1940 Scout #4 (58" Stroker Scout "Bonneville"Motor) Info

Here is my last of the (8) Scout Stroker Motors, I had enough good left-over parts to be able to build yet another 58" Scout Stroker motor. I had my rear cases from My Twin-Scout LSR bike left-over, as well as the T&O flywheels that I used for (4) Land Speed records. I had an issue at Bonneville, where ALL the cylinder nuts, and (7) of the cylinder studs vibrated out of the rear motor at over 155 mph. It was my very first "Streamlined/NOS-Oxide run", and the bike was really reving high. The cylinders lifted 1/4" up, and a lot of oil was coming out onto the rider. The top motor mount was bent from the cylinders trying to rise. Luckily, it stopped the rise, and it suffered NO cylinder damage (or pistons). But, the right front cylinder base stud was loose, but still there, and the cylinder movement cracked the right case near that stud. I had the crack welded professionally, and I decked the block a couple thousands. In (6) weeks from the day of the damage, I was back at Bonneville for the next meet (The World of Speed), with these cases, and it set the Land Speed Record of 156.788 in the "1,350 APS-VG" class record (1,350cc Altered Partial Streamlining-Vintage Fuel)! These are great cases, but for the next year, when I developed my "Big Bore" motors, I replaced them. They are still great cases due to all the other good work that went into them. I kept all the flywheel, shafts, and other parts to use on some other future build. This is that build!

I added a set of new Scout heads from Jerry Greer's, and I fly-cut them to give a .050" squish. I then added a set of new cylinders from Enfield Racing. I detailed them, ported them, and added new intake nipples, and Starklite Valve guides. The guides were honed to fit, and Teflon intake seals have been added. I have a new performance intake manifold, and adapter for the Mikuni VM36 Round-Slide carb that works so very well with these Stroker motors. I have the new head studs, beveled washers, and ARP Grade-10, 12-point "Flange Nuts" that I use instead of head bolts. I have new valve guides, valve covers, 7-coil valve springs, Titanium Retainers, keepers, shims, and fiber washers to complete the cylinders. I also have new Manley severe duty Stainless Steel valves that I have made. I also have Kibble-White "Black Diamond" exhaust valves. When I got the cylinders, I did a porting job to enhance flow, installed the guides, honed the guides to fit the valves, and calculated for the correct valve spring tension. They got a "5-angle" racing valve job, and bored, and honed to suit the new "Low Expansion" Forged pistons (of my design). Then painted in high-gloss engine enamel. Ready to go!

The bottom end is completed, with a set of heavy duty late Scout rods. The balance job, and flywheel truing is done, and perfect. The cam chest is all finished, and I am using a NOS set of original Scout "Bonneville" cams on new shafts. I am using a good set of original Scout "Bonneville" lifters that I have upgraded. Scout lifters (as well as Chiefs) get a lot of wear on the arched pads, where the push rods are lifted from. I have a grinding jig for these arched pads, when making my new racing lifters. I use "Stellite-1" rod, and do a Tig weld repair to these pads, then they get precision ground to a better profile than the factory did. The "Stellite-1" hardens to a Rockwell 62-64 when welded, so there is no need to re-heat treat the parts after. Then, I add a set of my "Needle Bearing Rollers" for long life, and better performance. Indian always used a solid pin in a solid roller, and with any kind of lift, or spring pressures, the rollers would stop rolling at the top of valve lift, and skid down the rest of the cam lobe, causing premature, and serious damage to the cam lobes. So, it is absolutely impossible to now find a usable set of Bonneville Cams, or lifters. Mine are NEW cams, and improved lifters. Many years ago, I was seeing these selling for around $1,200.00 per set. My performance cams/lifter package will out-perform these cam/lifters, but these are the factory "Hot Rod" parts in new shape. I was going to keep them, but I figured that if I added them to the cases and flywheels that have a huge Bonneville racing history, then I would end up with a "True" Bonneville Scout, that has "Bonneville DNA" all over it.

I added a new "Joe Hunt" magneto, that I like to lock at 30 degrees BTDC (no Advance/Retard). I am using a very good 1939-1946 Iron oil pump with new gears, and fully rebuilt, including the fittings. I converted over to a 1947 Chief oil sump "Scraper", plus all the other little mods that I do for a longer life motor. I'm glad that I decided to pull all these parts together for this special Scout Stroker "Bonneville" motor! This motor, with better carburation, more cc's, higher compression, porting, and more should make right at double the power of an original Scout "Bonneville" 45" motor.

Motor Spec Sheets

Parts List, Prices, and Total Costs

Picture Gallery below, during the Build

So, what do you think?

James R. Mosher
(505) 466-7870