Rather than just leaving things 'up in the air', here is a brief update on the FAB 500 racer.
Since being rebuilt with Ace's high ratio rockers and other modifications, we gained power, but have been plagued with reliability issues and it was hard to understand why - we even had a big split occur in the left hand crankcase and I was seriously thinking of giving it up altogether with this machine. Was it the crank? Was it my modified main bearings' arrangement? Were the high ratio rockers a bridge too far? ... Well, actually, none of the above, not directly, in any case.
It turned out that even with a matched Redditch factory pair of crankcases, the main bearing bosses were out of line on the vertical plane by 0.018", this was all ok for all the years where just the one timing side race had been used and even where two timing side races were fitted, with a 5 piece crank assembly. The last straw was when I fitted a 3 piece crank and an even larger inner timing side bearing, along with the smaller outrigger one, as before. Now we had a crank assembly trying to force the bearing bosses into line, resulting in the cracked crankcase.
I won't go into fine details, but I have fixed the problem and a test ride earlier today was very promising, with the engine much smoother [surprise] and the whole bike much smoother, too. The power from low to medium rpm's appears to have increased by a large amount and there may be a small gain at the top, due to the above being sorted, as well as piston to bore clearance issues dealt with and a better squish clearance now being possible.
I have always had reservations about the 500, preferring the 350 by far, until today, when the 500 rode and performed better than I have ever felt it to before.
All being well, it will be present at Cadwell Park for the last round of this year's BHR racing, where a championship position is out of the question, but I hope we may find some big gremlins laid to rest at last
B.W.
https://www.youtube.com/watch?v=4DTpjvcOM8k