Oil leaking from cylinder head chrome nut!

I wonder if there could be a problem with the o-ring and head gasket? If so, it's possible that some oil is being pushed up through the hole in the cylinder head that the head bolt passes through since there is oil pressure present there. This might be possible even though cylinder compression is unaffected. Ed

I wouldn't rule out a crack, but a simpler answer would be oil seepage from the head oil feed to the stud tunnel. And simpler still would be leakage from somewhere else.

But in case there's a crack, it would probably be from the oil feed gallery to the stud tunnel, as they do come within proximity to each other. The oil feed goes up at an angle toward the front of the motor to feed the horizontal pressure gallery (not the larger return gallery), thus passing close by the stud.



I only have access to 550 parts, but the 550 is just a smaller replica of the 650. (You can tell the 550 by the outer exhaust studs. They are inverted, top to bottom, from the 650.) Notice the stud in question has a larger opening to accommodate the block alignment ferrules. So maybe something is gong on there which allowed oil to seep in from the restrictor at the head gasket, or maybe even at the base gasket, for that matter.

I see Ed posted a similar photo from a 650 block. The hole marked "bolt hole" on his photo is the rear one. The larger hole is the front one. So it is the same layout, 550 vs 650.

This is a stretch, but you might want to pull your plugs and see if #1 has oil or more carbon than the others. If oil is leaking from the restrictor area, it might be seeping into cylinder 1 as well. But the cylinder seal is meant to handle a lot more pressure, so it's probably unlikely.

Once again, thanks so much for your help everyone.
I think I'll just whip the top end off & have a look at what's going on inside.
Never done this on one of these bike before as my other bikes are singles, & a BSA 500 royal star twin.
Watch this space. Will hopefully get it apart this evening as in England UK the time is 5:15 pm now.
Bet you haven't seen one of these lately !!

Ok then, I've been busy & now have the head off. Can't see any problems with the head gasket leaking from the o ring . The stud looks dry down below. The oil is 100% not coming from the rocker cover or the end black seals.
Had enough for this evening and I've got loads of rocker gasket to remove too (ugh)
Will give the head a clean & get out my spy glass and have a look for crack's.
Will be a shame if it's the head as she's only done 16,000 miles & everything inside looks great.

I don't see them in your pictures; were the "pins - part #92043-1266" (see 1st image below) in place when you removed the head? The other images below show them in place. I don't know how or if it would contribute to the oil leak if they were missing, but if they are missing I would buy and install them. Ed

]Evening Ed, they are both still in the head, I hadn't looked underneath as there's still a load of oil floating around in the recesses!
By the way when I checked the valve clearances all but one were within limits but the last one I checked was only 2 thou or .0508 mm. My shim is 2.65.is it worth changing it ?
Cheers from David ( now drinking a pint of English ale & smoking a rollup cigarette !!

Just a feeling but this area looks like someone have try to seal it with liquid gasket like JB weld

Good eye.
Steve

I think Scirocco has spotted the trouble spot - GOOD EYE! Make sure there is not leakage from the patch, but also check to see if the crack runs down inside recessed area where the nut and washer sit. If so, the repair doesn't look like it covers that area. Ed

Yikes. Yeah that picture from above is worth a whole lot of words.