clacking noise and only cylinder 3 and 4 are firing

[BunnyPlanet169]

Did you check head bolt torque? All around? Including thermostat bolts? I thought you had 70 psi all around..... Spark plugs tight?

I just can't imagine that a few minutes of running at low compression would somehow damage head gaskets???

[sastanley]

I'd squirt some MMO in the cylinders, blip the starter/spin it with a hand crank to spread that around, and let it sit for a day or two..it may just be a stuck valve(s).

Cleaning off the old gasket and all that is such a pain, I'd try anything before pulling the head because I "think" I have a leak between cyls.

Earlier in the post you thought it was a coil/spark problem. I'd solve that first, then tackle the compression problem.

[tenders]

You can also often pop stuck valves down into place again with an angled screwdriver through the spark plug hole, aided with a small flashlight for some visibility. They make a nice "click" when you hit them just right and seat themselves - they want to go down, they really do, they just need a little help. I suppose you could use one of those cheap USB "snake" cameras that plugs into a laptop that lets you see in small, dark, places - I have one from eBay that I think cost $12 but haven't used it for this purpose (yet). The little flashlight and the neck craning works well enough, though, and is a lot better than opening up the can of worms associated with removing the head.

Once lubricated with MMO, and cycled a few times, and then run using fuel spiked with MMO (which is how I run 100% of the time with zero sticking valves, even with an engine that runs without a thermostat and thus quite cold), they might not stick any more. You might have to put the plugs back, start the engine, wait for the valves to stick again, and repeat the process a few times before they stop sticking.

A4 head gaskets used to blow ALL THE TIME in the mid 1980s through the mid 1990s, when the replacement gaskets were made from what I recall as green- or manila-colored paper, as opposed to the original asbestos, or whatever they were. In my experience these bad gaskets were the primary reason for the A4's bad reputation during that time. Repeatedly unreliable head gaskets and the frustrations that come along with them are actually pretty good reasons to end up despising an engine, which led a lot of people to repower with diesels with extreme prejudice.

Our patron saint Don Moyer was actually instrumental in persuading the Victor company to produce the current graphite gaskets we all know and love, and now head gasket failure is really quite a rare event. In fact I can't even recall the last time somebody on this board had what turned out to be a bona fide graphite head gasket failure.

[nyiftos]

99% sure you have stuck valves.
Remove side cover to valves, and inspect for stuck valves in open position. If so, use a lot of carb cleen and wd-40 spray, a long pry bar and pry valves back down to close. Rotate crank until such valves open and stick again and pry down to close again. A tedious and time consuming job but patience they will free up. Leave cover open and start eng. at idle you may carefully help valves close over and over again until they are working on their own. Let it run and make sure your eng, temp runs on the high side/180. Good luck. If it works our change oil right away.

[tcatoe]

Head off no stuck valves and gasket looks ok.

Ok another hot weekend in the belly of the boat head down and hot as hell!

I took the head off no problem everything came off without a hitch. the head gasket that was revealed was copper clad what I assumed to be asbestos, which is what I thought the old gasket were made of. The gasket was easily removed and left behind a lot of copper material on both the head and the block. It all cleaned off nicely which tells me it has never been run for long with that gasket on it. All the valves were operating as expected and nothing was sticking. There were no signs of the gasket material being breached anywhere. This single copper clad gasket has me perplexed as I was under the impression from this forum that they were no longer available. The engine has been rebuilt and the pistons and cylinder walls all look newly finished no hours on them, as they should. So from what I understand this copper clad gasket was not available after the 90's. At any rate I have ordered and received the new double gasket set from MM.
You can see that cylinder one and two are NOT firing correctly, they did fire some, but not like three and four judging by the amount of carbon on three and four as compared to one and two.
My current theory is that the head was improperly torqued and as it warmed up starting loosing compression in number one and two which starved one and two of gas because of lack of vacume to bring fuel mixture into those cylinders. I have changed the coil, plugs, distributor cap, and wires. Short of putting the new gaskets in place does anyone have any other clues I should look for with the head off? I know that several of you had asked me to re-torque the head but I did not have the torque wrench with me at the time and thought that for sure the head gasket was the problem. At any rate I have the tool now and will be putting this back together tomorrow night. Hope for the best.
Thank you all for your responses I have learned a lot about this engine from you and love its simplicity. Just need to put all together and get back on the water.

[BunnyPlanet169]

As long as the head is off, I would take a few minutes and make sure the cooling passages were all clear, in both the head and the block. Only time you get this access.

[romantic comedy]

someone might have had that old gasket hanging around. For instance, I bought a head gasket from MMI in 1997 or 98. It has been on the boat for 20 years now. I just wanted a spare...you never know.

[JOHN COOKSON]

I'm going to an area I don't known a lot about but anyway....Any chance the head is warped and won't torque correctly?
Maybe while the head is off take it to a machine shop and have it tested for flatness - or what ever it is called.

TRUE GRIT

[tenders]

> I have changed the coil, plugs, distributor cap, and wires.

Rotor too?

[capnward]

Yes, it is best to change cap and rotor at the same time, their contact points wear out together.

[tcatoe]

Finally dianosed the issue

So back out in the heat I replaced the head gasket and got everything back together and while I had the head off inspected all the valves and they are going up down without issue no visible problems. Made sure that I had TDC set correctly. she started right up and ran great for about 3 mins then the clacking started again. I had a mechanics stethoscope and was able to isolate the clacking coming from the tappet valve stem area. shut her down and removed the valve cover and all looked fine.

I put everything back together leaving the valve cover off and started the engine which ran fine and the noise started this time I shined a light on the number 1 exhaust valve while running and can see the valve either getting stuck in the up position or maybe it is the tappet that is staying in the up position. It is very obvious when you shine the light on it while running that it is not working in unison with all the other moving parts. I read a very similar post to mine located here:

http://www.moyermarine.com/forums/showthread.php?t=7989&highlight=sticking+valve&page=5

The gentlemen here ended up replacing the tappet which is what I think needs to happen. Can this be replaced from the top or do you have to pull the engine and hone out the tappet cylinder? I will go ahead and pull the valve for inspection as it could be slightly bent. I did check all valve adjustment and the #1 was to tight. It did run good after adjusting all the valves but number 1 E is still sticking.

Ordering the valve stem, spring today. Just wondering if I should change out the tappet as well if possible without pulling the whole engine?

Thanks everyone for all the help I think I am very close to getting this done. At least I know what and where the noise is coming from.

[Revive]

Similar to my problem

What was the final outcome? I have a similar situation.