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New from MB Developments:
For years now we have improved our Lambrettas by replacing various Japanese and European better quality pistons, we've improved the engine's speed and cured the piston's reliability. Over the years new barrels have appeared including aluminium 125's, 220's and 225's, we've had barrels bored to 250's, fitted larger carbs, exhausts, cylinder heads and various other modifications to increase the Lambretta's power and speed. But crankshafts have hardly been touched.
Various cranks have been used by Lambretta, but Li/SX/GT cranks tend to shear the big end pins and flywheel tapers. An improvement is to convert to GP, which is the strongest. Slight differences occurred from the Li/SX con rod to the TV175 and GP range. But how many of you have blown the big end bearings, snapped a big end pin or snapped a con rod? Most of you I bet!
Even the 60mm and 54mm improvement cranks never altered the bearings on con rod. Why not? They blow up too many times, obliterating the crank, piston, head, barrel and sometimes the casing, which can be very expensive, especially if you've just replaced everything a week before.
I personally have snapped a con rod at 70mph and shot over the handlebars, which is not very nice! That led me to look into a stronger con rod assembly and big end bearings. I searched high and low until a few came to light. The first to be used was a Suzuki fitted to a 60mm stroke crank. This had an 18mm gudgeon pin and involved a lot of work, making it expensive. The second was for a J125 rod which again required a lot of work but became a direct replacement for a standard rod, but was twice as strong.
I wasn't happy until I found a replacement for the Li/GP and TV rods. I used various rods of all shapes and sizes, trying various machining methods, but it wasn't until I spent a lot of money in developing the cranks that I finally found some joy and now there are some excellent conversions:
1. GP cranks 54, 58, 60mm stroked cranks have a direct replacement. These have a stronger con rod and larger small end (16mm gudgeon pin).
2. SX/Li/GT/GP125 cranks use the same as the above, but with a different big end bearing.
3. TV175 cranks: There is a replacement for this crank which can also be used in the above cranks.
4. SX/Li/GT/GP125: Yet another replacement rod using a wider big end bearing and rod, but this uses an 18mm gudgeon pin ideal for Suzuki and Yamaha pistons, illuminating the problem of bushing down the pistons.
With all the above the con rod and bearings will take more rpm and power, no crankcase machining is needed, they just bolt straight in. If you supply the crankshaft, then I can strip it, machine and refit the new rods and true them up.
Prices are as follows:
1. GP150/200/Li/SX/GT cranks including 54mm stroked, are £59.00
2. GP150/200/Li/SX/GT cranks using a TV175 replacement rod costs £70.00
Diagram 1 shows an average kit, this being a standard GP200 racing crank with a Yamaha con rod conversion, showing also the various high load bearings, seals, gaskets and spacer plate.
Diagram 2 shows the difference between the con rods, big ends and small end applications. Starting from the left:
1. Standard Li con rod, pin and bearings;
2. Racing GP con rod, bearings and pin;
3. The uprated Yamaha con rod for Li/GP cranks with various larger small end bearings;
4. The Yamaha conversion for the TV length con rod;
5. The imported 18mm stronger con rod for Li/TV/ GP125 which uses various sized small end bearings depending on piston application.
