oil leak

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Aug 21, 2006
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Happy New Year to everyone. I have had a slight oil leak from the head gasket area on my 74 Commando since I bought it two years ago and wondered if anyone has had similar leaks and whether or not it is anything to worry about. The leak is quite minor spraying a bit of oil on the front parts of the side covers and frame after a 100 mile ride. Appears to be coming from the front part of the engine and then migrating around and spraying off the back of the cylinder fins while driving. Is this most likely a leak from the pushrod tunnels? What can be done about it and do I need to do anything immediately?


Mine had a leaking head gasket when I first got it. You might want to check carefully to make sure that the oil is not coming from somewhere other than the head joint . Check the valve covers , oil lines and connections. Also check that the oil is not coming out around the bottom of the exhaust ports. If everything around these areas is dry, and the oil only shows up below the head joint, then try torqueing the head bolts and studs.
I took the tank off to do this.
If the leak persists after even after torqueing (mine did), then the next step is to replace the head gasket. I could actually hear mine leaking compression, making a pffft pfft noise at idle.
The supplier I used offered both a cheap gasket and a better quality copper head gasket for a few bucks more. The copper one should not require retorqueing, whereas the cheaper composite one does, so I went with the copper gasket. My fix held for a couple of thousand miles and gave quite a lot of added power because I had been losing so much compression along with the oil. One day on the freeway, after being passed by a couple of Harleys at about 75 MPH, I took the old bike up to 115 MPH, flew by the Harleys and blew the head gasket all over again (always pride before a fall). This time one of the studs had pulled loose. This stud had already been on it's way as it didn't really feel solid when I torqued it previously. I pulled the head again and helicoiled the stripped stud hole. I did not buy a new gasket, which might have been advisable, but it has held just fine for about 3,000 miles so it looks like I got away with that.

I may be getting confused with some work I did on my other bike, but I seem to recall that I could not get a socket on a couple of the nuts, the ones that are located near the bottom of the cylinder. I had to use the box end of a spanner on these. Real mechanics have much better tools, but I rigged a up a torque spanner by using a 25 lb fishing scale hooked onto the end of the spanner. I have extended the spanner by clamping a piece of wood (5/8ths X about 1" wide hardwood)onto it. This was done in order to get enough leverage to give sufficient torque . If you make the setup one foot from the centre of the spanner end to the point where the spring scale attaches and pull the scale to 25 lbs, you have 25 foot lbs. If you need more torque, use an 18' or 24" extension and use the appropriate multiplier. Sounds a bit hokey, but works fine.
If you need, I could look up the torque values and sequence for these bolts and studs.

If you have a shop manual for the bike, head torques and sequence are listed in there.
If the oil is leaking from the frontal area around the push rod tunnels you can bet it's coming from the front two studs that screw into the barrels. These two break through into the push rod tunnels and oil works its way up the threads.
I do know of a fix by fitting a check valve into the 850 engine breather pipe. However. The best solution is to remove the head, unscrew the two studs from the barrels, remove all the oil residue and loctite the studs back in.
To get a good head seal and to ensure an even torque down on rebuild check the head and barrels are flat, all studs nuts and bolts are in good knick and run smoothly.(I wouldn't use stainless steel fastenings in a stressed area like the head, they look good but can stretch), leave the push rods and head gasket out and set the head on to the barrels, it should fall in place. Fit all the bolts checking they all run easily and smoothly to full depth finger tight. You may find you'll need to run a clearance drill through some holes to achieve this. The best head gasket I've used to date is the Norvil latest by Reins (I think that's the spelling) Fit it dry with both faces degreased and torque the head down as best you can to the book, then check again after a short run. And it wouldn't hurt to do it again after 500 miles.
It works for me.
Do check its not a weep from the rear rocker inspection cover as it trickles down through the head & comes out at the front. Otherwise I agree with the other replies re front studs. Better to use threaded insert than helicoil
Thanks everybody! You have given me some good suggestions for where to start to look.

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