CB750 K3 Oil leak

[sim2011]

Hi
According to Mark Paris's book a skim of .010" (0.25mm) is fine on the K3 as they had 1mm more deck height than the K0-K2 engines , I cant see that .5mm will make any diference to cam chain tension.
Any way just reasemmbled the engine this morning, I will recheck head bolt torque later on today.
I opted for Blue Hylor for both the base and head gaskets after checking their site its perfectly ok for High temp.
Just a thin smear was used both sides.
Next report will be later this week when I get a helping hand to put the lump back in.
Thanks for everyones input.
Simon

[Bryanj]

Simon I did check that cylinder as i said and the deck height is approx 1mm with the counterbore being 0.9mm Cant remember how that ties up with yours

[K2-K6]

Hope you've got it with that, it's nice when they run well and you know you can get a reliable run out on it.

[UK Pete]

Fingers crossed, hope all turns out well this time
pete

[K2-K6]

Here's a slightly different angle on it which may explain some of the experience old-v-new gaskets etc.

This era or production has covered the removal of asbestos from head gaskets so any original specs that used it would have to have been re-formulated. Commonly they went from asbestos to graphite and one of the characteristics that changed was it was more common for liquids to creep through the new ones, making it common practice to have a sealant where none was needed prior to this.

Graphite type gaskets also need retorqueing on some arrangements also and this is never part of the plan for SOHC 750 motors due to the need to remove from frame to work on. I'm guessing this but it may be why they are more succesful with sealant with the types available now both Honda and pattern.

There is a piece written in current "Classice Bike" along these lines, not specfically dealing with this application but if you overlay the info contained with our experience and the timeline involved I think you can form a more thorough resoning as to the use of sealant or not.

I guess this impacts many of the bikes on here.

[sim2011]

Moment of truth is looming !! Engine back in and should be able to fire it up tonight, I'll keep you all posted.
Si (Nearly running K3)

[sim2011]

Well just done 10 miles and all seems well on the leak front    I need to do a longer run just to be sure , the front end feels a bit stiff new seals and oil , so I will monitor that as well.

Many thanks to everyones input , I think I can conclude that using some form of sealant is a must on the head gasket.

Thanks
Simon K3 (No Leaks)

[K2-K6]

Seems like optimistic news so far. It's a good thread for anyone else looking in and working in the same area as I guess there are some relevant changes to consider since they were originally produced.

Thanks for considering our opinions of value, hopefully you get to enjoy it now.

[UK Pete]

Nice one Simon, you done well to turn around the problem so quick and fix it , if that were me i probably would have let it sit there for a while and got all depressed about it, your rewards are deserved.
Pete

[notobikeparkingtax]

Nice one Simon, you done well to turn around the problem so quick and fix it , if that were me i probably would have let it sit there for a while and got all depressed about it, your rewards are deserved.
Pete

 Hehe  +1

 Are you noticing any difference in performance due to the skimming ?

[sim2011]

I didnt ride it before the skimmimg, I also have one less tooth on the front sprocket therefore its not a top end bike , more fun I hope.

Pete
I did get depressed for about 30 mins then thought lets do it ! it only takes about 1 hour to get the lump out then about 1 hour to strip the top end down, then ages to clean all the base gasket off properly.

I've done a total resto on this one in my spare time in less than 3 months so it can be done ( even with 1 wife & 3 kids)

I'll keep everyone posted with its progress, next is My Suzuki GT550 which I have already stripped down , Crank is at SEP in Kegworth who also skimmed my head and barrels (proper Mc engineering company)
Thanks again to everyone I hope this will help others.
Si

[UK Pete]

SEP are one of the best out there, i used them to re-sleeve a barrel and some other work, they are top notch
Pete

[K2-K6]

SEP sounds like a good recommendation? I've no knowledge of them but it seems from what they have done for you that they can do the work to a level you need.

My reasons for being careful about skimming barrels is that they are hard to do correctly without some experienced engineering behind them, I've seen a few that have not been successful so If you can get this level of service it makes it much more of an option.

The cam chain comment I made is I believe relevant as if you consider when you adjust the drive chain you only make a small move in length but the slack changes out of all proportion to how far you've just moved the spindle. I'm not clever enough to do the calculation but it must have something to do with sprocket diameter, I don't think it's a straight no ratio effect though.