Mystery sound- solved !

[rpowers]

After all the great suggestions, I went after the mystery sound (loud knocking only under load), by attacking the valves as the source of the problem.

I changed the remaining three springs after cutting a new access panel in the engine hatch area of the cabin.

That allowed me to really get at the first two cylinder's valves.

I had checked the clearances before, and they seemed good. But a more careful measurement showed that while a 0.010 feeler gauge felt snug, I was able to get a 0.012 size in there as well.

And for the 0.012 gap, even though a 0.012 feeler felt snug, I was able to get a 0.014 in there too.

So, it was pretty easy to adjust the tappet clearance with the new access panel, and using the "feeler-in-place" method, I closed the tappet clearances until the correct size fit snug, but the next size up would not enter the gap.

Duh!

After re-assembly of everything, the engine started right up (whew!), and after a warm-up period, I gave it full throttle under load, and THE NOISE WAS GONE !

The mystery noise was valve tappet clearance too great in cylinder #1 and #2.

A big prize to the member who guessed that possibility.

And a Big Thanks to this great community for helping me get a really hard job (1 week!) done.

-Rick

[lat 64]

You must have been working hard today.
Congrats!
Now send a video of the boat underway, I can't go sailing yet, so you have to for me

Waiting vicariously,
rus

[Mo]

Nice work.

Congrats on the fix there Rick. That was a big job so hopefully no more trouble for a while. Enjoy your season.

[sastanley]

Rick..nice work. I detached my 4# ground cable from the flywheel cover and my 4# (+) cable from starter today. I am still disassembling instead of reassembling.

I did some other stuff too, but the engine is far from running again!

[67c&ccorv]

Don't keep us in suspense...who guessed it right???

[rpowers]

Video in production

For Russ,

I am in the process of making another short video showing the engine in action (boat in motion!).

Nowdays I'm able to cruise at 2200rpm with lots of excess power.

Stay tuned for the next video release!

-Rick

[Bruce A]

Hi Rick,

I am in the process of replacing the head gasket on my A4. My question is can you adjust the valve clearance, as you did, without removing the manifold/carb/exhaust connection?

Thanks,

Bruce

[Mo]

Bruce,

You will need to remove the exhaust manifold and carb to do it. I was looking at mine just this morning but luckily I don't have a valve problem...I was contemplating having to haul it apart.

Carb: Turn off fuel valve and let go fuel line (have something to catch gasoline dribble). Let go choke cable and throttle cable from carb. Also little copper line at rear of it....let it go from the manifold. 2 bolts then and the carb is off.

Exhaust Manifold: Let go the aft end of the hot section. It might be a hose and clamp on it (very likely). Remove the 3 bolts on the manifold and wiggle the manifold and hot section as one piece off over the manifold studs. Then wiggle it out of the space and the valve access cover is there for you to remove.

I have a bit of room on my boat to get at the sides and the whole removal would take about 20 minutes tops. It looks worse than it is.

[rpowers]

Carb out, manifold in place

Just need the carb out of the way, manifold can be in place for valve adjustment.

-Rick

[Bruce A]

Thanks,

I am just now investigating the valves and am not sure what the need (if anything). One question: does anyone know of a method to test for a leaky valve once the head is removed?

Bruce

[roadnsky]

Just need the carb out of the way, manifold can be in place for valve adjustment.

Ditto.
I did mine with the manifold in place too.

EDIT: (Pic added for Shawn for ID-4th present )

[jpian0923]

Bruce,
Compression test should tell you something about the valves.

For the most part, compression above 85 in each cylinder should imply that the valves are seating properly.

With the head off I would hand crank the engine and watch each valve as it seats.
It's not scientific but if you can't see a gap (do a full 360 view of each valve as it seats) you should be ok. Clean up any carbon deposits.

[Ajax]

Oh man, best thread EVER!

I've been wondering what the valve arrangement of this engine was, and how to adjust them, and observe what's going on.

Is it possible to put a crank handle on the flywheel and manually rotate the engine to detect valve problems?

Thanks.

[sastanley]

Ajax, yes..the crank handle is an excellent tool to use for fiddling with the valves.

There is another thread too..check this one out...rigspelt's drawings & stickboy's picture in this thread are invaluable. --> rigs' valve thread

[Ajax]

Thanks, that second thread is awesome too. This will be a great help this winter.