Torque setting fo nut on magneto shaft

[orabanda]

Hi all,
made some changes to tuning of my 51 plunger, as engine could only manage 18.5 hp on dyno (with 365 cam), whereas 51 rigid (with 334 cam) could make 20.3! pistons, timing, etc were the same!

I found that the gasket between the head and the fuel splash plate had a 1.5mm smaller ID than the hole in the plate so opened the gasket up so it matched the hole in the deflector plate.

The other change was to replace the original air cleaner element (media) with K&N air cleaner media. I also fitted an anti-bias spacer, as my other iron head A10's have benefited from it

Back on the dyno, and here is the result:



photobucket clickable thumb added :O) adm


Like the other bikes, there is still a mixture bias (RH pot runs richer), but installingt the anti-bias spacer improved the situation.

The mixture was too lean at small throttle opening; I will be changing to a richer slide to correct this.

A hotter plug was fitted to the RH pot (B6HS), and this slightly leaned out the RH pot mixture curve.

Before the run, the mag was sent to Dave Robertson for re-magnetising.

Dave had to replace the armature in this mag about 1,000 miles ago, to fix a strange problem.

I noticed a "wobble" on the auto advance unit, when I had removed the timing cover for another reason.

I extracted the pinion, and found the shaft was cracked through, just before the taper, and about to fall off!

I put this down to an act of God!

So, after the dyno run, and with my new found horsepower, Mario and I hopped on our A10's and rumbled up the Meekatharra highway at 65 mph.

30 miles later, the plunger's engine cut out!

Plenty of compression; I removed the points cover to observe that the points would not rotate, but the engine would turn over; no drive to the maggie!!

Removed the points; the drive tang on the bronze backing plate is in good condition, and engaging in the armature.

So now the bike is in the shed, awaiting removal of the timing cover. I suspect another failure of the shaft, or the Auto advance unit, or the fibre gear.


Advice please; is there a recommended torque for the nut. It is possible trhat I am over-tightening the drive, as I use an 11" ring spanner, and do it up with a couple of blows.

In hindsight, this could be over stressing the shaft, and / or drive gear.

Down but not out,

Richard

[Brian]

I dont know if there is an actual torque figure for this nut but I dont do mine up very tight. I use a 3/8" drive socket with a handle thats about 8" long (sidchrome).

I have a plastic piston stop that screws into the plug hole so after I have set the timing and nipped the nut up I put the piston stop in and give the nut a bit more of a tighten. Just at a guess I would reckon about 20 ft lbs.

I've done a lot of miles on A7's and A10's and never had one slip or come loose (yet!)

[muskrat]

Loose the hammer Richard. I agree with Brian, 20 ft/lb tops. The gear might need a trip to the dentist.
Figures look good, did you loose any torque ?
Cheers

[orabanda]

Muskrat, gained a few foot lbs of torque as well!

Anyway, I know what ails the old girl; half of the teeth stripped off the (nearly new) fibre timing gear!

I can only assume that over loading of the gear occured when I did the mag nut up?

Richard

[bsa-bill]

next time Richard leave the Kangaroo steaks and 4X until after you torque it up

[Triton Thrasher]

I try to support the pinion against the direction of nut tightening by sticking a screwdriver into the auto advance, to take the strain off the fibre teeth while tightening the nut.

[RichardL]

Muskrat,

Everyone knew what you meant, but, just funnin' with you, "Loose the hammer..." could be taken to have exactly the opposite meaning of "lose the hammer."  (Speaking of typographical errors, one of my favorites is "apologive," for when your fingers say your sorry, but your brain says you don't mean it.)

Richard L.