Blowing Oil Out OF Oil Tank

[bikertucker]

Just purchased a 1975 cb750, all seems well except it is soaking the right rear of the bike
with oil. Have found it is flowing from the lower (what looks like a vent ) on the back
of the oil tank. Zip tied a sandwich bag to the hose attached to this (vent?) and in an eight
mile ride collected about 2- tablespoons of oil in the bag. My maint. book gives no
info, so hoping someone here could help.

Thanks

Tim

[shinyribs]

If you connect that hose to the ranny case breather you will be fine.That way it will recirculate the oil vapor you are seeing now,instead of just losing it. The nipple for the tranny breather is in the very rear,center of the engine.Right above the swing arm pivot. It's a little tough to get at,but that will cure your problem.

Of course,the engine does have to breathe somewhere. The breather nipple on the top of the vlavecover can vent to atmosphere,and then circulate the oil tank back into the tranny and you'll be good to go

[bikertucker]

Thanks for your prompt reply shinyribs. That sounds like great news to me. Will route and connect
hose as soon as I'm able tomorrow.

[shinyribs]

Glad to help.

[bikertucker]

Routed the hose to the tranny vent and all is well. took a 20-min ride and right side of bike was
free of oil. Back tire nice and dry. Of course I have to ask. What could be causing the oil
tank to vent so much oil? If I had wanted to ride for the afternoon I would have run out of
oil long before I ran out of a tank of gas. This bike sat in a shop close to a year and a half
dissembled. To include the engine, parts being stored in four different containers. All was
assembled together by me. Did I miss something, or did a componet get tampered with?
Orginal problem was transmission slipping out of 2nd, and third gear. Still slips out of 2nd.

Thanks

Tim

[shinyribs]

Normal for that tank to vent like that. I have a clear hose on mine and once the bike is good and hot,and the oil is flowing freely,I can just watch it run through the hose.


BTW,thank you for bringing this up. I had a mystery oil leak myself. You question jogged my memory and caused me to go fix my bike. I had the exact same issue as you LOL


I cant help with the gear slips. Both of my bikes slip out of 4th. I mentioned it to my Dad the other day and he said all four of his CB750's did that. And he was buying them off the showroom floor!

[bikertucker]

Once again, thanks for the info. This engine had no vent hoses when I first saw it. Thought the oil tank
hose in question was just a vent like the crankcase vent hose, and that blowing oil was a symtom of
another problem. Now understand this is normal, and factory hose is made to attach to transmission
nipple. The xmission gears slipping sucks. I've heard having them undercut solves the problem.
Can you verify that info? When I put the transmission together all looked ok. It slips out of 2nd every time
while upshifting. But when down shifting it's solid. Even when downshifting fairly hard, it stays in place
and works normal. Seemed undercutting the gears might be valid.


Tim