Seeley mk3 engine plates (2021)

+1 about your experience with Constant's help. HnW is by far my best provider in terms of reactivity, reliability and "fair deal".

Laurent

Hi, thought I would chime in on this thread. Im building my own Mk3 frame and pairing it with a Commando 750 drive train. Frame is done, and I now am going to add engine mounts, but first Im doing the engine plates from some templates I kindly got from Minovation. I have done the crank case holes on the rough cut plates, and am about to set the holes for the gearbox. As Im wanting to use a std, Commando primary case, I thought I would check the hole pattern from a std, Commando Isolastic cradle against the set holese on the Minovation plates. The problem is that the two boltholes that holds the gearbox (top bottom) are set about an inch lower on the std, isolastic cradle, than on the mk3 engine plate templates from Minovation.(these are intended for a Titchmarch frame.) From what I can gather I will get problems with fitting the commando primary as the inner case is bolted onto the crank case, and would not hit the mainshaft if I drill the gear box holes like the Minovation templates... This also rises the next question.. Is there any Ideal distance from centre swing arm to centre mainshaft? And should It be on a horisontal line from the swing arm? (using the seat rails as a datum for horisontal..) Can anyone enlighten me on these issues?

Using the Commando primary cover puts an unwelcome restriction on what you are doing. Are you building a road bike or a replica of a race bike for use on public roads ? If you are using a belt primasry drive, you do not need an oil bath. On my bike, I use a neat cover made out of a 50mm wide strip of thin steel to form an outer surround, and four Dzus fasteners which hold an aluminium cover plate. If you take a line between the crank centre and the rear axle, the gearbox mainshaft centre should be about 8mm higher than the line. That way. when you accelerate the pull of the chain acts against the tendency for the rear end to squat. If you have the mainshaft too low, you might get too much squat. With a Seeley Mk3 frame, when you increase the trail by using less yoke offset, the bike can self-steer in the correct direction when the rear end of the bike squats. How it feels when you gas the motor in corners is important. The rear suspension units provide adjustment.
I am glad to see you doing this, you should end up with a very lovely motorcycle.

To make the holes in the engine plates,, I took a piece of 3/8 inch round steel rod and turned a point in the end of it. Lay the plates against the casing and use the rod as a centre punch. It is better to drill the hole slightly under size then ream them. It is better to get youe motor as far forward as possible and you gearbox as far back as possible without the clutch fouling. My motor is probably about 6mm too high in the frame. The cables on the rubber-mounted twin carbs rub the bottom of the aluminium tank and are staring to wear a grove. My head steady consists of four large rose joints on two short tubes. Two are held to the head by shoulder bolts. I don't use the Seeley ladder in front of my motor - it is a gusseted piece of chrome-moly tube from a push-bike maker. With a Seeley MK3 frame, it is possible to make the front end walk when you have the ladder.