rearenginekarts.com

Hello everyone,
I need a +020 piston to put my MC 30 back together. Any help appreciated. I know these are not common these days.
PRuit Ginsberg

I believe a later 100cc piston would work, however they use the shorter wrist pin. Mc-7, 8, 9, 40, and 45 pistons should fit also.
I have a later piston with a later rod in a modified Mc-20.

The Mc30 pistons used the narrow boss rod so unless you change the rod you will need a 0.020" over piston from an Mc30 or Mc7 or a 0.060" over for an Mc20.

If you put in a later rod which would be best anyway you could use a full skirt piston from Mc8, Mc9, Mc40, Mc45 or an Mc90.

Remember that if you use the 9-port piston, you'll have to block the third port. I don't care who says that it isn't needed. It is, unless you're planning to 9-port the engine, or run a bottom carb. We use the 91 rods and grind the sides of the "eye" end to fit the pistons with the narrow boss. That's what we did on the twin Mc7's, and they run really nice. TJ

Thanks for the info on other options, guys. I have a 91 rod that could be used. I assume that it is a better rod, certainly less hours on it, and that is why you recommend it Scott? But I don't want to modify the nice block right now, so I need a full skirt piston like Scott is suggesting, ie 8,9,49,45.
Pruit

So my search is expanded to Mc8, Mc9, Mc40, Mc45 or an Mc90 + 020 piston. The MC 49 in the previous post is a typo, but these engines do have the MC 30 bore size, but don't work in a 30?.
Thanks
Pruit

Some bad news regarding my earlier reply, according to the McCulloch piston chart you would need to find a 740 or 840 thin ring saw piston +.020" PN 62879 (rings PN 59587) and this size piston was no longer available from the factory as of 1973.
McCulloch Mc-7, Mc-8, Mc-30 etc. factory kart pistons only go to +.010" while the 740/840 saw did have the same thin ring piston available in + .010", +.020" and +.030". They also had thick ring pistons available for the saw only. All I can figure is after .010" the kart engine was no longer legal so McCulloch didn't supply the larger pistons to the kart market.
Sounds like your search should focus on McCulloch pistons originally made by one of the after-market suppliers, like Moss, Wiseco, Salih, etc. Call Larry Fairfield.
If you have an Mc-30 intake manifold it looks quite simple to block off the third port with a thin shim between the carb adapter and the reed cage to me.