front sprocket seal replacement

[mycrew]

Hi Guys, I just joined this group. I have a 79 CB750k that I bought in the summer to restore and ride.
I have just got my collector plates and noticed a small oil leak when I finished riding. I bought some new seals for the
shifter anf the front sprocket. I pulled the side covers off and had no proplem changing the shifter seal (it just fell out!)
but I had a hard time trying to get the sprocket seal out and destroyed the seal removing it. Now I notice that it has a lip
that has to fit into a groove. The new seal will not go in. Does anyone know a trick to get it back in or is there an aftermarket
seal that will go in? I really do not want to crack open the crankcase at this time to replace this seal.
Help me please.
Mycrew.

 

[Travis]

lip? on the seal? you shouldnt have to split the cases. Maybe try using a large socket as a seal driver.

 

[dirtdigger]

Send a picture of the lip on the seal you are talking about. I think I know what you are talking about and if it is what I think it is then you will have to split the case. Do you have a shop manual for the bike? I am in the process of getting one for my 1980 but shipping is slow this time of year. If you dont have it done by the time I get my manual I will let you know what I find.

 

[mycrew]

Hi Dirtdigger, Here is a stock photo of the seal (It is the big one)


I tried to push it in but it bent and mangled the edge of the seal. It is metal coated in rubber.
So I modified it with my dremmel and a small cutting disc. I cut the lip off from 9-3 O'clock (the top half) and ground it down.
I then pushed it in after inserting the bottom first so that the lip would fit into the groove in the crankcase and set it in with a piece of pipe and the end of a 3/8" socket extension.
I ran it in the garage in gear to look for leaks and there were none so I put it backk together and took it out on the road.
NO LEAKS!!
This will buy me some time.
thanks

 

[dirtdigger]

Glad you got it in there. That's kind of what I thought the seal was. The crank seal on the sohc 750 motors has a lip on it like that also, in a pinch you can cut the lip off and push it in. Glad you got it going!

 

[Travis]

Well at least you got it in and it doesn't leak.

 

[ryan_dynamite]

Hi. i am new to all this 'thread' stuff. but i just read this one and its the exact situation i am in right now. I am going to try cracking the case and doing it that, have tried the sneaking the seal in approach but it is still leaking, I have figured the easy way of removing the engine, it's just now opening her up and putting the new one in. Do you have any hints or tips? Sorry i am not trying to take over this thread or anything, just adding to it. My bike is however the 1982 cb750f, I can't imagine much diference though. Any help is much appreciated.

 

[mycrew]

Ryan, Before you crack open the crankcase and have to do a complete rebuild try takingn a new seal. What I did was took a dremmel with a diamond grit bit and put the seal in my vise and ground the flange off the seal. I left the bottom half or so to engage it into the groove in the engine. I have spoken to a few mechanic friends of mine and they said that I could have ground down the entire flange. The seal has a metal ring in it that comes out inside the flange so you need to grind down the metal until it is flat. I stuck the bottom in first into the groove and used a piece of 2" ABS black plumbing pipe with an od of about 2 3/8" to push it in with a rubber mallet. watch for the metal lip catching might have to grind it down all the way around the seal. Are you sure the leak is on that seal? The shifter seal on my bike is what was also leaking and it also needed to be changed.
MyCrew

 

[Cb750srule]

Yes the cases have to be split. I tried too

 

[Cb750srule]

Does the cylinders have to come off to split the cases?

 

[amc49]

No but alt rotor does if the 750-900, the rotor has a thicker backside that won't allow cases to separate fully.