Benelli 250 SuperSport (egg)

[John H]

What determines how far out the dogs extend. Is this a common shift fork in the smaller Benellis?

[Lotus54]

The pins are different lengths I think.
I found out the long one is for the 4-speed models, this one is a 5-speed. There are only three ‘pins’ on the 4 speed, so the dogs have to be longer. Using the longer ones on the 5 speed meant the tapered part would not hit the pin on the return, allowing the pedal to full come back. It would hit on the ‘solid’ part and tend to not allow proper return.

[Lotus54]

I will include some pictures (I don’t think I can upload videos?) to better explain.
The shifter (called Preselector) has ‘dogs’ that are spring loaded. The ‘dogs’ on the preselector push against the pins on the shift drum (they call the part that actually moves the shift forks a ‘desmodronic shaft’). This causes the drum to rotate. Then the taper on the dog will push agains the pin on the shift drum allowing the preselector (and shift lever) to return back to centre position.
With the longer dogs, the taper was too high, so the shaft did not easily return to centre.


https://youtube.com/shorts/kO1psOkNDMU?feature=share

[John H]

The video explains the situation clearly.

[Lotus54]

I wanted to replace the locking washers and pins on the shift forks, so I was waiting for them to arrive.

I had the 250 2C (2-stroke twin) apart at the same time, I got all the parts for it first, so I put it back together and into the bike. Then other stuff came up so I had not done anything on the ‘egg’.

I now have the cases back together, clutch, pinion and cam gears and shifter in.
Next I will put on ignition flywheel etc.

[Lotus54]

Working on flywheel side.

[Lotus54]

Clutch, cam gear etc on.
Piston, rings, cylinder- on.
Sprocket, magento, flywheel- on (final timing to be done.

I have the head ready to cut the seat/lap valves. But then I found I did not have a pilot shaft the correct size. It has rather large (for a 250) diameter valve stems. I had some HSS rod- but not really tooling to cut that. Plus no way it needs to be that strong.
I didn’t have any regular steel, but did have some brass. I figured as long as I am careful that should be fine for light cuts. I will check it out. If I notice any issues, I will order some steel rod. None of the ‘standard’ pilots for my valve cutter are correct, I would have to get one of the expanding type. Those are quite expensive and seems a lot to do two valves.

[Lotus54]

It took about 5 minutes to put the engine in the frame.
Now I need to locktite/tighten all mounting bolts, pop on valve and clutch covers, install chain and carb etc.
Not very long now to see if I did the gearbox repairs right.

[Lotus54]

Fired up the 250. At first, it would not start. Then I noticed that after taking plug out to test for spark before trying- I put plug in but forgot the cap! Ha, what a dope.
After installing, it fired right up and ran great. I set the timing and took it for spin. It now shifts fantastically, it was parked at 800 miles due to poor shifting (I believe) and while I got it better, it was never right.
Now it is great.

Just a few more little jobs and take it out on the road.

[Lotus54]

A couple pics.