Tech Torque: Aftermarket tuning options: Part 6
Lambretta crankshafts – the heart of the motor...
The crankshaft in your Lambretta engine is at the heart of power transmission. Stu Owen takes a look at some of the current offerings in the marketplace.
The crankshaft in your Lambretta engine is at the heart of power transmission, connecting the power created from the cylinder and transferring it on one side – to create the energy for the ignition – while on the other, driving the transmission chain and gearbox. Not only does it have a hard job doing all this, but it is also required to spin at high rpm under extreme load. If any part of the crankshaft should fail, then the engine simply ceases to exist as a power unit.
The biggest problem in deciding what crankshaft suits a certain type of Lambretta engine really depends on how much power it is producing. The main areas of concern are big end bearing being insufficient, con rod not being strong enough and the web pin not having enough strength to hold the two webs together without moving, more commonly known as twisting. Basically, the more power the top end is creating then the stronger it needs to be all round. For example, an Li150 engine which is producing 7bhp only needs a standard crank, whereas a high-powered engine which is producing 20+bhp clearly needs something far superior to cope.
In theory, a low-powered engine can of course utilise a crank which has been developed to suit a higher bhp range, but that is probably overengineering it and an unnecessary cost. However, when done the other way around (too much power for a lowquality crank) the engine will most probably fail very quickly, causing all sorts of damage and expense. The list of cranks is therefore here to help you make the right decision on which one you should choose to suit a particular type of engine.
Note: All of the cranks listed use the wider GP-style taper. While it is okay to use the narrower Li/SX taper it should only be on low bhp standard engines as using one on a highpowered engine usually results in problems. All cranks fit any Lambretta model engine from Li Series 1 up to Grand Prix.
Words: Stuart Owen
Photographs and special thanks: Scooter Center Koln, AF Rayspeed, SIP, Gran Turismo and Taylor Tuning
Brand name/ manufacturer: Mazzuchelli
Price: £125 (58/107) or £240 (60/107)
Stroke and con rod lengths: 58/107, 60/107 (or 58/116 for TV)
Overview: Italian brand Mazzuchelli offers a basic 58mm stroke crank with standard 107mm con rod, which is suitable for those with standard motors who simply wish to replace a worn or broken crankshaft, like for like, in terms of size of stroke/rod. A similar item sized for the standard TV175 (58/116) is also available. For those wishing to add extra cc to the equation, then the higher specification 60/107 version is offered. For the most part, these will slot straight into a lot of casings without extra work; however the big end of the con rod does protrude beyond the webs, so can often leave the owner needing to ‘trench out' the case with a flap wheel or send for proper machining.
Brand name/manufacturer: Tameni
Price: £155
Stroke and con rod lengths: 58, 60, 62mm stroke options, with 107, 110, 115, 116mm con rod options
Overview: Though at the lower end of the price scale,
Tameni makes a good entrylevel crank, and many users report great suitability for standard engines as well as mid-range power units up to around 20bhp. It has plenty of configurations regarding stroke and con rod length to suit the exact requirements needed for almost every
Brand name/manufacturer: BGM Pro HP competition Price: £240-260
Stroke and con rod lengths: 58, 60mm stroke options, with 107, 110, 115, 116mm con rod options
Overview: The new Pro range of BGM cranks are extremely well made and available in a wide variety of stroke and rod lengths. Points to note are the precisionground crank pin holes on the crank webs for added anti-twisting qualities, precision-ground and coated crank pin, forged con rod with CNC finishing, hardened and precision-ground bearing surfaces and oil seal seats. The full circle webs promote increased primary compression and reduced engine vibration thanks to copper and tungsten balance weights, lubrication of the lower con rod bearing via two large lubrication slots. Ideal in higher bhp engines and good value for money. configuration imaginable. The 58/107 is a straight fit into a standard engine; 60mm units may require slight alterations to the casing, same as the Mazz crank on the facing page. Thanks to the 110mm rod option, base packers can be added to adopt different cylinder port times, and the 116 version can accommodate low compression height pistons. Stroke lengths come in 58, 60 or even 62 for those wanting all the cc possible, however above 20bhp, although the Tameni may well cope, we would recommend ‘belt ‘n' braces' by looking at stronger rod options.
Brand name/manufacturer: SIP Premium and Performance
Price: £180-£250
Stroke and conrod lengths: 58, 60, 62mm stroke options, with 107, 110, 116mm con rod options
Overview: German supergiant SIP offers its own range of Lambretta crankshafts. Made especially for SIP in Italy, they offer various sizes in stroke and con rod length, with stroke choices going up to 62mm. The Premium range has a standard type con rod which is untreated, being suitable for standard and mid-power motors. The Performance type comes with big end shims and has a highquality con rod with upgraded surface finish, providing a stable structure and is suited to higher bhp engines. There are also revised big end design and lubrication slots, vital in increasing lubrication and reducing bearing friction and wear. The premium cranks are ideal for any low to mid-range power engine while performance is aimed at high-powered engines. Having used this crank in his own Lambretta engine, Big Stan found the item fitted and performed very well indeed.
Brand name/manufacturer: AF Rayspeed Price: £245
Stroke and con rod lengths: 62/107 or 62/116
Overview: AF offers a 62/107 or 62/116 Italianmade race crank, which it describes as ‘RB spec with 18 roller IKO big end'. I (editor Dan) have personally used these cranks in RB200 (takes cc to 212cc) and also RB252 motors with huge success, and AF even offers a machining service (circa £20?) to reduce the big end rod thickness, in order to negate the need to trench the casings. Good quality cranks, proven on racetrack and road alike.
Brand name/manufacturer: Taylor Tuning
Price: £220-£370
Stroke and con rod lengths: 58, 60, 62, 64, 65mm stroke options – 107, 110, 115, 116, 118mm con rod options
Overview: Taylor Tuning offers a different option when it comes to the Lambretta crankshaft because they are individually made, bespoke to each customer. Having spent years working on race engines and understanding their weaknesses, Darrell Taylor has developed ideas to make them as strong as possible. That knowledge is now being used on component selection and the cranks he produces.
The 58, 60 and 62mmm cranks are made using Tameni webs, IKO race bearings and high-quality con rods which range in size from 107mm right up to 118mm in length. Darrell has tested many different methods of building cranks and uses a particular procedure combined with Loctite product to prevent twisting. The result, he tells us, is a ‘bulletproof' crank which has been used in many highpowered Lambretta engines up to 50bhp. Tested in BSSO race engines as well as that of 127mph sprinter Eric Cope, and they have proven ultra-reliable. Normally the big end section of the 60 and 62mm rods are exposed at BDC, requiring a trench cutting out of the crankcase. To get around the problem the con rods are milled so there is no need for a trench to be cut out as there is now enough clearance. Also available are the 64 and 65mm stroke options which use crank webs specifically made for Taylor Tuning. These have 100mm diameter compared with the normal 96mm diameter, meaning more meat around the crankpin, thus making them even stronger. Webs of that size won't fit into a normal Lambretta crankcase, so by machining it out to the same size of the mag housing internal diameter they fit and, using the milled con rods, means no extra trench is required. This allows for an even bigger capacity and was designed by Darrell when developing his T-Type 265 engine.
Brand name/manufacturer:
Ultimate/Cambridge Lambretta
Price: £330-£399
Stroke and con rod lengths: 58/107, 58/116, 62/110
Overview: Cambridge Lambretta came up with a crank design capable of handling high bhp initially for its Super Imola and Super Monza engines to give them the best reliability possible. Now the cranks are offered to anyone who wants the best fitted in their Lambretta engine. With unique balance weights, the cranks have been used at up to 12,000rpm without any problems.
The forged con rod is precision machined and treated and has larger passages to allow for better oil lubrication. The different inserts for balancing mean the crank can be perfectly set up depending on the weight and size of the piston being used, thus significantly reducing vibration. That means the cranks can be made individually but there is a waiting time for this process. Even so, the Ultimate is one of the best options on the market, certainly when fitted in a high-powered engine.
Brand name/manufacturer: GT/Grand Turismo
Price: £245-£275
Stroke and con rod lengths: 60, 62, 64mm stroke options, with 110, 115, 118, 125mm con rod options.
Overview: The GT range of cranks offers various sizes but, unlike some manufacturers, there is no 58mm or Li taper option.
Standard GT cranks use the 110mm GT con rod with 18mm gudgeon pin but can be used with standard Lambretta 16mm gudgeon pins by fitting the GT stepdown small-end bearing which has larger needles, making them 16 ID. The GT stepdown smallend bearing is available in 22mm and 20mm wide to suit different types of pistons. All GT cranks are assembled in the UK and use silver cage big-end bearings. The design and tooling is exclusively owned by Gran Turismo.
The 62 and 64mm stroke cranks would also need some material removing from the crankcase area of the engine casing to allow for the throw of the big end and rod, the only exception to this would be the GT InterContinental engine cases which are designed with a trench in this area of the crankcase to facilitate the use of longer stroke cranks.
All GT cranks are full circle webbed to reduce parasitic drag utilising nylon stuffers which replace the material which is machined away to obtain the correct balance; the packer material and process is commonly used in motorcycle crank manufacturing. They have been regularly used in high bhp Lambretta engines with good reliability and over a long duration of time.
Richard Taylor, owner of Gran Turismo tells us: “Every element of existing cranks was really scrutinised, it took three years to develop and test and a year to deliver. There are four forging tools and an injection moulding tool – it was not a simple job at all.”