The Engine-Crankcase

The engine seems a real basket case: the flywheel was held on by a single nut and when the cases were split I found that the studs and bolts holding the two halves together were bent and had virtually all their threads stripped. The inside was no better: all bearings were rusted and barely moved. There was a strange plate covering the gearbox output shaft bearing in the RH case that seemed to be some kind of an oil seal. The outside of this bearing was even worse: the case had broken off when, I assume, the chain smashed into the cover. It later turned out that the bearing and housing were not standard and needed machining of which, more later!

First, I heated the cases in the oven and with a little help with my Makita HG1100 heat gun and knocked out the old main bearings. I say "knocked out" but after warnings from Patrick Hayes and Jerry Kimberlin about entire 3" disks of cranckase casting getting torn off, I amend knock to light taps on the bearing. The gearbox bearings, however, needed my Motion Pro blind bearing puller. I next sprayed the cases with Gunk engine degreaser. With the oil and grease removed it was time to head to the blast cabinet. I used "First Choice abrasive" from TP Tools & Equipment. It removes rust and scale quite rapidly but provides a smooth finish. The makers claim that the rounded beads prevent embedding in aluminium.

Once done with the blasting, it was time to weld the RH side case where chunks of casting had broken off just above the chain sprocket. I tried to degrease it again by using mineral spirits and Gunk degreaser since aluminum welding needs extremely clean surfaces. Using my Lincoln MIG welder and a roll of 0.035" ER4043 aluminum wire I slowly built up the surface. It was really messy because of the oil impregnated in the material. I then smoothed it out with a grinder to get the curves.

On the SA, the gearbox output shaft bearing that sits behind the chain sprocket is not a standard size and was not available till recently. Given the mayhem that occurred at some point and smashed the cases - locked gearbox(!), thrown chain - the bearing housing and the shaft must have been damaged. Someone added a metal ring to the bearing housing to allow the smaller diameter standard size bearings to be fitted (retained with a thin metal disk and four screws), machined away a recess on the outside that is used to keep the felt seal ring, and added a modern lipped oil seal (see photo above). To bring it back to original, I machined the outside boss away to the face of the bearing. I removed the metal ring inside the bearing housing to allow the use of the original larger OD bearing (a-a 66mm) which is now available and machined two aluminum disks, one to seal the outside of the bearing, and the second to hold the steel plate next to the bearing and felt oil seal (b-b 50mm) and the second disk (c-c 41.05mm) to hold the felt seal in place. I welded these two plates to the machined case effectively creating a new cavity for the seal. The photo shows the new housing with the shaft protruding. Lots of measurements of the distance from the inside of the sprocket, the various spacers, the length of the shaft and the width of the bearing were needed before I could figure out how thick to make the spacer. Too thick and it would rub against the face of the chain sprocket, too thin and the seal and metal plate would not fit. Patrick Hayes and Jerry Kimberlin's emails provided the answers of what the original looked like.

If anyone accidentally knocks out this boss the attached dimensions should help in the reconstruction.

I wanted to make sure that the faces of the crankcase were flat. I bought some plate glass and then taped 1000 wet/dry sanding paper to this glass and then rubbed the cases gently over the sanding paper till I got a shiny surface at all points of the case. The first couple of passes over the plate glass showed that the cases were not flat. Both cases needed quite a bit of smoothing before I managed to get an even surface on both cases.

Let me jump ahead a couple of months. When I finally assembled the crank in the cases and tightened the case up I found the crank binding. The cylinder did not fit into the mouth of the case. Clearly, I had removed little too much from the faces of the crankcase. I put a level on the face of the case and measured from the case face to the face of the bearing inner race. On the RHS it was 37.05mm and on the LHS 36.25mm for a total width from bearing to bearing when the cases are closed of 73.75mm. I then measured the crank at the hub which butts against the bearing races at 74.78mm. The difference is 1.03mm. I had to make a gasket which compresses to 1.02mm. I ordered 0.4" 6061-T6 aluminum sheet from onlinemetals.com, a place that Jerry Kimberlin suggested. I placed the case on the sheet and with a Sharpie carefully outlined the case. I cut the outline out with metal shears and punched out the bolt holes with my gasket punch set and smoothed down the edges. When I bolted the cases back up the cylinder slid smoothly into the cavity and the crank turned freely.

The various screws, bolts, and studs were acquired from MSC Industrial. The Italian verion of the parts manual has the thread sizes and dimensions for each fastener. The screws were 45deg slotted oval head stainless steel screws.

The cases were put together without any paper gaskets. Instead, on Jerry Kimberlin's recommendation, I used a thin smear of Dirko, an RTV sealer originally developed for the air-cooled VW engines all round the cases. It is expensive and can only be found on the internet but it works!

Next, the bearings....