Head Gasket, Breather, Both / Neither?

Hi,

I have an oil leak, which looks to be coming from the head gasket region. 1975, mk3 850, which I've had since March. I think it has probably always seeped from the gasket, but was masked, I also had leaks from the rocker covers (now fixed) and a lot of splattering from the oil tank cap (also done). The recent fix to the oil tank cap seems to coincide with an increase in the rate the gasket area leaks, maybe.

I've attached pics of the leakage. I would appreciate advice on whether it could be anything other than the head gasket leaking. I don't believe the oil trail extends to the bottom of the exhaust roses, it does look to be the front head bolts area, possibly the central rear too, but I may be deceived?

Is there a fix without head off, which I've never done, so feels a bit overwhelming right now? I am also wondering what caused this:
- I seem to have good compression (very difficult to kick the motor over)
- I run with oil halfway up the dipstick (with regular use, no sumping to speak of)
- I appear to have a stock breather pipe exiting the case, feeding to the oil tank, just below the oil tank cap, with a herringbone pipe coming off the front top of the oil tank, routed to the rear of the LH swingarm. Not sure it does much though? I have no knowledge of what is inside the case.

Be grateful for advice and also, am I ok to carry on riding the bike with this problem, leaving the fix to the winter?

Thanks, Martin

Have you tried re-torquing the fasteners to specification? It's always worth doing.
You mention head gasket and breather but don't mention "waisted" 3/8" bolts. Both cNw and Jim Schmidt supply these and I'm certain (have done the strength/differental expansion calculations) they stop "creep" squashing of cylinder heads along with the associated leaks from head gaskets. They are position numbers 1, 3, 4, 5 & 6 on the torque sequence diagram.
Cheers

BTW - there's a good chance of recovery (temporary) by simply retorquing.
The 5 bolts I mentioned can be replaced (one-by-one and retorque as you go) without head removal.
Must be done cold - retorque and bolt replacement.

I've had a seep in that region leaving an unsightly mess forever. Re-torqued head, new rocker cover gaskets, checked everything and have never been able to rid myself of it.... Now being too old to worry myself with minor nuisances, since it neither increases or decreases, I just ride it and occasionally clean the spatters and leave it be. I'll concern myself further if or when I take it apart..... Yours appears to leak more than mine so it could possibly annoy me more.

banjo bolts..................?

A leak or weep in this area of the head gasket is common on many Norton heavy twins.
Sometimes it is due to nothing more than loose headbolts, sometimes it is due to a head bolt bore that has broken into the pushrod tunnel.

Use the search function .... there have been many posts on this issue.

I had one such weep. It seems to be cured now by:

1) milling head to remove a slight warp
2) using Jim Schmidt's copper wire supplement technique.

I used the copper wire on the head gasket to barrel side .... I was hesitant to use it on the gasket to head side for fear the wire might indent the alloy head.

Be sure to re-torque the head bolts several times .... a lot of "settling " occurs.

Slick

Also, a crank case breather like the one from MikesXS can reduce oil leaks a LOT.

Thank you all. Yes I did search before posting and pages and pages came up! I will try torquing the 5 bolts suggested, but on initial inspection, all seemed tight. But, I don't see how I get to no.1? Is it the centre front bolt, hidden deep between the castings for the exhaust valves/ports? If so, I can't get a socket on to the nut buried in there, let alone the head of a torque wrench! Is there a workaround? Ill be taking the tank off anyway this weekend, but expect the frame will stop me going in from the top? Thanks. Also, just so I'm reading the manual right, 3 and 4 are the ones clearly visible, directly each side of the spark plug?

Mart UK said:

I will try torquing the 5 bolts suggested, but on initial inspection, all seemed tight.

Click to expand...

You should check all ten in the tightening sequence (Mk3 manual section C, Fig. C2).

Mart UK said:

But, I don't see how I get to no.1? Is it the centre front bolt, hidden deep between the castings for the exhaust valves/ports? If so, I can't get a socket on to the nut buried in there, let alone the head of a torque wrench! Is there a workaround?

Click to expand...

You need a 1/4" Whitworth, 3/8" square drive socket and extension bar.

#1, 7 and 8 will require you to remove the ignition coils and use a thin wall 3/8 drive 1/4 Whit socket. It's the #2 in the back that's a bitch. Air cleaner must come out.

maylar said:

#1, 7 and 8 will require you to remove the ignition coils and use a thin wall 3/8 drive 1/4 Whit socket.

Click to expand...

1, 9 & 10.
7 & 8 are the sleeve nuts below the exhaust ports.

What's the best link to an online service manual now? The one I've been using has been unavailable for a while...
http://rocbo.lautre.net/technique/norton_workshop/index.html

maylar said:

What's the best link to an online service manual now? The one I've been using has been unavailable for a while...
http://rocbo.lautre.net/technique/norton_workshop/index.html

Click to expand...

I assume you mean the '70-'74 manual as this bike is a Mk3?

That manual is still available here:

Or:


850 Mk3:

Thanks LAB.

Thats a lot of oil and looks very familiar.
Check the oil line circulation/connectors/banjos on both sides at the top of the head. Those connections, if not tight/sealed allow oil to run down into the front center of the jugs below the head and run out over the fins looking just like an oil leak around the head gasket. I
This leak can be very deceptive. I found this only after pulling the head and replacing the HG only to find the leak alive and well upon restart.
I stopped the leaking after sealing the banjos but more importantly employing a PCV in the system.
Leaks gone, clean engine and no fresh droppings on the shop floor.

Hi, no sign of oil up at that point of the head, nor where it might pool from there, so looks like that's oil tight. But, think you're right about needing to do something about the pressure, that may come if I have to admit defeat and take it off the road for a while to remove the head.

Had to remove the head steady bracket as well as the tank to get to no.1. Four of the bolts moved perhaps just under 1/16th of a turn, including no.1. But, no.2 I could only check with a spanner, no way I'd fit a torque wrench and socket, even though I don't have the big Airbus in the way. It felt tight. No.s 9 and 10, my socket wouldn't fit down, just too wide. Shame, they are possibly in just the most likely leak spot.

Will see if that does anything... Thanks for your input / advice.
Ps. If anyone near Colchester has a socket known to fit in 9 and 10.....

are they the two accessed from the top at the front?

EstuaryBoy said:

are they the two accessed from the top at the front?

Click to expand...

Yup. In front of the pushrod tunnels.

I've PM'd the man as I'm 16 miles away with the tool of choice.....

Fantastic. Thanks.