View Full Version : Atc90 Crankcase Pressure Problem.

06-28-2008, 04:24 AM
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!!

One more thing, this whole forum site is very hard to work out where to post what. I dont know if the forum discriptions are suppose to be funny or what!? What ever they are, they sure do put me off posting here often.
Im not even sure if I have posted this in the rite one.

06-28-2008, 10:33 AM
this should be in trikeslvainia

presure in a 90 bottom end is normal... this is why they used to make aftermarket vent kits that screwed into the dipstick hole and it came with a longer dipstick.

what i have done in the past is to instale a air stem (like in a wheel) in my clutch cover and i took the valve out of it and ran a hose to the ground

06-29-2008, 04:12 AM
Ok sorry for posting this in the wrong forum............

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!!







06-29-2008, 04:23 AM
yeah thats the vent but like you have found out its tough to get it to work