help deciding what direction to go on new project

[agentoragnge]

another project fell into my lap this weekend and i have nothing but time and unlimited funds to throw into this sled....

Reality just slapped me in the face and i'm back to my senses now... got a couple power plants a 290, 340, 400. I really want to make a work horse for trail work with my local club. maybe a high torque stump puller that can pull a cutter full of tools (n beer for later) through unbroken trails and deep powder. a real boondocker so to speak. so naturally i want to drop in the biggest motor i got but have been reading that my specific 400 may have a 50/50 chance of being recalled for bad center seals, and i need realiability. i wanna be the tow truck not the guy who calls for one. so should i chance it with the 400 or sacrifice power over realiablity with the 340 i know is good? or something i missed completely like another engine i should be on the look out for. what about longer tracks? slighly wider ski stance since this old girl seems like she might be a lil drunk? kinda tipsy what direction would you go? let the voting begin

oh yeah it's a 72 tunnel n para rail but 73 drive train super stinger II TK (on the hood)

[mooreperformance]

The early Rockwell JLO engines (1971-1973) had an aluminum labyrinth seal between the cylinders. Much like the bad Kawasaki seals.
If you pull the engine down and it has a rubber seal, similar to the outer seals, it will work great. If it has the aluminum labyrinth seal you will need to have the crank pressed apart and the rubber seal installed.
I will go out on a limb and say that all 400 and 440 Rockwell engines with the six bolt heads were equipped with the good rubber center seal.
Symptoms of a bad center seal are the engine running on one cylinder (even with excellent compression on the dead cylinder) erratic idle, hard starting and constantly seizing pistons.
A bad center seal will drive you crazy trying to diagnose the problem!!!

If you have a Walbro diaphragm carb that has been rebuilt with a
Walbro carb kit (not aftermarket) and you use a Power Thrust I clutch you should have a reliable snowmobile (although with a high center of gravity and a heavy sled).

One last comment, it is hard to tell the difference between a Rockwell/JLO engine with a bad center seal and one with a Walbro diaphragm carburetor rebuilt with a cheap rebuild kit.
They will both drive you up a wall!!!

Been there, done that!

[mooreperformance]

Labyrinth seal

[agentoragnge]

Well i'll break into the case and see what i got on the crank as far as aluminum or rubber and go from there. I'm tempted to just put the 340CCW i have in it's place since it's a LOT lighter and runs "around the same" HP as the 400Rockwell. thoughts?

I'm just not familiar enough with these motors to know whats the pros n cons of em (polaris guy n all) but slowly learning here, so thansk for all your help

[mooreperformance]

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Rubber crankshaft center seal