Topic: CB750 K0 Leak after rebuild - ***Solved! I think***

[MCRider]

I'll bet it's still the head gasket... (yeah, I know it's been replaced.)

The problem with that diagnoses is the oil is coming from the mid fin area, between the 2nd and 3rd fins down. To be the head gasket the oil would have to travel out the underside of the bottom fin and blow itself up to the mid fin area without leaving a trace.

I was there and had hoped for the same thing. Wasn't.

Likely either the pucks or the front cam bearing stud holes. IMO   

[CycleRanger]

I'll bet it's still the head gasket... (yeah, I know it's been replaced.)

The problem with that diagnoses is the oil is coming from the mid fin area, between the 2nd and 3rd fins down. To be the head gasket the oil would have to travel out the underside of the bottom fin and blow itself up to the mid fin area without leaving a trace.

I was there and had hoped for the same thing. Wasn't.

Likely either the pucks or the front cam bearing stud holes. IMO   

Ok, after he pulls the engine we'll see who's right.     (You probably are...)

[MCRider]

So this is a picture of the valve cover gasket above the leak...
Yeahhhh.... this might be it? 

Good thing is I can change the gasket without taking the engine out.

I missed that post. Doesn't look good. Easier to fix than what i've been talking about.

[Simpson]

Thanks for the input all!

Just to be clear here, there are two leaks. The first was a simple gasket rip on the valve cover.
Fixed that one easily with a gasket replacement.

This one appears to be coming from the inside of the cylinder. I took a picture before installing the head.

I circled the areas where maybe this could be coming through.

Really either its the stud posts or the tapped hole I guess?

Does that make sense?

[MCRider]

Thanks for the input all!

Just to be clear here, there are two leaks. The first was a simple gasket rip on the valve cover.
Fixed that one easily with a gasket replacement.

This one appears to be coming from the inside of the cylinder. I took a picture before installing the head.

I circled the areas where maybe this could be coming through.

Really either its the stud posts or the tapped hole I guess?

Does that make sense?

Doesn't make sense to me, but lets talk it thru. First the rear one with the ORing. If that's leaking, it's the head gasket. And the oil would come out the back, pretty well blocked from movingforward and the wind would also blow it back to drip down the back side.

That center threaded hole is not an oil issue. No oil anywhere near there. And the hole is blind IIRC.

Same for that front main stud. No oil. IIRC

So is your leak at the headgasket level? Or a few fins higher, which is the way it looked on your picture. If its a few fins higher than head gasket level, then it pucks or cam bearing studs.

[Simpson]

No, I guess this does not make sense to me either... 

All I can say is it slowly comes out of the hole between the 2 and 3 cylinder.

[MCRider]

No, I guess this does not make sense to me either... 

All I can say is it slowly comes out of the hole between the 2 and 3 cylinder.

I'm sorry to persist, but that's not descriptive enough for me. I'm not familiar with a hole between 2/3 at the cylinder level. I'm looking at my engine. Is it at the head gasket level? Or is it higher as it is in your picture. Or is that oil all from the valve cover leak?

If its necessary, one trick is to clean the engine thoroughly, then powder it with baby powder. Then run it. This will tell you where the oil is coming from usually pretty definitely.

I just went out and looked at my spare engine which has the cam train stripped off. The hole from the number 2 front cam bearing stud opens right smack above the front cylinder stud you circled in your picture. If it is leaking it would drip right on top of that stud, which is in the #2 spark plug cavity.

Did you pull the 4 front cam bearing studs during your rebuild?

[Simpson]

No, I guess this does not make sense to me either... 

All I can say is it slowly comes out of the hole between the 2 and 3 cylinder.

Are you sure the head gasket was put on correctly?  I.e. right side up.  It's not symmetrical.

Thanks for the input all!

Just to be clear here, there are two leaks. The first was a simple gasket rip on the valve cover.
Fixed that one easily with a gasket replacement.

This one appears to be coming from the inside of the cylinder. I took a picture before installing the head.

I circled the areas where maybe this could be coming through.

Really either its the stud posts or the tapped hole I guess?

Does that make sense?

Doesn't make sense to me, but lets talk it thru. First the rear one with the ORing. If that's leaking, it's the head gasket. And the oil would come out the back, pretty well blocked from movingforward and the wind would also blow it back to drip down the back side.

That center threaded hole is not an oil issue. No oil anywhere near there. And the hole is blind IIRC.

Same for that front main stud. No oil. IIRC

So is your leak at the headgasket level? Or a few fins higher, which is the way it looked on your picture. If its a few fins higher than head gasket level, then it pucks or cam bearing studs.

I'm reposting my pictures from earlier I don't know how else to demonstrate where the oil is coming from  and the condition the cylinder was in before assembling.

1.) This is a picture of my cylinder before assembling, is the gasket on wrong?


2.) These are pictures of where the oil travels out. top fin of the cylinder favoring the #2 cylinder side.



I can make a video if it helps...

[MCRider]

head gaskets on correct. If it was flipped over nothing would line up.

I'll look at my dummy engine. You are definitely pointing at BELOW the head gasket level, in the cylinder fins. That's a new one on me.

So I looked.

The center of the 3 red circles is definitely a blind hole (has a bottom) and is nowhere near an oil source besides.

If the top hole were leaking, it would be making a mess on the back side of the engine. And at the head gasket level there is no thru breeze to blow it back, which is what it would have to do, to drip over the fins and then run back to the front. Which it could possibly do as where you are pointing there is a passage clear from front to back.

The front circle I don't think has any oil in the vicinity either.

But basically I'm stumped. Sorry.

[Simpson]

Thanks for check MCRider. I'll do some more investigating and see what else I can turn up.
I use to have a fiber probe until i lent it out and it got broke.

[Magpie]

Not sure if this means anything but here's a picture of the cylinders on my K0, engine number 21790, and it doesn't have the hole in front of the cam chain area that yours does. Are you sure, with respect, it's a K0 set of cylinders? And a copy of the head off mine. I have something bouncing around in my head but can't come up why it should matter. Cliff.

[Simpson]

Couple more pictures of the oil running after cleaning and running in my garage for a few minutes.
I have noticed one thing after several runs in my garage or around town.
It doesn't seem to leak until I shut the engine off or maybe the engine idles real low.
Yeah, I know that sounds odd... 

Here's a couple more shots, best I can do, can't seem to squeeze camera in there and light up cylinder hole.
 



Click on picture to enlarge

[Prospect]

Just a theory. If the circled red stud towards the exhaust side is getting oil in there from the cylinders and there is a hairline crack deep in the stud hole hole then it might cause a leak where you have one.  not sure.

[andy750]

Hairline cracks do cause nasty oil leaks...I had a spare K2 head that I had ported, rebuilt etc etc...put it all in the bike started it up then it leaked after a 20 mile test ride. Wasnt obvious where it leaked from. Lucky I had a frame kit installed and pulled the head...MikeR retorqued everything, out copper washers here and there...tried everything...put it all back together...after a few miles test ride leaked ;(...again pulled the head again...hairline crack barely visible.

Solution - use my original K2 head and get it re-ported, cleaned up etc etc...

It was very disappointing but in the end it all worked out and the engine is now very very good and I love this bike.

I hope this dosent happen to you but only way to be sure is pull the engine and go over it in very fine detail.

Good luck
Andy

[hondaseven]

  I had the same oil leak on my ko, I just pulled the plugs mixed up some locktight 2 pack metal hardener, same as your j b weld, put it up in all 4 blind holes with my finger and left it overnight,done 3000 miles  no leaks, costs next to nothing to try and maybe a simple fix, good luck.

[Simpson]

  I had the same oil leak on my ko, I just pulled the plugs mixed up some locktight 2 pack metal hardener, same as your j b weld, put it up in all 4 blind holes with my finger and left it overnight,done 3000 miles  no leaks, costs next to nothing to try and maybe a simple fix, good luck.

Interesting:

Did you pull the engine?
Did you take the engine apart?
How did you get to the holes?

Please tell more!

[hondaseven]

No I didnt pull the engine,  just pull the tank off, plug leads, then plugs. Feel inside with your finger, where the plug goes, you can feel the bottom of the blind thread it feels a bit jagged, it is easy to find, try no1 or no4  they are more accessable, use acetone to remove oil and grease then apply hardener with your finger,worked a treat for me.

[Simpson]

No I didnt pull the engine,  just pull the tank off, plug leads, then plugs. Feel inside with your finger, where the plug goes, you can feel the bottom of the blind thread it feels a bit jagged, it is easy to find, try no1 or no4  they are more accessable, use acetone to remove oil and grease then apply hardener with your finger,worked a treat for me.

After looking at my bike I see what you are referring. My oil leak seems to be below the head, coming from inside the cylinder.
Those holes are in the head.

Spark plug sockets are bone dry.

[hondaseven]

 I am not at home now to look at my bike but I think oil was leaking from the second or third fin down the head, while riding wind blows the oil out thru the fins and it ends up everywhere, PLEASE  TRY THIS FIX.

[Simpson]

I am not at home now to look at my bike but I think oil was leaking from the second or third fin down the head, while riding wind blows the oil out thru the fins and it ends up everywhere, PLEASE  TRY THIS FIX.

Let me know what you see on your bike when you get home. My oil leak just slowly wells on the top cylinder fin, usually after I shut the engine off. I cannot find even a hint of oil throughout the head now.

[MCRider]

Wow, Andy, hairline cracks! Very rare and must be (been) frustrating.

The old 305 Super Hawks had an issue with porous castings and oil would wick out the sparkplug hole!

[andy750]

Wow, Andy, hairline cracks! Very rare and must be (been) frustrating.

Super frustrating and yeah one of those very rare events...I am so lucky MikeR has renamed me "Oil Spill Andy" Someday Ill have a leak free CB750!!!

Good luck Simpson!!
Andy

[Simpson]

Thanks all. When I get more info I'll report back.
On a somewhat bright side the bike has never run better 

[AbbyRider]

No I didnt pull the engine,  just pull the tank off, plug leads, then plugs. Feel inside with your finger, where the plug goes, you can feel the bottom of the blind thread it feels a bit jagged, it is easy to find, try no1 or no4  they are more accessable, use acetone to remove oil and grease then apply hardener with your finger,worked a treat for me.

I think I may have the same leak that you experienced, and am going to try this fix. Is JB Weld (or similar) the best way to seal those holes up? Or is there some sort of high temp silicone or other more flexible material that would be better suited?

[MCRider]

I am not at home now to look at my bike but I think oil was leaking from the second or third fin down the head, while riding wind blows the oil out thru the fins and it ends up everywhere, PLEASE  TRY THIS FIX.

When mine leaked it truly went everywhere. I was in denial that it could be coming from those holes. But sure enough i could look in there betwen the fins with a flashlight and watcvh them drip while it was idling. Wish I'd thought of hondaseven's fix!

Still that may not be Simpson's problem.