Chainsaw Repair

Probabley if it would work you'd jamb the piston through the top of the head deck .

You can get into all kinds of problems .Like for instance clearance on the stuffer .On a Mac 125 for example they  use a special six splined screw on the rod because believe it or not a standard grade 8 #10-32 socket head will hit the stuffer .That just one of many problems you might encounter .

Although I'm not exactly certain I'd imagine talking a standard 250 at 80 cc as to a super 250 at 87 cc ,they most likely used a shorter rod .I'd have to wade through a ton of IPL's to be certain .

I am going to mod this one! I've actually got another 250 powerhead on the way that is supposed to run well. I'll also find a 1-70 or a 1-75 and do some swapping...if it will work I have a mill and the necessary tooling to bore the cylinder. I just don't care to start welding on the crank to stroke it like we do on our antique pulling tractors if a crank swap will work.

Remember Al, you got myself and many others in to this souped-up-saw thing. Now the way I see things, you need to help me out along the way.

Time for work. Thanks

A little fly in the ointment .According to the IPL's the super 250 uses a ball bearing on the clutch side while a standard 250 uses a needle bearing .Which is not to say you can't use a needle with a super crank providing the shaft size is the same ,dunno .

An I-70,Super 44a is a right hand start saw which uses a right thread nut so you don't spin the clutch off starting it ,keyed clutch which has a tendency to tear out the keyway which is why in later years Mac used just the taper to hold the clutch,no key .A standard 250 uses a left hand thread screwed on clutch .

Now then  the rods on a 250 and a super are the same which I assumed them not to be  but they list a different piston so I assume if you use a standard 250 piston with a long throw crank  you'd  chunk it through the head deck .

I-75 have no idea .It's not on my micro film nor in the big black book that weighs 20 pounds .According to Mike Acres site they only made it a year .So reading between the lines it's rare as a hens tooth .

Now before you get the idea you can take a crank from a 650 gear drive here's that deal .They are also rare as a hens tooth .That I know of they were made for 10 months .I have one,Mike Acres has one and there are only two others I've heard of .Besides being a geardrive that crankshaft is not designed to run a direct drive clutch .

They pop up on flea bay every so often but are often oversized ,left over new oldstock .

FWIW I turned a set of rings out of tool steel for a Mac 125 but never finish them because I found a set for 14 bucks .It can be done but it takes hours and hours of tedious machine work .

Now if you are serious about all this why don't you just bolt that block up in a face plate and cut the head deck off .Make another head and punch the iron liner out or make a new one .

If you really want to go whole hog find a kart piston .Wiseco made them for the 101's that were 100 thou over sized .Of course it would just be easier to find a 101 rather than all that fiddling around but they are very proud of those things as far as price .

Stroking a crank is very easy, as is shortening a rod. I've taken WC Allis Chalmers cranks (4.0" stroke stock) and added two inches to the stroke. That usually takes about a full day of welding. The compression height is so tall on those old tractors that we can usually add stroke, go to an automotive style piston, and then actually make the rods longer than they were stock. I usually buy 8 SB Chevy rods(5 bucks each), strategically cut them, weld them back together, box them in for strength, then balance each end.
As far as the welding of the crank and shortening of the rod goes, I can't see that taking even a day. A machine shop a few towns over can grind it(the crank) for me for 50-80 bucks. So far the biggest hold ups right now appear to finding a set of rings and reeds. Chainswr can't help me, and I'm not finding anything on fleabey.
And speaking of reeds, if I get a fog of gas near the inlet of the carb at WOT, thats usually an indication of reeds not sealing properly, isn't it?