Lambretta crank lapping

Laping the crankshaft to the flywheel taper on a Series 3 SX/TV Lambretta crank shaft. This is to fix and or prep the 2 surfaces for positive contact. Can be done on almost any point where 2 tapered surfaces meet together. Will work for Vespa also.

[@Onthelambretta]

There are a couple of schools of thought on that. If you look at the later GP cranks they did not have holes in the webs. I know you can get new cranks with tungstun plugs to change the web weight. I guess it depends on what you are trying to achieve. It's all about trade offs. Personally I like to do what Yamha did, they had the two strokes figured out better than anyone.

[@testacorsa150]

Hi. Thanks for this tutorial. I have a problem with my scooters crank (aermacchi h-d brezza) The flywheel nut cam off (bad threads), and the flywheel spun of an the crank leaving deep marks. I have ground down the high spots, but would like the mating surfaces to be as good as they can get, so I will try to lap them together as you demonstrate here. My question is: Why only turn in one direction when you are lapping? When you lap in engine valves it looks like it's done in both directions.
thanks and cheers form Denmark.

[@Onthelambretta]

Sorry for the late reply, I didn't realize there was comment waiting on me. I talked to my old timer machinist about that and here's what he said. By going in one direction it makes it makes for a more uniform grind on the taper as all the pressure is basically going to same way. If you go back and forth you can create an uneven grind on the taper due to the way the hand holds the flywheel. I guess if you were to do this with a machine it would be more even in the end. I'm sure any variations in the surface would be minimal if you went back and forth but why mess with success?