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The TTR250 FAQ web pages -> TTR250 -> Repairs and maintenance -> URGENT HELP PLEASE - OIL LEAK DIAGNOSIS
Post Info TOPIC: URGENT HELP PLEASE - OIL LEAK DIAGNOSIS
heffh084


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URGENT HELP PLEASE - OIL LEAK DIAGNOSIS
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Hi all,

 

So I'm heading off to Mongolia in 10 days and my bike starts drinking oil, 1.4L in 400 miles!

With help from a spectator rode up and down the road and deem that oil smoke is constant, not just after coasting with throttle closed, so i was pretty sure its rings not valve seals.

Off comes the head and I find this:

DSC_0493.JPG

Clearly burning oil, but its very hard carbon beneath indicating rich running...

DSC_0502.JPG

 

DSC_0504.JPG

exhaust ports have been apparently growing carbon crystals for quite some time, but blue smoke only a recent symptom...???

DSC_0509.JPG

Next I checked the piston ring end gap. The manual specifies a max of 0.35mm for the top two rings. Mine are sitting pretty at 1.3mm and 0.5mm! Oil rings are in spec.

No indication that the top ring end snapped off, so why such a huge gap??? Rings are genuine Yamaha +0.50mm, installed the right way up on a genuine Yam +0.50mm piston.

 

Piston skirt is in great condition but showing signs of blow by above the rings. Piston bore is looking as if it has been honed with builders sand - no gouges but the cross hatching is very coarse compared to another cylinder I had re-bored 3 months ago.

 

So what I'm thinking is that my faulty choke CLICKY (Last two Posts) was causing the bike to run very rich constantly for a long time before I owned it (only ridden her 100 miles in the 6 months I've had her, before the blue smoke started), causing the dry carbon build up. I know the choke was working correctly at some stage as under the black soot on the valve heads was a nice tan deposit.

 

Recently carbon build up must have broken off and started scoring the rings and cylinder, causing my sudden blue smoke symptom.

 

Thoughts anyone???

 

I'm confused as to why my piston is such a lovely snug fit, with no damage I can see, but the rings are so sloppy.

 

Advice for going forward... A new set of rings and valve seals with a fresh hone, or a new +1.00mm piston, rings and rebore???

I'm leaving for Mongolia in 10 days one way or another!

Thanks TTR Fans!

 

But i



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heffh084


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Piston pics before and after the crown was cleaned...

DSC_0495.JPG

DSC_0496.JPG

 

 



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TTRfan


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Bad luck!

A very rich mixture will cause petrol "wash" down the bore which takes away the oil and leads to premature wear. On the TTR250, the piston rings seem to be the sacrificial parts and are the first parts to wear.

You have a difficult decision to make with your upcoming Mongolian ride. TBH, I wouldn't take a chance that new rings would fix the problem and would personally go for a new piston kit and rebore.

With your timescale I would suggest an off-the-shelf solution. Steve has a rebored barrel and new piston kit in the Totally TTRs shop here which could be with you very quickly if you move soon - see here

I would suggest fitting new valve stem oil seals whilst you have the head off if that hasn't been done recently. 

Also get the valves cleaned asap to make sure the seats are OK and don't need grinding.

Good luck!

Brian



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heffh084


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Jut as I thought.

I have ordered replacement parts from steve and should have her up and running next week some time!

Have plenty to do in the mean time.

cheers Brian.

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mossproof


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Sorry to say, but your valves and seats look none too healthy either, and poor compression from valve blowby would cause incomplete burn as well. Good luck with the rebuild (Totally TTRs also has heads for sale if time runs out and you have to lob some money at the problem) and have a great trip,
Simon.

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Padowan


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Whatever your decide to do (and i agree that a piston and bore is the safest option for the trip you have planned) i think you'll be very pleased with the increase in power and responsiveness that you'll get if you clean up and re seat or lap in the valves.

A few years ago my ttr was burning some oil (not as much as yours) and the compression was poor due to both worn rings and poor valves seats. The rings are replaced, along with valve stem seals (cause of oil consumption) and i cleaned and lapped in the valves. I increased compression by about 50% and the bike was a different beast afterwards.

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ttr steve


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Keep us posted Howard

We would all like to know how you get on and photos please.

Good luck.

Steve



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petenz


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i would check around the vavle seats for cracks....



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heffh084


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Hi all.

Well I got a new piston, rings, gaskets and valve seals and had the rebore done at SRS in Sutton. Great service from them and an inspection returned no worrying issues with valves\head. They lapped in nicely so Hopefully all will be well with compression

Sorry, no photos of the rebuild, I did not stop to take any! she started first time on the button, no blue oily smoke and is much easier to kick now too.

I'm going to have to take it easy to Utrecht, keeping off the motorways so as to not stress the engine while the rings bed in, and a fresh oil change on the first day!

not ideal, but cant let this set me back.

thanks for all the replies, and a big thanks to Steve and Lisa for getting the parts out to me next day.,

Keep your fingers crossed for me!

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ttr steve


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Good work and fingers well and truly crossed!

Have a great trip!



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TTRfan


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Excellent news - good luck on your trip!

PS Out of interest, what does a rebore cost these days?



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