As i am using my 1939 BSA M21 for beach race (1/8 mile) I am always looking for more power. As alternative to the standard cam I am looking for a ZB 65-2438 inlet cam but the best i can find is a 65-2436 exhaust. However - I think i seen somevhere that 65-2438 and 65-2436 are identical except for the marking. Is that true? If so then i can use a 65-2436ex as an inlet? Best regards Per Garbos
Are you still running a standard port and cylinder head internal profile?...If you are nothing much will be gained from a change of cams as they won't produce great results in isolation...
If you have, or intend to, improve the engine in these areas (and lighten the flywheels) then a pair of Gold Star scrambles cams would be a good start (65-2446)....Ultimately the inlet in particular needs as much lift and duration as is practical combined with breathing improvements to the port and head, crank weight reduction and the largest possible inlet valve...Ian
Hi Ian, I have done the usual stuff.. welded op the cast iron cylinderhead -sligthly bigger piston - portet intake to Ø30 and got a Ø 30 R57 amal bronze carburattor.(modified alcohol carb) removed the tulip shape from the bachside of inlet valve - rounded cylinder shape for better inlet flow. Adjusted the exhaust pipe length ect on testbench + jetting.
I got almost 20 HP at the rearwheel and thats enough to run faster than most VLC Harleys over the 1/8 mile at the latest pre-war Rømø beach race.
As its beach race in sand from a standing position a god low end performance is important and thats why i think a mild cam would be best.
The topspeed in beach sand from standing position is just more than 91 km/hour at the 1/8 mile mark.
Its acceptable but it could be nice with a litte bit more.
By the way - the crankshaft is the stronger cast steel - not cast iron.
Hi Per..It seems you've done your homework and improved the engine in the important areas...Scrambles cams aren't anything like as fierce as the Clubmans cam...Consider the fact that bottom end and midrange performance were desirable features on a Gold Star scrambler....Ian
Hi Ian, You got a point with the scrambler performance and it migth work fine on a sidevalve even the duration is much longer than the at ZB cams.
It comes with the significant higher lift and thats for sure a benefit.
I will se what i can find. Best regards Per
I came across some Goldstar cams the latest days - scrambler cams(2444) and Touring cams (2448 / 2452).
All these cams have a groundcircle of around Ø22,9 mm where all my M21 cams (2420) have a groundcircle of Ø25 mm.
However if i am going to use one of those Goldstar cams, there is not much left before the camfollower is getting in contact with the axle or the aluminiumhouse- (0,2 mm) - It is possible to remove material but it will most likely weaken the aluminiumhouse.
My impression was that all cams had the same groundcirle (ø25) but it seems not to be so. Or is it only aftermarket cams - these I was looking at was from Phil Pearson.
I would prefer not to mill in the house and in the axle.
I was looking at touring cams 2448 and 2450 - sorry wrong writing - both with groundcircle of 22,9 mm
then i was looking at some other cams 2444 (to hot) and a 2454 (scrambler) also with both with a groundcircle og 22,9 mm
It seems (from photo) that only the ZB cams 2436 and 2438 have the bigger gronudcircle as 2420 - but i an not sure
