Crankcase breather

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ScottMDMC

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Oct 1, 2012
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Hey Guys,
I have a 75 MK3 and have been reading about installing a reed valve breather to reduce engine leaks. Is this a special part or can I pick up something at the local auto parts or bike shop? Does any one have pics on what it entails?
Thanks, Scott
 
Pretty dang good, and affordable, especially for '74 & 75

Crankcase breather


$25 + postage. I have 4 of them on the shelf
 
Hmmmm...

Looking at the backside of the timing case, I see our two cases are different in the casting in that area. Mine is smooth above the horizontal casting line, yours has a hump shape casting...

Maybe this is a slight difference between an earlier and later casting; I wonder which is which?
 
Scot,
I use the valve that goes on a ford brake booster. Works great and cost about 5 bucks. Also it's ends are at a 90 deg angle so it fits better and the diameters of each end are correct. Forgot with year ford but I believe any 70s model will do.
 
Hey there scottMDMC, I got mine from a fellow forum member (comnoz) orJames Comstock of the nortonmachineshop.com , it may not be the cheapest but it is a really well made option that is out there and available for us. Cj
 
I installed Jim Comstock's sump plug breather - great product if you aren't/don't want to spit the cases.

Crankcase breather
 
+ 1 on this. vent it at the source NOT some convoluted path through the few small holes in to the timing chest than out .

steelcap said:
I installed Jim Comstock's sump plug breather - great product if you aren't/don't want to spit the cases.

Crankcase breather
Click to expand...
 
steelcap said:
I installed Jim Comstock's sump plug breather - great product if you aren't/don't want to spit the cases.

Crankcase breather
Click to expand...

+1.

Vent at the source... screws straight in... no mods or other work required... works great...

What not to like !?!
 
I don't have room for most of those types since the e start sits right there. Looks like I will probably use the ford part and tuck it underneath where the air box was. Thanks for the info.
 
kommando said:
The large breather screws into the sump and replaces the sump filter.
Click to expand...

how much are they, are they comparable in performance to Jims other one or do they give up a bit
 
Apparently BMW did a bit or research into crankcase breating many years ago and ended up using a single reed valve. About the diameter of a UK 50 p piece but thicker. In the 1980s we incorporated on into our very cheopo 68 x 68 500 Dommy mounted on the top of the timing chest running the output back into the oil tank. Upon start up the reed clicked away merrily over the first few engine revs then settled down to the odd click every now and then due to blow bye on the rings ????. The pressure pulses being fed back into the top of the oil tank would indent the surface of the oil a couple of inches or so beneath the entry pipe...it amazed me the first time i watched it happen.
Of course a very cheap idea that apparently works very well is to run a say 3/8 -1/2 inch breather pipe directly into a screw cap oil tank and shove a very small hole in the screw cap. at engine start up the compression in the cases pressurises the oil tank forcing some of it out through the small hole...as the pistons go back up trying to suck air back in the small hole allows very little back into the oil tank...over a few engine revs everything settles down......Cheap and easy as I believe used by Triumph at one time and recommended by Quiet Power Drive in the USA for a great many years for use with their dry running primary belt systems for BSA and Triumph motors etc.
Worth a read is the section on crank case breathing in the book 'Tuning BLs A Series Engine' by Mr David Vizard ISBN 0-85429-732-4. Page 397. You dont even have to buy the book... borrowing books for free is what libraries are for which, if we dont use them will soon no longer exist.
 
"Apparently BMW did a bit or research into crankcase breathing many years ago and ended up using a single reed valve. About the diameter of a UK 50 p piece but thicker."

100 % agree. Used one for many years on Dominator 500 race bike and never leaked a drop of oil.

On the race bike used three breather pipes. 1 off where the generator used to mount, 1 off the original breather on the nearside crankcase at the back, and 1 off a tappet cover. Plumbed all three together and then through the BMW reed valve to a bottle. Got less than a 1 ml of oil every meeting in the bottle.

With Castrol R oil you must blow a bit of brake clean through the valve every few meetings otherwise the oil will "glue" it shut.

This is a photo of the reed valve and a small chamber I made on the lath to mount it in.

Crankcase breather
 
J. M. Leadbeater said:
Apparently BMW did a bit or research into crankcase breating many years ago and ended up using a single reed valve. About the diameter of a UK 50 p piece but thicker. In the 1980s we incorporated on into our very cheopo 68 x 68 500 Dommy mounted on the top of the timing chest running the output back into the oil tank. Upon start up the reed clicked away merrily over the first few engine revs then settled down to the odd click every now and then due to blow bye on the rings ????. The pressure pulses being fed back into the top of the oil tank would indent the surface of the oil a couple of inches or so beneath the entry pipe...it amazed me the first time i watched it happen.
Of course a very cheap idea that apparently works very well is to run a say 3/8 -1/2 inch breather pipe directly into a screw cap oil tank and shove a very small hole in the screw cap. at engine start up the compression in the cases pressurises the oil tank forcing some of it out through the small hole...as the pistons go back up trying to suck air back in the small hole allows very little back into the oil tank...over a few engine revs everything settles down......Cheap and easy as I believe used by Triumph at one time and recommended by Quiet Power Drive in the USA for a great many years for use with their dry running primary belt systems for BSA and Triumph motors etc.
Worth a read is the section on crank case breathing in the book 'Tuning BLs A Series Engine' by Mr David Vizard ISBN 0-85429-732-4. Page 397. You dont even have to buy the book... borrowing books for free is what libraries are for which, if we dont use them will soon no longer exist.
Click to expand...
My library has dumptruck loads of feel good fairy tail books for kids and their mommies, but no motorhead literature to be found. Not even a copy of ANY motorcycle periodical.
 
" My library has dumptruck loads of feel good fairy tail books for kids and their mommies, "

OK :lol:

I can't agree.

A bit more of a somewhat annoying confession.

MY Dommie race bike will leak oil !!!!! If it is parked up for a few months and wet sumps. About half way up the cranckcases at the front joint there is a leak which I have tried to fix twice with no success. So if park it and you let the cases fill up to this point it will leak oil pretty badly.

But when it is racing with the BMW reed valve working there is not even a mist of oil at this point. For the last two seasons we ran with a full Peel Mountain mile type faring with a bath catch right under the bike. No oil ever seen under racing conditions.

So I am a really big fan of the BMW read valve. Very cheap. Almost no engineering to fit and won't leak while running even when there is a leak from the cases while parked !!!!!

The only downside is that it offends the purists because there are a few extra pipes running here and there.

How clean is this ?

Crankcase breather
 
johnm said:
"Apparently BMW did a bit or research into crankcase breathing many years ago and ended up using a single reed valve. About the diameter of a UK 50 p piece but thicker."

100 % agree. Used one for many years on Dominator 500 race bike and never leaked a drop of oil.

On the race bike used three breather pipes. 1 off where the generator used to mount, 1 off the original breather on the nearside crankcase at the back, and 1 off a tappet cover. Plumbed all three together and then through the BMW reed valve to a bottle. Got less than a 1 ml of oil every meeting in the bottle.

With Castrol R oil you must blow a bit of brake clean through the valve every few meetings otherwise the oil will "glue" it shut.

This is a photo of the reed valve and a small chamber I made on the lath to mount it in.

Crankcase breather
Click to expand...

That is a great idea. Small and simple. There has to be a market for it.
 
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