Cast or forged pistons

[Hunter]

I'm rebuilding the engine from a 79 Invader, and even though the sled ran when I took it apart(125 lb on each cylinder) I've decided I'd like to get new pistons for it. Question is should find a OEM style set of cast pistons or a forged set like the ones made by wiseco? I've heard good and bad things about forged and wonder what your experience with them has been.

[mswyka]

We have two sleds with Wisco pistons.  A 1980 440 Invader (sleeved for 0.020 over) and a 1979 Intruder (sleeved for 0.010 over). The Invader is a workhorse, 160 psi compression and plenty of power.  The 79 Intruder is so-so.  But our fastest sled off the line is a 78 440 Intruder with aftermarket OEM style pistons.  They say that you get what you pay for, but as far as our experience just riding around the farm I can't really tell any difference.

[Hunter]

Yeah I'm probably just going to go with cast pistons, they're a lot cheaper and I don't think I'm going to race with it.

Something else I was wondering whats the best way to break in one of these motors after a complete rebuild? Somebody told me to run pemix in the tank(ratio 32:1)along with the oil injection. That can't be right though that would be way to much oil.

[Interceptor398]

25-1 premix in the first 3 gallons of gas and don't run it hard for the first 10 hours of operation per a ST440-A3 Intruder owners manual.

[mswyka]

What he said.  And judging from the one sled that we had with a failed oil pump, these engines have the capacity to burn a very high concentration of oil.  We will also use a liberal application of 2 stroke oil on the bearings when we re-assemble an engine.