Mac 21 Piston & Rod

[Rick Sowell]

Guy's: I have a Mac 21 that I bought used and would like to know which is the correct way the rod faces when looking in the rear of the case. when I took this apart it had the oil hole in the rod facing the rear, or the rotor end of the case, also the clearence cut in the piston skirt also was facing rearward and not facing the crank counter weight. is this correct or not, because I have another Mac that has a different piston and the clearence was facing the counter weight like it probably should be. what is the correct way. I would post pictures but I can't figure out how to attach them. Thanks Rick

 

[carlnoki]

rick;

look at the big end of the rod carefully and you will notice that one side of the big end (bronze bushing)

has been chamfored. (spelling)

This is the side that goes against the crank shaft.

If you are talking about the piston being skirted (material being removed from about 1/2 or so of the circumference of the bottom of the piston), the removed section should be facing the drum rotor and NOT the exhaust side of the motor.

hope this helps.

carl

 

[jetpack]

With single oil passage rods I always turn the rod to face the fuel charge. Front induction the hole faces forward, rear induction facing backwards. The most obvious chamfer on the bushing goes to the crankpin. Some of my motors you cannot tell by the chamfer it is equal both sides, and so is the amount of spot facing around the bushing.

Some rods theres really no right side and can be flipped either way. These are the kinds of rods where you are glad you marked with an X before taking them off the first time if your intending to re-use them.