Crankcase Breather Issue

[CaptainBillK]

I have a 1971 750 Commando. About 1.5 years ago the engine seized and destroyed the case. Luckily I found a mechanic at Fair Spares New England who specializes in Nortons. He rebuilt the engine using a Combat case. The problem is, that case has a rather robust vent behind the cylinders towards the left side. I am getting significant oil "mist" that is spewing a lot of oil. I have about 30psi of oil pressure. I was able to install a 5/8" rubber hose to it and used a cheap aftermarket breather filter - all as an experiment. It doesn't work. I'm still getting significant oil loss through this vent. I'm looking for possible solutions. It would be nice if I could vent it directly back to the oil tank, but again... that's a big hose.

 

[jseng1]

See the combat case breather solution on this page:
https://jsmotorsport.com/reed-valve-crank-case-breather/

 

[CaptainBillK]

See the combat case breather on this page:
https://jsmotorsport.com/reed-valve-crank-case-breather/

Sadly that won't resolve the issue of the vent on the top of the engine case. Additionally, the sump drain is no longer that size... it's a simple bolt.

 

[kommando]

Keep the breather body, its in the right place for good breathing. However it also allows a lot of oil out at high revs which you need to stop. So just above the breather in the rubber line fit an inline reed valve. This will allow the initial breathing on startup but the reduce the amount of air and oil once an equilibrium is reached. I will post an example shortly.

 

[kommando]

This is the one repurposed for the XS650 as a breather valve and used on Commando's, need to be mounted higher to get around the 90 degree turn.

Pardon our interruption...

You can get it in the US from

PCV Reed Valve - Crankcase Breather

Color/Finish: Silver Material: Metal Dimensions: Overall Length: 86.50mm Width (at widest point): 28.85mm Engine Inlet OD: 14.15mm Engine Inlet 11.85mm Filter (Air) Outlet OD: 12.00mm Filter (Air) Outlet ID: 9.45mm Fits: Universal Note: Easy Installation (Linked Below)

www.mikesxs.net

Its from a Chinese scooter.

 

[CaptainBillK]

This is the one repurposed for the XS650 as a breather valve and used on Commando's, need to be mounted higher to get around the 90 degree turn.

Pardon our interruption...

You can get it in the US from

PCV Reed Valve - Crankcase Breather

Color/Finish: Silver Material: Metal Dimensions: Overall Length: 86.50mm Width (at widest point): 28.85mm Engine Inlet OD: 14.15mm Engine Inlet 11.85mm Filter (Air) Outlet OD: 12.00mm Filter (Air) Outlet ID: 9.45mm Fits: Universal Note: Easy Installation (Linked Below)

www.mikesxs.net

Its from a Chinese scooter.

That looks like a great solution. Of course, they're out of stock... but, I'll wait. My only question is... I see that I can put it in the line... but, would it be better leading back to oil tank? I'm getting a lot of oil there even at idle.

 

[jseng1]

There are several things you need to do to fix the Combat oiling problem and they are described at the bottom of this page:
https://jsmotorsport.com/reed-valve-crank-case-breather/

The breather in the photo is specifically for a Combat and its a drop in kit. But eventually you still need to address the case oiling problems mentioned in the link in the above paragraph or the case can wet sump at higher RPM. You also have to plug any other case vent if there is one. You want your breather attached directly to the case so it gets warm. If you use a hose to a reed breather it can clog with foam in cold weather. Yes CaptainBillK the hose should return to the oil tank.

 

[kommando]

I see that I can put it in the line... but, would it be better leading back to oil tank? I'm getting a lot of oil there even at idle.

It goes into the current line which should be leading to the tank and so remains leading to the tank.

If your line is not currently leading back to the tank then reroute so its is as this is how it left the factory on a 72.

Part 44 goes from the breather up to the oil tank with the reducer 46 joining onto 45 to join the tank at the top. As the pressure builds its let out of the tank via 47 and enters the air filter to be sucked into the engine.

 

[marshg246]

I have a 1971 750 Commando. About 1.5 years ago the engine seized and destroyed the case. Luckily I found a mechanic at Fair Spares New England who specializes in Nortons. He rebuilt the engine using a Combat case. The problem is, that case has a rather robust vent behind the cylinders towards the left side. I am getting significant oil "mist" that is spewing a lot of oil. I have about 30psi of oil pressure. I was able to install a 5/8" rubber hose to it and used a cheap aftermarket breather filter - all as an experiment. It doesn't work. I'm still getting significant oil loss through this vent. I'm looking for possible solutions. It would be nice if I could vent it directly back to the oil tank, but again... that's a big hose.

Connect the vent to the oil tank neck - that's where it goes. You do that using 06.2617 which is standard.

Better still, install the cNw reed valve for 1972 and it will all be 3/8" hose. https://coloradonortonworks.net/1972-breather-modification.html

 

[MichaelB]

Sadly that won't resolve the issue of the vent on the top of the engine case. Additionally, the sump drain is no longer that size... it's a simple bolt.

That will blow oil forever.
As mentioned above, it was designed to be routes to the oil tank on the top fitting.
Will require the reducer as shown.
Reed valve can be fitted inline or on crankcase but is an improvement and not a fix for your issue. Route it to oil tank.

 

[cliffa]

You can get inline reed valves as well. Search on EBay for EGR valve such as this one. You would only need the bit in picture 3.

Yamaha YFZ450R YFZ 450 R Air Cut Induction EGR Valve Assy fits 2014-2021 | eBay

Fits YFZ450R. Yamaha YFZ450R, 2014-2021. 5GD-14803-00-00 AIR INDUCTION SYSTEM ASSY. Complete EGR Valve Assembly. 1TD-14840-00-00 AIR CUT VALVE ASSY. We strive for 5-Star service in all categories. exactly what you're getting.

www.ebay.com