Atc90 Crankcase Pressure Problem. Sorry, no its not a monkey.......

[hxr400]

Ive just got the engine back together & in my 74 ATC90 after fixing a couple problems.

But now I have a crankcase pressure problem. If you run it for a few seconds, then turn it off & take the dipstick out, allot of air pressure comes out.

If I leave it like that it will blow a gasket So do you know where the crank case breather is? We have never had this problem on any of out ATC's & dont really know where to start looking. Its just a pain cause everything is all back in finished. Dont want to take the engine out again. But, we have to fix this......

On more modern bike engine's they have a big crank case breather hose sticking out the top of the engine. But this is completely sealed.

If we cant work it out we could just make a breather pipe that fits into the inlet tappet cover. Screw a small fitting into the center & have a rubber breather hose go up & hide it away. That will solve the problem. But its not fixing the problem.

What do you reckon?

Thanks for you help!!

 

[Sidney]

Theres meant to be one on top of the engine.....

 

[hxr400]

Theres meant to be one on top of the engine.....

Ment to be what? A breather hose?

Nope, no breather hose here.

It has to be something internal.

& my guess is somewhere here.

(ignore the broken case next to the sprocket shaft. I have replaced the case)

 

[corey58]

it could be the top head gasket on my 4valve it not quit sealing leting the buring gasers (not alot cos my bike has apout 170+and it was only down to 150 so jst a very little) bipass in tho the sump puming oil out everwhere

 

[orion125proseries06]

i have one too, only its a 75-76 model, ive looked in the manual and talked to dad and there is no crank breather hose, if there is one it will be on the other side, but there wont be one.

and if you have the bike running and u take the dipstick out of course thee will be pressure, and same if you do it st raight away after running it

 

[hxr400]

I think we have worked out the crankcase pressure problem.

We have found the breather hole. It was a big help having the spare engine case to follow through the oil galleries through & find the breather.

Here are a few photo's of where it is. The first photo is of the case. That hole lines up with the left engine cover, this passage goes down to the bottom of the cover & exits.

So the problem must be that the gasket is covering that hole between the case & cover. Or something is covering it. I dont think its blocked with rubbish, cause we poked a bit of wire up there & it was clean. It seems like something solid like a gasket. I will drain the oil & remove the side cover next week end & suss it out.............Nothing is ever easy is it!!

 

[hxr400]