Burning Oil again bugger

[nx650]

My 1997 Dominator motor has done 40,000 hard ish miles and was burning oil on over run. ie No blue smoke on start up or exceleration but when I back off the throttle lets say going down hill I get a blue haze forming around me. About 750 mls of oil for 600 miles. Pulled it out and got it rebuilt new rings valve seals guides etc.... Fantastic for 3000 miles and now suddenly (after one 300 mile day) I'm back to exactly the same. The motor runs great pulls well and does 50 to the gallon but why is it doing this again? Answers on the back of a postcard please I want to go to south america but I don't trust it like this help me please

[beat_]

you didi all that
and not the cilinder and install a new piston?

[Dodger]

It sounds like it's sucking oil down the inlet valve guide on the overrun.
Check the inlet valve oil seal .
I'm not familiar with that bike ,it may not have a seal ,in which case it could be a worn valve guide .

Richard,
Did you find the cause for the original oil consumption?
As Dodger said, it does sound like oil being sucked down the inlet valve guide on the overrun, this could be worn valve stem or guide or faulty guide seal. Did you change the valves and guides? If new guides are put in the valve seats should be recut to make sure they line up, if not the guides could fail prematurely.
Another cause could be excess crankcase pressure forcing oil into the air box so check for excessive oil in the air box. Check all your breather pipes.
If possible do a hot compression check, if it's good and the air box is dry must be valve/guide issue. One other possible cause could be the head gasket failed between the cylinder and oil way.
I know it's frustrating when a repair does not work but if you persevere and fix it you'll have more confidence in the bike and you ability to fix it. That feeling will be worth something on your South American trip.

Steve

[JonStobbs]

As Steve says,check the engine crankcase breathers especially that they're not kinked or pinched.Another cause i've found for this is non genuine valve stem sealsbeing fitted and being a little bit loose on the valve guide,coming adrift and letting oil in that way.

[nx650]

Thanks people sounds like what I expected looks like I will have to pull out the motor again as I can't work out any other way of getting the head off to have a look. A lesson learnt though I'm glad I got the motor done well before my trip at least I'm only in NZ and not the middle of Peru!!!!!!!!!!!!!!!!!!!!
Have any of you dommie owners done the carb modifications that are posted under the xrl post? I'm almost tempted when I get the motor out again but would like some feedback

[beat_]

i was bussy with the carb mods but crashed my bike during test runs and haven't fixed it jet to make a dyno run.
the only bike i'm riding at the moment is a pushbike

[nx650]

Well after pulling the motor apart it turns out that it's been sucking dirt in through the airbox from the drain hole in the bottom and also where the filter wasn't sitting properly. I can't belive how much damage a bit of dust can do in 3000 kilometers the valves are all pitted around the edges. The new valves are scored and so is the bore. You live and learn I suppose just goes to show how important clean air is bugger

Richard,
Did you have the standard air filter?

I traveled with two friends with identical Hondas in very dusty conditions, one had the Honda filter and started to run badly as it cloged up, the other with an aftermarket filter (I think it was a cotton type filter) kept running OK but when we checked dust was getting past the filter, we could see a layer of dust on the carb inlets. I think foam filters are possibly the best option for re-usable filters.

Hope you get the bike up and running quickly without to much expense.

Steve