Oil leak - magneto mounting?

Not really much help in the present circumstances, and yes that bottom nut is a pain BUT there is a solution. There is an extended bolt available, I think originally for the A10 but will fit most brit bikes of the era. About 3"/15cm and less than a fiver. But you would of course have to faff about removing the original nut in the first place.

https://www.feked.com/bsa-a7-a10-magneto-bolt-67-1259.html

Several potential leak points and causes on this model.
a)  On a cold start-up, the pressure release valve inside the timing cover will get pushed back and allow oil to flood that part of the bike. It will continue to do this if the PRV spring is tired or until the oil has warmed up.  Using 20W/50 oil may help.

b)  You might have a leak in the oil pipes to the feed block.....or the gasket behind the block is leaking.  perhaps one of the block arms or its solder has cracked. 
c)   Leaking Magneto gasket or bolts/studs.
d)   Dodgy timing cover gasket or warped cover.

Richard, 
one dodge is to totally degrease the area with degreaser, when it's dry spray talcum powder over the area, and start the engine. 
The leak will be very obvious. 

is the engine breather clear. its already been mentioned. but ive had a leak from a crack in the solder on a pipe that fits into the junction block. at first i couldnt spot where the leak was coming from. so took the pipes off and you could swivel one of the pipes from side to side. so i had them re soldered.

barry

I only use the extended bolt shown in Michael's earlier post. Makes it simple to ensure that the magneto flange is uniformly tightened.
There are spanners available which give better access but the extended stud is by far the best way to go.  Available from all of the major parts suppliers 
 

Did the '59 99's get the bulged cases? If so, then the long bolt wont work as it hits the crankcase centre flange.

The 650's and up had the inaccessible bottom bolt reversed, ie. the nut was inside the timing case. Does make it a lot easier to tighten the mag/dizzy/ei housing, but a pita as it is yet another oil leak path to be resealed.

Can the bolt be reversed on earlier engines? That I don't know. 

Regards George 

Earlier crankcases generally had 3 external studs

leaks in the mag area can stem from too much engine "breathing"  from bad or not run in rings, Also a 6 start pump sending too much oil through the PRV , A stuck piston in the PRV , A collapsed or bent breather pipe . thick cold oil causing higher than neccessary oil pressue ,try a 20/50 . The Bulge cases may have been fitted to a few of the later 88/99 engines ,but not a 59 . 

As can bee seen in the photo below the crankcase bulges are well clear of any extended bolt used to fit the magneto. The problem with all of the Dominator engine is the flange lips which could be trimmed a little to clear the bolt shaft.

The extended bolts themselves do tend to vary in dimensions depending on the source of manufacture. Michael C in his posting above agrees with my findings. eg the BSA bolts have a thinnish, unform shaft that generally  clears the Norton Crankcase flanges. A trial fitting is a smart move and if required, some metal removing is easily done with a drill and file.
 

Look for this spanner. It's great to use on the centre rear head to barrel nut as well. It gives much better access to the nut (and some other hard to access nuts).

External bolt and nut inside timing cover: I did this many years ago on a Dommie engine I was working on. Difficult to remember for certain, but you might need to remove some of the "meat" where the base of the stud sits inside the case, to ensure enough clearance when you have the nut in place so it clears the back of the magneto gear. 

hello,
        is the oil seal on the magneto and the crank ok. worth checking.

barry

Michael has raised another good point.  The reversed bolt into the crankcase is one solution to the magneto flange issue but can cause other issues such as clearance for the magneto chain. 
With the bolt facing outwards, it can have a thin, domed head due to the need of only 12flb torquing of its external nut.
Reverse this set-up and you then have to consider bolt thread length, nut thickness and secure fitment.
With regard to oil in the timing cover......a cold engine start-up will almost certainly trigger the pressure release valve into dumping oil inside the cover.
This is added to by oil in the sump which the descending pistons will actually push up through the two oil drain tunnels into the timing cover. This is part of the engine design and is known as the 'bellows effect'. The idea behind the design is to lubricate the chains, timing gears and oil pump from the first turn of the motor.
Pressure inside the crankcase is high and unfortunately, the tiniest of gaps in gaskets or mating surfaces will allow oil vapour to pass through and form stains, drips and puddles.

I have a dedicated flat combination spanner.  The edges of the open end have been ground back from about 3/16" maximum to a point at each tip. The edges of the ring also ground away.  And the offset angle of the ring from the handle is hammered flat so it can be reversed.  Remove the oil union and it works.  Hard part is getting the nut started.

A great magneto to have on a Dommie - K2FR quite rare and expensive these days. The later Atlas and 650 SS (and Mercury) had a waisted bolt with a reduced hex bolt head, reduced diameter 5/16th flat washer, a small 5/16th fibre washer and inside the timing cover, another 5/16th fibre washer, followed by a flat washer and lastly the 5/16th cycle nut.  This makes an oil- tight sandwich around the mag/ or twin-points holder , gasket and crankcase.   It is probably hardened so that it does not snap off at the 1/4 inch step.  Even with the waisted studs on the earlier bikes, the three 5/16th cycle nuts and washers should be reduced hex for easy access !  Good luck, Howard