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My new Mototrans TS125 project was sold to me as a runner. When the bike was brought out of storage the company had a problem starting it, and replaced the piston rings prior to delivery. It starts first or second kick, and runs well enough. The problems begin about 2 mins after starting, as the blue smoke builds and builds over the next 5 mins, and eventually it cuts out.

Any thoughts?

Worn piston and barrel? new rings not correct size? Replacement rings will not cure worn bore. Worn valve guides? I would remove head and barrel to check wear and if put together properly by seller.

I reckon this is a valve guide issue. My 900 showed the same symptoms when the valve guide oil seals perished; I would start it, and about two or three minutes later it would smoke and misfire until it cleared. The problem disappeared after I replaced the valve guide oil seals. When you start these engines the camboxes fill with oil until the engine gets sufficiently hot enough to thin the oil which is then able to drain away.

Presumably the plug gets oiled up and stops sparking?
Hopefully this is just worn parts. Maybe check that the head is draining oil properly? It probably is, there are some big drain holes there.
Unfortunate to have this problem, but the good news is that you can get rocker pins, valves, guides and pistons without too much trouble.
Cam and rockers can be re-furbished if worn.

Do what George suggests, it's not difficult. If someone really has replaced the rings, then it 'should' come apart without much trouble.

Good luck!

Thanks for the replies

Yes the plug is covered in oil.

So what I am getting here is that I should check that the piston rings are correctly fitted, but unlikely to be that if they are and new fitted.

More likely valve guides and seals which can be replaced

Have I got that right?

If so where can I get valve guides and seal from?

Thanks everyone

Max

The trouble is that you cannot presume anything - the person who fitted the rings may have broken one when fitting the barrel or fitted them upside down, so I think that you will have to follow George's advice and remove the head and barrel to see if everything is ok. AFAIK, the 125 does not use oil seals on the guides, so if the guides are the problem it will mean renewing them. I don't know where you are in the world, but Lacey Ducati will be your first stop for spares if you are in the UK.

Interesting update

The shop fitted a 55.7mm oversize high compression piston from classicducati, and honed the cylinder liner to size. He said there were a few marks in the cylinder wall, but mostly all disappeared in honing.

They did not do anything to the cylinder head.

It looks like the valves is where I need to look first.

There is an flea bay person called guzman175 who has valve guides listed for a 125. I have bought a pair so can vouch that he is a good trader.

Steve

I would get someone who knows how to do it to measure the cylinder bore for you to insure it is the correct size, if the "shop" honed the cylinder to remove marks it may now be too big and out of factory spec, if the "shop" honed the cylinder to make it fit an oversize piston instead of getting it rebored it again may not be a great fit, if that's all checks out ok then check your valve guides.
Cheers,
George

If bike was bought from shop as a runner surely it is for shop to put right. I would not consider a bike that oils plug enough to stop running within five minutes to be in running order