Author Topic: Oil leak above the head gasket  (Read 4964 times)

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Offline Stoli

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Oil leak above the head gasket
« on: April 28, 2014, 12:56:28 PM »

Model: CB750 K8

About 2000 miles after a rebuild, I noticed a little oil on the head fins after a ride. Not too bad, but a few drips would result. This is not a pic of my engine, but just to show where the oil leak is -



- Area A seems to be where the heaviest concentration of oil is after a ride.
- Eventually it will drip from point B after resting on the side stand.
- No oil above or below, so the head and valve cover gaskets are good.

Soooo ...  You assume pucks or valve tower stud, right? That's what I did, so I recently pulled the engine, took off the valve cover and valve tower assembly, sealed the studs with some high temp thread sealer and the pucks with some non-hardening gasket seal, re-torqued the head nuts while I was in there and then put her all back together.

First ride - same exact leak.

Ran a q-tip up inside the puck area and the hole where the leftmost valve tower stud threads into and it came back dry. The immediate area around the spark plug is also dry. 

The only place left that I can guess where the oil might be coming from is the nut/washer that is on the cylinder stud in front of the spark plug. There looks to be a little oil around the base of that (although it is a low point in that area so inconclusive at best). The rest of the plug cavity is pretty clean.

So my question(s) -

- Is it possible/likely for oil to come out of that cylinder stud?
- If so, what is the easiest way to seal it?

I haven't tried yet but it looks like I might be able to get that nut and washer on and off without removing the valve cover, so I might be able to remove and retorque without removing the engine again.

Thoughts?


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Offline flybox1

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Re: Oil leak above the head gasket
« Reply #1 on: April 28, 2014, 01:09:07 PM »
stumped.  :-\
time to break out the spray foot powder  :P
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
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Offline KayOne

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Re: Oil leak above the head gasket
« Reply #2 on: April 28, 2014, 01:49:45 PM »
Don't know about area A, but I had oil in the B area from the valve cover screw threads that are open on the bottom (pretty sure all but 4 cam cover screws are open to the bottom). Used thread sealant when I assembled the motor initially too. Had to remove the two forward screws nearest the outside of the cam cover, clean holes and threads with brake clean and reseal...holding up so far.
CB750 K1 restored
1979 CB750Fz - original except for exhaust, 14000km
1984 VF45F Interceptor - all original, 12000 km
1968 S90 - all original, 2100 miles
1973 H2a, Restored
1973 H1D, next project
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Offline Stoli

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Re: Oil leak above the head gasket
« Reply #3 on: April 28, 2014, 02:14:39 PM »
I've been studying all the oil passages and it seems very unlikely that oil would be around that particular cylinder stud and now that you mention it, the oil does seem to be concentrated directly below the leftmost valve cover screw. Man I hope that's it. I really don't want to pull this engine again. My stands are busy holding other projects.
« Last Edit: April 28, 2014, 02:19:56 PM by Stoli »
My Project Threads:
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Project #2 - http://forums.sohc4.net/index.php?topic=127364.0  Something different
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Offline mcswny

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Re: Oil leak above the head gasket
« Reply #4 on: April 28, 2014, 02:36:53 PM »
I'm sure its a long shot, but did you check your valve tappat inspection gaskets? Might as well as throw out the brain dead easy options first...
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Offline Stoli

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Re: Oil leak above the head gasket
« Reply #5 on: April 29, 2014, 05:21:14 AM »
I'm sure its a long shot, but did you check your valve tappat inspection gaskets? Might as well as throw out the brain dead easy options first...

Yes, they look fine as does the valve cover gasket. I'm putting my money on the valve cover bolt holes. It is most likely the one on the end but will clean and seal all 3 of them. Unfortunately it'll be another week before I can test it out.
My Project Threads:
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Offline mcswny

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Re: Oil leak above the head gasket
« Reply #6 on: April 29, 2014, 05:24:02 AM »

I'm sure its a long shot, but did you check your valve tappat inspection gaskets? Might as well as throw out the brain dead easy options first...

Yes, they look fine as does the valve cover gasket. I'm putting my money on the valve cover bolt holes. It is most likely the one on the end but will clean and seal all 3 of them. Unfortunately it'll be another week before I can test it out.

Is it stripped or just dirty? If stripped heli coil or time/sert
1972 CB750 K2
1997 XR600r (street legal)
1975 XL250
198 XR80

Offline Stoli

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Re: Oil leak above the head gasket
« Reply #7 on: April 29, 2014, 05:38:43 AM »
I don't think it is stripped or dirty. When the head heats up, I'm guessing the threaded hole expands enough for oil to easily seep down between the bolt and the threads. Technically, the valve cover gasket should be preventing oil from ever getting to that area but I probably have a slight imperfection, maybe a small gouge in the head or valve cover that is allowing the oil to get by the gasket in the area around that bolt on the end of the cover.
My Project Threads:
Project #1 - http://forums.sohc4.net/index.php?topic=117106.0  First bike
Project #2 - http://forums.sohc4.net/index.php?topic=127364.0  Something different
Project #3 - http://forums.sohc4.net/index.php?topic=123831.0  Long and Low

Offline mcswny

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Re: Oil leak above the head gasket
« Reply #8 on: April 29, 2014, 06:16:25 AM »

I don't think it is stripped or dirty. When the head heats up, I'm guessing the threaded hole expands enough for oil to easily seep down between the bolt and the threads. Technically, the valve cover gasket should be preventing oil from ever getting to that area but I probably have a slight imperfection, maybe a small gouge in the head or valve cover that is allowing the oil to get by the gasket in the area around that bolt on the end of the cover.

Ahh that's a bummer.
1972 CB750 K2
1997 XR600r (street legal)
1975 XL250
198 XR80

Offline Stoli

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Re: Oil leak above the head gasket
« Reply #9 on: April 29, 2014, 06:37:10 AM »
Sort of, but the fix is actually easier than installing a heli-coil. Assuming I am correct, a little thread sealant should do the trick and there is no need to remove the cover. There shouldn't be much if any pressure under the valve cover so the seal is just working against gravity.
My Project Threads:
Project #1 - http://forums.sohc4.net/index.php?topic=117106.0  First bike
Project #2 - http://forums.sohc4.net/index.php?topic=127364.0  Something different
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Offline mcswny

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Re: Oil leak above the head gasket
« Reply #10 on: April 29, 2014, 06:58:03 AM »
hope thats it, good luck! keep us posted
1972 CB750 K2
1997 XR600r (street legal)
1975 XL250
198 XR80

Offline madScientist

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Re: Oil leak above the head gasket
« Reply #11 on: April 29, 2014, 07:28:54 AM »
Question...when you had your head off I assume being rebuilt...did you remove the cam tower studs?

If so there's a possibility oil could be seeping past the threads. What I did with mine is put some permatex sealer on the threads as I installed them.
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Offline Stoli

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Re: Oil leak above the head gasket
« Reply #12 on: April 29, 2014, 08:39:28 AM »
On the initial rebuild, I didn't get that memo, so, yes I removed the studs and no, I did not seal them during reassembly. That is why my first thought was to pull the valve towers and seal those studs as well as the pucks. I did that recently but it didn't fix the leak. So the only other holes in that area that I know of are the cylinder stud, spark plug and valve cover bolts. The valve cover bolts make the most sense.
« Last Edit: April 29, 2014, 08:44:20 AM by Stoli »
My Project Threads:
Project #1 - http://forums.sohc4.net/index.php?topic=117106.0  First bike
Project #2 - http://forums.sohc4.net/index.php?topic=127364.0  Something different
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Offline evanphi

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Re: Oil leak above the head gasket
« Reply #13 on: April 30, 2014, 05:21:08 AM »
I'm keeping a close eye on this... I think I have a similar issue.
--Evan

1975 CB750K "Rhonda"
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Offline Stoli

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Re: Oil leak above the head gasket
« Reply #14 on: May 05, 2014, 07:06:29 PM »

Still have a leak. To recap, I have sealed the pucks, sealed the valve tower studs and sealed the 3 valve cover bolts on the end, There is no oil leaking from the valve cover gasket or above it and the head gasket is good as well. Only places left that I can tell are the cylinder stud and the bolt as shown in the pic. for those that noticed, the bolt is not standard size. The stock was stripped so I tapped with a 1/4" bolt and used that for the rebuild. Anyone have any thoughts? Guess it's time to break out the Dr. Scholls.

My Project Threads:
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Offline flybox1

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Re: Oil leak above the head gasket
« Reply #15 on: May 05, 2014, 08:38:02 PM »
Positive it's oil?
Exhaust blow by from a bad ex. seal depositing there?
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline Stoli

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Re: Oil leak above the head gasket
« Reply #16 on: May 06, 2014, 12:47:28 PM »

Hey Fly,

Well, its brownish and slippery. Curious about the exhaust blow by. What would that look like?
My Project Threads:
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Offline grumpy

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Re: Oil leak above the head gasket
« Reply #17 on: May 06, 2014, 01:44:03 PM »
exhaust blow-by is soot very black soot.

check the head cover gasket seal around the cam tunnel above plugs 2/3 (you'd be surprised how far oil will flow)

also, try smooshing some epoxy putty or high temp RTV into the the open ends of the cam tower studs - in case the thread sealant failed.

is there any oil present on the cam chain tensioner cover and/or the fronts of the carb bowls?
« Last Edit: May 06, 2014, 01:47:06 PM by grumpy »

Offline Stoli

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Re: Oil leak above the head gasket
« Reply #18 on: May 06, 2014, 02:23:32 PM »
Well, it isn't sooty at all. My engine is very clean so there is no mistake there. Still looks like this only it's in the bike:



The head gasket cover is spotless all the way around. Also checked the carb bowls and tensioner area and all are clean.

Just the few drops of oil that show up between the bottom 4 fins on the head in the area shown in my first pic. I'll try the putty suggestion but that orifice seemed pretty clean after my last ride.

Is there any possibility at all that oil can come up and out of the cylinder stud or bolt that my previous picture is pointing to?
« Last Edit: May 06, 2014, 02:36:12 PM by Stoli »
My Project Threads:
Project #1 - http://forums.sohc4.net/index.php?topic=117106.0  First bike
Project #2 - http://forums.sohc4.net/index.php?topic=127364.0  Something different
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Offline flybox1

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Re: Oil leak above the head gasket
« Reply #19 on: May 06, 2014, 02:28:09 PM »
head gasket on backwards creates an awful alignment issue right between plugs 2&3, and possible gasket tears when installing the cover bolts in that area. 
could any oil be weeping out of this area and riding turbulence pushing it to this side?
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline Stoli

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Re: Oil leak above the head gasket
« Reply #20 on: May 06, 2014, 02:34:49 PM »

I've run a clean white paper towel all over the cover gasket area as well as the rest of the head and the only place that it picks up oil is on those fins. Can the wind clean it off that well? Maybe. I guess that is why the foot powder test is probably necessary.

Funny you should mention the gasket. I did in fact have it backwards when I last reassembled the head cover but I noticed it before I put the screws in, so I am positive that the gasket is installed correctly. It is one of the few things I am sure of.  ::)
My Project Threads:
Project #1 - http://forums.sohc4.net/index.php?topic=117106.0  First bike
Project #2 - http://forums.sohc4.net/index.php?topic=127364.0  Something different
Project #3 - http://forums.sohc4.net/index.php?topic=123831.0  Long and Low