A forum for owners of Yamaha TTR250 trail and enduro bikes!

Irve · Member

grey smoke and oil consumption

TT-R250M · Super Guru

From the picture-

There is no way that the cam timing could be out a tooth, it would not be so close. Some blue TTR's seem to have a discrepancy with where top dead center is. Does not seem to be an issue to me.

However- even if the timing was out a little it would not cause white smoke.

Are you sure there is no water in the oil? water in the breather pipe- built-up from not draining the water/oil separator? fuel?

If it continues to blow smoke I would suggest to check your rings and replace the valve stem seals (even as a precautionary measure).

Jarrah

ttr steve · Super Guru

Sounds like new piston and ring's, if it is, re-bore out to the max 2mm as it makes a big difference. wink

I put new piston and ring's, the bore measured ok, but let go a few months later and I had to get a re- bore, new piston and ring's again cry so went for the biggest oversize and I am really, really pleased with it smile smile

Irve · Member

I was on vacation so I couldn't progress but..

There is no chance for any water in oil or gasoline.

I've checked cylinder piston and rings.

The end gap for ring is out of spec. 0,65 instead of 0,25-0,35.

The piston seems to be in spec but I have only a caliper with precision 0,05. I don't know if it is enough.

I'm not an expert but the surface of cylinder and piston seems to be ok. I can see some micro scraches (picture below) but I don't feel them with my finger.

There is as well a lot of carbon on the head of the piston and valves could it be a reason of consumption?

AGman · Veteran Member

Doesn't seem to be much blow-by on the piston...I wonder if the valve guide seals need replacing? I would install a set of rings, clean the carbon from offending areas, do the valve clearances and seats, replace the valve guide seals and your done.

ttboof · Super Guru

Go the re bore .and definatly valve seals looks like the carbon build up is from the oil going past the seals and burning on the valve

Irve · Member

I bought a new piston and rebored the cilinder. I have new seals for valves.

But cleaning the valves i have noticed something strange I'm guessing they have been burned :/. They are uneven on the steams closed to the head. One inlet valve has uneven head.

zawor 2.jpg

I assume they have to be change. Am I right?

TTRfan · Super Guru

Hi Rafal

That is really odd wear. I haven't seen anything like it before confuse

Having invested in a rebore, it makes sense to replace the damaged valve(s).

Carefully check that the valve guides are not damaged. They can crack if the valves have ever hit the piston through incorrect valve timing.

Also, check that the valve seats are OK when you get the new valve(s). They should match the valve exactly.

Brian

Irve · Member

I already have new valves :).

Unfortunately they don't seal properly. I don't know should I lapp the seats or give them to recut. Recutting is the cost and a risk - you never know if it will be done properly (i know that is theoreticaly simple). I've read about this two methods and some people consider lapping as XX age technic and not good for vales as you grind them and make prone to wear. But as our bikes are XX age desing and not high performance machines I wonder if this is not an exaggeration. I can not assess the seats due to lack of experience I just can see they are not ok at the moment. What would you recommend for them?

TTRfan · Super Guru

I was hoping we had an engineer on the forum who could have given you a technical answer but so far nothing so here is my view.

I spoke to a knowledgeable friend who reckoned that the wear on your valve seats was too much to remove with lapping and, unless you used the old valves to do the lapping, you would lose too much off the face of the new valves.

The answer seems to be that you need to have the seats recut. My friend suggested that you let the engineer have the new valves and ask him to lap them in after cutting the new seats. It will then be obvious to the engineer whether or not the seats have been re-cut properly.

Brian

Haggis Hunter · Veteran Member

Do check for valve guide wear. I have seen uneven wear on valve seats (on diesels) caused by the guides being worn. Worth checking before you cut the seats. You will not get a good concentric seat if the guide is worn.

Peter.

Irve · Member

I've made the wiggle test. According to different sources (for different valves) the max was 0,5mm-1,3mm. The another way was multiplication of recommended/max clearance by 3,5. For my intake I measured 0,2 and for exhaust 0,3. So it seems not to be in recommended but below maximal (from manual). Is it enough for the checking?