Crankcase PCV

72Combat

72Combat

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Jan 4, 2011
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I've been running my race BMW with no valve, just a hose and a catch bottle.
Both pistons rise and fall together so for all intents an purposes its like a parallel twin.
My BMW former engine reconditioner mate is dubious about how it will work at 7500 rpm...?
I bought one of the Mikes Yamaha type ones and are going to fit it to the top of the motor breather hose then to the bottle.
Theory I have read is that when the pistons fall they are having to pump air out of the crankcase.
I read claims on a Triumph forum of butt dyno horsepower increases, hmmmm
Any thoughts from the panel? :mrgreen:
 
Yes the British Boxer engines smack a pressure wave in cases as pistons approach each other so would benefit if the blow by pressure could be kept below ambient and could show up with more power from better ring seal and less suspended oil mist in less dense air. If the reed valve don't float its valve till 8000 should work a treat if placed not to suck oil out too. Comnoz has measured a handfull of extra hp on Nortons when done right. Win Win. I'd scan search BMW forums for insights of what's been done.
 
hobot said:
Yes the British Boxer engines smack a pressure wave in cases as pistons approach each other so would benefit if the blow by pressure could be kept below ambient and could show up with more power from better ring seal and less suspended oil mist in less dense air. If the reed valve don't float its valve till 8000 should work a treat if placed not to suck oil out too. Comnoz has measured a handfull of extra hp on Nortons when done right. Win Win. I'd scan search BMW forums for insights of what's been done.
Click to expand...

Cheers Hobot, BMW airhead forums are a waste of time for modifications, the depth of knowledge on this one is great.
Running no crank valve means that I have to watch the oil level as too much and bottle fills up pretty quick....
I can't find out much about modifying heads on any BMW forums but here you get flow charts and everything.
 
Back when, the Butler & Smith BMWs ridden by Reg Pridmore and others had huge reed valves; they used Yamaha two stroke reeds, IIRC.
 
Have a look at a late'ish model 2 valve (air cooled) Ducati reed valve.
You'll have to turn up a alloy fitting for the end that screws into the Ducati crank case to accept your breather hose.
Fit it as close to the cases as possible.
They have a small hole between the two reeds to allow oil to drain back to the cases when the engine is off and to allow the oil to be drained. This hole can be easily blocked if needed. Cheap on eBay too.

Graeme
 
72Combat said:
I've been running my race BMW with no valve, just a hose and a catch bottle.
Both pistons rise and fall together so for all intents an purposes its like a parallel twin.
My BMW former engine reconditioner mate is dubious about how it will work at 7500 rpm...?
I bought one of the Mikes Yamaha type ones and are going to fit it to the top of the motor breather hose then to the bottle.
Theory I have read is that when the pistons fall they are having to pump air out of the crankcase.
I read claims on a Triumph forum of butt dyno horsepower increases, hmmmm
Any thoughts from the panel? :mrgreen:
Click to expand...

I use the normal BMW reed valve on my 1070 bike that produces a lot more power than standard. I would not see any reason to start mucking about with Yamaha PCV valves, because you have a perfectly usable one fitted (assuming that your bike is post 78 or thereabouts, and if you do have the earlier valve it is SOP to fit the later reed valve, especially if you are improving the performance of your engine.
 
chasbmw said:
I use the normal BMW reed valve on my 1070 bike that produces a lot more power than standard. I would not see any reason to start mucking about with Yamaha PCV valves, because you have a perfectly usable one fitted (assuming that your bike is post 78 or thereabouts, and if you do have the earlier valve it is SOP to fit the later reed valve, especially if you are improving the performance of your engine.
Click to expand...

Hi, its a 73 with the poppet valve. I have a later case on the shelf but they don't look to be reverse compatible.
This thing gets thrashed, I have the rev limiter set to 7500 and thats when I change up.
I've fitted the yamaha one as it was cheap so will see how it goes in a couple of weeks.
Was planning on building up a larger motor but got sidetracked by the 500 one. :mrgreen:
Your motor sounds interesting.
 
I'm fairly sure that the reed valve will fit into the earlier cases.....

My engine is based on a 82RT, engine wasbuilt up by Jim Cray, with seibenrock 1070 kit, dells, twin plugs etc etc. it goes well, if had the bike since 93, and it has gone through a few changes.
Crankcase PCV
 
I've seen your bike on ADV rider , nice.
I've collected lots of bits for my Mk2 engine, and was looking at Richie Moore pistons.
I got some D port R80 heads which I gather are the ones to use.
 
I've never dealt with Ritchie, Jim is a bit more old school, does not do the internet, phone calls only. I like him,and his work is good. he started off tuning Nortons........one of his race engines is still doing good work in the hands of Pommie John.
 
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