TEA20 engine knock -- update

An update for you all. The good news is I seem to be ruling out potential sources for the engine knock. The bad news is it's the cheap stuff that's getting ruled out!

I adjusted the valve clearance this past weekend which cut down on a lot of the racket that was making the knocking hard to locate precisely.

Now it's pretty clear it seems to be the cylinder closest to the battery, part way down the block, directly to the right of the oil filler. Perhaps a wrist pin then?

So I would cautiously say at this point I can also rule out:
-governor
-exhaust (although I did discover a big bead of weld on the exhaust manifold...)


I also tried the plug pulling exercise again too and noted that while not much difference was to be heard when pulling the plug with the engine running, there was a bigger difference if I stopped the engine, pulled the plug, then started. By doing that I noted the knocking was much quieter when running on three cylinders. When I stopped the engine again and reattached the plug wire and restarted, the noise came back.

Anyway, two more videos posted for those interested. First running with the fuel tank and rocker cover off before the valve adjustment, second after the adjustment, including segments with three cylinders firing versus four. The knocking is easiest to hear during the segment with the engine running with the rocker cover back on.

One other item of note -- the pushrods are not rotating on a couple of valves -- you can see it in the video. Is this serious?
As before, all opinions welcome. Thanks to everyone for their input.

As for next steps, if I drop the pan, move the piston to the bottom of its stroke and try to wiggle the con rod, will that tell me anything conclusive?

Before adjustment
http://www.youtube.com/watch?v=u84YcKyZ7AA

After adjustment
http://www.youtube.com/watch?v=HCjworKPXDA

I think the most convincing piece of info is the drop in the noise after you removed the plug wire with the valve cover on.
It sounds like a rod ticking to me. If you pull the pan, Plastigage the connecting rod clearance nearest the noise and see what you get for a clearance as opposed to the spec. It's should be a number like 0.0015-0.0025 ". I doubt that trying to move it by hand is going to give you any info. If it was that loose, it might have come through the block all ready!

I think I ventured the opinion originally that the knock was deeper in the engine (big end bearing or little end/wrist pin bush), rather than in the top end.

I still hold that view.

I think you are going to be pulling the sump and head and hoping it is not in a big end bearing, with crank shaft damage.

Sounds to me like rod knock. Try running slightly above an idle and turn off switch and before it stops turn switch back on,see if it makes one slightly louder knock just as the key is turned back on. You might have a loose flywheel. Remove starter and move flywheel with a pry bar back and forth as if you were trying to turn crankshaft but just enough to see if the bolts are loose. Luck

I just went through all that with my TO-20. I was the wrist pin bushing on mine. It was so worn that the pin had worn clear through the bushing at one edge. About one more tractor ride at 2/3 trottle and I think it would have come out the side!! I did a complete overhaul and $700-800 later it runs sweeeeet!!

Irv*