Quotequote:Originally posted by Bryson Williams
I'm interested in your cylinder,specifically your porting. You mention your porting is actually wider then the GS PRO spec's.
Would you mind sharing the port spec's measurments?.
I guess my question is that, IF the GS pinned pistons are right there on the GS and GS PRO? Ported bikes. I don't see how you could port wider and not knowingy expose the rings to either the intake or exhaust port. OR was that ring exposure by design, is there an advantage?.
This is a quick list of the port sizes, as hastly measured right now:
Inlet 39.5mm wide, 25mm high, 65mm from top of cylinder
Exhaust 35.7mm wide, 24.8mm high, 28mm from top of cylinder
Transfer 26.2mm wide, 15mm high, 41mm from top of cylinder
Compared to the GS PRO port chart at http://www.vintagemonark.com/images/modifications.jpg the exhaust and inlet are wider, while the transfer is narrower, probably more equal to a standard 6B? I guess this also means that I can do with a standard piston?
I cannot see that the transfer is raised 2 mm at the rear, as the chart suggests.
From what I can see now, and compared to the vintagemonark chart, I would guess this is a porting that is done by some swedish motocrosser to try to hang on to the big guys with the factory-prepared GS and GP engines. Or perhaps the GP engine was like this all the time? I don't have too much experience with 2-stroke porting, but to me it seems like the transfer ports don't match the inlet and exhaust?
I cannot reall tell if this is a better or worse porting than anything else, because we have nothing to compare to in a scinetific manner. I have seen another Monark that was slightly quicker than this one on a very long straight (running flat out on 1000m oval), but that might also be due to gearing, or the 26mm Mikuni.
The piston found in the cylinder, had 2 rings, one at 6 o'clock (facing rearwards), and one at approx half past 7, in between the inlet and left-hand transfer ports. As far as I have been able to find out, the Wiseco pistons are pinned similarily. Are these the standard piston's pinning?
I guess the ring breakage of the original piston is due to one of 3 causes;
1: inferior quality
2: Too sharp edges of the ports
3: Too wide ports.
Any thoughts on this? Perhaps I should round off the exhaust and transfer port top and bottom edges?
Anders
Anders Hørtvedt
1973 Monark ISDT