BSA B50 -500 APG Build

[Koncretekid]

Jim,
It ain't gonna be me this year, because I'm not planning to go to SCTA, only BUB.  I just landed (drove) in Lafayette, Colorado about 15 minutes ago, just long enough to have a cold one on the sun deck (72*).  If you're stopping in the area on your way to Moab, email me and I'll give you a contact number.
Tom

[JimL]

Thanks, send me a PM with a phone number, you're not far from Longmont.

JimL

[wobblywalrus]

Tom, this is a reply to your post about carb size on the walrusmobile build diary.  BSA were pretty good experts at carbs, ports, and valves.  They had 1.5 inch (38 mm) Amals on their hotter Gold Stars.  They needed a close ratio gearbox and a skilled rider to make everything work.  I always considered that to be the upper limit for carb size on a 500 cc bike.

The hotter Hinckley Bonnevilles run 39 mm Keihin flatslides or 35 mm Keihin smoothbores, mostly.  I have never measured a smoothbore.  The 39 mm flatslides measure out to 36 mm choke size.  My engine has a race port job.  The port diameter is somewhere between 36 to 38 mm between the carbs and where the ports widen near the valves.  Folks use this port work and the 39 mm flatslides for bored and stroked Bonneville engines producing over 100 horsepower.  That would be over 50 horsepower for a 500cc cylinder and a 36 mm carb.

These are just some numbers for reference. 

[Jon]

To save cluttering up wobblie's thread this is the company that makes the quickshifter  switch I am using.
http://www.rscycles.com/images/electricshift/kart_battle_shifter.htm
There's a lot of high dollar quickshifters and some really budget ones, the main price difference appears to be in the switch.
Some guys even use a thumb switch, just loading the shift lever and hitting the thumbswitch for the programmed time, this unloads the trans enough to let it pop through.

As I said in Wobblie's thread I dont think that the small amount of time saved would help us but maintaing velocity & mixture by not chopping the throttle would help pull the next gear easier IMHO.

Cheers
jon

[wobblywalrus]

The air shifter seems to be a good idea.  There is a lot of linkage between the foot and the shift shaft on a lay down bike and it is hard to make a really quick and clean shift.

[Koncretekid]

Bo,
Interesting about the 39mm flatslides being used on the new Bonnevilles.  My only real experience in the increase in carb size, is when I first took my roadrace B50 to Bonnevile. My first run, using a 36mm Amal Mk II (clone of a Mikuni round slide) I went 99mph.  For my second run, I changed to a 40mm Amal Mk II, and went 104mph.  Unfortunately, I also changed the rear sprocket from a 47 to a 49, so I'll never know which change had the biggest effect.  I chose a 42mm Mikuni Flatslide for the short stroke motor, even though the guru of B50 flattrack builders (Ed Valiket)  told me he uses 44mm roundslides (which are monsters!)  It's just too time consuming to try all the possibilities when we only have a 4 day event with a couple of runs per day.  In any case, the motor dynoed at 42hp in Longmont, Colorado (elevation 5200 feet), so it is not doing too bad for a 40 year old 30 cubic inch pushrod 2 valve motor on gas.

Jon,
Thanks for the link on the shift interrupter.  I won't get a chance to try one this year, but it makes sense.  I did source a close ratio gearbox for this year, so that should help if I can get off the line (1st gear is 1.94 to 1, and I added a tooth, or maybe 2 to the front sprocket).  I think Bo is thinking about an air shifter as well as a spark interrupter, but that would of course be more $ and time.  At least in my class, I only need about 1/2 mile to get up to speed, so a few burps along the way are no big deal. Don't know about your build though, Jon!

Tom

[Nortonist 592]

I'm using a 45mm round slide Mikuni on my Weslake and a 38mm flatslide Kehin on the Weslake in the sidecar.  Both are elderly four valve pushrod motors.  The 45mm Mikuni has run just on 130 at El Mirage and the sidecar just on 126 at Bonneville.  I'm going to bring the 45mm with me this year to SpeedWeek.

[wobblywalrus]

Tom, 42 hp at that altitude is very good for an old two valve air hammer.  Excellent job. 

[Koncretekid]

Back to the Build!
Got back to Nova Scotia from Colorado 2 weeks ago after a 4 day drive.  Missed the ferry to N.S. from N.B. by 9 minutes, so had to drive around.  It gave us a chance to visit some old friends near New Glasgow, N.S., so broke up the additional 7 hours it takes to drive around.

On the trip home, we collected one (or maybe 100) of every species of north eastern insect known to man.  It proves that the proverbial "wall"  of air being pushed ahead of a moving vehicle doesn't totally divert the air.

I picked up the bike with the finished bodywork last week, and started on some changes required.  Since I moved the footpegs ahead to keep the rear end as narrow as possible, I had to remake the shift and brake linkage.  I can't seem to articulate my foot as well, so I fabricated a toe-heel type lever.  It is still difficult to shift, but may be easier with the motor running.  The third photo shows the alternate shift handle.  I also had to mount new tires, as the front one was only rated for 118mph, and the rear one needed to be bigger to get a little more ground clearance.  Front is not a 110/70-17, while the rear one is now 120/80-17.  I now feel qualified to write an article on pinching tubes, or not.  I may do that in the Tech section.  These new, higher speed rated tires were probably never designed to be installed using a pair of 6" tire irons. 

I still have to make a new exhaust which exits thru the side of the fairing, and add a hand control for the rear brake, as I found it very unsettling to try to come up to a stop dragging my feet on the ground.  It will be worse with the fairing.

Tom

[55chevr]

I see that you and Lars use the same shifter ... Joe

[Koncretekid]

I see that you and Lars use the same shifter ... Joe

Yes, and on the right side you will find another alternative shifter in the following photos.

I connected the right side foot brake, but was not completely satisfied with foot only, so I added a hand brake cable as well. (three alternative shift levers, two alternative brake levers - - probably overkill!)   I would have just used a cable to the handlebar handle, but my cable wasn't long enough, so I just connected the cable to the brake arm.  I also fabricated a new exhaust exiting out the fiberglass side cover.  I left 1/4" of clearance which I probably should insulate with something.  The last photo shows the front right side of the fairing and the exhaust exiting thru it.  Also note there's no hole behind the wheel for cooling - - just a 2" hole in either side and the fork holes.  Will I have cooling problems?

Tom

[Old Scrambler]

Tom.......overheating, yes

I see you have no room to direct the exhaust further to the rear and keep the side-air clean.....but maybe it could exist the bottom of the fairing rather than the side.

Maybe you could exchange the big battery for a lighter unit and install a cold-water tank with a coil or two around the head and the oil tank

Otherwise.......it looks real FAST

[wobblywalrus]

Sending a PM to the folks at Speed Team Doo might help.  They have been dealing with cooling issues on enclosed engines like yours.  One of their bikes has a BSA or Triumph 250 engine in a wooden box.

   

[MattGuzzetta]

I don"t know if this will help, but we ran a 125 Suzuki in a streamlined shell with only air for cooling passing through the cylinder with a tight shroud around the fins.  We ran the bike 8 hours a day like that without any hint of overheating.  The shrouding was made by forming 1/8" pattern wax around the cylinder fins and fiberglassing over the wax.  We then cut the glass off, cleaned the wax off and then adding aluminum tape to protect the glass from heat. (Probably not needed, but it did make the inside smooth) We use a NACA duct to bring the air in and ducted the air out the opposite side.  I have attached two photos of the details that should help explain the system, I hope.  The other benefit was the shroud kept the hot air away from the carb which can't hurt. 

   This photo shows the inlet side.

    This photo shows the exhaust side.

The intake for the cooling was 4inch diameter if that is any help.
Your build is looking great, it would be good to be able to run as little aerodynamic drag as possible with the cooling. 

[Koncretekid]

Scrambler: Yes, some sort of extra cooling is probably necessary.  As for the exhaust exiting beneath, it must be directed away from the salt.  I wanted to keep it short to try to pick up the third harmonic of the exhaust wave.
Wobbly: I have seen Ed Bennett's (Speed Team Doo) bike, and I will have to get in touch with him regarding cooling.
Matt: I am very interested in your cooling arrangement. Do you have photos of the inlet and the exhaust from the outside?  How does the air know which way to flow?  I can find high pressure zones, but low pressure would seem to need to be further back in the diverging area of the fairing. Also, I see that the top of the cylinder head is exposed.  Did you get a lot of heat rising up into the driver's compartment?  And when you say you ran this configuration 8 hours per day, was that several runs at Bonneville, or some kind of endurance non-stop running?  Did you have a temperature gauge of some kind?
Tom