Aloha again,

Leaving the previous oil related topic and moving in to the next:

Having sorted out clutch issues and some others I the other day took my M21 for the first proper test run (I live in Stockholm and my bikes are in Gothenburg so progress is kinda slow).

And I found there to be a rather massive oil leak up by the magneto, the joint where the magneto meets the the crankcase.
I do not know if I have missed to put in some kind of seal or gasket or if there is some other problem? All I know is that this obviously won’t do! I have oil returning to the tank so not an issue of wet sumping while running (something I suppose would have caused the oil to overflow from all kind of places).

Apart from this the bike actually ran quite well. Always I special feeling the first time you take something you put together for a ride!

/simon

email (option): SimonofSweden

Hi Simon
My M20 has an oil seal in the crankcase behind the magneto pinion. It's a modern looking seal, from memory the type with a circular spring to compress the seal around the magneto shaft. This works well. I'm just looking at a manual that refers to an "oil seal washer" behind the pinion but doesn't show a picture.

No. 72. Ron


chemical formula for aluminium bromide

email (option): ronpier@talk21.com

The standard 'oil seal' which pre dates modern sprung lipped seals is an odd mixture of fibres and rubber and doesn't work particularly well...

There are modern replacements which are a straight fit with no modification required...

Other factors to consider are the degree of wear in the housing that holds the seal. If worn this affects both the fit of the seal into the casing, a source of a possible leak and how central the seal is to the magneto armature...That is quite important for obvious reasons as the seal can only accommodate a limited amount of 'offset'...

Although the seals centrality is estimated visually by sighting the armature position before fitting the mag drive gear it actually runs/seals on the shoulder machined onto the back of the gear...So, the condition of the shoulders 'running surface' is also relevant to achieve a good seal...

Bad wear on the crank case mag. platform and/or excessive wear of the magneto base surface can also detrimentally affect the relative positions of the armature and seal...

Generally I address any of these problems during the engine rebuild when the opportunity can be taken to repair/replace any of the problem areas or components...

If you have an original seal (or no seal) but everything else is OK then sourcing a modern seal would be the first move...Ian

email (option): ian@wright52.plus.com

I can’t believe it!

I totally missed that one. Looking back at it now I feel more than a little stupid to have not realized there should be something there to stop the oil.

Fuck me I really am dumb at times. Oh well...

Thank you for all the good advice!

/Simon

email (option): SimonofSweden

Don't worry about it Simon...
I once rebuilt a B50 engine and forgot to put the pushrods in!...Of course I found out when I went to set the tappet clearances...The problem though, was I had to take the engine out of the frame again to refit them...DOH!!...Ian:laughing:

email (option): ian@wright52.plus.com

“There are modern replacements which are a straight fit with no modification required...”

Do you have some sort of parts number for this Ian?

/Simon

email (option): SimonofSweden

https://www.draganfly.co.uk/index.php/accessories-a-misc/product/12522-

Ron

email (option): ronpier@talk21.com

Thanx a bunch Ron!

/Simon

email (option): SimonofSweden

There is not much of a lip to hold the seal in place.
Mine is glued in.
Just about the only place oil does not leak from

email (option): bsansw1@tpg.com.au

a CR8088 oil seal from your local bearing shop will fit. :grinning:

email (option): petercomley@web.de

Thanx Pete!

/Simon

email (option): SimonofSweden

I had some problems installing the seal because of the REME-made reinforcement of the carter. I had to remove part of the lip.

That REME modification was also done in brass and they are usually held in with countersunk screws, not rivets as on Hans' example...However, I think it is a rather drastic solution as a large hole has to be machined in the casing....

I made up a jig to enable the centre of a worn seal housing to be accurately determined, clocking up with a DTI to ensure accuracy.....

On most cases the seal housing boss can then be remachined true/round and either an oversize seal fitted or a thin aluminium ring machined up and fitted to restore the housing to the original dimension....Ian

email (option): ian@wright52.plus.com

Wasn't the whole idea of that thick seal with no backing to allow for variations in the height of the drive pinion caused by the shims used in order to get proper meshing of the gears ?
If so converting it to a fixed rather than floating seal would defeat the whole design.

email (option): bsansw1@tpg.com.au

If the drive gears are meshed correctly and the mag base and crankcase platform are not worn, the centre to centre dimension between the intermediate gear and the mag drive gear will be pretty consistent (in line with the running clearances of correctly meshed gears and the machining tolerances of the crank case mag mounting and seal housing etc.)

As a consequence the relationship between the the drive gear position and the (fixed) seal will also display an equal degree of consistancy...

Shimming under the mag allows for compensation due to wear and machining tolerances to ensure that the relationship is correct and/or maintained within those limits...

The seal itself can compensate for a small degree of inaccuracy whilst still maintaining a viable seal but correct positioning of the various components is pretty much essential...The seal should not be 'floating' in its housing. That condition is the result of wear caused by incorrect initial set up and/or running with loose mag straps for extended periods....

The fit of the seal into NOS crank cases or any good used crank cases is a light interference fit....Ian

email (option): ian@wright52.plus.com

Interesting as always Ian!

/simon

email (option): SimonofSweden

Aloha,

Seal in place and no oil leak (from this particular area)!

The lip to hold the seal was in a rather poor Sri Lankan-shape like some other parts of this bike has been, ended up glueing the thing in place. Time will tell if this was a good idea or not. But as for now; Great Success!

/simon