Rebuilding a 300 Hirth into a MOD motor
Here is our subject. It's a Hirth 300 (54R4) that looks to be from a 1968 Snow Prince. * * * We will be making it into a modified 55R1 for a 1969 Panther MOD.
Typical grease, grime, and dirt. It has the correct Tillotson HR3A carb, but we will be replacing it with a period-correct HD14A. * * * The Sno Prince (St. Lawrence) drive clutch will not be re-used.
The 54R4 has a 24 mm tapered crank with threaded stub for a screw on clutch. With the cylinder stuffed with nylon rope to stop rotation, the pipe wrench is in place and ready. It took a few heating/cooling cycles but it came off without too much trouble. * * * The motor did not have a recoil on it (the one pictured is a replacement) and the starter cup was modified by someone to be used with a rope. A good starter cup was included with the replacement recoil.
Flywheel pulling lesson #1: I didn't have the proper puller, so I thought I would try using the old starter cup and a three-jaw puller. The cup screws onto the flywheel and the rim of the cup allowed a good place for the puller jaws. So I tightened it up as far as I thought wise, and it didn't come off. I used a little penetrating oil, heating/cooling cycles, rapping the puller bolt with a hammer, and leaving it under pressure for a couple of days. * * * I was also tightening the puller bolt a little bit at a time but, ...nothing. So, I tightened it up a little more ...and ...POP! The cup pulled apart but the flywheel didn't move.
So, while I waited for the proper puller (that I found online from Art S.) to arrive, I finished taking off the shrouding, carb, exhaust, etc. * * * The piston looks good (what I could see through the ports) but the rubber grommets for the wiring will need to be replaced.
The PTO side. The 55R1 used the "normal" drilled and threaded crank, so this one will have to be converted. The new drive clutch will be a Salsbury 770 with a "Hi-Rev" spring kit. * * * Exhaust side. Lots of oil and carbon build up, but overall, the engine looks good.
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