I remember removing a large felt washer from the back of the timing gear case where the magdyno assembly butted up against it. I cant seem to find it on any parts diagrams (currently doing a big parts order on Dragonfly!). Im replacing the oil seal inside the timing case - do I need the felt one also? From memory it was about 2-3mm thick, so it might affect the position of the drive gear if I dont replace it...
If the shoulder on the back of the mag drive gear is in good condition, the oil seal used is a modern replacement and the mag is positioned correctly the seal in the crankcase should render this mod unnecessary...that's the reason the oilseal is there..Ian
The last thing you'd want to do if your oil seal was leaking is put the felt washer in there, but it is a good idea to keep crud and water out of the seal-less mag body
I have seen this type of mod on a number of occasions made of felt, gasket material and even cardboard. I can say with some confidence that the reason it was done was an attempt to stop the oil that was leaking past the
seal.
This is really a classic case of treating the symptom not the cause.
Running for extended periods with the mag straps not fully tightened is the main cause of the problem. This leads to (sometimes severe)wear of the base of the mag and the mag platform on the crankcase. As a result the mag moves out of its correct position and exerts pressure on the seal and this can result in severe wear of the seal housing in the crankcase as well.
Also the original type of oilseal was not as effective in the first place as the modern types.
All of this wear can be rectified but it involves a complete strip down of the engine to carry out the repairs.
So, to avoid this a temporary or attempted 'fix' is the insertion of an additional 'seal' or 'gasket' as described.
With an engine that has the mag platform and seal housing in good condition (or properly repaired), a good base on the mag body, a modern seal fitted and a mag drive gear that is not worn/corroded heavily on the sealing surface no additional seals are required.
This method of sealing is not particularly effective anyway as the back of the seal housing and the front face of the mag are often not square to each other and it would be difficult to exert any pressure against the felt seal when tightening the mag straps.
The best thing to do in my opinion is to prepare the engine so that everything functions as intended..Ian
Thanks for all of the replies - the rubber seal in the timing case was pretty well shot, so this perhaps explains why the felt washer was installed. I've ordered a new one - so hopefully the felt one will not be required.