Hi Rootsman,let's see if I can help a little.First off,if you are quite heavy,a recognised mod is to use Pursang springs in the forks as they are a bit longer than the usual Sherpa ones. I use aftermarket Magicals in my Alpina. Next,I have not tried this,but have seen mention to use a Yamaha brake cable on the front as they are made much heavier than others,resulting in the outer not compressing when braking hard.Look for 77-84 YZ or DT 125 MX. The brakes are known to be feeble,another piece of info I came across is to use brake lining used on fork lift trucks. I did this on a road bike,it now brakes really well.Engine. All trials models used a 60 mm stroke. The M92 & Alpina M99 are unique. The crankshaft is slightly bigger in diameter than the 250's , but I think the cases are basically the same. If you put a 250 centre gasket on a M92 case it overlaps inwards a little towards the crankshaft,needing a little careful trimming. This I did when building my M92. Important!!! Use C3 clearance bearings when building the crankshaft. Also a good idea to use a roller bearing on the flywheel mag side. It is a NJ 205 ECP/C3. That's a SKF number. These 326cc motors give loads of torque when set up nicely,a delight to ride.i hope the above is of help,and wish you well.
