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Oil leaking -front of head


I recently acquired a 74 Commando 850 which runs very well and I love it. I just replaced the kick start seal, having read up on the topic in the forums went with an x ring seal, so far so good.


There was a slight oil weep at the front of the head where it sits on the cylinder block when I purchased the bike, just been for a ride and the leak has worsened. I'm guessing its coming from the head gasket at the push rod tubes. Ive looked at the manual and appears fairly straight forward to replace the gasket. The manual talks about replacing with a gasket incorporating a flame ring. Any tips before I start ordering parts. The bike runs well, is quiet and doesn't blow smoke so I'm thinking if the valve clearances etc are good it may not be necessary to pull the head completely apart.

Any thoughts appreciated.


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 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.


Thanks guys, appreciate the advice, I'm reasonably mechanical but new to Norton so not sure of the peculiarities as yet.

I've just checked the tach drive and there is some oil leaking but the bulk is at the joint of the head and barrel, its blowing up under the first head fin and back along the side of the motor onto the air filter box and driping off the top barrel fin in the center of the barrel. I'll check the torque settings on the bolts and try retightening if its appropriate. There has been just a weep and today its just increased, wasn't a long ride but had to go up the highway for a couple of miles and went to about 70mph and bingo, got home and noticed a lot more oil than usual.

If the head has to come off is there any brand or type of head gasket thats best, Ive also read mixed theories on whether you should use any sealant or not.


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.


Thanks guys, I'm off to buy a torque wrench, here's hoping its not cracked, porous or stripped threads, hoping for a bit of a tighten or failed head gasket (eternal optomist). I'm an Aussie but live in the US,  North Carolina at the moment, do you know of any Norton specialists over here, theres a few on line but I don't know much about any of them.


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.







All the nuts and studs needed tightening but unfortunately I thinknthe rear center stud has stripped the thread. The nut won't tighten but thenstud is coming through the nut.


Heads off, rear center stud was stripped in the head, gasket was leaking, I'm wondering if the head torque settings were checked after the last gasket replacement as they were all way under torqued. The left side exhaust valve needs the guide doing so might as well do the whole head now its off.


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.


Thanks for the guidance over the past couple of days, its been appreciated. I dare say it won't be the last time I ask for a bit assistance.


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 (

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


An update on my Commando head. It turns out that the rear center stud had stripped the threads in the head and the front two (the ones that tighten from below) were starting to pull the treads. I've had helicoils fitted and am about to start reassembly. 

I have a question regarding the rear center stud bolt. I can't get the torque wrench in position, I think the only way to access it will be by putting a spanner on the bolt and connecting the spanner to the torque wrench. My question is what does that do the the torque setting if anything, do I need to adjust the setting.


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.


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. 


I went with the spanner at 90 degrees to the torque wrench and it seemed to do the trick. Just the carbs and exhausts to go and hopefully I'll be enjoying ride soon.


Hopefully the last question, need to replace the tachometer drive oring, I've removed the cable from the drive and taken the 2 screws out but the tachometer housing is rather solid in the case.  I dont want to damage it, is there a trick.

Best heat the tacho drive with a hot gun or similar then twist it loose with vice grips.

Forget about the o ring, have your tacho drive machined to take a proper oil seal.


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


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