850 Cylinder head leak

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Gerard Rowley

Gerard Rowley

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A fellow Norton owner has asked me to have a look at an oil leak from the cylinder head on his 850
He has just had the engine rebuilt by a mechanic but they can’t work out why it is leaking. I cleaned the oil away and started the engine and in about 30 seconds quite a steady stream of oil is coming from under the two nuts in the front of the head the ones that join with the studs from the barrel. I think that this has been discussed on here before but can’t find it. Is there a fix for this and where would the oil be coming from
 
Usually that's due to using a copper head gasket. Or one of the studs is projecting into the pushrod tunnel. Need to pull the head and look.
 
I can see that it has a copper head gasket, I seen to remember someone previously saying it could be from the pushrod tunnel, I don’t have a barrel to look at but how does the stud project into the pushrod tunnel
 
www.accessnorton.com

Oil leak at the head?

Got my new to me 74 Mk2A started today. Second kick and she was running. Then I noticed that it was leaking oil again. I just replaced the head gasket due to an oil leak and pretty much the same spot. It is not as bad but any leak is not a good thing. I installed a new copper head gasket...
www.accessnorton.com www.accessnorton.com
 
Gerard Rowley said:
I can see that it has a copper head gasket, I seen to remember someone previously saying it could be from the pushrod tunnel, I don’t have a barrel to look at but how does the stud project into the pushrod tunnel
Click to expand...

The barrel stud drillings are known to break through into the pushrod tunnels which seems to be a reasonably common problem so the studs probably need to be removed and sealant applied to the threads.
 
The small head studs thread into the barrels adjacent to the pushrod tunnels.

Sometimes the thread in the barrel actually opens into the pushrod tunnel and leaks oil up the stud and out under the nut/washer.

If this the case using a sealant on the studs into the barrel can and most likely will cure it.

I have barrels where the studs break through, others where they don't.

You still need to take the head off to fix it. Then consider what general sealant you might use on the copper gasket, which you should anneal before reuse.

I tried Pliobond as referenced by Jim Scmitt and elsewhere by lcrken. It definitely works.

My only issue was breaking the seal afterwards, since mine is a race bike and often stripped, more recently I have just used a smear of Wellseal each side of the copper gasket! Works for me.
 
Yes it could be oil passing from the pushrod tunnels across the gasket face. Hence the JS copper wire and Pliobond trick (with a copper gasket).

Also, as already mentioned, those stud holes are sometimes open into the tunnel, due to the angle of the tunnel, it runs VERY close to the bottom of that hole. If it breaks through, oil can definitely leak past the threads in such instances.

But first things first, have you properly checked the head fasteners torque??

Here‘s what a broken through stud hole can look like:

7C6CEDC2-9283-4470-88CC-72173306B2CC.jpeg
 
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I had what sounds to be a very similar problem.

Looked like the pics below with oil filling the bolt access holes and then running down the front fins and dripping. I was convinced the leak was at the HG, which looked good upon removal. On the next startup with new HG the same problem popped up immediately.

The kids in the neighborhood learned some new words that afternoon.

I finally found the leak was being generated from the oil lines connected to either side of the head, running down into the same two front head bolt holes and flowing on down the front convincing me it had to be a HG leak or a cracked head. :eek:


That oil coming out of the oil line to head connection is damn near invisible and I never would have found it without the input from some helpful AN forum members.
I cleaned the head surface around and below the OL connection to the head. Shiny and dry. Started the engine and wiped it with a tissue. Oil. Leaking down and in to the head bolt hole access hole.
New copper sealing washers fixed it.
Its worth a look.


.
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InkedL1100088 - Copy_LI.jpg
 
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Lineslinger said:
I had what sounds to be the same problem as well.

Looked like this with oil running down into the bolt access holes and then running down the front fins and dripping. I replaced the HG, which looked good and upon startup same problem popped up immediately.

I finally found the leak was being generated from the oil lines connected to either side of the head, running down into the same two front head bolt hole and flowing on.
That oil coming out of the oil line to head connection is damn near invisible and I never would have found it without the input from some helpful forum members.
I cleaned the head surface below the connection to the head. Shiny and dry. Started the engine and wiped it with a tissue. Oil. Leaking down and in to the head bolt hole.
Its worth checking out.
Click to expand...
And, the same can be true of the exhaust rocker covers. So, you need to look everywhere. It can be like a house roof leak - the actual leak may not be directly above where it shows on the ceiling.
 
I have had 2 850 heads that were cracked where the cylinder head is fly cut to give the retaining nuts for the discussed studs clearance, the crack went across the outside of the pushrod tube one head on the left side the other head on the right.
 
Fast Eddie said:
Yes it could be oil passing from the pushrod tunnels across the gasket face. Hence the JS copper wire and Pliobond trick.

Also, as already mentioned, those stud holes are sometimes open into the tunnel though, due to the angle of the tunnel, it runs VERY close to that hole. If it breaks through, oil can definitely leak past the threads in such instances.

But first things first, have you properly checked the head fasteners torque??

Here‘s what a broken through stud hole can look like:

View attachment 21548
Click to expand...
 
Eddie thanks for your very informative reply and images at the rate the oil comes out of the head I reckon that is what it is I have done a retorque and one of the rocker spindle covers was leaking and running forward of which I fixed
Started the bike again and can’t believe how much oil is coming out under the two head nuts
I will see if he wants me to pull the head or send it back to his mechanic
Thanks again for your help I will report back
 
Fast Eddie said:
I think it should do.
Click to expand...

It worked for me.
I forgot to relay this in my earlier post but another, and important cause of my oil line leaking was caused by excess pressure via clogged breather.
I disconnected the line from the crankcase and opened up the PCV with compressed air, which I do a couple times a year now.
 

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Lineslinger said:
It worked for me.
I forgot to relay this in my earlier post but another, and important cause of my oil line leaking was caused by excess pressure via clogged breather.
I disconnected the line from the crankcase and opened up the PCV with compressed air, which I do a couple times a year now.
Click to expand...
One of the disadvantages of the reed valve (PCV) coming off the timing case is I think there's less pressure to blow that crap through compared to being right on the crankcase. If you were to located the valve closer to the engine it might also not get clogged. But I understand why you put it where you did.
 
I did understand about pressure relief and location. Here is one solution I came up with on a 427 side-oiler build I sold , rather than a catch can.
This motor could develop enough crankcase pressure to look like oil was being drilled for (and discovered) in the engine bay.


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My 850 engine was too far along to tear down and send off the cases for milling and relief valve fitting/mounting...what IMHO is the best solution.
And, as you noted I didn't want to hang what looked like a giant metallic kidney bean in the engine valley so I did some tap and die work, dug out some unused AN fittings and hose, fabbed up a bracket and hid it behind the Z plate.

My hard earned lesson (seems these lessons are never ending) was not checking for valve clog before renewing the head gasket.
 
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Lineslinger said:
I did understand about pressure relief and location. Here is one solution I came up with on a 427 side-oiler build I sold , rather than a catch can.
This motor could develop enough crankcase pressure to look like oil was being drilled for (and discovered) in the engine bay.


View attachment 21566View attachment 21567


My 850 engine was too far along to tear down and send off the cases for milling and relief valve fitting/mounting...what IMHO is the best solution.
And, as you noted I didn't want to hang what looked like a giant metallic kidney bean in the engine valley so I did some tap and die work, dug out some unused AN fittings and hose, fabbed up a bracket and hid it behind the Z plate.

My hard earned lesson (seems these lessons are never ending) was not checking for valve clog before renewing the head gasket.
Click to expand...

Nice!!
 
swooshdave said:
One of the disadvantages of the reed valve (PCV) coming off the timing case is I think there's less pressure to blow that crap through compared to being right on the crankcase. If you were to located the valve closer to the engine it might also not get clogged. But I understand why you put it where you did.
Click to expand...
That is for the most part why I didn't remove my shade tree engineered steam punk PCV plus catch can plumbing on my Atlas 750 engine, and install a JS reed valve in its place. There is crank case pressure being released at the old magneto hole location, but it's got a lot of oil mist in it and I have to keep an eye on the catch can. I would have the same issue with a reed valve, but it would be harder to clean out.

One other thing I did to reduce crank case pressure even further is put a 5/16ths inch hose barb fitting in the left side exhaust valve cover and one in the intake valve cover. I run the hoses back to a T fitting and then into a small vented prescription bottle catch can. The valve cover vents also made a noticeable difference in top end performance on my motor. The not so great thing about that modification besides ruining the valve covers is vacuum is very low with the 2S cam, so cold starts require a lot of leg. I don't have any valve cover or other engine oil leaks. I've been using the same hard as rock valve cover gaskets forever.

850 Cylinder head leak


850 Cylinder head leak

Milky goo in the high end prescription catch can. It has a foam filter and a bunch of holes in the top. The hoses use to go out to the bottom of my rear fender, but the guys on 916 Ducs used to complain about the white goo getting on their face shields. Street hooligans.
 
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