[Slymo]

I’ve just comprehensively rebuilt a 1960 Constellation. New mains, ground and balanced crank, new conrods. Pistons and bores were within spec. Cam bushes replaced. All new chains. New exhaust valves, guides are good and not loose. The bike starts and runs smoothly for 2-3 minutes and then develops a loud tappet like clack. Can’t locate the source using a stick stethoscope. Pulled everything down two or three times and found no discernible cause. Really appreciate any informed advice. S

[grumbern]

Maybe you got a copycat... https://www.youtube.com/watch?v=nGIF3_vB6DY

[Slymo]

Well that's interesting. I did have the bores checked top and bottom but I don't remember if the middles were done. Good suggestion thanks.

[Slymo]

So pulled the Constellation down again and mic'd up the bores to discover that there is a maximum clearance at any point of .004". Clearly not the cause of the death rattle clanking that comes in as the engine warms up. What I did discover is that the copper head gaskets both overlapped the bores in certain spots and that the piston is definitely impeded if it at any stage appears above the lip of the bore. Have filed clearance now so will see tomorrow if anything has changed.

[grumbern]

I just remembered, I once had a similar thing that sounded like excessive valve clearence. In the end, it turned out to be a broken valve spring! This way the claerence was ok, but the spring tension too weak so the valve would bounce. As it was the inner springand it was split lengthwise to the wire, it wasn't even visible before disassembly. The result wasquite a chatter and I'd recon this might be worse in certain rpms.

Or maybe it's really just worn valve springs. Have you measured the length and tension yet?

[Slymo]

Checked the valve springs quite closely and made a new set of steel tops as the aluminium ones were starting to crack. I thought that was the problem once (sigh!). The gasket fettling made no difference whatsoever and the 5th or 6th reassembly (I lose count) resulted in precisely the same noise. https://youtube.com/shorts/bvIPjfkzwoo?si=_ZWeF_ThdHm9ufLK

[Slymo]

Inserted some rubber wedges between the head fins to dampen the generalised noise and investigated with a screwdriver/stethoscope. Seems there might be noise coming from the exhaust camshaft. Finding a replacement for an A-B test is not really an option in NZ where these machines were rare even in their day. Time to ponder 🤔

[Adrian II]

This any use?

https://accessories.hitchcocksmotorcycles.com/51603?cont_page=Timing

A.

[Slymo]

Yes quite possibly thanks. Going to see if my existing cams can be reground and if not then this is an excellent option.  Cheers S

[Adrian II]

Might be worth buying it for a spare, anyway. Shipping from the UK shouldn't be too much for just a camshaft.

A.

[Slymo]

Sadly on closer examination I don’t think it’s cam related. Despite repeated close examination with no signs of any issues I’m more convinced that it’s either a cracked piston or bore. It make a progressively worse noise the warmer it gets. Starting in total silence and getting louder after a couple of minutes. Retarded and ticking over slowly it’s phenomenally loud and terminal sounding. My plan is to disassemble once again and take the bores and pistons for crack testing.

[grumbern]

Did you check the small and big end clearence of the connecting rods? Also the pitson pin could be loose in the bore. It should sit quite firm when cold and not be moving.
I don't think a cracked piston skirt would create such noise. The older style pistons all have a slitted skirt from factory. This of course doesn't mean it can't be, but first I would check that there is no excessive bearing clearence anywhere.
Fingers crossed!
Andreas

[Slymo]

No conrods are new from Hitchcocks, mains and bigends new, little ends nice sliding fit. It's a total mystery.

[classicrider]

Not a tappet body loose?above the cam,I know 1 or 2 were loose in a twin I owned.You could lightly tap them on the oil return side.

[Slymo]

Just gave those a thorough test today. Taking the barrels and pistons out to an engineers for crack testing tomorrow. There is nothing that looks suspicious but I've got to rule everything out.