam timing. This could also be why you lost a ring land on your last pistons. Over 200 lbs of cranking compression is pretty high on an iron head engine. Detonation could have blasted off the ring land.

With valve leaks, it could be a good time to spring for a set of aluminum heads.

Mike

 

If you have or can borrow a bore scope, it is probably worth looking into that cylinder and see if anything "jumps out" at you.

I would check the valves (seats if you can get the valves open and see them with the scope) as well as the cylinder walls. Move the piston down to check as much of the wall as you can. Look for scoring or evidence of ring damage.

Good luck... GUSTO

 

Before rebuilding the original engine in my 69 L36 compression on all cylinders was just over 150 and all were within 4% of each other. After the rebuild with forged Keith Black Icons compression was about 170 and all are within 2% from the highest to lowest. I found that with the stock heads there was wear on the valve seats as there were no hardened seats for today's fuel. Your compression test seems very high but I would be looking at the cylinder that is showing that much lower than the others especially with a wiggle on the vacuum gauge. I would pull the head and go from there. You can put some oil in the cylinder and if it's a ring problem the compression should come up and if it's a valve it won't but either way, the head(s) has to come off....

 

Compression testing is a total waste of time. throw it in the garbage where it belongs. leak down testers is what every good mechanic has in his tool box. It actually tells you whats wrong an the engines health!


My solid roller motor with 15K miles is at 2.5%

 

George, he used a leak down tester. He had 55% to 58% n one of the cylinders and could hear air through the exhaust crossover.

Mike

 

My Bad! I reread everything it is hard on a smart phone



I personally have not seen a valve carbon up to the point of cause a seat to valve leak. I have seen burnt and cracked valves, bent valves, and bad seats.

If you took off the header pipe..... You could scope the exhaust valves

 

Thanks to all who have responded so far-
I should have mentioned my cam has 110º lobe centers and 218º duration on both intake and exhaust (at tappet) with slightly longer duration intake from stock 214º. Valve lift is both .520 as opposed to .461 and .480.
I will see if any one has a bore scope or if one can be rented or borrowed from a local parts store. That's a great idea.
Upon rebuild in 1990, I replaced valves with stainless steel with concern for no lead anymore, but don't recall if seats in head were addressed. It was a reputable machine shop that did the original heads but I don't know what technology was available then. Can they be hardened in original head or are hardened inserts possible or recommended back then. I did whatever they recommended at that time.
I will check all cylinders now using the leak down tester and listen for more escaping air. Will also do wet compression test to see if compression improves. Sounds like heads might need to come off after all

 

[QUOTE=gkull;1594983748]Compression testing is a total waste of time. throw it in the garbage where it belongs. leak down testers is what every good mechanic has in his tool box. It actually tells you whats wrong an the engines health!]

A leak down test will tell you what is really going on but on a quick compression check and finding one cylinder 30-35 psi less than the rest kind of makes it redundant. Especially with the vacuum check.

OP - "With larger piston to bore clearances for forged pistons (.0036-0063) as opposed to cast which run around (.0007-.0015), is it normal to hear a certain amount of blow-by in the lifter valley, or should it be silent? In other words, do compression rings do the same amount of sealing whether for cast or forged pistons?"


The rings are the same on cast or forged pistons and it's the cylinder wall diameter and the builder that determines ring gap.
Look at it this way. If 7 are silent and one is not and it's the same one that is down on compression....? It's already talking like a duck.