Dtr125 top end tapping after rebuild

[Mattmanley]

Hello everyone, first time post but I've stumbled across some useful stuff in the past on this forum, so thanks for that! In this case however I am truly stumped...

I bought a dtr125 about 4 weeks a go. Had 15k kms on it (I'm in France). Been riding it around town and in the forest fairly aggressively. I'd planned to redo the top end when I bought it and took it out for a good run the Sunday before I was going to start. I hit some deep sand on a hill and had to push the bike and rev it quite hard for a while in 1st to get it up. This promptly sent the temperature rocketing and the water in the radiator bubbling. Was fine after cooling down and riding home as enthusiastically as always. That's the only time I've had any worries win this bike.

Took the top end apart, piston wrecked, cylinder not too bad. Gave everything a good clean, local bike shop honed cylinder and ordered new piston etc. Put everything back together with new plug, new gaskets, new top end bearing. Rattles pretty good as soon as started, took bike to 5k revs still rattles. Clutch in still rattles. Screwdriver tells me top end, possibly power valve. Bike shop tells me piston hitting plug, bottom con rod bearing gone. Rip everything apart again, plug fine, no damage to top of piston. Pulled carb and reeds apart and cleaned throughly. No play in con rod up and down. Everything back together and still rattles.... Euuurrrrgh.

Any one out there had a similar problem? Is it the power valve? Is there anyway to check? The new piston didn't have any serious marking after running a bit. If it needs a bottom end rebuild is it feasibly done alone for my first time or should I find someone who's done it before?

Sorry that's a bit of a read, everyone likes a story tho ey?! Box of Bordeaux red to the man with the answer!

Cheers,
Matt

[-]

Is it standard bore or oversized? Sometimes putting a standard new head gasket on can cause tapping if it hasn't been widened out to fit the oversized bore and piston.

What base gasket was used? Genuine or aftermarket? Was it exactly the same thickness?

Are you sure it's also not just the exhaust leaking a bit at the cylinder end? Can sound like tapping.
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[Mattmanley]

Thanks.

Standard bore, 56mm.

Base gasket was after market, will take head off again and have a look.

There's 2 things I'm not sure about with the set the shop sold me, perhaps that will clear it up... Both rings were exactly the same, so maybe that's a problem?

As well there were 3 o rings in the set which I have no idea where they go! There wasn't anything on the exhaust gasket when I removed it, neither on the head. Haynes manual doesn't mention them anywhere....

[Mattmanley]

Ok, I took the head and cylinder back off. Base gasket was torn so I put the old one back on for now. Power valve was dirty as so I cleaned that and found where the o-rings go! Put it all back together and same rattling noise, but only really at idle, or very low revs. Rode it around for 20mins in 1st and 2nd, less than 5k revs, seemed to go ok. Started it up again this morning, lots of white smoke. Let it warm up and took it for another ride. Couldn't get more than 7k revs then it would bog, eventually died after bogging and not running well at all. Wouldn't start again. Pushed it home and cleaned spark plug, nothing. Took carb off and lots of fuel inside, drained that and put it back on. Started on second kick. Still won't rev above 7k even in neutral.

I've cleaned the air filter and the fuel line seems fine. I've ordered a new gasket set for the top end. Is it worth getting another piston and ring set and trying that? The guys at the shop seem reasonably on to it so I doubt they mis measured the cylinder. I'm not sure about the rings though, even though the cylinder and piston looked fine when I took the cylinder off. I don't really think ( hope) it's the bottom end as it ran fine before and there was no play in the con rod. I guess water might have got into the engine because of the base gasket but it runs pretty good until 6k?

Please if someone could suggest anything I can try would be much appreciated, cheers

[331X2]

I'm not a big fan of 'a light hone' and new piston to be honest, is the sound the piston rattling around an oversized cylinder?

[Mattmanley]

Wouldn't I see marks on the cylinder and piston if it was slapping?

Cheers