Up and Down Play in Bottom End

I have been noticing and lower end knock on my 1965 S65. I have a aftermarket crank std stroke.

I removed the cylinder head and put my fingers on the piston and rotated the crank. I noticed about halfway down the stroke there was a flat spot where the piston doesnt move but the crank does.

FYI the knock was there with the stock crank as well that is why I changed the crank.

What can cause this knock? Are the cases worn?

Going way out on a limb with this one. The only example I've seen, that follows your description, was an old pushrod 49cc motor. All of the big end rod bearings were gone, leaving miles of clearance between the rod & crankpin. I never heard it run, must've sounded like a jackhammer! Amazingly, nothing beyond the crank assembly was damaged. And the crank was successfully rebuilt.

I did remove the piston and I could not get any play in the rod up or down. I only felt the play with the piston installed and the rings dragging the cylinder walls. The cylinder was still bolted the the crankcase. I will have to split the cases and inspect. The only thing I can think of is when I had the 88cc top end installed I had to bore the cases over so the jug would slide into the case halves, maybe with the added clearance the jug is moving a bit?

Or could it be in the pin? since I only felt it with the piston installed? I am using a nos piston and pin. so maybe if the rod on the aftermarket crank is different.

Either way I will have to pull the engine and split cases to inspect.

I have always had metal shavings in the oil that I could not find the cause. the shavings are aluminum.

I don't want to start taking wild, blind, guesses. Sitting behind a desk, with minimal information, there's only so much that can be done.

If the cylinder were moving with the piston then, presumably, you'd notice that. What you've described is beyond excessive clearance, if we are both on the same page. Fortunately, I doubt that we are. As for the source of your aluminum filings possibilities include: round cam cover, cylinder head (unlikely), case halves, clutch basket, primary driven gear, clutch cover. As the parts are removed and cleaned, you should be able to find "witness marks" where the aluminum was being eroded.

Beyond that, I'd need more information. Might be easy to figure out in-person/firsthand. The US of A occupies a huge amount of real estate, making that impractical.

How were you rotating the crank/piston? Via the flywheel/magneto?
How much are you rotating the flywheel with no movement in the piston ?
Is the flywheel tight to the crank?
What does the woodruff key and keyway of the flywheel look?

I don't think you would have a problem with the cases being bored. The cylinder to case has an alignment dowel along with the head to cylinder. Also boring the cases doesn't change the tie rod diameter or the diameter of the holes for the tie rods in the cylinder and head.

A loose clutch nut will give a knocking sound. Are you torqueing the nut to specs or just tightening it?

Yes I'm torquing the clutch nut.

As for the aluminium. I did take a look at easy parts to get to and the round cam cover does have wear, where I can see it riding the cam. Why is this. Am I tightening the bolt too tight? I will source a new cover.

I was rotating via the flywheel. It rotates smoothly. With the cylinder head bolted on I can hear the knock just by rotating the crank my hand. Is it possible that the metal filings actually damaged the crank bearing?

I'm going to pull the engine in a day or two and disassemble.

A cam sprocket bolt contacting the round cover would make a knocking sound. Does the noise remain, unchanged, with that cover removed?

Yes the noise is there with the cover removed.

curtie94 said:

Yes the noise is there with the cover removed.

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In that case, time to remove something else, the flywheel. That might not make much sense, and it's highly unlikely to be the source of the noise. However, it's the easiest part to remove and I have seen two instances where the flywheel made light contact with the stator asm. The overall approach is basic; systematic teardown, one part (or assembly) at a time, followed by a retest, until the noise is isolated enough to tell you where to look closely.

From there, the next piece to come off would be the clutch. After that you'd be able to isolate the transmission and the crank + top end assemblies, by spinning each, independently. If the noise is in the transmission, time to split the cases. If the noise is tied-into crankshaft rotation, time to pull the cam chain, etc. With a substantial amount of metal filings circulating throughout the engine, a complete teardown & cleaning really should come down to a question of "when" not "if". The step-by-step teardown would only save you the work of splitting the cases if everything were clean and the problem existed outside of the crankcase.

Last night I started to remove 1 item at a time starting with the round cam cover, noise was still present. So I removed the flywheel, no difference. I drained the oil and removed the clutch cover, I did find the clutch gears to make a slight clunk noise, but even after removing the clutch the noise was still there.

I then removed the cam chain from the equation and still nothing, The noise is definitely crankcase. It doest make the sound in all spots of rotation either, I need to get the crank into the right spot then I can hear the clunk.

I did see that the crank has some side to side movment, The bearings dont seem to be a tight enough fit in the cases.

Are there thrust washers behind the crank bearings to take up some slack that the aftermarket crank didnt have?

curtie94 said:

Are there thrust washers behind the crank bearings to take up some slack that the aftermarket crank didnt have?

Click to expand...

You've reached the limits of my present S65 knowledge. A few thousandths of crankshaft endplay is normal, more than that would be problematic and you make it sound like there's an abnormal amount. How much endplay/"walk" is actually present?

None of the later motors, based on the 49cc lower end (Z50, CRF50/70, CT70, CL70, SL70, C90, etc) were fitted with main bearing shims. IDK if that applies to the earlier S65, or could be a viable solution. There could be case damage (seems unlikely that you'd have overlooked that, if it had been present), excessive gasket thickness, maybe you got the wrong crankshaft. That's too many maybes for a definitive answer.

Once you have the cases apart, you should be able to see where aluminum has been gnawed. Might also be worth partially reassembling the lower end, sans center gasket, to recheck crankshaft endplay.

That's about as far as I can take this discussion, for now. With additional info, that can change.