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  #41  
Old 17-03-2018
goose202 goose202 is offline
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Yeah checking gearbox level through the check bolt. Oil is right on the level now just as it was before the ride.

Much unlike my normal nature, I'm not stressing too much about this.
Top end isn't that expensive. I'll just keep a close eye on it from now on.
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  #42  
Old 17-03-2018
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Chewy Chewy is offline
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Are you letting the oil dribble out the check bolt till it stops?
Otherwise you can take the big plug off the RHS and see the exact level. From memory its usually about level with the bottom of the hole.
Or drain and measure.
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  #43  
Old 18-03-2018
goose202 goose202 is offline
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Yeah. Bike upright with check bolt out, no oil dribbles out. Lean it over slightly and oil emerges.
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  #44  
Old 18-03-2018
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Prob be right.. sounds like you know what you're doing.

I doubt it needs it, but when the time comes, yes, top ends are pretty cheap. I usually go with the honda pistons... i noticed the ring gap etc can be a bit hit and miss on other brands.. and i stick to stock compression ratio's.

I seem to get much better piston life on mobil 15w50 than the motul, penrite and other oils i've used.

Pays to run in properly.. i use a flex-hone as well. Then hopefully no oil useage. http://www.mototuneusa.com/break_in_secrets.htm
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  #45  
Old 03-04-2018
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So, oil consumption.

The bike had it's second outing this weekend.
1. Still used heaps of oil. Like 100ml per hour heaps.
2. Still not a single bit of evidence it's burning it. Not a spot of blue smoke ever. Starts easy, runs great. Crankcase breather that goes into the air boot appears dry. No evidence of leaks from the engine. Only a drop of oil in the crankcase breather plugged downtube contraption.
3. After one ride, we noticed oil spots all over the rear wheel, oily dirt all under the rear guard. Only evidence of the source was from the gearbox and carby breather hose collection.
4. Gearbox oil was also a little low. Topped up both.
5. Zip tied the gearbox breather away in a spot that would make it clear if oil was emerging from the breather.
6. Final 30-45 minutes of riding did not show any oil emerging from the breather, and, oddly, it didn't seem to use any crankcase oil.

So my current speculation is an intermittent crank seal failure which pumps oil into the gearbox, pressurising the gearbox which then blows all that oil out the breather. Seems unlikely but I'm out of ideas.

It also seems unlikely that if it's been going out the breather the whole time that I wouldn't have noticed oil everywhere over the rear wheel like I did this time.

Not even sure what to do next. I'm reluctant to do the top end since there's no evidence of it burning oil. Replace the crank seal and see what happens?


The bike itself:
It's a cracker of a thing through tightish hardpack single trail. For this stuff it feels every bit the 20kg lighter than the '08 WR450 I was riding.
More open flat track though you do really miss the grunt the 450 has though. You have to ride it in a different way, not just relying on the grunt to shove the back around through the corner. I have no doubt though time on the 250 will make my kid a better rider than jumping straight to a 450.
It goes well enough with a 57kg rider on it. In a drag race across the paddock, my ~90kg on the WR450 means there was only about 2-3 car lengths by about 100km/h in it.
My son has taken to it very well - the days of me being faster are numbered.
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  #46  
Old 03-04-2018
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Takes months to learn how to ride a 250F coming off a 450, once it clicks in your head, it's a whole different games. Takes a full year to adapt in my opinion. A 2502t will pull away at 80 i find, and a 450 starts at about 60. But how often do you vary your speed in a ride by 60km/h in one go ? 250 will make up every bit plus some under brakes for the next corner.

I overfill my gearbox and it never comes out, you might wanna check the breather that runs out the rocker cover, it goes into a T with a plug that needs to be regularly removed out of one end.

I reckon it's just not run in properly and you're doing high load riding. Keeps the oil fresh at least :-) I'm onto my 6th crf250 with 180-350hrs on each bike, never seen a blown crank seal.
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  #47  
Old 03-04-2018
goose202 goose202 is offline
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Yep that's the breather I was talking about. All seems in order there.

You're probably right on both counts, disco.
For me, I'm a just a hack who enjoys blasting around with as much power as possible, so the 300 two strokes and 450 foureys do it for me. But it's fun to have my son's bike available for something different too. He understands that the team owner gets to ride whatever team bike he likes whenever he likes...
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  #48  
Old 03-04-2018
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oh ok, there's a crank breather there as well above the clutch side toward the centre of the motor...

maybe the ring seal is that bad that it's pressuring the crank and pushing a bit more out the breather sometimes... u can put a compression tester on it and remove the decomp weight to get a reading or put air into spark plug hole and listen where it comes out i.e engine oil filler, exh or intake ports etc to check for sealing too (poor mans leak down test)

but it's prob ok til u inspect the piston, those oems can wear out the skirt at about 70hrs...

the power does it for you on the bigger bikes, but the 250 does it for you when you learn not to slow down as much and carry more speed through everything (which takes a bit of time to master) and that's when i get the biggest buzz :-)
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  #49  
Old 03-04-2018
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And a 250 or a 125 2 stroke does it for you when you pass one of those 450s on a much smaller bike.
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  #50  
Old 29-04-2018
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So, another day out riding and it didn't use any noticeable amount oil on the dipstick.


I guess we'll keep riding it as is and checking regularly.
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