Reducing crankcase pressure

[Chris in NC]

I've been thinking about figuring out a way to decrease the amount of internal pressure inside the crankcase of my '08 T100, and my son's '02 904cc Bonnie. Both bikes tend to blow excessive amounts of oil through the breather tube.

The latest issue of Cycle World and Motorcyclist magazines both show photos of Norman Hyde's "Hyde Harrier", and in both magazines you can see what appears to be an external braided hose coming out of the upper side of the primary cover. I have to assume it's there to allow the engine's internals to breath better.

I'm thinking that a low-buck solution might be to take stock oil filler cap, cut a hole in it (say 1/2"), weld a 1" 'tube' over the hole, making sure that the inside diameter of the tube is the same diameter as the hold in the cap, install a 1/2" diameter hose over the tube, clamp it tight and run it toward the rear of the bike.

I can't help but think that increasing the cc's in a Hinckley Bonnie motor, or running the dog-sh!t out of one for extended periods, causes the internal pressures to blow excessive amounts of oil out through the stock (small) breather hose.

Any thoughts or comments on whether this is a viable solution to a simple problem, or is there something already out there that will fit the bill.

Thanks ahead of time for your words of wisdom.

 

[nigel]

I saw the "Hyde Harrier" at a show in England in September 2010 and spoke to Norman Hyde about the breather, the 1st harrier he made had an early 790cc engine which has a much smaller crank case breather, this was pressurising from the big bore kit hence the modified cases , it's not pretty , but it was his 1st atempt, might be worth looking at his website and seeing what he suggests, another English tuner getting good reasults is "Bob Farnham" not sure who does things your side of the pond?
Good luck.

 

[TC_Dick]

run the breather into a small reservoir, angled so the oil can drip back down the hose.

problem = solved

 

[Bonniebret]

Sounds like a visit to Rex is in order.

 

[sweatmachine]

You should be able to drill a hole in the oil fill cap, and get some kind of screw on hose barb that you could slip the hose over instead of having to weld a tube onto it.

It'd also be neat to machine a whole new oil fill cap with a hex head (instead of the slot), with a hose barb machined all in one piece. I'd buy that in a second.

 

[ivar]

over on the 'other site' , there's a thread called "winter dyno fun" by tonna, he claims 5-10HP with his hi-performance breather setup.

In that thread, I also read that the early cases had a 6mm breather hole, newer has twice the diameter (and 4x the capacity)

 

[sweatmachine]

ok here is Bill Gately's solution:

Vent The Crank To A Canister And Then From The Canister Back To The Oil Filler Cap. Simply Machine The Filler Cap To Accept A 1/8 Pipe X 3/8 Barb Fitting And Place A Similar Open Drain Fitting On The Bottom Of The Canister.
They Run Great And Stay Dry As A bone.

and here's a picture of a vented fill cap:

 

[sweatmachine]

over on the 'other site' , there's a thread called "winter dyno fun" by tonna, he claims 5-10HP with his hi-performance breather setup.

In that thread, I also read that the early cases had a 6mm breather hole, newer has twice the diameter (and 4x the capacity)

that thread is pretty funny. I'd highly recommend reading the entire thing.

 

[nohawk]

I have been wondering about that HUGE hose on the clutch cover of the Hyde bike. Figured it was some sorta vent, Ive just got my vent hose routed into the old k&n air filter in my chopped up airbox with an old rag stuffed in the filter around the hose. cheap bastard.

 

[Aussie_T100]

Crankcase ventilation seems to be the subject of the week on quite a few forums. It's not as straight forward and clear cut a science as it would first appear though:-

http://bunnbreather.bigblog.com.au/index.do

If reading that lot doesn't get you thinking nothing will. :d

 

[Texas94fs]

I have been wondering about that HUGE hose on the clutch cover of the Hyde bike. Figured it was some sorta vent, Ive just got my vent hose routed into the old k&n air filter in my chopped up airbox with an old rag stuffed in the filter around the hose. cheap bastard.

I like the way you think. It's cheap and it works. It's also the same exact fucking thing I've done.

 

[mikenva]

if its blowing oil something is not right in the motor .If its a old style block the seal might be bad. The only times any of my motors have ever blown oil was with the 988 do to it leaking inside the steel sleeve motors have trouble with that .my stock 790 never blew oil 904 tpusa didnt ether my 1087 dont ether.The stock breather is big enough but not if you have blow by and no breather will cure that.When the motor is right theres no real pressure on the breather tube it just kinda flutters in and out.
If you compare the size of the hoseon your bike to a v8 car its bigger per CI then the car. There is allso lots of room in the motor the crank case and trans are one in the same trans part is not even close to full.

 

[nohawk]

Broke minds think alike Matt!
Mikeinva, what's the difference between the two blocks?

 

[mikenva]

on the old block the breather has a seal that rides on a thing that is bolted to the end of the crankshaft. The newer blocks just has a nipple that presses into the block .The older one the seal will wear out ( the seal is below oil level ) so the tube fills with oil when the seal goes bad. The new block has the vent near the top behind a plate the block has like a box cast into it with a oil drains tube that drains to the sump.