Vintage Motorcycle Eccentrics

The gearbox and clutch sprocket is taking more adjusting with shims than I anticicpated. So while waiting for more shims to arrive I've been fine tuning every part in the gearbox trying to make for smoother shifting. This includes polishing the shafts, bores in the gears and points where the selector forks ride.
The gear selector cam plate was slightly warped so required dressing on the surface grinder. It was then burnished with a diamond lap then polished to a mirror finish on the surface that contacts the selector forks.
The surface of the selector forks that slides against the gear selector plate received a series of small dimples to help retain oil.
The new selector fork shaft was anything but smooth and while manually sliding the forks on it the drag was very noticeable. After lapping with 600 grit, crocus cloth and buffing to a polished finish, the forks now glide nicely when run through all the gears.
A lot of extra labor but in the end I think it will be time well spent.

Just making the jig to hold gearbox had to take a fair amount of time with excellent precision.

I have a shifting issue on my 72 Benelli 250 ‘egg’. It only had 800 miles when I got it, and I suspect a lot of that was due to this issue- perhaps from new. I have not quite isolated it yet- although the bushing the shifter pawl rides in has wear. I have some oiled bronze rod to make a new one- but I think cases require being split. With so low hours I was hoping to avoid that.
Fortunately, I have a spare engine I can take apart and see what the issue may be.

On the winter project list. (I didn’t say which winter)

Always nice to have a spare motor for R&D.
My gearbox simulator is an awesome tool for watching the movement of gears and to see just how much they engage when shifting, especially between third and fourth. This is where the shimming is important. The shims came in today so the gearbox is now finished. Now I can shim the clutch sprocket so it aligns with the engine sprocket.

John, do you have a photo of your gearbox simulator? I also wanted to ask you if you have worked on the Burman gearbox for the Comets? Mine could use an overhaul and would be great to visit your shop again some time.

Here's a photo of the gearbox simulator for the 'B & C" twin. I do have a couple of Burman gearboxes here.
Never worked on one but they should be pretty simple.


Yes, let's get together again sometime.

I'm slowly getting things done that are required before painting the engine cases. Certain bearings will go in while the cases are heated to 300º, including timing side spindles for cams and cam followers. The outer sleeve of the oil pump will be fitted at the same time.
Theory is that the engine cases expand quicker than the bearings causing them to loosen until the engine is completely warmed up. The factory used a small chisel to 'stake' the bearings in place before they went to the assembly area. Loose bearings can cause a lot of damage over time as you can see from these crank pin nuts. This mod with two screws holds the main bearings in place.

Haven't had time to work on the Shadow lately but still tinkering with the gearbox selector forks, trying to eliminate the slide friction effect which is a natural phenomenon. This guy explains this in this video, about 5 minutes in.
https://www.youtube.com/watch?v=QJXqHpSh3SE
Now if I can just figure out a way to scrape a round shaft maybe it will help

I'm going to jump back to the wheels for a while. I think riding season is over for this year, at least for me
This is a bit more complicated than a couple of bearings and a handful of spokes.
The hollow axle tapered bearings are preloaded using shims.


Next the dust seals are fitted so the lip rubs lightly on the outer bearing race. This requires more shims. Now the brake drums can be added. These are new drums so the 5/16" holes need to be aligned perfectly for the bolts to fit in.


This is a temporary assembly to make sure the surface of the drum is concentric and true. Once trued the bolts are loosened as half of the spoke heads have to be inserted between the spoke flange and the brake drum. Spokes are ordered.

Does it have two drums on the rear?
I like tapered bearings a lot, but now sealed ball bearings are cheap and can have quite low runout.
I except back when the Shadow was designed, things were a lot different.

Yes, dual brake drums front and rear. Fortunately all the taper bearings in later Vinnie’s were std Timkens. They aren’t ideal for swing arm pivots though as they rotate (rock) less than 3 degrees. This caused brinneling where the rollers contacted the outer race.