Give me a call at the shop today and I’ll give you exact measurements. I have them written down in “The Book”. I understand your thinking behind this and feel you may have some success. Here are a few issues you may run into:
The crankcase of the Blaster is a casting with a hole bored very close to its center for the crankshaft bearing. I’m pretty sure (not looking at “The Book”) that we open the case diameter 3mm to accept the longer 4mm stroke crankshaft. We do this off of the machined surface for the outer bearing race, not the inside of the case. Our initial cut is usually about .030” or .015” per side. Even with a cut this big, the case never cleans up in less than 2 cuts. This tells us that the inside of the crankcase isn’t concentric to the hole bored for the crank bearing outer race. The other issue is the case isn’t perpendicular to the hole for the bearing. This is the reason that some 3mm cranks will fit with no grinding and some won’t.
When trenching the case, you’re going to find that it gets paper thin in two areas. The first is where the locating pin that aligns the cases is and the other is the area between the case and the counter balance shaft. You want to be very careful in both of these areas. You want to keep the area as thick as possible and still have the .020” of clearance.
We already know that both cases are castings. The chances that they’re both the same are slim to none and Slim just left town. After the cases are both opened up 3mm, the freshly machined surface of the cases will need to parallel to each other in order to seal correctly.
I wish you the best of luck and feel it will work if you have almost mirror cases and if the bearing holes are almost dead on center with the crank case ID.
