OZ ATV :: The Australian ATV Forum

[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!!

[HondaGrant]

They do have a breather I think its behind the hi / lo sub-transmission in front of output shaft sprocket (hope that makes sense ).
I had a 90 a few years back and I think I had a chain come off and it stuffed the crank case including the breather.
_________________
If a Quad is a Quad Bike,
Is a Trike a Trike Bike ????? ....

[hxr400]

HondaGrant wrote:

They do have a breather I think its behind the hi / lo sub-transmission in front of output shaft sprocket (hope that makes sense ). I had a 90 a few years back and I think I had a chain come off and it stuffed the crank case including the breather.

Thanks for the info mate!

I know what you mean about stuffing the case when the chain comes off. My old crank case had the same problem.

But I scored a 90 wreck & swaped all the good bits from it over to mine. The case was in better condition so I used it as well.

So my old case did have a broken part near the sprocket from the chain, but the new one does not, but does have the pressure problem.

Here is a photo of the old engine case.

See the broken part? Are you able to point out where you think the breather is? Save the photo & circle it in MS paint. Then up load it again if you can.

Cheers!

[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!!

[HondaGrant]

Good to hear you tracked down the breather .
I had a look at a old CT90 engine today and they have a similar set up.
Make sure the gaskets you used have the right holes in the right places and there's no sealant or any other crap blocking the holes and you should be good to go .
_________________
If a Quad is a Quad Bike,
Is a Trike a Trike Bike ????? ....

[hxr400]

HondaGrant wrote:

Good to hear you tracked down the breather . I had a look at a old CT90 engine today and they have a similar set up. Make sure the gaskets you used have the right holes in the right places and there's no sealant or any other crap blocking the holes and you should be good to go .

Thanks mate!

& thanks for pointing me in the rite direction to start with. That helped allot.

Yes I agree, I think the gaskit must on have a hole in it or something silly like that.

I asked the guy who I scored this engine case from & he said he never had a problem like that. So somethings wrong since we assembled it.

[greenhuman]

Did you put a new gasket on? Sometimes you have to poke out all the little holes for the case screws etc. Ill bet there is a piece of gasket still there, stamped but not removed. You can put in a 1/8 gas fitting in the top of the centre engine case like an ATC 110 if you can't work it out.

[hxr400]

greenhuman wrote:

Did you put a new gasket on? Sometimes you have to poke out all the little holes for the case screws etc. Ill bet there is a piece of gasket still there, stamped but not removed. You can put in a 1/8 gas fitting in the top of the centre engine case like an ATC 110 if you can't work it out.

Yes I agree, I think thats the problem.

[hxr400]

On Monday I had a sicky from work.... Got the flu. But I wasnt too sick to
do a bit on the 90 in the arvo.

So I took the left engine cover off in search for what was blocking the breather hole. But I couldnt find anything, it was all as it should be. I was a bit annoyed about that.

So I put it back together expecting it to do the same thing................... I started it up, let it run for a sec then turned it off. Took the dipstick out & no pressure! I don't know what happened there. But something had moved & it is fixed. I was pretty happy about it.

So its all fixed. Thanks for you help!