Can it be saved?

1. Crankcases apart

The interior of the crankcases are corroded beyond repair. The walls of the flywheel chamber are paper-thin and nearly breached into the gearbox in a number of places. The gearbox has, however, remained intact and oily and largely free of moisture. Almost everything in the gearbox can be reused. A search on ebay found a cheap set of matching crankcases and these have been ordered.

2. Flywheel and crankshaft

The flywheel and crankshaft are badly damaged. Corrosion on the seal faces of the crankshaft is enough to prevent a good seal (essential for two strokes) so two crankshaft stubs and a full conrod assembly have been ordered from Jawashop. We are keen to renovate as much of the original bike as possible so we were interested in a method of rust removal we read about on the net.

 

3. Flywheel rust removal

We submerged the flywheel in a mixture of white vinegar and salt. (2 litres vinegar to about 50g of salt). After 24 hours it was clear that the mixture was really chewing into the rust and we kept looking at it each day. After 5 days we lifted the flywheel out. To our surprise the conrod was free and much of the rust could be wiped off.

4. Flywheel after the rust removal

Out of the vinegar, quick rinse with water then a buff with the wire brush and a spray with WD40. It doesn't look pretty but with a new conrod and crank stubs that flywheel has life left in it. Once the parts arrive from Jawashop we'll drop everything into our local engineer.

5. Gear selectors

The big news of the engine disassembly was the discovery of bent gear selectors which had jammed the gearbox. The first owner sidelined the bike at 800km because it was seized. The owner took the head and barrel off - expecting that to unseize the bike - and found the engine was still seized. Bent gear selectors are not an uncommon problem on this model. This is not due to any mechanical weakness, Jawa/CZ motorcycles have an uncommonly long movement in the gearbox selection mechanism and people new to the machines can stomp on the lever causing problems. We suspect this bike suffered such a fate.

6. The Ebay crankcases

Two weeks after buying them on ebay a perfect set of crankcases arrived all the way from the USA! We'll send them off to be water blasted but a check shows everything to be in order. There is a big shipment from Jawashop due soon and once it arrives engine assembly can begin. In the meantime we have lots more to do.