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Discussion in 'Thumpers' started by onaXR, Jan 18, 2006.
Not sure if the current models are this way, but I had both a 2008 and 2012 Yamaha WR450F and both of them had a breather that came off the top of the valve cover. The hose had a "Y" joint with the higher hose going to a nipple on the air box and the lower hose was routed back to a nipple where the electric start/stator cover was. I always thought that was a slick system as it seemed like the way they did it it dropped the oil over the gears between the e-start motor and the starter clutch. Basically the same as what you are referring to so it could be that the spinning action of the flywheel or starter clutch has an effect of pulling air in. Here you can see it right at about 2 o'clock on top of the starter motor.
It seems that the problem has two parts - a) separating the oil from the oil mist that's pumped out of the crankcase and b) getting the separated oil back into the engine so that it can be pumped back into the frame by the oil pump's scavenge side.
Here's a picture lifted from Perrin illustrating how an air/oil separator works -
Our oil separator probably looks similar inside but the way that it's plumbed appears to be trying to drain the separated oil back down into the crankcase vent, fighting positive pressure pulses from the piston's down stroke. I've been wondering if a return line to the magneto cover with a reed-type pcv valve between the separator air outlet and the air filter might cut down on high RPM oil loss? There's also the question of how to vent the frame if the engine is running negative crankcase pressure since it's currently vented to the engine's top end.
The earlier XLR series, like the XL600R didn't return the condensate, they had a drain tube that ran to the bottom of the frame.
Every oil change, there's a small amount of condensate that I drain.
That condensate is not just oil, it is combustion process by products, or blowby. All engines have blowby, no piston ring makes a perfect seal. That is why the PCV system was developed for automobiles and is still used today. Fresh air is pulled into the crankcase and removed from another point, evacuating the combustion byproducts from the crankcase, so they don't condense and contaminate the oil. The XR650L is doing the best it can with essentially a old school blowby tube with a separator plumbed in.
Designing an actual crankcase ventilation system, like PCV, which doesn't solely rely on the reversing crankcase pressure to just bounce pulses back and forth through a tube while dribbling out condensate, may be the best modification for blowby control at sustained, high RPM.
I don't ride at sustained, high RPM (desert race/travel California interstate), and I'm not opening that can of worms.
Guys that race old British singles and 360 degree twins appear to be having success with the Yamaha XS650 reed valve. There's also a guy who uses the BMW crankcase breather reed valve in a custom case to prevent high RPM oil loss in old Brit bikes that are being raced. I'm thinking that there might be potential but things have been kinda' crazy here for the last two years.
Good info on a reed valve design.
Some KLR owners have tried an automotive PCV valve. May be a place to look also.
I've got too many projects to be opening a can of worms on anything. It's enough just trying to get and keep everything back together and running.
I recently bought a custom mini bike project that I've already spent too much time and money on for what it is. A one-off build though and quite a bit different from anything else I've seen, so it's fun. I've got to get rid of it though and quit keeping all these little projects after I get them going.
You think you've got a stretched cam chain...
A stretched chain is the least of that engines problems.
I can't see your image.
Very cool!! Where at?
How about now?
Ya, you have bigger issues...
Just like a scab, it's best to not start picking, next thing you have a bunch of parts on order! Worn top spherical bearing on the shock turned into lets just rebuild everything while I'm in there.
The Chevy & Ford I6s don't have cam chains, so they don't have that problem. Regular oil changes help too.
Not using Pennzoil or Quaker state helps too. At least the 60's and 70's blends. They were a parafin base oil. I had another old slant six that had Quakers state run thru it that looked very similar.
did the straight up trade today. my 02 Sportster 883 hugger for the 2015 XR650L. 2500 miles on it. got the stock tank, headlight bezel, and muffler.
Cool trade, looked like that harley was leaving a spot on your floor anyways.