Sealant on Head Bolt ??

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Jul 27, 2009
Got a 1973 850 with a cylinder head oil seep coming up head bolt in front of right spark plug (number 3, I believe). Would it be wise to pull out that bolt, then put some permatex #2 (stays flexible, good up to 400 degrees F) on the bolt threads, and maybe some along the bolt shaft, then reinstall bolt, and torque to
20 lb/ft (fits my 5/16 Whitworth socket)? Or, should I just leave it alone, and live with the oil stains on the fins, and floor. BTW, I have a XS650 PVC valve on the way....once installed, would that alleviate some of the oil seepage?
No, because the oil is probably coming from another place and simply pooling there, this comes up fairly often. The usual suspects seem to be the rocker shaft connection to the head and the exhaust valve covers. The oil becomes very fluid and transparent at operating temp so that you can't seem to find a source. A leak combined with a ton of air pushing it around is what you get, and that low point between the heads is where it's seen.

Baby power or shoe powder if puffed on the suspicious areas will show the trail.
It looks like both powders are just corn starch with zinc and other additives.

Blow some corn starch on it then!
I happen to have an oil leak in the same spot right now. It's dribbling from the rocker feed lines on the right side of the head. It does look like it's comming from the head bolt (but there's no oil in there).

Also have a leak at the tach cable drive in the front. Oil wicks up the cable and blows all over the fins.

Both conditions will be fixed this weekend.
I fought oil leaks for years on my Combat. Tach drive, crankshaft seal, head. Once I installed the XS PCV valve the oil leaks mysteriously disappeared. Hmm!
Re: XS PVC valve

Would some kind rider enlighten me regarding this Yamaha part and possible part #.
Marshal :?:
I wonder how many breather valves Mikes XS has sold to Commando owners. I see reommendations for it on all the forums. Got mine in the mail yesterday..
I had ordered the XS650 PCV valve, and I got it yesterday. Easy is a right-angle device, so best spot to install was where the breather hose curves up and around the front of the oil tank. Then cleaned up old oil spots on head, cylinder, everywhere. Went for a ride, and first thing I noticed was the increase in HP and torque...easy 5-10 increase in both...WOW...did a lot of city riding, then went out on highway. Came home, parked the bike, put fresh cardboard under it to trace any leaks, then waited for the drips, and waited and waited.....nothing, NOTHING. Before, my right boot would get covered in oil, now it's dry as a bone. Checked again after a few hours....not a drip had formed. Man, oh man, this was the best $30 (item plus shipping) I ever spent. Solved a lot of leaking issuses, and increased performance. Lovely device.
The usual tacho drive and oil seeping head leaks troubled me for years on my 850mk2. No need to waste money on a PCV valve just drill and fit an extra engine breather pipe to the inlet rocker cover and leaks just cease! :D
No more horrible sludge in the oil tank either, as the motor heats up any condensation within escapes through the inlet rocker cover breather instead of into the oil tank.
Is that like the gearbox breather on the Mk3?

Sounds a good idea, will have to look out another cover to try it on.
I'm now trying to recall where I saw it but i think years ago I saw a Norton with a breather fitted to the rear valve cover. That may have been on a race bike.
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