Crankcase back pressure?

Spacecowboy

Spacecowboy

Club Member
Help, my old 1200 sportster is blowing oil out through the crankcase vent to the carb.
The attached photo shows where I have tried to fit a small reservoir to catch any excess oil and a small filter on top to let it vent.
I've just started the engine after a bit of a lay up and it was frothing oil out of the filter. It was running on to the exhaust and engine.
I've checked the compression in both cylendrs and they are the same and pretty good. The rings and pistons were in good shape when the top end was stripped after I got the bike.
Will this mean a full engine rebuild, or might there be some further checks. I guess blocking it off isn't a good idea for the engine seals.
 

Attachments

  • 20220320_113522.jpg
    20220320_113522.jpg
    2.7 MB · Views: 33
Sounds like it's wet sump'd after sitting for a while, ie, the oil from the tank has slowly leaked passed the check valve over time filling your sump with oil. If it's just blown most of it out the crankcase vent you might've got away with it and not blown any seals.
Someone will be along shortly with far more knowledge of Sportsters than me but hopefully your ok.
 
Thanks, I've been reading lots on the problems with bottom breather motors throwing oil into the air filters.
I'm going to try and run it for a bit and see just how much is coming out of the breather.
 
I'm on my third 1990 bottom breather Sportster and have never seen a drop of oil coming out of the breather hose on any of them.
Big twins and ironhead Sportsters puke it out regularly but the Evo has a good valve system in the cam chest
Suspect you must have had most of the oil tank contents in the sump for that to happen.
 
dodgyloner said:
I'm on my third 1990 bottom breather Sportster and have never seen a drop of oil coming out of the breather hose on any of them.
Big twins and ironhead Sportsters puke it out regularly but the Evo has a good valve system in the cam chest
Suspect you must have had most of the oil tank contents in the sump for that to happen.
Click to expand...
Cheers, I think you are right. It's just been sitting too long and the sump has filled up. I'll run it over the next few days and see if I can get to the bottom of it.
 
Hi again, ran the bike for a bit this morning.
The oil stopped frothing out of my homemade breather after a few minutes. After about 30 min, I stopped the engine and checked the oil tank. It was almost overflowing.
Anyway, emptied about a pint or two out of it, cleaned the breather filter and ran her up again.
Clean as a whistle, as they say. Chuffed to bits.
My next question is how did the oil get into the sump in the first place and what could stop this.
I reckon there must be a non-return valve somewhere near or in the oil pump that's failing.
Any info would be appreciated. 😎
 
While I can't give you chapter and verse on Evo Sportsters, having the sump fill up with oil when the bike is unused for a while has been happening for decades. The Ironhead Sportsters have been doing it since 1957. Not all of them and not all the time but it happens.
The Panheads had oil leaking back through the tappets in the fifties and in the Sportsters it went through the oil pump.
There's probably nothing wrong and the cure would be to try to use it more often and if it has stood for a while run the engine to get the oil back into the tank before toping up the oil tank. A drip tray cuts down on the cleaning up.
I have read, on here I think, that the Evo Sportster does not like the oil tank filled to the top and tends to leak if it is but this need checking.
I don't think there is a non-return valve in the system but again I'm not certain.
My Velo used to do it overnight if I'd covered less than 7 miles but not if I'd gone further, go figure that one.
Good Luck

Ron.
 
Thanks Ron. I think I've sussed it out now.
It was laid up to get some work done, which was delayed a bit. It had a little leak, but I stopped it up thinking it was low of the mark. 😕
Seems fine now. Just need to use it to pop to the shops more. 😎
 
You need to make sure then engine has been run for a minute or so before checking the oil level. Don't worry about oil in the sump, it gets pumped out pretty quickly when the engine starts.
My old Sportster never filled the sump, the current one does it after a couple of weeks.
Never fill the tank and only go to about half way on the dipstick with the bike level. Overfilling causes leaks.
 
In terms of oil height in oil tank :- There’s a breather from the crank case to the oil tank, from the back of the cam chest on my 2005 which equalises the crank & oil tank air pressure. This is why most don’t fill the tank to the high mark as oil then leaks down to the sump, through this breather, which in sporty with head breathers doesn’t help with oil being blown into the air filter especially with worn breather valves.
 
Might add that on my 2005 1200R the non return valve is behind the hollow tube the oil filter screws onto & is a 5 min fix to replace the ball, spring and hollow tube the filter screws on.
 
You must log in or register to reply here.
Back
Top