My brothers bike consists of an early crankcase breather Evo big twin, Santee frame, Shovel four speed gearbox and oil tank. The bike has run without any problems for years but a few months back we decided to do some motor work as it was leaking oil from the base gaskets. It ended up with a rebore, hi- comp pistons, headwork, highlift cam, crane ignition and mikuni 42.
We also replaced the lifters with maddog units.
Bike runs strong BUT, after a few miles it starts to blow oil out the breather filter.
I’m not talking a few drops hear. It covers the back of the bike with oil!
I’ve rechecked the breather timing marks (steel S&S unit) and also checked the breather timing and all appears fine. Have dropped the oil level in the oil tank thinking it may have been overfull but that made no difference.
Oil pressure is good. One thing I did notice was that, with the oil filter cap removed there seems to be a lot of oil being returned to the oil tank at idle. It’s a steady stream and never seems to break up with air. Its obviously aerated but it’s a constant flow and there seems to be lots of it. Does that sound normal?? I’m suspecting there is too much oil getting to the crank or top end and the oil pump cant handle it all so it ends up blowing out the breather filter. Do Evo lifters have oil restrictors in them??? Maybe I have a bad set of Chinese lifters. Any help would be appreciated.

 

A common problem is the filter, be sure it is the filter for the evo, not the twin cam. The filter for the twin cam does cause problems on the evo. When our evo top end was done with 10:1 pistons, head work, cam etc etc I also had a problem with oil out the breather, perhaps not as much as yours. I learned to keep the oil at half full when cold helps and I installed a pvc type valve called something like a crank vent plus which helped some as well but in the end I hooked up a hose and ran it back under my bags to the rear fender - now all I get is a little oil on the end of the mufflers - I plan on mud flaps next to run the oil line further down behind the tire.

 

Hey pajoe, I've heard about that filter issue before.

Just to be clear since this is an oil issue, you're talking about the air filter and not the oil filter, right?

I'm no expert, but like you I've not heard of the filter causing that much oil to come out.

Tims, how much oil are you losing, based on checking the oil? Is it a quart in ten miles, or is it barely noticeable on the dipstick, or something in between? A little bit of oil makes a big mess.

I had an evo do that after I switched to a screamin eagle breather. Had to route the hose down between the frame rails. Turned out it wasn't as much oil as I thought. Once it purged itself it was just a couple of drops here and there.

How many miles have you put on it since the work? Sometimes someevos will get oil in the sump after being worked on or after sitting a long time and then have to blow themselves out. Makes a big mess but it goes away.

I had another evo do something like that and I had to have the checkvalve replaced - the one that's down low at the back of the engine for the oil return line, I think.

 

Hi does the amount of oil die down afterawhileor is it constant ? it could be just something lodged under the check valve so the crankcase fills up with oil when sitting resulting in a load of oil being blown out when started .
Was the motor removed from the frame when all the work mentioned was carried out if so check your oil line routing
good luck on finding and fixing the problem

 

No. There doesnt seem to be a problem when the bike is first started. On the last ride my brother said the bike was ok for a few miles at low speed but once he rides it harder, the oiling problems started again. It covers the back of the bike in oil. The bottom end was not pulled. Just the cam and the top end. Barrels were bored with torque plates but maybe its excessive piston ring leakdown or something causing excessive crankcase pressure. The oil filter is a shovel style cartridge that sits in the tank and its a new genuine filter.

 

I should have mentioned that the rebuild is no more than 100 miles old. HAd about three runs and has puked oil on all of them

 

You might want to pull the timed breather and make sure the small orifice is clear ( pulls oil from the vapor chamber) also check that there is no damage to the timed breather bore. you may want to replace the oil pump seal.

 

Don't know if this applies, found this thread:
RE: Oil pumping out the crankcase breather tube. - 8/17/2005 3:21:41 PM
His pushrods were oversize aluminum(.420dia)and were restricting flow from the heads causing the oil pumping out breather. If you put in new pushrods, I'd check this out. Also verify your oil lines are hooked up right. Good Luck.