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The TTR250 FAQ web pages -> TTR250 -> Repairs and maintenance -> Smokin' on "The Vince"
Post Info TOPIC: Smokin' on "The Vince"
TTRfan


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Smokin' on "The Vince"
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Good to hear you enjoyed "The Vince" Simon - some of our Devon TRF members have done it and enjoyed it. One on a Honda C90 wink

Regarding the smoking, Cubber is right. You can't ignore it and it needs sorting.

It is quite a lot of work to get the head off but that won't necessarily show you exactly what the problem is except the state of the combustion chamber and exhaust valves will show if you have been burning oil. If you have, they will have a covering of "soft" carbon deposits. In my view, it is almost certainly the valve stem oil seals need replacing or worn rings - or both.

Whilst you have the head off it isn't much extra work to lift the barrel off to examine the piston and bore.

My suggestion is that you arm yourself with a head and base gasket kit (you are going to need that whatever), 4 valve stem oil seals and a set of standard Yamaha piston rings (very good chance you are still on the original piston).

When the barrel and piston are off, take off the old top ring and put it about a half inch down the bore. Square it with the piston. Then put in the new top ring above it and compare the gap. My guess is that there will be quite a difference.

Whilst the head is off, take the opportunity to drop out and clean the valves and lap them back in if they aren't damaged. Fit the new valve stem oil seals, new rings and put it all back together. I have done this on a number of engines and it has cured the smoking every time plus given the engine a bit more zip.

I am just putting an engine back together where I have done exactly as I have suggested. I didn't realise the engine was smoking until I had an email from a mate who was behind me at some lights and said he saw the TTR smoking. I will know in a few days if I have cured the problem and the test will be to get Mrs TTR to follow me around for a few miles checking for smoke wink

The piston and bore looked fine although there was evidence of some blowby on the piston. The old rings were quite worn and the exhaust valve stem oil seals were black and brittle so I am confident I have sorted it.

Famous last words smile

Brian



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mossproof


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Just done the best part of 700km on mountainous and rocky trails over 2 days on my '94 OE on The Vince - excellent "navigation enduro" in the Spanish Pyrenees organised by Austin Vince. Absolutely fantastic event and highly recommended... BUT, got a peculiar blue smoking problem that I need to pick your brains on before I start taking things apart: Occasional cloud of blue smoke, seems to usually be under power (ie when accelerating) although I think it happened once or twice on the overrun. No loss of power or change in engine note, just I can hear the guys behind me coughing! Over the 2 days I'm guessing it happened 10 - 15 times. Just happened again here at home (UK midlands) once on a post jetwash and carb clean test run, 5 mins after startup and not again in 45 mins of riding. The 2 things I'm thinking are stuck piston rings (but wouldn't it happen all the time?) or valve guide seals. Any ideas folks?

Simon.  



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Cubber


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Welcome, Simon, and congratulations on your Spanish adventure.

If your TTR is nearing (or is over) 16 years old then it's allowed to have an occasional smoke. You must be warned, however, that it can cause complications later. biggrin

The most common cause of smoking is worn valve guides, followed closely by worn rings. cry

Guides usually present themselves with smoke on the over-run/decelartion whereas rings present themselves gradually at first and getting more smokey constantly as they wear. hmm

Are you sure your smoke is oil generated? Are you topping up more than usual?

It could be simply that the valve seals are a tad worn rather than the guides being worn.

A quick "lid-off" to check may tell you more. wink

Martyn



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mossproof


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Thanks for the rapid responses chaps. Agreed top-off al la the Duchess of Cambridge is the only answer really! It was the intermittent nature of the blue (hence assumption of oil burning) smoke that intrigues me. Repeating the my home test circuit didn't cause a recurrance. I thought if it was worn rings there would be a more regular smoke at certain speeds/acceleration rates? Anyway I'll keep you posted...
Simon.

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TTRfan


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An afterthought. If the motor hasn't been apart for a while then there is a good chance that the cylinder base O ring will be a bit "flattened" and it is probably worthwhile replacing that when you have it all apart.

Good luck!

Brian



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