Engine noise

[burger uk]

Ok, tonight located the plug on the back of the crankcase but it was impossible to set the mark on the crank casing as the crank kept either spinning past on the what felt like compression?? but i did manage to get someone to hold the variator with a long wrench on the tdc mark on the crank and the cam marks were aligned with the cam journal. also on the decompression bdc the same phenomonan ocoured with the compression type springing. i am wondering if as the piston hits tdc it is hitting a or multiple valves and pushing the piston back hence me not being able to set the tdc mark. i was thinking of removing the generator casing to inspect and make sure everything is free and looking normal and if i can remove the variator nut i will remove the variator but i have no air gun or pulley holder thingy.

oh by the way, i thought id check the valves and the inlet was about 0.40mm and exhaust 0.30mm!! inlet is around 0.10mm now and exhaust is around 0.20mm

do you think the valves could have been making the noise if they were that far out?

[pikey]

Have you taken spark plug out shouldnt be any compression .Julian

[burger uk]

yes the plug is out but it wont sit on tdc it springs either side of it

[Data]

On start up from cold, if you get a nasty noise like this, it may be the timing chain tensioner has let go. On suzy's they make quite a din. However, they normally click back up to a good tension if you blip the throttle. it just may be from what you are saying that yours has maybe let go and the chain has jumped a tooth, but that's not easy and won't normally happen. However, if the chain and tensioner are very worn I supose it just could happen. Good luck in tracing the problem.

[TmaX9]

If the piston was hitting a valve it would only do it on the end of the exhaust stroke and start of inlet, as on the compression stroke the inlet is shut since BDC and the exhaust valve only starts to open just before BDC next time around so the noise should be only every second cycle.
One possibility is that the engine has inhaled a foreign object such as a small nut or even the tip off a burned spark plug. This would bang against the cylinder head and eventually embed itself in the top of the piston, the noise getting less as this happens. This would happen at each turn so also give the 'hard to keep at TDC' problem you describe.
I'd whip the head off but tie up the timing chain first, you don't want to drop it down inside the gallery!

[dominic]

is the noise engine speed or twice as fast, (camshaft noises are always double time as they turn faster). if it sounds twice as fast its top end. same speed as cranking bottom end, not so good. take a look down the cam chain tunnel, see if a guide has let go or part of decompression mech. good luck. all problems are reparable.

[Dave Weller]

I would drain the oil out, into a container, look carefully for bits. Is the noise at each turn of the engine or once for every 2 turns, the camshaft rotates at half the speed of the crankshaft. Being watercooled, the first thing to seize is the exhaust valve picking up in the valve guide, The engine does burn oil, so it could have run out of oil.
If the valve has picked up(seized) the guide can come loose and make a loud noise. Information from many a Meriden Triumph failure.

[Ralph]

These early 400's are know to burn oil, if it's been run with very low or out of oil
it could be almost any thing in the engine, the new or clean oil would make me
suspicious that it's had new oil put in to disguise it.