I built a custom streetfighter with a 1186 wiseco big bore kit. The bike has about 500 miles on it now and the motor is slowly breaking in. I am having a problem where the crankcase breather is blowing out a lot of oil. It is enough that after a 150 mile ride it almost pumped out 1 litre of oil into the airbox. I have read before thet it can be caused by the overbore kit. The bike pumps 220 psi of static pressure right across the board so I know I dont have a broken ring, also it doesn't smoke a bit until the airbox takes on too much oil.I have seen a lot of built engines with a line coming out of the oil fill cap. Is this to relieve some of the pressure? Is there any way to cure this without installing a catch boottle?

sounds to me that itys not a compression issue but maybe a leak down issue.....have someone leak the motor down even new it should have no more then 12 percent ....cylinder wall finish is very imprortant on any motor if the rings havent seated within the first 10 miles they usally wont.....i would leak it down first then go from there ......it shouldent blow oil out ...ever

Sounds like you have huge pumping losses. This is normally from the pressure caused by the pistons going down and so pumping air down from their underside.

There is a way of relieving this by cutting channels in the crankcase webs between cylinders 1-2 and 3-4 but you have to strip the motor to do so.

The other way round it is to run a crankcase breather line all the way to the rear number plate where you fit an oil catch tank. Set it up so any oil will flow back to the engine.

Hey sparky I had the same problem when I built my 1216 motor, and the answer is very simple. Remove your valve cover then remove the four bolts that hold the breather cover and when you look inside you will see 1 1/4 inch hole. that small hole is through where your oil returns, well not fast enough. drill four more holes in each corner and your problem will be solved. make the holes about 3/8 size. good luck!! http://www.gixxer.com/forums/images/graemlins/cool.gif

Ill try drilling the holes and see what happens. Thanks for the help

mmm, I never have any trouble with my 1216 kit....

if youre using a top end oiler, then its my understanding that such may happen, as the oil return lines are not big enough for the amount of oil the head gets.

If not, then I'd bet excessive blowby caused by rings not broken in properly....

Im with Flaco, the bigger holes in the cover would be a
band-aid.
Give it a leak down test.

Mike http://www.gixxer.com/forums/images/graemlins/cool.gif

flaco said:
mmm, I never have any trouble with my 1216 kit....

if youre using a top end oiler, then its my understanding that such may happen, as the oil return lines are not big enough for the amount of oil the head gets.

If not, then I'd bet excessive blowby caused by rings not broken in properly....



I would love to know how using a top end oil cooler causes oil to be pumped out the crankcases?

As I said before, the bike has 220 lbs of static compression right across the board. And also it doesnt smoke at all. It cant be blowby with such good even compression.Ive been told its from the extra heat and pumping volume of a big bore kit.

then why doesnt everybody with a big bore has the same issue??? Static compression numbers are meaningless vs a leakdown test.

Extra heat and pumping? http://www.gixxer.com/forums/images/graemlins/bs.gif

Ok I cant start a new poll.... even tried a new post but no luck.... who changed the start poll option????

HOW many of you have had this issue with your big bore kits??

ONE vote for NO.

sickpup said:

flaco said:
mmm, I never have any trouble with my 1216 kit....

if youre using a top end oiler, then its my understanding that such may happen, as the oil return lines are not big enough for the amount of oil the head gets.

If not, then I'd bet excessive blowby caused by rings not broken in properly....



I would love to know how using a top end oil cooler causes oil to be pumped out the crankcases?



NOT a top end cooler, a top end oiler. Do a search, this was brought up by someone else here, not me.... was it you 317?

i agree with flaco man ... run a leak down test . thats the only way to be sure , you do not want to band-aid all the work you did .
i run the same motor 1186 with nitrous and never had this problem ..

this may sound stupid, but how much oil is in your bike? I had similar problems with my 1216 kit. I was puting to much oil in the bike. When the bike is level, the site glass should be about half way full. I also ran my crankcase ventilation hose all the way to the back of my bike since i no longer had a air box. Like i said, this may not be your problem.....

gsxrcide-

Or maybe that gasket in the rocker cover is the wrong way round so oil cannot drain back out...

[QUOTE]
flaco said:
then why doesnt everybody with a big bore has the same issue??? Static compression numbers are meaningless vs a leakdown test.
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While a leakdown test is best to check engine condition, static compression has a lot to do with blow-by. Rings seal the piston to the cyl' The higher the compression, both static and dynamic, the more air can get by the rings into the crankcase. SICKPUP is also correct about pumping loss, that's why crankcase evac systems are used. For you drag race guys, you know what that is.