CB450 Blowing Oil From Vent

S

Skyeye

Life 1/4 mile at at time!
Good morning everyone! I've been working on cars with my son and haven't been wrenching in bikes for some time, riding yes, wrenching, no.

Now I have a problem. I'm working on a 1973 Honda CB450 that I brought back from 8 years in storage. It's been running great for about a year. Yesterday it started blowing oil out of the vent tube, lots of oil.

I'm stumped, this is a wet sump engine and all the oil passages are internal. It looks like the cam chest is filling up with oil and coming out the vent.

Any ideas?

Skyeye
 
Skyeye said:
It looks like the cam chest is filling up with oil and coming out the vent.
Click to expand...

Methinks you just solved your own problem. Time to pull the head cover off and make sure the oil drains are clear.
 
Even if they were plugged, wouldn't the oil make it back down to the sump through the path the cam chain uses?

If it were me, I'd pull the breather cover off the top of the head and take a look. Possible damage to the breather separator?
 
Sonreir said:
Even if they were plugged, wouldn't the oil make it back down to the sump through the path the cam chain uses?
Click to expand...

I'm not sure. That might make the oil be in inch deep or so before it was high enough to drain into the opening for the chain. (I haven't been inside of one of those engines, so I am not sure if there is a raised area around the cam chain opening.) Even if the oil drains, an elevated level in that chamber could make a lot of oil get slung up against the vent opening.
 
If it is BLOWING oil out, check your compression on each cylinder. You could have broke a ring and that is causing blowby through the vent.... :'(
 
Yeah there is a baffle/separator plate that that should keep the oil from being THROWN out of the vent. The cam chain passage way is very large, big enough to loose a 10mm wrench or two and actually slopes DOWN into the head, no ridges to hold oil back.

The only way I could say that you could be blowing oil out of it is if you have a mechanical failure like loss of compression or the baffle plate damaged or missing.

Well, unless it is GROSSLY overfilled with oil.
 
Even then, I don't know how you'd get that much oil into it. The only way I could even think of is to pour it in through the head, somewhere. The oil filling location is lower than the bottom of the stroke.
 
frogman said:
Well, unless it is GROSSLY overfilled with oil.
Click to expand...

I didn't go there, assuming the owner knows better, but it does warrant mentioning. I have had two bikes in my shop for no reason other than they were overfilled with oil, and blowing it out all over the place.
 
Guys,

Thanks for all the suggestions.

Here's what I have so far

1) I did the oil change two months ago so I know it was done right and no problems until now. Probably 500+ miles since the oil change.

2) Just did a compression check and got 80 psi in the left cylinder and 100 in the right. Seems low but it is enough to show blown rings?

Skyeye
 
Looks like a top end rebuild is in order. Thanks for the help.

I'll take lots of pictures and post the rebuild. Hope to start in a week or two.

Skyeye
 
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