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

pekkal · Member

What can make valve clearance grow? (a.k.a How to kill a perfectly good engine...)

TT-R250M · Super Guru

Hi Pekka,

Sorry to hear about your ''cooked'' engine

Usually valves get tight from metal expansion i.e.. heat. In your case, it is loose valves from the camshaft journals being scored. You can do as Brian does and sand the journals down with sandpaper on a round stick, then machine the camshaft caps down to suit. Not sure how long that would last though.

I would be worried about what the heat and lack of oil has done to main bearings, cylinder, gears etc. It would be worth checking the state of these before spending too much on the top end rebuild.

Sounds to me like your in for a complete rebuild as the bottom end may be cooked as well? disbelief

Jarrah

TTRfan · Super Guru

TT-R250M wrote:
You can do as Brian does and sand the journals down with sandpaper on a round stick, then machine the camshaft caps down to suit. Not sure how long that would last though.

Please don't use sandpaper on your camshaft journals Pekkal!

The method I have used once before was with very fine wet and dry (800 grit I think) used in association with WD40 as a lubricant and cleaning agent. It was on a head where the journals were so tight that the cams wouldn't turn when the caps were torqued up. Easing the journals just enough to allow the cams to move freely was quite straightforward. There was no machining of the caps involved.

On a TTR engine where there has been a complete loss of oil, you may be lucky as it is likely that the engine will seize before any other major damage is done because it will have happened quickly but, as Jarrah says, it needs checking out as something caused the journals to score - probably starting to overheat through lack of lubrication. My guess is that at the very least you will need a new piston and rebore. Check your conrod little end is OK as that may have been damaged by the seizure.

Brian

TT-R250M · Super Guru

TTRfan wrote:
TT-R250M wrote:
You can do as Brian does and sand the journals down with sandpaper on a round stick, then machine the camshaft caps down to suit. Not sure how long that would last though.
Please don't use sandpaper on your camshaft journals Pekkal!
The method I have used once before was with very fine wet and dry (800 grit I think) used in association with WD40 as a lubricant and cleaning agent. It was on a head where the journals were so tight that the cams wouldn't turn when the caps were torqued up. Easing the journals just enough to allow the cams to move freely was quite straightforward. There was no machining of the caps involved.
Brian

Maybe I should have said fine sandpaper= wet & dry. When talking sandpaper for this kinda thing it is obvious one would use fine wet & dry though.

I was thinking- use JB weld to fill the score marks then sand out? Not sure how that would go though?

I do not see why the journals could not be machined and the caps and cylinder head machined to suit making sure that the valve clearance limit is not exceeded. Except for the fact that a second hand replacement may be cheaper?

I would be checking the spec's of the oil pump as this may be worth replacing.

Jarrah

TT-R250M · Super Guru

If I was you I would be replacing the cam chain, tensioner and guides (sprockets if need be).

The ttr250 should not make any noise other than the normal whirring noise, NO TICKING!

Jarrah