Clank sound on re-assembly

[panama911]

Originally Posted by smokintr6

The only thing I noticed from watching the video is that the noise seems to happen at a different point relative to TDC each time. This can be observed because the crank is being turned with a non ratcheting breaker bar. It looks like the noise is advancing 30* ish per revolution. Not exactly sure what that means, but it's the only thing that stood out. If the noise is advancing each revolution its certainly not piston to valve clearance, if it's happening on the same cylinder each time. Does it seem like the noise is moving around to different cylinders?

Just a guess - but IF the clanking it is advancing or retarding relative to the crank rotation, following a certain, reproducable pattern, I would probably investigate the following:

The cams are rotating by half the crankshaft speed and almost everything else also moves in sync to the crank movement - but the intermediate shaft (and oil pump) DON'T: the drive gear on the crank has 28 teeth, the aluminum gear on the intermediate shaft has 48 theeth, the chain sprocket on the intermediate shaft has 24 teeth and the chain sprocket at the cam again has 28 teeth. This makes the intermediate shaft rotate 28/48=0,5833 times per crank rotation (and the cams rotate (28/48)/(28/24)=24/48=0,5 times per crank revolution) or to put it another way, it takes 1,714 crank rotations for one turn of the intermediate shaft and pump.

Again, this is just a GUESS and where I'd start to look IF you have a regular advance or retard of your clanking sound relative to the crank and could nail it to these relations...

[Tori]

WOW, thanks panama911 for all that. This is a tough one to monitor as the sound seems louder the faster you rotate the engine. So sometimes it will make the sound but if your in the part of the rotation where you maybe switch hands/grip it can be quieter making you second guess if it was the same sound as before...

I wonder if it could be the rod touching the case or cylinder. Can the rod be installed 180* off, and now its contacting something ?

damn, i don't want to take this thing apart again,.......... but i just ordered up the cam tool and will tear into it next week..... maybe.

[panama911]

well... it's just a guess based on the observation of smokintr6 above, that it would be advancing in relation to the crank (I could not really tell from your video). Make a mark on the end of the intermediate shaft (cover off) and see if you could relate the clank to it's movement...

[David Goodman]

That sounds to me like a valve snapping back into its seat. Maybe the guides or seals are too tight?

It's random because it's not the same valve every time.

Just a thought.

Edit: I might also check the alignment of the rocker shafts. If they are not aligned properly and the rockers are not moving freely, it might be holding the valve open until the piston gives it a nudge.

[Tippy]

That is crazy. To me, at 1st, it sounded like a small end of a connecting rod dropping onto the cylinder to my mind. But the evolving index of the crank indicates that it must be IMS related as panama pointed out.

But what could make that noise IMS related is very baffling.

Maybe a borescope through the oil return tube bosses?

[Tippy]

It can’t be a valve as it’s a 4 cycle motor. You’d only hear the noise once per 2 crank revolutions, not 4 times per revolution.

Plus, the angle of the crank would repeat every time every 2 revolutions when the noise occurs.

['78 SC]

Check the right side chain. Mark it and see if the noise happens at the same point each time in the chain movement. Maybe a link not engaging the sprocket smoothly? That would cause the tensioner to move also.

[Tippy]

Originally Posted by '78 SC

Check the right side chain. Mark it and see if the noise happens at the same point each time in the chain movement. Maybe a link not engaging the sprocket smoothly? That would cause the tensioner to move also.

Great point. Maybe the tensioner is being compressed bottoming due to the chain?