Oil leaking -front of head

You could try re-tightening the head down.   May not stop the leak but may reduce to a seep. 

Before you go tightening the head bolts etc  check the torque settings. If you try and pull it down more you could crack the head. You will need a 3/8 inch drive and socket set to get to the front 3 bolts between the rocker covers.

Before you ride it again,  clean the head thoroughly, then ride it to about 5000rpm. Go home and check the leak. Use a small torch to look between the fins. If the oils coming from the gasket its a head off job, get a mate to help, its easier. 

Another test is to put loo paper or tissue between the fins at the front. That will pin point the leak. 

It is possible that the rev counter cable is leaking, and that makes a mess of the front of the engine too.

If the oil is coming from between 3&4 head fin you have a problem. The head may be cracked and no ammount of tightening will help, it will actually make it worse. I hope this isn't your problem, but if it is, take the head to Norman WHITE, he will explain all. 

I have experienced this problem myself. Good luck.

you could try tightening down Like robert say do to the two front 7/16 bolts which are under the front of the barrels as they sometimes work lose .....but I did try that and it did not work.....so ended up having to take the head off and get it simmed

as around the the two front push rod tubes they do have a problem with leaks....anyway had mine done and I put it back together last year and No more leaks..... hope that helps.

Also had head leak develop on my Mk 3 850 (RH4 head) three years ago. Oil literally poured out from between fins somewhere at the front suddenly one day on start up and was obviously not the gasket but the infamous crack problem. Norman White at Thruxton will have a look at the head and advise if can be fixed or not by laser welding. Luckily still had the original head from the bike I'd changed for a brand new head years ago so took it to a specialist for a complete refurb including repair of broken fins , new valves , guides , etc. Back on bike and all well. Use the composite gasket with flame ring.

From memory the Norman White repair , if doable , was going to be around 350 quid - cracked head still lying in garage for possible future repair. Original head complete refurb cost 500 quid. Both these options still somewhat cheaper than the 1,000 quid odd for a brand new head. 

There is plenty of good advice above but a couple of points. Don't be tempted to just tighten the two 7/16th bolts, the torgue setting is 20ftlb whereas for the others it is 30ftlb. Before tightenning make sure that you have the necessary spanners, try all nuts and bolts first first. For the  front 5/16th bolts I use a box spanner with a socket on the end, a bit crude but it works. Tighten down in the correct sequence. You will not be able to get a torgue wrench on the rear two. One possible problem is that one or both of the front 7/16th bolts have been stripped due to over tightenning, this would manifest itself when tightenning. This is not uncommon and would be a head off job.

Early 850 heads have a reputation for being porous at the front as mentioned already. If you clean the area very thoroughly and run the bike you may be able to detect the source of the problem. Often there is a build up of pressure from within and fitting a (yamaha) in line reed valve in the crankcase breather may solve this and other oil misting problems. I was sceptical about this but I now believe that most norton engines benefit from this modification. 

... on my early 850 the threaded holes for the upward pointing studs at the front (the ones that the nuts (with washers) drop down onto) had broken through into the pushrod tunnels (or at least one had), so oil seeped through and found its way up the studs. Refitting the studs with loctite cured that.

I found that a 3/8" drive slim socket from Williams fitted down the tunnel nicely.

Hi Jon,

Before you pull the head off here's another one to check:-

Be sure there is no oil leaking from around your intake rocker cover. Oil leaking from there can be drawn forward through the small holes in the barrels that are between the cylinders. This is apparently done by a vacuum effect. It is then blown around by normal air passage and makes it look like a front cylinder head leak
I learned this from Brian Slark years ago when I thought I had a recurring cylinder head leak.

Try degreasing the head, go for a road test and then use talcum powder to help show up the oil leaks.

I'd take a critical look at the three head-steady mountings, and the exhaust port threads. They are all candidates for suitable inserts to reclaim them. 

... and finally once you're ready to refit head , what has always worked for me on the three Commandos I've owned is a composite gasket with flame ring , fitted dry , followed by a retorque of all reachable bolts / nuts after about 100 miles.

As you see, there's lots of sensible advice on offer here for particular problems.

You might also find it useful to join the Commando Facebook group, where the files page offers lots of useful material (https://www.facebook.com/groups/10302209470/files).

Norman White's new book is indispensable reading; I also commend the videos available from the Club shop.

Gave up trying to get a proper torque reading on that one and just tightened it by feel - have never had a problem with a gasket leak using this method.

Never used a torque wrench on that head nut either. But if you do find a way then having the torque wrench at 90 degrees to the spanner means the torque setting is the same regardless of spanner length. Any other orientation will need new settings to be calculated.

https://www.finishing.com/118/94_crows_foot_torque.shtml

No disrespect implied to anyone, but everyones 'feel' is different.

If you use a spring balance or luggage scale (the ones with a hook or strap on that you lift up to get a reading) and a spanner,  you have a torque wrench! (Combination spanners are best for this as the balance can't slip off.)

Some simple maths will geet you the pull required.

For example, If your spanner is 6" long (centre of nut distance) and you need a torque of 15lb-ft, then you need to pull on the spanner with a pull of 15×12/6, = 30lbs. For a 9" spanner it would be 15x12/9, =20lbs.

Of course, the spring balance needs to be maintained at 90°to the spanner for accuracy.

Old time dodge but it does  work.

Regards, George. 

AN offer an updated drive housing incorporating a proper seal: https://andover-norton.co.uk/en/shop-details/16977/tacho-drive-housing-with-oil-seal-06-1090-06-5200-

Old Brits claim to carry a full range of A-N spare parts.

http://www.oldbritts.com/ob_main.html