Random tapping

[ndutton]

There is no downside to a valve adjustment and he'll be able to visually check their motion and spring condition.

[chrisoelder]

Valve Adjustment

@roadnsky

Send it over please! Would be good to know either way. Do i need a lot of room to accomplish this?


Before i dive in, do you think pouring MMO or Sea Foam into the head would help at all?


Thanks All!

[wristwister]

In your original post you mentioned oil pressure dropping ~30% when the tapping started, right? When you depower #4 the tapping stops. I'm not seeing how these are related to valve adjustment. I hate to tell you this, but these symptoms DO point to connecting rod knock. Something may be going on with that #4 rod bearing.

But ... by all means rule out the easy stuff first; Valve sticking/adjustment, exhaust manifold leak.

[chrisoelder]

@wristwister

That is very possible. Here is the situation:

I had been under power for a total of 7.25 hours heading to Catalina Island. We were healing over for the last 2.5 hours, I noticed my oil pressure around 25-30. There were some big rolling swells and wind gusts. Very confused seas for that 2.5 hours. I heard the small tapping sound and brought down the throttle completely. Investigated and determined it wasn't major. Checked the oil and the level was just about full (i did an oil change a couple months ago). Got safely into Catalina and started poking around.

After a couple days of being at the island and diagnosing I thought it was a valve tap. I poured some MMO into my oil and fuel. I power sailed on the way back for about 7.5 hours with very little issue. The tapping was still happening but the oil pressure looked good and the engine didnt have a problem running on low RPM.

Since the sound was coming from the right side i thought it was a valve tap. (I have a video of it in the first section linked) I also checked my spark plugs to make sure they were solid. While running the engine when i remove the spark plug wire from the 4th plug the tapping stopped. There was no change when testing the others.

I am not much of an engine person but am trying to learn. Hence why i bought a boat with an Atomic. Any and all help is greatly appreciated! I have a compression test arriving today or tomorrow, im not sure if it will help.

Thanks all!

[lat 64]

I am sure Neil is right.

See attached screen shot. There is black soot coming out from a bad exhaust gasket n on number 4 ex port.

Put in a new exhaust gasket.

Also, understand you now have a carbon monoxide leak in your boat! Get it fixed ASAP. Don't die.

Russ

[Peter]

Has the possibility of an exhaust leak been eliminated?

Peter

[lat 64]

Has the possibility of an exhaust leak been eliminated?

Peter

Not in my view. the noise is more like "piss piss piss" than clacking.

[chrisoelder]

@lat 64

Thank you! That does make sense. It isnt a very loud sound, its very subtle. Would preforming a compression test confirm the exhaust leak issue?

Also would disconnecting the spark plug wire stop the sound?

Past history: When i first got the boat/engine (Apr 2018) i had an overheating issue. Found out that it was the stern facing L was clogged with gunk. Cleaned it and the overheating issue when away. Correct my assumption but is it possibly that the pressure build up caused by the blocked L (water and exhaust) put pressure on the exhaust manifold and the gasket causing this issue to eventually happen?

I took a few more screen shots of my exhaust manifold. To show the soot towards the back

https://drive.google.com/open?id=1nA88QUQftI6Yh09A2cDOEpLSBq0zmsvZ

https://drive.google.com/open?id=1V2ArkNuX1vdzlEWKnUSDilj7-ZYQ8wNo

https://drive.google.com/open?id=1UhHJ-MrTQQhQVOjctHWq2Yvk11dqyFwp

Thanks all!
Chris

[lat 64]

Your screen shots show rust where the paint burned off the nuts. I think.

The exhaust gasket is on the other side of the manifold, between it and the block.

Neil had you disconnect the plug so the #4 cylinder would not fire. If there is no fire, It will not burn the fuel/air mixture and there will be no combustion sound—no pop or the "Pisst" that we hear. The "Pisst" is the hot exhaust gas leaking out the failed gasket.
So the noise is gone in that test.

A compression test will not be useful testing for a gasket leak at this spot. A compression test measures only the pressure inside the combustion chamber when both valves are closed. The gasket in question is outside of that; downstream of the ex valve.

Great video, by the way.

Cheers,

Russ

[chrisoelder]

@lat 64

Its all making sense, learning a lot! Thanks again for the explanation.

Alright so what i need to do is order a new gasket and replace it.

Does anyone have any tips or tricks to removing an old gasket and installing a new one? Anything i should know?


To confirm: this is what i am replacing.

https://drive.google.com/open?id=1SnpblAVHAiH_YQLqCEUuYd6-eZefk-wy

[lat 64]

No, I think it's the big one that covers all the ports.

https://moyermarine.com/product/manifold-gasket-gask_08_147/

It will be a pain for a beginner, sorry. Lots of rusty bolts and blood

But, yes, order that one too. They are all old at this point. The folks at Moyer may advise better which ones to get.


I'm off to work now, bye,
R.

Edit:
This is all assuming I am correct in thinking Neil is right. YOU should confirm this leak yourself.

[wristwister]

Before diving into that exhaust manifold gasket, you should be able to easily confirm that this is indeed an exhaust leak. If you feel around the joint between the block and the exhaust manifold while the engine is running, you should be able to clearly feel the exhaust leak. If access is too limited, a couple feet of tubing, with one end in your ear and the other end poking arounb the manifold, should do the trick.

[ndutton]

I don't think the head gasket or exhaust valve hanging open is off the table yet. There is minimal combustion pressure on the manifold when the valves are seating properly. Exhaust gases are merely pushed out by the piston on the exhaust stroke (note: well AFTER combustion has occurred). For high pressure combustion gases to escape it has to happen at TDC which is when the valves are supposed to be sealed. This is where the compression test may point us in a direction.

[thatch]

After putting on a headset and listening to your video, I agree with Neil and Russ that it is a spitting sound and not a knock. The lowered oil pressure is most likely the result of the oil naturally thinning over a long motor trip. A compression test of all of the cylinders should show if there is a head gasket problem in the #4 hole. It is also not unusual for a manifold gasket leak to show up at the rear of the engine first. Depending on how much clearance you have on that side of the engine, removing the manifold may require removing the three block studs at the same time.
Tom

[chrisoelder]

This is all great! Thank you all for the help! I may just be optimistic but it is more of a psst sound. I looked up someone who had an engine knock with an A4 and it sounds more violent.

I am going to try out the "hand" test to see if i can feel any exhaust releasing. I will also check the nuts with my torque wrench (maybe a nuts is loose-if i am lucky). I am also going to run a compression test too. I will post my results (probably this weekend).

If i do feel there is some exhaust coming from in between the block and manifold i will replace the gaskets. Planning on ordering gaskets for the manifold, one for the exhaust, and (maybe) one for the carburetor.

In the meantime, for my edification, does anyone have a good guide of how to replace the gasket? I know i need to remove it completely but should i also remove the carburetor or can that stay attached to the manifold.


Im excited to get working on the engine! Bring on the rust, blood, and a bit of frustration!