D32 magneto help

[Dewey]

Hi all. I have been asked bring the life back into the engine fitted to the famous Robert Fulton Jrs. ride. The engine arrived today via FedX in a beautifully constructed crate and I immediately broke the crate down. The first thing I checked was for compression and it passed nicely. Next on the list was spark which is poor to non existent. I believe the magnet has weakened over the years and am looking for suggestions as to where I can have it checked out. It's a BTH M2-AP2, serial OM559561.
Thanks in advance - Dewey

[Doug]

Dewey,

While not impossible, it is rare that the BTH magnet has weakened. Or, there are certainly plenty of other things I would check first. But before leaving the magnet, with the magneto removed from the engine, does the magnetic field give a decidedly 'lumpy' feel when you spin the magneto over by hand? If it does, then the magnet is o.k.

Poor condition of the condenser, points, maladjusted points, carbon tracking of the slip ring, and the wrong point plate fitted (incorrect internal timing) will all sap current or prevent the maximum current from building up.

I've recharged magnets with a homemade magnetizer, but the proper kit uses a capacitor discharge to dump a lot of joules very suddenly into the apparatus. And that I never arranged. It has been a number of years since I have had a magneto reworked; and back then I was sending them to firms in the UK.

-Doug

[Dewey]

Doug - I don't have specific in-depth knowledge of older magnetos but I have had enough experience to remember that the vast majority of cam ring mags of the older variety had fairly close point settings. The points on this mag were set at .021" which I thought was much wider than I expected. I thought they should be set somewhere around .010", possibly even less. I know that the point opening relationship to the armature position is very important to creating a strong spark. I reset the points to .011" and now have a decent spark. I suspect this is the root of reason there was so much trouble in starting this engine of late. Or perhaps setting these points so wide was a last ditch effort to get the bike running. I can't say, I wasn't there.

Anyway - after receiving approval from the owner/s of this bike I proceeded with the teardown. Pistons worn right out (.012" skirt clearance) and still scored. Engine timing side case cracked all the way from one side to the other. Valves have stripped threads at the adjuster nuts. Some might find that arrangement a bit odd but Mercedes Benz has used that system on their older diesels for decades. No problem for a slow turning, heavy valve train engine. Cam rollers badly worn throughout. Worn exhaust cam lobes - we've already discussed that in a thread started in the Tech section. About the only things not needing immediate attention are the main bearings, rod bearings and the oil pump.

I've found some pistons that I think will work after boring out the barrels another .020". The valves selected as replacements before would most likely be more suitable with modifications beyond putting some threads on the end. Rebuilding the cam rockers will take a little time to find competent machinists to create the rollers that need to be hardened as well. The roller pins could be made from old valve stems. And lastly, I have to find someone who can duplicate the crank pinion gear as it is badly worn.

I'm still truly excited to build this engine for a machine owning such an incredible piece of motorcycle history and I am by no means discounting the amazing effort by its' rider, REF Jr.

Dewey

[Doug]

Dewey,

0.012 inch is the standard gap for the BTH magneto contacts. The points are timed internally to break at the moment the magnetic field reverses and so collapses, yielding the highest potential spark.

It is surprising the crankcases are cracked; the S6 types are quite robust. Mind you, this one has had a hard life. Perhaps it happened when Fulton rode it off that uncompleted bridge in Turkey! Cracked crankcases are more typically seen on the Dirt Track models. Welding Douglas aluminum is a real challenge. It is quite porous, filled with impurities, and has had nearly eighty years to soak up dirty oil. If the crack does not appear structural, it might be advisable to leave well enough alone.

The cam follower rollers are notorious for wear. They cease to roll and just skid around the cam. After a while they develop flats and the engine settles down for many trouble free miles! Since the rollers do not see any particularly heavy shock, through hardening steel would be o.k. and avoid the difficulties of case hardening. You can grind them or turn on a conventional lathe using CBN tipped tools. The roller follower pins can also be made from hardened steel dowel pins. I would advise against valve stems as many of these are stainless steel or a variation of. Stainless tends to gall when run against steel.

There were enough S6 types made I would try advertising for a engine pinion. They will not be all that rare.

-Doug

[graeme]

Hi Dewey
I will add also that new S6 valves and springs are available through the LDMCC spares scheme.
Cheers, Graeme

[Dewey]

Doug - I had posted in the wanted section the need for parts but no replies yet. Here are pics of the case cracks -

Graeme - new proper valves & springs would be terrific. Only one of the springs appears to have not softened with heat.  I have to ask tho, as to the durability of the valves with todays fuel. Also, the valve seats are cut to accept a 44mm (1.725"), 45deg. valve head. I'm fairly certain they are from a 70-71 Ford 429 exhaust application. They had then cut the 11/32 32 threads onto the stem but had to skip over the single groove which left them vulnerable to stripping, which was was the case for 3 out of 4. They may be larger than stock so it would help to know the size of the valves you can offer.