crankcase breather blowback

[chrs4757c]

Hello,

I ride a 1997 1200 sportster with 1400 big bore kit upgrade. Runs great except it is pushing oil back thru the crankcase breather when hot and is at it worst at highway speeds.
I've heard this could be due to a faulty seating of the oil pump check ball but I would then expect wet sumping to occur which does not.


This seems a common problem on earlier (pre 1980) models but unusual on the evos.

I'd appreciate any suggestions.

Chris

[Phil]

I presume you mean the breathers on the heads.
This can be due to a couple of reasons: The breather `Umbrella` valves may have got dry & stiff, not allowing them to seal.
Oil may be pooling in the rockers then blowing through the breather.
You can space the umbrella valves a little higher which will stop the problem. There are a couple of kits available to do this.
This may help;
MKL's Harley-Davidson Sportster 1200 Custom - How to Deal With The Oil Blowby Phenomenon

[chrs4757c]

Phil - Thanks for the response. I don't think its the blowby problem. There is a tube situated to the rear of my back
pot joined to a nipple right on the inner engine casing.
This is where the blowback is originating from. I had the compression tested recently as leakage here would have been one explanation for excessive pressure at the crank. But this was fine.

Does anyone know what would be the pros/cons of routing this pipe back to the oil tank and providing a breather at the tank end?

Chris

[HOG maniac]

My Evo has been blowing out oil for quite some time. I have fitted a breather kit as it made a mess on the bike.

[Sportsterboy1974]

Originally Posted by HOG maniac

My Evo has been blowing out oil for quite some time. I have fitted a breather kit as it made a mess on the bike.

Mine too...i have recently replaced the umbrella valves but still find that the bike is using up quite a lot of oil when ridden fairly hard. I also use a breather kit. I recently did a 1200 conversion using KB pistons and have put about 1000miles on the bike since. My mate said that the oil usage was maybe due to the bike running in? It's definetly losing most of it from the breathers and gets worse the hotter the bike gets. I put about 400 miles on the bike this weekend and was riding 80mph plus on motorways for long periods..the air was hot! I reckon it must of used almost a quart of oil! That seems excessive to me! I would be interested if Phil could explain about spacing the umbrella valves...what does this involve? Cheers

[HOG maniac]

Min also only done it when Running hard or at constant Motorway speeds.

I have not noticed any oil running out of my Breather filter.

I only had a small amount coming out of the air filter but it made a mess of the battery cover.

[chrs4757c]

Same problem - highway speeds/hot weather are the worst.

In the meantime I did some reading around and am about to try one suggested fix -a one way crank breather - the argument being that the extra unwanted air drawn in by the breather on the compression that then needs to be expelled out the breather on the power/intake stroke thereby circumventing the air fogging issues. Its cheap so I'll give it a shot and report back to the list.

part no. JP cycles #400-538

Chris

[Hawkeye]

I had one of these breathers fitted to my FXR, it made a right mess.
My solution was to run the breather pipe up high say under the tank or seat then drop it down low on the pipe side.

For me this was the cure, i did have a little oil come out but that was my fault for putting a little to much oil in the tank.