Topic: Think my main output shaft seal is blown, she won't stop leaking :(

[killersoundz]

My cb750k4 has a major artery rupture. I thought it was the chain oiler for a long time but  tightened it up as tight as it goes, even took the whole bolt out and tightened the little center screw up and then put the bolt back in. All seemed ok after the first ride it wasn't really leaking at all but after leaving it sit over night it's still flowing oil out down the chain and kickstand.

After I originally got this motor back together it wasn't leaking at all and this has just gotten progressively worse.

PLEASE tell me you can replace the main output shaft seal without having to split the cases or even take the motor out?

[brandEn]

Although I have never done it I know it can be done. Try a forum search I know I have read about people using a couple screws screwed into it in order to remove it.

[nccb]

did the chain oiler have the rubber sleeve still intact when you pulled it out?

[MCRider]

did the chain oiler have the rubber sleeve still intact when you pulled it out?

Right. And even if it does, there is not an "off" setting. There is only a "less" setting. I'd confirm the oiler is shut off. Screw a plug (spark plug with the ceramic broken off) in to be sure.

[70CB750]

Correct, the oiler will leak even at the all the way in position.  You have to replace the poiler with some kind of a plug to stop the oil.

The main shaft seal actually came out on me when I got the bike, I cleaned it and put it back in and stayed there ever since.  It is easy to take the seal out if you don't have to reuse it.

[lucky]

You can replace the seal without taking the engine apart.
Also if your crankcase breather is not working it can cause the seals to blow out or leak.

Make sure your crankcase breather is not plugged up. Otherwise seals will have too much pressure on them.

When the piston is on the down stroke air is trapped under the piston and that air pressure must have a way to get out. Crankcase breather.

[Dream750]

The 1969-75 CB750 K bikes had three different styles of chain oilers. Diagram group numbers 18 and 25 have the earlier type and cannot be fully shut off. Group number 10 applies to the OP and his K4. This type can be shut off if desired by turning the adjusting screw clockwise until it gently bottoms out. This is assuming all the parts are present and in good working condition. The problem now is, that many of the oiler replacement parts are no longer available from Honda. The often messy chain oiler was eliminated altogether with the introduction of the 750 K6.

Joker Machine offers a machined plug when looks are important.

http://jokermachine.com/products/cafe-racer/honda-cb750-parts/cb750-chain-oiler-plug.html


(click on diagram for larger view)

[MCRider]

Dream: we had a thread on this a few weeks ago. The adjustable oiler will not adjust to a fully closed position. No matter how far you crank the screw it will still pass some oil.

Several of us posit the Joker part does not appear to be long enough to cut off the flow either, though that should be confirmed.

That is why i mentioned the spark plug. The long thread of the "E" plug is long enough to reach in and cover the oiler hole.

PS: I just called Joker and while he (clerk) couldn't confirm it first hand, he says he never had one returned. So it probably works. Machinist not available at the time.

[70CB750]

I got M14 die on my list for the next time I am placing order at Enco, will make an aluminum plug with o-ring to seal it for good.

[Dream750]

Dream: we had a thread on this a few weeks ago. The adjustable oiler will not adjust to a fully closed position. No matter how far you crank the screw it will still pass some oil.

Several of us posit the Joker part does not appear to be long enough to cut off the flow either, though that should be confirmed.

That is why i mentioned the spark plug. The long thread of the "E" plug is long enough to reach in and cover the oiler hole.

MC, perhaps our experiences are different and I stand by my unedited post.

My 750 K4 oiler has the all parts in the diagram (group 10) and is fully shut off. If part #14 is deformed and/or damaged from being too tight, then it will leak as it’s made from soft rubber then a replacement will be needed. Ask me how I know.   

The short-looking Joker Machine plug does in fact work as it requires a sealer to fill the output shaft cavity before installation.

The spark plug trick you suggested is really the best solution so far, when its hidden by the sprocket cover.

I got M14 die on my list for the next time I am placing order at Enco, will make an aluminum plug with o-ring to seal it for good.

Having more options is always a good thing, looking forward to seeing your new plug!

[MCRider]

Dream: If that's your experience, sounds good to me.    Maybe mine was futzed up.

[Bru-tom]

its self lubricating itself

good luck with the ifx

[killersoundz]

Thanks for the valuable info guys, I'll take a closer look at it and try to narrow down the issue. Curious to check out my crankcase breather as well. I'll post a pic of my oiler.....it doesn't really look like whats in the diagram, sort of but not sure

[seanbarney41]

Also, have you fully cleaned and checked the case for cracks  around the sprocket?  I had this same problem.  Stopped up chain oiler did not fix it.  New main shaft seal did not fix it. (yes you can remove that seal without splitting the cases.  You just have to screw a couple drywall screws through the sheetmetal of the seal and pull/pry it out...although, I have read on here that certain years have a lip that prevents this.  Sorry, don't know  what years.  My k1 didn't.)  JB Weld over the crack in the case fixed it.