Topic: CB750 leaky head gasket

[The other Derek]

So my very slow weeping head gasket has worsened to splatters on my pant leg with each ride.  My plan is to replace the gasket soon, but is it worth trying to re-torque the head for now?

My bike's frame was cut when I purchased it so getting to the nuts will not be an issue.  I figured it might be worth a try to slow down the leak until this winter, but I really don't want to waste the time if it isn't going to make any difference.  As far as replacement goes, I'd rather wait until I have some down time this winter to do it.  Chances are it'll take me 3 times longer than it should and I don't want to miss any of the beautiful riding weather that we'll have coming up.

[Coyote13]

I've been waiting about 3 years to fix a leaky gasket, just ride through the season and do it right in the winter.

[calj737]

It's certainly worth checking the torque on your head, but probably a teardown is looming.

Regarding riding if the leak is growing, consider the safety of having oil spill onto the road surface where your rear tire tracks. If it's that bad, stop riding it. If it's merely some splatter marks on your pants and none on the frame rail, then proceed with caution.

When you do repair the leak, check out this thread for great info:

http://forums.sohc4.net/index.php?topic=107040.0

[Jerry Rxman Griffin aka MuthaF'er]

Definitely it's worth a try anyway. I'd bet you find loosened nuts. If you do this please report back what torque you found them to be. You may also find leaking pucks so be prepared with a fresh set of those from Honda. Double check the cam tower studs for leaks and seal them if needed. I'd consider you lucky that you can do this EASILY with the frame cut. Most guys would let it go until 'it's time'.

[MCRider]

My money is on retorquing it will fix it. It did mine. Brand new K1 just outside of warranty. Shop wrench did it for a 6 pack and ... well it was the 70s.

Also just did my new motor too.

And follow Ccal's suggested thread.

[The other Derek]

Ok.  I'll give it a shot and hopefully report back with happy results.  It'll probably have to wait until next weekend though.

Thanks for the help and link to Branden's write up.  It'll be really nice to have that as a resource when I get around to fixing it right.

[flybox1]

Definitely try a retorque.  You're ahead of the game if you have a frame kit and can get the valve cover off without pulling the engine.
Be sure you bookmark brandEns thread.  I referred to it often during my rebuild.

[seanbarney41]

If it's getting on your pants, I say ten to one it's mainly the pucks.  If you got a cut frame, replacing pucks and re-torque is like a 3 hour job (really should seal the pucks with non hardening gasket goop though and let it set up over night)  I rode for two whole seasons (25,000 miles at least) wearing only black jeans!

[ekpent]

Could do the ole' rope or other stuffing trick in the fins for awhile if your wearing your white dance pants to the disco.   

[The other Derek]

Gonna start getting prepped to do this next weekend.  Just want to verify that the pucks are part no. 18 in the diagram.

[70CB750]

Yes.

[flybox1]

yes, #18
IF you are installing NEW pucks:
For a good, leak-free seal, pucks need to be .030" - .040" taller than the hole they sit in BEFORE you goop them up.
if they are short, find thicker ones or shim the hole.

[PeWe]

Frame kit will make a complete head job easy. Weekend job if you have experience of cam timing that might be the case if you have a hotter cam with slotted cam sprocket. You can turn engine to 1:4 T mark + mark cam sprocket+ cam before removal of cam. Then put it together and align the marks... work OK.

This is how I took my engine apart and together several times during the 80's. My tuner made the marks on cam and cam. My task to put chain on correct. You will see when turning the engine without plugs and cam tensioner stretched. If wrong do it correct. Easy that cam chain slack is on wrong side.

If you must lift the head, remove valve springs and lap the valves, replace valve seals. Thin layer of copper spray on fiber head gasket. New 4 small o-rings under the cam towers, and new rubber packs with sealer under against head.

Then retighten the head 500 miles after. My head nuts were rather lose when I retightened just for sure when I changed cam. Easy with frame kit allowing head, cylinder removal without pulling the engine.

[Nic]

Frame kit will make a complete head job easy. Weekend job if you have experience of cam timing that might be the case if you have a hotter cam with slotted cam sprocket. You can turn engine to 1:4 T mark + mark cam sprocket+ cam before removal of cam. Then put it together and align the marks... work OK.

This is how I took my engine apart and together several times during the 80's. My tuner made the marks on cam and cam. My task to put chain on correct. You will see when turning the engine without plugs and cam tensioner stretched. If wrong do it correct. Easy that cam chain slack is on wrong side.

If you must lift the head, remove valve springs and lap the valves, replace valve seals. Thin layer of copper spray on fiber head gasket. New 4 small o-rings under the cam towers, and new rubber packs with sealer under against head.

Then retighten the head 500 miles after. My head nuts were rather lose when I retightened just for sure when I changed cam. Easy with frame kit allowing head, cylinder removal without pulling the engine.

what he said.

[greddm]

I'm having a similar problem (leaking badly from the front corner). How do you determine its the pucks and not the head gasket? I did add some non-hardening sealer to the pucks per Hondaman's instructions when I put the engine back together. I also tried re-torquing the nuts without success.

[MCRider]

I'm having a similar problem (leaking badly from the front corner). How do you determine its the pucks and not the head gasket? I did add some non-hardening sealer to the pucks per Hondaman's instructions when I put the engine back together. I also tried re-torquing the nuts without success.

Clean it thoughly, then dust with talc powder. IF the oil is coming from the split between the head and cylinder, only on the top fin of the cylinder, never on the bottom fin of the head, its a head gasket.

If the oil is higher than the split, like 2-3 fins up, its pucks. IF the cam tower studs have been disturbed in a prior rebuild it could be them also.

[Nic]

There was a post somewhere where someone said one of his cam tower bolts was too long, it had been put in by the PO and when tightened down had broken through the bottom of the hole into atmosphere causing leaking there, he ended up putting a stud in there with sealer, this could be something to look at also, if you can't get a stud at least put some sealer on the bolt, I would check all four next time you're in there to make sure none have the floor broken through with or without longer bolts.

[greddm]

Ok, some good clues here. From what everyone is saying, it's definitely my gasket.


1977 CB750