piston slapping when cold

[vespaskin86]

hi all
i did bridlington rally there and back with no problems (only one from club on a scoot to make it in one piece) it rode really nice for the 90 odd miles there and the same trip back..
a few days later after i got back when starting her up to go work i got a horrid metal on metal clinking popping noise coming from cylinder head area of engine when it got a some rev's curiously/in-patiently and needing to get to work i did it a couple of times and the same noise then it stopped doing it assuming as the engine got warm overall 2/3 bangs then nothing and rode really nice.

i'm just wondering why this could have started happening been told the timing might have slipped but never heard of that happening also to put new and maybe a extra gasket on between the casing and barrel but that was done when my casing thread were timeserted not so long ago.

any diagnosis or other ideas why this could be happening be greatly appreciated?

thanks

[bryno]

If it's a mechanical sound (not just a backfire etc) then not anything to do with the timing.

Why did you have an extra base gasket fitted?

Piston slap is due to excessive wear, so it would tend to do it all the time in the same circumstances and only get worse over time.

If it is running fine now, not done it again, not down on power or compression I'd not worry much.

If it's not running well or noisy I'd be taking the head and barrel off and take a look at piston & rings.

[henri]

piston slap is pretty distinctive noise that gets better as engine warms up,as bryno says thats indicative of a high-mileage worn piston,
you describe a "clinking/popping " noise ,that sounds vaguelly like "pinking" or pre-detonation ,usually only happens under load bout 2/3rds throttle ,sounds tinkly if ya see what i mean , pre-det can also happen if timing is out an too far advanced but would also cause backfires an kickback on the engine,or if theres a hot-spot of glowing carbon on your piston crown , either way i think i'd follow bryno's suggestion an pull the head off n have a look/see for any contact marks or damage ,as "funny noises" that go away where probably present on everbody elses scoots on the brid run that broke .
is it just this once its done it ,or every start up since , H

[vespaskin86]

cheers i've not put a extra gasket on it were a suggestion it didnt make sense to me either bryno i do think its a mechanical sound until gthe engine gets hot and expands i will be checking the barrel and piston later.

hi h its pretty much every time i start it up when its cold and give it a little rev maybe half throttle it happens a couple of times then goes away im really confused it does get the odd back fire too oh well better get checking

[pxguru]

Sounds like it might just be the head not tightened down properly. Take the barrel cover off and re torque the head before going any further.

[vespaskin86]

hi cheers for the replies ive checked barrel and piston there's a slight mark on both but hardly noticeable and all good so i've been told and shouldn't cause the slapping and i've re-torqued it when putting it back together and it seems better cheers guys