still smoking 2

[franz]

a previous thread started by aussie dan , smoking on start up--turned out on mine to be the cylinder head studs needed re torqued after recent top end rebuild 1000 miles ago or so--bit like the old british bikes used to be.
havent had any more smoke probs since (500 miles) so there yea go ive quit smoking for the new year!

[Aussie_Dan]

Glad to hear that you got your machine sorted Franz.
Unfortunately my bike still has problems... It's now been sitting in my garage for nearly 3 months. I haven't even bothered to start it.
I will look at it again in 6 weeks or so, but I now believe that the bore may be glazed over... It's been run all of its life on semi-synthetic oil (as recommended by my yamaha dealer) and after speaking to a few people, i've been told that these big air-cooled thumpers are best run on plain old mineral oil, which allows the rings and bore to bed in and seal properly.
So, it might need to be honed, with a new set of rings and a change to mineral oil.
Will keep all you guys posted as to what happens anyway!
Cheers, Dan.

[Ratrap]

Dan

I've been watching your thread with some sympathy.
I rebuilt an XT500 a few years ago after it seized up due to oil starvation.
I used genuine Yammie parts throughout. The rings arrived in an unsealed box but end gaps checked out OK and I buttoned the motor up.
It smoked like hell when I started it and didnt stop. Eventually the exhaust was wet with oil. It smoked worse on the overrun even while just revving it in neutral. I stripped the head off and the piston had a small pool of oil on it.
I had many experienced people look at the motor as I changed cylinder heads, then valve guides and valves all to no avail. I had that motor out three times in a week!

Eventually someone suggested I fit just the oil ring to the piston and check what happenes when the piston was inserted into the barrell. Well it fell right through. I ordered another set of rings from yamaha and the despite a sealed box the oil ring expander just wasnt expanding the oil rings sufficiently to even vaguely scrape the bore. I carefully opened up the expander to provide more tension and the problem was solved. I have noticed that the bike does smoke a bit on startup now and I have no doubt that my solution hasnt stood up to the test of time. I have ordered a set of Deves rings (5 piece oil ring) as I have had excellent service from them in an array of motors.

This may just throw some light on your problem. I studiously conduct the "mike" test on all oil rings I install now in honour of the guy who solved the problem. The oil ring on its own should support the weight of the piston in the bore.

Cheers

Gavin

[Aussie_Dan]

Thanks Gavin.
What you have just said could most definately be the problem that my bike is suffering from...
Just like your XT, all of my head is perfect. New valve stem seals and even had the 'suspect' valve guide replaced with a custom made bronze one. The only thing it really leaves is the rings & bore.
Thank god these engines are simple and easy to work on!
Like i said, i'll let you know what I find after I get back from my honeymoon in a month or so and I dust my bike off and drag it out of the shed!
Cheers, Dan.

[big t]

very interesting gavin, i will try this test this weekend as my engine is already dismantled! where can i get those rings you mentioned?

[Ratrap]

www.deves.com

I order them from a local agent.

Gavin

[*Touring Ted*]

Aussie dan: Have you ever bothered to measure the diameter of the bore properly ?

High milers or over zelous honing can take too much off the bore and original sized rings just wont have the spring in them to cope. Oversized rings will be necessary and available from Yamaha. Manually prizing open rings is a bad bodge and they will only close up again or cause even wear.

If oversized rings dont help (measure the bore first before fitting) then you may need a new bore fitted into the barrel.

A pool of oil on the piston means either your rings are leaking, valve seals are mush or cylinder head gasket is toast or not sealing properly.

You might want to get your hands on a cylinder leakage tester too.