I do love a proper tool and in this game – there’s plenty of tools!
Here we have new Lambretta crankshaft dummy bearing bush tools from MB Scooterss. One for the drive side and one for the mag housing.
These are precision made in stainless steel so they don’t rust in the workshop and are perfect for anyone building a Lambretta engine.
The idea is – on an engine rebuild you can do a dry build without fitting bearings. These dummy bushes replace the bearings.
Theres nothing worse than fitting the bearings, greasing them, fitting the crank only to find the con rod touches the casing!
With a bare casing on a rebuild you fit the drive dummy bearing into the casing, then fit the crank, no need for the drive plate or screws. With a mag housing with no bearing, fit the dummy mag housing bearing bush and offer into the casing and tighten up. The mag bush spins on the seal face so you can use these on Li or Gp type cranks and it doesn’t matter which inner bearing race is fitted, no need to fit the big circlip.
Now you can check the crank turns freely and doesn’t lock up. If it locks you can simply remove the mag, crank and bushes and modify the casing. You don’t need any other tools for this job, clean it out and refit again to check. Theres no worrying about dust and crap getting into your newly fitted greased bearings!
Once the crank is spinning. You can now easily check and set port timings and port heights with various packers. Then you can fit the head and gaskets and quick check the squish clearance. If you’re going to get dust and grit in the engine all you have to worry about is you keep it away from the big end bearing.
Once every thing is set, clean the parts and fit the bearings and crank as normal and rebuild the top end as you should. These save a lot of time if you get a pain in the arse rebuild!
Always double check the squish clearance/timings on the final rebuild when everything is torqued up.
Casings and mag housings do vary in size. Some may need the casing or mag warming up, cranks usually hold size across manufacturers, but you may need to polish the inside holes.