Topic: Help with K0 motor assessment

[WideAWAKE]

The head gasket leak(?) seems to be quite dry and I’m wondering if it was possibly just blow back from the exhaust flange as they were pretty dirty.  To me it doesn’t appear to be running down the motor like a typical leak, just where the manifold and exhaust mounts are.

If it is a leak, I know these motors can have their heads retorqued with the motor in, is retorquing really an issue with a standard gasket? And should I use a cycle x instead?

Also, if it looks to be a typical leak with a standard gasket, is this something that’s usually remedied with the head being retorqued? Or only real solution a new gasket?

Any and all help appreciated.  Your thoughts?

[MauiK3]

Looks like it could be more than 1 problem. The gunk around the sprocket could be just build up from neglect or it could be a leak. The head pucks may be leaking, hard to tell. Would be easier after a good cleaning and run to check for leaks.
Too bad it’s not in the frame.

[seanbarney41]

These things are hard to diagnose with out cleaning and then some riding, repeat if necessary.  Really it just depends on the quality of bike you think you need...scruffy daily rider good enough?, survivor that gets used gently with lots of extra care?, or has it got to be as new from Honda? (really very difficult to achieve and even more difficult to mantain over many miles.)  As restorers, I don't believe we are capable of achieving the durability and dependability of some of these original machines.  That is why I often decide to leave stuff well enough alone...as much as possible.

More specifically, it does not look like your head gasket has any problems.  If anything, I would replace the cam tower seals.  And yes, I have had good success re-torqueing head gaskets.

[Don R]

 Remove the sprocket cover, the crankcase may be broken from a chain failure.

[MauiK3]

+1 sprocket cover

[WideAWAKE]

Thanks for all the replies.

It will be getting a deep steam clean later this week. Just figured I’d ask if anything stuck out before cleaning.

I had the sprocket cover off before and there didn’t seem to be any (obvious) damage. Just a lot of build up like almost every other bike I’ve had. I will get a good look once clean.

I believe my oil lines were leaking which were contributing to some of the grime on the engine case.

I agree it would be easier in the bike but timing and space wise it had to come out for a cosmetic rebuild of the bike.  I’ll clean it, get it in the bike when I can and run it to see what if anything is leaking.


On a side note, with the engine out, are there any typical must dos just cause it’s out?


 

[newday777]

"On a side note, with the engine out, are there any typical must dos just cause it’s out?"

Like Sean said, and while it's out, cam tower Seals and re-torque the head bolts.

[ekpent]

New tach seal is cheap and easy to replace also while the engine is out. Seems to be some grime in that area from possible blow back.

[WideAWAKE]

Thank you all for the replies!!!

I pulled the sprocket cover and did a decent cleaning - no damage BUT my chain oiler was pretty much all the way out so I think that is the mail cause of all the liquid by the sprocket. Forgot to snap a pic.

I will get it deep cleaned later this week (hopefully)

[PeWe]

The worst job is done, pulling the engine.
Sure no leak from headgasket?

I retorqued the head on my K2 just for sure this winter after 650km. Frame kit and stock cam so not that big job.

Nuts were not loose at all.
I retorqued head a day after when gasket was assembled. This was enough. 
Stock type gasket from a gasket kit.

Oil can flow when riding. A leaking top cover on valve cover can spread some oil too.

Remove spark plugs and check the cavities with a lamp.
Finger inside, roof for oil  check.
If the rubber coins under cam holders leak, oil goes down here. Also if studs on head holding cam are leaking.

M6 bolts holding the valve cover might have a leak from inside. A few of them have threads with holes thru the head outside.
Yamiya bolt kit has sealer on the threads.

[newday777]

Thank you all for the replies!!!

I pulled the sprocket cover and did a decent cleaning - no damage BUT my chain oiler was pretty much all the way out so I think that is the mail cause of all the liquid by the sprocket. Forgot to snap a pic.

I will get it deep cleaned later this week (hopefully)

Pull the oiler out of the shaft. The oring could be toast.  I just pulled mine from my K5 and found why I had so much oil dribbling like a limey Brit bike of the 70s would do...... and found the oring wasn't doing it's job.

Thankfully I had another in a K4 that was better to get me by until I get a new oring.

[BenelliSEI]

Read PeWe’s email carefully. He has a LOT of experience opening up these motors. My experience has been most leaks are not head gasket. On an old, dry, unused motor, it’s usually those damn rubber pucks under the cam towers. Pull the plugs and dig around in their recesses. If they are full crud and oil, chances are the pucks are leaking....

[WideAWAKE]

Well there is definitely some spewage down by the plugs and in their cavities.

I’m guessing the valve cover has to come off to replace those pucks (as stated I’m quite ignorant to these motors, all of my bikes have been Yamaha or Honda twins)

Is there a good thread on their replacement? I’ve tried to gather all I can about them But still a bit limited (seems they should be sealed??). If anyone has Hondaman book, does it cover stuff like this?And sealer on the bolts for the cover.


Again - really appreciate the help. Giving me a good direction and things to prep for. I’m sure I’ll know more once I get it cleaned and pull the cover.

And Newday - I’ll check my oiler.

[ekpent]

For the pucks the valve cover, cam and cam towers come out as the pucks are hiding under them (cam towers).

[MauiK3]

Get Hondaman's book, it's a must have and it will save you lots of heartache.

[MauiK3]

https://www.amazon.com/CB750-book-Putting-Them-Back/dp/0557310237

[WideAWAKE]

Well that settles that. I’ll pick up his book.

Also, it appears I’m missing the rubber bit on the end of my oiler. I suppose that would be a main culprit for some fluids leaking in the area.

[ekpent]

There are ways to permanently plug that from special made plugs to old spark plugs -  I have not done one but some suggestions might roll in if you do.

[newday777]

https://www.amazon.com/CB750-book-Putting-Them-Back/dp/0557310237

Stinking over priced on am a zon...zone....
Get it directly from hondaman

https://www.lulu.com/search

[Stev-o]

https://www.amazon.com/CB750-book-Putting-Them-Back/dp/0557310237

Stinking over priced on am a zon...zone....
Get it directly from hondaman

https://www.lulu.com/search

+1 buy the book....

https://www.lulu.com/search?page=1&q=my+cb750+book&adult_audience_rating=00

[WideAWAKE]

There are ways to permanently plug that from special made plugs to old spark plugs -  I have not done one but some suggestions might roll in if you do.

I was reading about it last night.

I believe Yamiya has a direct plug and I’d imagine with modern chain lube, there isn’t much need to squirt dirty crank case oil on your chain any longer.

[newday777]

There are ways to permanently plug that from special made plugs to old spark plugs -  I have not done one but some suggestions might roll in if you do.

I was reading about it last night.

I believe Yamiya has a direct plug and I’d imagine with modern chain lube, there isn’t much need to squirt dirty crank case oil on your chain any longer.

If you find it on Yamiya post the link for the plug.

[WideAWAKE]

There are ways to permanently plug that from special made plugs to old spark plugs -  I have not done one but some suggestions might roll in if you do.

I was reading about it last night.

I believe Yamiya has a direct plug and I’d imagine with modern chain lube, there isn’t much need to squirt dirty crank case oil on your chain any longer.

If you find it on Yamiya post the link for the plug.

https://www.yamiya750.com/index.php?main_page=product_info&cPath=21_53&products_id=115


I believe that is a block off plug.

[PeWe]

If lifting the head which might open up for finding more things like valve- guide-seat job. Exhaust will go bad first.

- Head gasket and the 2 o-rings for oil flow.

Hondaman has written about it several times.
Stock o-ring that is 2.5 mm thick is made for head gasket that is 0.8mm thick on a stock cylinder.

Later gaskets often 1mm thick.
The o-ring will then not compress and seal as needed. Thicker o-ring  is needed.
There is one size, 2.62mm thick that will provide better seal.
Cylinder not decked.

I found an o-ring supplier webpage that stated 20-30% compression for correct seal. Not less nor more.

This proved that Hondaman is right and how to calculate it.
It look more complicated when described than it really is.
http://forums.sohc4.net/index.php/topic,153549.msg2203559.html#msg2203559

[WideAWAKE]

Fantastic info!!

Saved to my build file. I’m sure I’ll need it in the future.