Topic: Valve seals leaking a bit oil

[Chuck Hahn]

My 76 CB750A has an issue in that if it sits for a while..say a week or two.. a little oil gets past the valve seals.  I know that sooner or later the head needs rebuilt, but till that day comes that funds are available, i was wondering if there are any seal "reconditioning" products out there that anyone has used with sucess.  I also have a 77 Suzuki GS 750 that has the same issue.  The Suzuki has a wet clutch though.  Guess if anyone knows of an all around treatment thats safe for wet clutches too I would be interested in your reviews.

[madmtnmotors]

My 78 CB750K started smoking on startup. It will only get worse. I pulled the engine, removed the valve cover, cam, rockers, and cam cradles. Replaced the "coin" (6) seals under the cradles (over the head nut pockets) for good measure and replaced the valve seals (cheap). The old valve seals were baked so hard that they shattered when I tried to remove them. There is no "reconditioning" for these tiny seals that old. Started taking things apart on a Friday afternoon and I was riding (smoke-free) by Sunday afternoon. All you need is:

*Valve cover gasket
*Head nut pocket seals under the cam cradles (6)
*Valve seals (
*Blue locktite (minimum) to bolt the cam sprocket back on the cam
*New o-rings for the tappet covers would be nice
*Some want-to (hardest part)

Tip: It's so much easier to adjust the valves while the valve cover is off, so be sure to adjust the valves BEFORE bolting the valve cover back on. I've got about 10,000 smoke-free miles so far since replacing the seals. The engine is closing in on 60,000, and this is the furthest I've had to go in so far.

[raymond10078]

And, since you're working on the fabulous auto bike - you don't have to remove the engine to do the work . . . !   

[madmtnmotors]

And, since you're working on the fabulous auto bike - you don't have to remove the engine to do the work . . . !   

Oh yeah! I forgot the "A" models permit removal of the valve cover with the engine left in the frame...

easy-peasy!

[Chuck Hahn]

They do!!!   I was under the impression tht ALL cb 750s had to pull the engine to remove the cover...that will also make putting the new gasket i have on easy.  Anyone have a source for the 76 autos valve seals and a tool to remove the old ones?

[madmtnmotors]

The valve seals are common and the spring compressing tools are referenced in many threads.

This thread: http://forums.sohc4.net/index.php?topic=80787.0

References this tool: http://www.sears.com/shc/s/p_10153_12605_00915017000P?sid=IDx20070921x00003h&srccode=cii_5784816&cpncode=31-25638612-2

And this tool: http://www.harborfreight.com/universal-overhead-valve-compressor-92900.html

And a similar tool: http://m.sears.com/productdetails.do?partNumber=00947704000P

And the seals: http://www.vintagecb750.com/products/4/engine (scroll down about halfway, $15.00 for a set of 8. I'm sure they might be found for even less)

To hold the valves closed I used the hose from my compression tester, threaded into the spark plug hole, and connected to my air compressor. I actually made a valve spring compressor that was a simple 1/8" thick by 1/2" wide piece of steel bar about 14" long. Bent this into a "U" shape (about 3/4" spacing) making for a tool about 7" long. Drilled a hole through the open ends to accept a 3/16" pin. Used the rocker pivot bore in the cam cradle for the fulcrum pin, laid the "U" shaped tool over the spring retainer and levered down. Someone makes a tool like this, I just couldn't find a link to it yet. I can recreate the process with pictures if necessary, I've got a loose head** and still have the homemade tool.




**And maybe a few loose screws!     

[77Pinto]

I prefer to use a section of small diameter soft rope inserted into the clyinder to hold the valves closed.



Bill

[lucky]

I prefer to use a section of small diameter soft rope inserted into the clyinder to hold the valves closed.



Bill

Yes that works well. I used 1/4 braided nylon rope too.
I made my own tool for doing this on the CB750. Here is a photo with my alien looking tool. The valve springs have been removed.
I put a piece of tubing around the rock shaft to protect it from getting a scratch.

[Chuck Hahn]

Tjhanks for the tips and the parts links..looks like i need to order some stuff soon.  And I am glad to hear that the Automatics head cover will come off without pulling the engine..I already have a new OEM cover gasket on hand.

[Dave B.]

 I two have bad valve seals and also the coin size seal between #1 and #2 is leaking out between the #1 and two exhaust ports. I am very happy to hear that I can make the necessary repairs on the engine mounted on the bike. I have done this job years ago on a 58 Chevy but I wasn't sure if it worked on a  Honda 750 A. I would like to know much line is stuffed into the cylinder to hold up the valves if I don't use air to inflate the cylinder. Thanks for a great post.