Topic: chasing oil leaks

[greenjeans]

73 CB750    Beautiful all stock 11k mile bike.  Chasing down the oil drips.  Got new engine cover gaskets, oil pan gasket, new exhaust gaskets.  Pretty much the easy stuff.   I have one more tiny leak/weep.   Looks like its from the pucks on the RH side.   So...out will come the engine.  Anyone just replaced the pucks and crossed their fingers ?   I think I know the answer, but I don't really want to hear it.

[CB750F2]

The other possibility for the leak is the studs that hold the cam tower bearing caps. One side is threaded through to the outside and so it is possible for oil teak down through the studs. If you remove the spark plugs and use a mirror and torch you can see the bottom of  the studs. If you are sure the leaks are not coming from the head gasket then all I would do is remove the cam towers re-torque the head, replace the pucks, reseal the studs if necessary and re-assemble. Pat

[flybox1]

+1 to what Pat said.
I bought a dozen pucks from two different vendors.  They surprisingly all had different thicknesses.
I chose the 6 thickest ones, and used a good sealant.  No issues so far.
HM's book lists the required minimum thickness above the head deck for a good seal

[evanphi]

1500 miles later, not a drop of oil...

The pucks I ordered were all too thin to make this spec, so I cut some 1" discs out of gasket material of the appropriate thickness.

From my build thread:

Got some more things ticked off "the list"...

I made some shims out of gasket material to get adequate compression of my stud pucks. Gasket material is 0.75mm, cut in 1" circles.

with the crop of too-thin head seals we keep seeing, here is a way you can check the ones you got in your gasket kit (or elsewhere, like PartsNmore or CB750Supply, etc.).

First, check the step depth of the head hole. Then, check the thickness of your seal. You need at LEAST .030" compression, .040" is better. The too-thin ones are only about .005" thicker, which won't seal when the head heats up and the hole becomes deeper.

The pics tell the story!




This would have resulted in only 0.010" of compression. Not enough!






Boom! 0.040" thicker than the recess!

Then all put together:

Finally got everything all buttoned up!
 
The blank canvas...


Permatex FormAGasket 2 goes in the recesses, then the 0.030" shims.


Then the pucks had a bit more Permatex put on their edges, and sat down into the recesses. Pressed them down as much as I could to force out any excess, then cleaned up.

[flybox1]

I can't suggest gasket material for puck shims as they'll dry up over time and may not weather the heat cycles.   Brass shims are a better option if thick pucks cannot be found.  Sealant should be use regardless....