Crankcase breather & disconnected air boxes.

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andybaggies
Cucciolo - the Lil Pup
Posts: 21
Joined: Thu Nov 01, 2018 12:52 pm

Crankcase breather & disconnected air boxes.

Post by andybaggies » Sat Jun 15, 2019 12:07 pm

I’m in a right old dither on understanding the crankcase breather setup as I'm planning to junk the air boxes & put pods on the (40mm) carbs. The reason behind this isn’t just bling because I’m wanting plenty of space for a re-wire, new regulator & ignition.

From what I’ve read the factory solutions for such a setup came with bellows (750ss) or a catch tank (MHR) and both using an exit flapper valve.

I can understand the valve stopping the crankcase drawing in dirt etc but does it also have another, perhaps more important, effect on the crankcase pressure :? And I also understand the catch tank collects any oil but, again, does it's capacity have any effect on the crankcase pressure :? :? And when using the airbox I'm assuming there's a natural tendency for the crankcase pressure relief to be assisted by the induction. Again this will also be lost, thrice :?

I’m planning on doing the usual, keeping the tower and putting a vent filter on the end of the tube with perhaps a spring inside but will the lack of any pressure ‘control’ have an unwelcome effect on the crankcase pressure?

Andy B

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81mhr900ss
Mach 3
Posts: 79
Joined: Tue May 31, 2016 3:49 pm

Re: Crankcase breather & disconnected air boxes.

Post by 81mhr900ss » Sun Jun 16, 2019 8:58 pm

Hi Andy: As you may have read already, I installed a Shendingen regulator (FH020AA), a Sachse ignition and better fuse box that uses new-style auto fuses plus a little K&N filter on the end of my original black plastic pipe. My 81 MHR never had the original black plastic breather box; the vent pipe fed forward over the vertical head to a little red metal tube that was mounted to the frame. No flapper valve but never had any oil mess either.

Here's a pic of my breather tube:
Image

Take a look at the electrical section for my other pictures of the ignition and charging set-up.

Good luck,

Rick

andybaggies
Cucciolo - the Lil Pup
Posts: 21
Joined: Thu Nov 01, 2018 12:52 pm

Re: Crankcase breather & disconnected air boxes.

Post by andybaggies » Mon Jun 17, 2019 11:39 am

plus a little K&N filter on the end of my original black plastic pipe. My 81 MHR never had the original black plastic breather box; the vent pipe fed forward over the vertical head to a little red metal tube that was mounted to the frame. No flapper valve but never had any oil mess either.
On mine, a Darmah, I also had no oil mess in the old airbox so it's reassuring to know that just an air filter doesn't seem to cause any issues. It's certainly the easiest & cheapest solution. :)
Take a look at the electrical section for my other pictures of the ignition and charging set-up.
Thanks, I had a quick look at the thread but I've got to get supper sorted first before I reply. Shepherds pie tonight, nom, nom, nom :-D

Cheers,

Andy B

Peter Mille
MHR / S2
Posts: 498
Joined: Fri Aug 13, 2004 2:12 am
Location: The Netherlands, Europe.

Re: Crankcase breather & disconnected air boxes.

Post by Peter Mille » Sun Jul 28, 2019 4:34 am

Just a small K&N filter does it on my '85 Mille MHR as well.

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BevHevSteve
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Re: Crankcase breather & disconnected air boxes.

Post by BevHevSteve » Sat Aug 03, 2019 12:46 pm

Image

https://store.bevelheaven.com/Carb-Fuel ... vel-twins/
Yep, the little K&N works very well for this.
Image
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