Royal Enfield 350 bullet crankcase breather modification

[stinkwheel]

I'm documenting this here because there isn't much info on the problem out there and it's hard to find. Hopefully anyone with a late model 350 Royal Enfield bullet which is burning oil and needs a crankcase breather modification will find this page.

This has caused me no end of greif and has consumed a frightening amount of oil over the last few years.

In order to get the last batch (2007/08) of original style carburetted, pre-unit Bullets through Euro emissions tests, they modified the crankcase breather so instead of it being on the crankcase, just below the barrel on the left hand side, it was on the oil tank.

On my 2007 one, not even the casting for the original breather was still present. This eliminated the inconvenient fumes being vented by the crankcase breather but failed to fulfill its intended purpose.

Notwithstanding the fitment of a catch-can and all manner of pipework to recirculate any oil vapour that was breathed out, by the time any blowpast fumes have got as far as the oil tank, they have already deposited a whole load of water vapour inside the engine. The one way valve (a rubber duckbill) also can't respond fast enough to changes in crankcase pressure and maintain a slight vacuum.

Net result, the piston descends into a slight pressure, any oil hanging about on the cylinder walls is forced up past the piston rings and is burned in the engine. Really environmental. It burned so much oil that the carbon particles destroyed my exhaust valve.

On my one, this meant the oil would be black within 20 miles of changing it and I would have to check the oil level as often as every 120 miles, in which time it could do a length of the dipstick. It could use a litre of oil every 350 miles if pushed.

So. I drilled a hole in my engine.

Literally. While I had the barrel off, I slowly and carefully drilled a pilot hole and took it out to 11.5mm, being careful not to get any swarf on the inside of the engine. I'd suggest sticking a big dollop of playdough on the inside where the hole will come out.

I then tapped the hole out using a 1/4" BSP tap and screwed in a 1/4" nipple whick I loctited and sealed with a fibre washer. I attached a 1/4BSP to 8mm compression elbow to the nipple and a piece of copper pipe running up along the back of the engine.
https://i48.photobucket.com/albums/f216/stinkwheel/distributor/CIMG1319_zpsa2ba5b70.jpg

The pipe should be as near vertical as possible to allow any oil to run back down. I used copper to a) Prevent melting and b) Transmit heat to stop any water vapour condensing.
https://i48.photobucket.com/albums/f216/stinkwheel/distributor/CIMG1318_zps7827d360.jpg

After it reached the level of the head-steady, I changed to 8mm ID silicone hose. This feeds into a bog standard diesel fuel line non-return valve (red circle) tucked neatly under the saddle.
https://i48.photobucket.com/albums/f216/stinkwheel/distributor/CIMG1321_zps7225fd8d.jpg

Then I ran the hose back along the bike to exit off the end of the back mudguard. The more fastidious may want to use a catch-can they empty periodically to stop it "marking its territory" with a small drip of oil emulsion when parked.
https://i48.photobucket.com/albums/f216/stinkwheel/distributor/CIMG1322_zps220d3c94.jpg

I removed the catch-can assembly from the factory setup, blanked off the stub into the timing chest which normally returns oil from the catch can and left a standard duckbill breather hose on the oil tank breather as insurance against the new breather becoming blocked.

Proof of the pudding. The factory fitted breather doesn't breathe at all. A steadily pulsing blast of gas comes out of the new breather (WAY more than comes out of the oiltank breather if you cover the end.

The oil is still clear 600 miles post oil change and I can now go out on a run without having to carry a bottle of oil. 400 miles the other weekend and still on the dipstick.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[blurredman]

Nice one.
____________________
CBT: 12/06/10, Theory: 22/09/10, Module 1: 09/11/10, Module 2: 19/01/11
Past: 1991 Honda CG125BR-J, 1992 (1980) Honda XL125S, 1996 Kawasaki GPZ500S, 1979 MZ TS150.
Current: 1973 MZ ES250/2 - 18k, 1979 Suzuki TS185ER - 10k, 1981 Honda CX500B - 91k, 1987 MZ ETZ250 (295cc) - 40k, 1989 MZ ETZ251 - 50k.

[pepperami]

Quality
____________________
I am the sum total of my own existence, what went before makes me who I am now!

[chris-red]

My dad's 60's Trophy had the oil overflow pipe over the chain, an early scotoiler
____________________
Well, you know what they say. If you want to save the world, you have to push a few old ladies down the stairs.
Skudd:- Perhaps she just thinks you are a window licker and is being nice just in case she becomes another Jill Dando.
WANTED:- Fujinon (Fuji) M42 (Screw on) lenses, let me know if you have anything.