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Discussion Starter #1
anyone using a pcv valve on their machine.
i found one on mikesxs.net that seems worthwhile, i read on eurospares about using an old mazda or similiar automotive valve. they run about twice as much. (30 for the oem automotive, and 15 for the mikesxs reed type)
any recommendations, also any modern Jap bikes have pcvs???
 

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MAP and Britech both sell them for british machines. i reckon the theory remains the same for jap bikes, though. however, the way it was explained to me is this: if you want a valve to make a difference, you need to have good rings. otherwise you're wasting time and money.
 

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I've ran them for years o several of my 360 degree twins, 5 bucks units from the parts store to fit SBC's

they work, they are cheap, change often and if you did it right, you'll find at least 10" of vacuum on your crankcases

My XLCH has the crank breathing opened up and a large snout with runs to a reed valve box which then dumps into a catch can
 

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I looked into running one on my 360 degree...200cc twin for a while. But...reseach seemed to indicate ...one: not much pumping losses on a 200cc machine with a 41mm stroke....and two: not many PCV type valves will cycle at 12-13,000 rpm where I need it.
I did see one expensive valve specially made for bikes that was supposed to be good in that rpm range..and was like $100+. Had some kind of real light "valve" that would cycle fast.

I always wanted to try something anyway....vacume in the cases at 12,000 rpm would have to be worth 1 hp....which would have been substantial on my bike.
JohnnyB
 

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Leo Geoff proved they worked, and did it both on the track and dyno, years ago

I will say I agree with the observation about the rings

I really dig Total Seal Gapless rings
 

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Discussion Starter #6
gapless rings? i thought the gap was for heat expansion?
the rings on my bike are likely the original, they have probably about 20,000 miles on them. it has excellent compression 170psi or so, i figure my rings can handle it, (do i figure correct?)
 

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sure but I was merely stating I like Total Seal rings

if your conventional rings are sealing (as in crank cases not being pressurized by blow by gases) then you are in good shape

do whatever you can do to put the bottom end in vacuum conditions

next best thing is breathing opened up and allowed to freely vent to the atmosphere
 

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Corey,
Total Seal gapless rings use a system where the ends of the rings overlap top to bottom but there is still room between them for expansion/contraction.
And yes...engines where one piston goes up, as the other comes down have much smaller pressure pulses since crankcase volume remains constant. But blow-by still must be removed from the crankcase, and the pistons still have to move air. The less dense the air is (vacume), the less resistance to movement. In many situations it would make no difference (or very little). On very high reving, or engines with large displacement and certain crankshaft arrangements it can make a big difference.
JohnnyB
 

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Discussion Starter #10
basically, its worth doing because its inexpensive and easy, but its not a huge gain, at least on something like a cb350 or xs400. are cb350's 180 or 360 cranks?

anyone run one of these to their exhaust to pull a vacuum?? or just a puke tank?
 

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Corey,for the less refined vintage machines that are notoriously difficult to make oil tight.....

it's well worth the effort even if it only keeps them from seeping dinosaur blood here and there........

I have never done an exhaust extractor/syphon/vac on a motorcycle but I have seen it done

the drag cars I've wrenched on that ran them more often upgraded to much more effective belt driven pumps...

the exhaust extractor needs to be variable (complicated and expensive) over a relatively wide range to be effective over a wide range of engine operating speeds.........
 

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I couldn't get an exhaust evac system to work right on my Chevelle with the full exhaust on it. Can't have any backpressure.
 
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