Topic: CB 750 K3 - Leak at the base of the head

[Gene]

This is a new leak. When I put it on the side stand after riding the leak is almost immediate. On the center stand, not so much. I can't tell if it's coming from the screw pictured or from the bottom of the head where it meets the case. L side as you're sitting on the bike.

My suspicion is that it's the latter, and maybe a problem with the pucks. I've never had this cover off, so maybe there's a seal back there to replace? That'd be happy time, but, if it's pucks then I have to pull the engine since they're at the bottom of the cam towers.

Just looking for any insight at this point, if it's a common issue.

[754]

Wipe it , run it hard a few nutes and have a close look.
 Some guys throw a bit of flour at it, I think a flashlight in the dark might show it..
 Watch where you pull over.

 You can always ride with Mooshie..

[scottly]

Leaking pucks are usually higher up, and run downwards. Is it dry above where the cylinder head sits on the cylinders?

[Gene]

Yes, aside from some light weeping around the head gasket- I'm used to that. This one is new, guess I'll have to pull that plate see what's behind it. That's good news actually, thank you. Or bad news . . . need to figure that out I s'pose.

Have to do the talcum powder test.

[Jerry Rxman Griffin aka MuthaF'er]

Gene, how in the world do you expect to trace it with clean oil?! 

[Gene]

I think I may have found the issue, btw. It looks like it's coming from the cam tensioner - I'm thinking maybe piece # 7 in the link here - the gasket - gave out. OR last time I made the adjustment I didn't tighten everything back up. But I imagine that would have caused much worse problems than a leak.

https://www.bikebandit.com/oem-parts/1973-honda-cb750k3/o/m9234#sch398980

I had a short chance to look as I set the bike on the side stand, and the oil is definitely running "south" for that general location. I'll look again tomorrow in the daylight and see if that's really the case. looks like something - if this is it - I can do engine-in, yes?

OR #11? Hell, grasping at straws. But also thinking out loud. K Bye.

[scottly]

Replacing the tensioner gasket is a piece of cake, Gene.
1. Rotate the engine 15 degrees past TDC on the 1/4 cylinders.
2. Remove the tensioner.
3. Compress the tensioner fully, and lightly lock it in the compressed state with the bolt. Don't bother with the lock nut at this time.
4. After replacing the gasket, bolt the tensioner to the cylinder block.
5. Release the lock bolt, allowing the rod to move under the spring pressure.
6. Tighten the lock bolt, then the lock nut.
7. Drink a beer.

[HondaMan]

The main oil galley plug is right behind that leak. It may be that it's O-ring has given up, so high-pressure oil is pushing against the gasket on the alternator cover. Also: if the bottom of the alternator cover is all scuffed up from a drop one day earlier, the cover is a little warped, so it will have a hard time sealing that journal when the O-ring is weak.

[Gene]

Thank you both. I'll update once I do the work.

[Gene]

Easy peasy. Kind of a PITA getting to the left side bolt on the tensioner - past the starter - but got it done. Old gasket came off in pieces.

I'll let you know if that fixes the issue. It obviously needed it anyway.

Now, replace the shifter seal (this I've done) cuz I think there's a slight leak in there, pretty her up and call it a day.

Mark, if it does end up being the main oil galley plug area, that'll be my next adventure.

Thanks, gents.

[PeWe]

Tensioner with gasket is an easy fix if it is attached by allen head bolts.

[754]

1/4 inch drive is your friend on the tensioner bolts ..

[ekpent]

 If you notice that tensioner gasket can be hard to find. I kept one out of a rebuild kit and when I need one nowadays which is rare, I trace around it on gasket paper and make my own. I do usually pull them off on new to me bikes just to make sure they aren't lightly seized or the shaft too badly pitted from over tightening the hold bolt.