Originally Posted by cannonball2
Ok heres an educated guess. If the rod is marked FM80 it should be the long rod GT5 crank(38mm stroke,114mm long) that's whats in my standard GT5. If the rod is marked ZAF80 then Im guessing its a 40mm crank as used in the GT5-SR Super Rat, that's whats in the picture if I am seeing correctly and they photoed the right parts.
So if you have a GT5 type engine with the FM80 rod, it uses the high pin piston and the 69.5mm jug. Thats what I have which makes it a GT5. I believe it would be the GT5A if it had the 40mm intake spacing.
The Super Rat adds 1.8mm to the stroke the jug is basically 1mm taller. In the pic it looks like it uses a low pin piston. This means there has to be a difference somewhere either in the case, or rod? Shorter rod, taller case deck, it is a new crankcase design so why not adjust case deck height.
Watch this vid. Fred is in the dark on the ZAF80 rod as hes never seen one and assumes it is the same length as the FM80 and uses the high pin piston. Maybe not. I bet the Super Rats are fairly rare as to the cost(WDs didn't order many) and they are not that common. Bottom line is I don think the GT5 38mm and the 40mm GT5SR parts will mix properly in any combination.
Or I could be totally wrong! https://www.youtube.com/watch?v=rzLWYSlpFEg
The ZAF80 ROD is also a 114mm rod and is used in the GT5 geometry engines and you have to use a high pin piston just the same as you do with an engine with the FM80 rod.
The GT5 38mm stroke engines I got from thatsdax both have the ZAF80 marked rods, these rod identify the rod as 114mm and the engine as being a GT5 38mm stroke.
Its the rods that are maked ZAE50 that identify the engine as a 38mm stroke but use the low pin piston just like a PK80 type and in these engines with the ZAE50 rod the piston is .062 below cylinder deck @ TDC when using the standard PK80 height cylinder.