Piston rings are cunning things. What many people don't even know is that they often have an order and an "up" and "down." And, oh yes: they must ensure that the compression and expansion takes place between the cylinder head and the convex side of the piston.
A 'blow by'
If the hot exhaust gases escape after the mixture has exploded via the 'gap' between the piston and the cylinder bore, this is called a 'blow by'. Then the sump comes under an overpressure caused by the 'leaked' gases. And because the temperature of the engine block increases greatly internally, this also comes at the expense of lubrication. That excess pressure escapes through the crankcase vent. With old classics that is just a pipe or hose that blows off in the open air. Later, when the environment was invented, the crankcase vented into the air filter (house). The bad oil fumes were then breathed in again during the intake battle and everyone was happy.
Smoking like a madman
With the Real Classics, where the carter overpressure can just go outside to play, things can get pretty out of hand. For example, the classic of which a piston in this story is the fashion model had to follow behind during excursions. When the time came for the engine to get really hot on summer day, the paint of the dynamo started to smoke, it was even so far that an innocent follower and oil haze got on his glasses. Then it was time for action.
Key friendliness
In that case it once again became clear how key-friendly push rod engines are. The dismantling of the head and cylinder was a breeze. For the record, the tumbler blocks and the pistons were marked for a while. It is usually useful for those things to return to the place where they first lived.
Then it was time to take a look at how things were doing. In this case that was pretty bad and a bit strange. The cylinders will be stroked with a honing block stone. The drillings did not look terminal yet. But the pistons and the piston rings? Trump would say, "sad, so sad." Yet the space between the ends of the piston rings in the bores was not so desperate. But the consequences of the blow by were more than clear.
New things
So there must be new pistons and piston rings. Plus new foot and head gaskets. Plus of course fresh spring springs for the piston pins. The original copies also seemed to be made from rejected paper clips. Just a spoiler alert: This is a classic Russian sidecar combination. And the quality of Russian motorcycle parts is not always of a constant level. And for those few duppies, you don't want a locking clip to escape in the greasy darkness of the block. Because that can lead to considerable consequential damage.
Mount and drive in
Since torque keys are available for sale at very reasonable prices through our advertisers (and sometimes at Aldi), it is wise to use them. Use the tightening torques as stated in the workshop manual, or at least focus on the Standard tables on the internet.
In any case, invest in new foot and head gaskets and therefore buy new piston pin retainers. In addition, ensure that the piston rings are mounted in the correct order and position. And the arrow that is engraved or cast on the piston must point to the front.
If the first 500 km is a bit slow and with varying speeds, then everything will be fine.
