A bit of progress with the build, I cut down the cross tubes on the seat post from 4" to 3" to allow the standard Scout rear engine plates to slide back and down into the frame. With the lower rails slightly spread to give some clearance, the bottom of the sump now sits level with the underside of the frame rails.
From the outset, I had hoped to keep the seat post intact but this would mean sitting the BSA gearbox further back than I would like and the motor would not sit centrally in the V of the front frame section. If the motor sits 0.5" further back it sits just right, if the gearbox is moved forward 2" it will sit at the same distance as the standard Scout box. With a bit of modification to the inner primary I can get the BSA box to work with an Indian primary case ... Similar to this set up for sale on Ziggy's site using a Triumph ( I think) gearbox
To do this the seat post will need trimmed below the top cross tube and a gearbox mount plate welded in to replace the lower half
I was gathering the parts together for the Fire Arrow Scout and the opportunity to get a '51 Warrior frame and fork turned up, so a bit of wheelin and dealin later the plan has changed. Still planning a hot 640 45cu" motor in a light chassis driving through a four sped foot shift box, but it will now be in a pukka pre '53 Indian frame.... albeit for a vertical twin instead of a V.
Wheels are a mix of straight pull Talon hubs, a grass track 19" rear and a 21" from a Beta trials iron. Option to run a single disc sprotor at the back or have small trials type discs either end.
" I just finished a motor for Matt Blake last night. It is a 648 "Big Base" 58" Stroker. It has all the best stuff in it. I used S&S 58" wheels, and Carrillo rods. I had light Arias "Tall Dome" pistons made with .180" pop-up. It has Enfield Racing's reproduction cylinders, that I ported. It has my racing lifters, and hi-lift cams. It has my new 36mm Mikuni setup that is perfectly suited for this motor. It has some original 648 parts, and alot of NOS parts. It's gonna be a screamer! I am just now putting my Twin-Scout motors back together now, after doing some mods, and clearance changes. It will be a much faster bike this year at the Bonneville "Speed Week" meet. I'll keep you posted. See Ya; Jim Mosher."
741b cases, Chris Ireland built 741b front frame, jigged on his old kitchen table and an Antig grasstrack tail section, frame could easily be modded to take SS cylinders to make a 45cu" class C style racer
"This engine design was of my own creation. I'd been spending countless nights going over the numbers - stroke, rod length, compression height - until I settled on this configuration. I was told I was the first to try this, but given all the builders out there I can't believe someone didn't beat me to it. Anyway, it has the 45" Scout flywheels & rods, and HD 45 stroker pistons from T&O. The pistons are ok, but just ok. I would have liked to see a little more effort in the machining end such as a true cam ground skirt. I assembled the bottom end, installed the old 741 pistons and barrels, and measured how far they protruded above the deck. Then I compared the difference in compression heights and calculated what the rod length actually needed to be with the stroker pistons. I had Rocky relieve a little from the inside of the piston pin boss, hone out the small end to accept a thicker bushing and then offset bore the bushings to get the deck height perfect with no shimming at all. One rod was offset .029" and the other was .039". The difference reflects inaccuracies in the machining of the case. All this was intended so I didn't end up with an engine that required changes in the frame. The 741 frame is quite small so a taller engine would require a lot more work. I'm using the original cams & lifters, carburetor too. I did put in larger intake valves. I found the intakes from a Ford 200 six worked fine after turning down the head diameter and then machining the valve head thinner for a normal margin. This also lightened it. I had to relieve a bit out of the cylinder head to make room for the valve. The key groove is about 1/16" farther down the stem so all I needed was a 1/16" thick shim under the spring. The only other thing that is home grown is my exhaust system. I made the headers almost 40 years ago out of 1 1/2" pipe and fabbed up the muffler last spring. There's a few other odds & ends that I had made over the years. A sidestand, my brake pedal which was out of a Datsun 240Z originally. The front fender is a mystery. I have no idea what it came from but think it could be from a Jr. Scout. If anybody could identify it I'd like to know. It's definitely NOT 741. I have one of those in the loft. I live in the mountains of Vermont and was always having to shift down to climb these steep grades with the original engine. That's a thing of the past now. I can zip up a 14% grade at 60+ mph and that's after stepping up the drive sprocket 4 teeth! My buddy from New Jersey came up on his Yamaha and after about 15 miles stated that I was a little hard to keep up with. Didn't hurt my feelings one bit!