Hello all! I started this thread over in 'vintage sleds only' but decided it would be more at home here! I apologize in advance for the lack of pictures, but stick-shift, rotary phone, analog everything me never graduated from photobucket academy. Instead, I'll do my best to paint vivid pictures with words! A couple weeks ago I stopped at my local sled salvage yard to search for parts and see what had arrived since my last visit. A forlorn '67 Rupp SSIII caught my eye. What a mess. It looked as though it had been sitting in the dirt under a pine tree for the past 40+ years. The single piece hood/pan had been removed and was sitting off to one side, faded to the familiar 'Neglected Rupp purple'. Every steel part on the sled was severely rusted and pitted. The outer half of the primary was gone and the 300 Hirth seized. The skis were removed but included, both bent and one missing it's leaf spring. The carburetor and throttle/brake cables were seized, and the whole thing was covered in a thick layer of frozen pine needles. Not a pretty sight.
I merely took note of it and kept walking. Later on at home, I couldn't stop thinking about it. I'd owned several '69 Rupps, but never a '67. In spite of my best efforts to resist, two days later I traded a 250 Rotax single and fifty bucks and dragged it back to the shop. First step was seeing exactly what I was up against. I ran my kerosene heater in my tight single stall garage until I was able to scrape/vacuum the majority of the dirt and pine needles up. Between the crud in the engine compartment and in the track/bogies I filled my shop vac about five times.
I removed the carb and sprayed 1.5 cans of Seafoam Deep Creep down the intake and into the crankcase pulse fitting in hopes that things would free up. Took the carb down to the basement and took it apart. The only casualty was the choke plate, which was so green from corrosion I had to cut it apart to remove it. The carb body itself and any other aluminum parts got several treatments of NAPA Aluminum Brightener. Between that and scrubbing with a brass brush, 99% of the crud came off.
The following day I removed the fiberglass muffler cover and again filled the vacuum with pine needles and dirt. Unfortunately the muffler is rotted out all along one side. Also removed the fiberglass drive chain cover and used my roto-zip to sever the rusted solid #40 chain. Picked up a new 10' length of it from work (farm store) one day later. Cool! With the chain off, the track and secondary actually roll over nice! Still need to tackle the fact that the secondary is seized though. One thing at a time.
Tried my biggest pipe wrench on the primary shaft in hopes of getting the engine to turn, but to no avail. I kept an eye on the level of Deep Creep in the intake, but it's not going down. Dang it. Finally got impatient and removed the cylinder shroud and head bolts. Naturally the cylinder and head were covered in a halo of mouse nest and mud dauber nest. The vacuum is getting well acquainted with mouse leavings on this project.
I was terrified to remove the head, but upon doing it, was shocked to find the piston and bore pretty clean! Not even any surface rust! Unfortunately, this points to the crankcase being a solid block of rust! Tried smacking the top of the piston with a block of wood and a hammer, but she didn't budge. Came to the conclusion that the engine would need to come off in order for things to proceed. Another shock, the engine mount bolts came right out! Unfortunately the frame mounts (which I tried first) snapped. I'll have to drill those out and source new bolts later.
Brought the engine to my basement work bench and removed the muffler. That rotten tin can had about 5lbs of mouse nest and rust flakes crammed into it tight! Holy crow! There aren't any baffles in this thing! This sled is going to be loud. Flipped the engine exhaust port up and found the source of my problem. When the critters filled the muffler, their acidic urine turned any piston blocking the exhaust port into white powder. Spent several minutes scraping with a pick and dosing with Aluminum Brightener. This helped, but the piston is obviously junk. Dang it.
Did some sleuthing online and found gaskets and seals for the engine, and secured a line on a piston and rings. With this done, I went full viking on the offending piston! Started by hole-sawing the top out of it. Dang those old Hirth pistons are thick! Removed most of the skirt through the ports with a punch, and drilled small holes in the top of the piston so I could then use a punch to remove big sections. After all this carnage, I was finally able to slide the cylinder off.
Stay tuned, more coming soon!~