Rebuilding crankshaft in 11 colour pictures

Our sponsor Janne P. offered generously to build crankshaft four our dragster in his shed. The crankwebs were from Mec-Eur "Race" crankshaft (58 mm stroke) that had twisted. Our conrod is from Yamaha RD400 (with length of 115 mm compared to original 107 mm).


First some grooves were cut to the crankwebs to help lubricating.


When the webs were ready for assembly the crankpin was pressed to drive side crankweb.


Then shim and big end bearing were installed...


...and after them conrod and another shim.


Then the flywheel side crankweb was pressed in.


Pressing was considered done when the conrod had side float of 0,30 mm and the pin was centered regarding to webs.


As the picture above shows, the conrod is considerably thicker than original one. That causes the whole crankshaft assembly being wider than original so we have to find a way to move it towards drive side so it will not twist the piston.


When the crankshaft was assembled begun the fun phase where clearances were measured...


...the crankshaft was hit with a copper hammer...


...and twisted in the vice...


...until it was straight enough. Acceptable tolerances in our case were 0,02 mm and 0,04 mm.

Crane oiled with factory grease

Instead of vigorous dragster building we made a scooter crane.


Small steps were also taken in the dragster front: we took the Vega front end apart and diagnosed what needs replacing. Outcome was little bit depressing as practically everything that can worn out had done so. This had happened even though there were some original Innocenti factory grease from sixties still left! The grease was obviously used to lubricate moving parts of the new crane. We also noticed that cast iron part of the brake drum was rusty inside so there is some rust removing in our ever growing agenda.

During next weekend Loonie #1 is going to his warehouses in countryside in look out for more parts. Hopefully he'll return with trunk full of NOS Vega front end parts and some other goodies. If things go as we have planned we can start working on the engine.

Bonneville Vibes

Build is on the way as we lined up the front brake to forks (Does anyone have an extra Lambretta Vega rim that's straight? We might be interested), cut down the headstock to suit the Vega fork and cut off the frame loop.

After quick dry build the direction of our project became clear as sky: the dragster will be inspired by salt flat racers used in Bonneville. The scooter will be ultra-long, extra-low with a very radical riding position. Sorry girls, this scoot will be impossible to ride with skirt on.

Dummy Engine

Before we can chop, strech & rake the frame to suit our taste we have to get couple of things done. Two of the most important of them are getting a frame jig which Loonie #1 is working on and finding a dummy engine which is now sorted out.

Our dummy engine is from dismantled Li 150 Special which has spent considerable time rottening outside. It consists of main engine casing, rear drum and siezed top end but it will serve our purpose to demonstrate what measurements the actual powerplant will have.



After little playing with welder and angle grinder we got the engine to stage where it was possibly to bolt it to our frame. Rear brake drum was so seized to brake shoes that we could remove layshaft and the drum was still stuck in it's place. That's not a problem because we now have a solid base to start building on.