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Crankshafts and con-rods

BASIC LAMBRETTA CRANKSHAFT FACTS

All crankshafts have a stroke of 58mm, the only difference was the TV175 series 1 which was 60mm and is not interchangeable with any other engine.
All crankshafts use the same flywheel bearing with the exception of the series 1 (this has a totally different bearing) also the GP200 has a wider bearing of its own.
All crankshafts apart from the GP200 and some GP150ís have a stepped crankpin with a smaller crank pin hole at 20mm.
GP 200 and some GP 150ís only use a straight crankpin of 22.9mm.
All Lambretta pistons and conrods use 16mm small end bearings and gudgeon pins.
With tuned Lambrettas where possible use a GP 200 or later GP150 type crankshafts or better still upgrade to racing crankshafts using their relevant high load flywheel / drive bearings and ignition systems.

Firstly you need to identify your crankshaft.

Series 1 Li125, 150

This has a short thin type flywheel taper with no shoulder for the flywheel bearing, 4 large balance holes in its crankwebs, it usually has a bronze bush in the small end eye, and the con rod length is 107mm.
It uses a different flywheel bearing, mag housing and only one mag seal compared to the later models, for tunes beyond stage 2 upgrade to series 3 or GP and change the mag housing bearing and ignition system.

Series 1 TV 175

This crankshaft is totally different to all other crankshafts and are not interchangeable.

Series 2 Li125, 150

This has a thin type flywheel taper a 13mm flywheel seal shoulder, 4 large balance holes in its crankwebs, it could have a bronze bush in the small end eye or could have a needle bearing, the con rod length is 107mm.
Apart from slight con rod differences it is basically the same as a series 3 type.

Series 2 TV175

This has the thin type flywheel taper a 13mm flywheel seal shoulder, 4 large balance holes in its crankwebs.
The con rod length is now 116mm.
(By using a longer rod the piston height from the gudgeon pin to the crown is shorter that all of the other Li range.)
Apart from the con rod difference it is the same as a series 3 type.

Series 3 Li125, 150, SX125, 150

This has the thin type flywheel taper a 13mm flywheel seal shoulder, 4 large balance holes in its crankwebs, and the con rod length is 107mm.
Apart from slight con rod differences it is basically the same as a series 2 type.

Series 3 TV175

This has the thin type flywheel taper a 13mm flywheel seal shoulder, 4 large balance holes in its crankwebs.
The con rod length is now 116mm.
(By using a longer rod the piston height from the gudgeon pin to the crown is shorter that all of the other Li range.)
Apart from the con rod difference it is the same as a series 3 type.

Series 3 TV (GT) 200

This has the thin type flywheel taper a 13mm flywheel seal shoulder, four large and four small balance holes with flats on the crankwebs close to the big end area, the con rod length is 107mm.
Apart from balance features and slight con rod differences it is basically the same as a series 2 and 3 Li type.

Series 3 SX 200

This has the thin type flywheel taper a 13mm flywheel seal shoulder, 4 large balance holes in its crankwebs, and the con rod length is 107mm.
Apart from slight con rod differences it is basically the same as a series 2 and 3 Li type.

Series 3 GP 125

This has the new fat type longer taper with a 13mm flywheel seal shoulder, 4 large balance holes in its crankwebs, and the con rod length is 107mm.
It uses the Li type con rod with a stepped crankpin of 20mm and wasn't hardened.
It uses the Li type flywheel bearing.
Consider this as strong as the Li type crankshaft so up grade to the later GP 200 type.

Series 3 GP 150

There are two types.
Type one is the same as a GP 125.
Type two is the same as a GP 200 but the only difference is the flywheel seal shoulder is 13mm long and used the Li type flywheel bearing.

Series 3 GP 200

This has the new fat type longer taper, a straight crankpin of 22.9mm.
No balance hole features and has the shortest flywheel side seal shoulder of 10mm to suit a wider flywheel bearing than all other crankshafts.
The GP200 or the later GP150 crankshaft is to be preferred for all tuned engines.

MB Developments always recommends replacing the crankshaft with the latest race crankshaft or converting the GP 200 crankshaft to an improved con rod conversion.

Li/SX/TV (GT) CRANKSHAFTS

These crankshafts have their faults.
The crankwebs are not made from hardened steel and the thin flywheel taper can snap off!
Stepped crankpins have been known to snap also.
Soft crankshafts if rebuilt can spin out of line as the soft metal gets pushed out on each rebuild.
Some con rods are thinner and can snap below the gudgeon pin.
When using any crankshaft with standard con rods regardless of con rod type always use pistons either with no small end side float or use piston shims, if you don't big end failure will occur.

There have been over the years various crankshaft manufacturers, all have been interchangeable between models.
The main differences were con rods but some had GP style crankpins and were hardened.
These cranks had smaller balance holes of 19mm.
The standard con rod is OK for mildly tuned or low revving engines, but the standard con rod is the weak link of all Lambretta crankshafts.

GP RACE CRANKSHAFTS - THE HISTORY

There have been in recent years a number of up-rated race type GP crankshafts introduced.
In the Seventies and early Eighties a short stroke 54mm GP crankshaft was available mainly for racing purposes, along with a long stroke 60mm GP crankshaft. Both crankshafts used the standard type con rods either 107mm or 116mm, apart from using standard con rods they were very good.

In 1985 a supposedly new race crankshaft was introduced by MDP, this was only a standard crankshaft with blacked crankwebs a polished standard con rod and with a silver-plated big end bearing.
Both the con rod and big end bearing failed! If they didn't the webs would spin out of line, they weren't assembled tight enough!
At the same time a standard version was introduced by the same manufacturer this was also loose on the crank pin.

In the same year after a con rod snapped on me I started developing Japanese con rod conversions to fit the GP cranks.
I learnt with failures but developed bulletproof con rod conversions still used to day.

In 1987 we saw the new first batch of real race crankshafts.
These cranks had beefed up polished con rods and improved big end bearings with smaller crankpins of 22mm and used .5mm big end crank shims, the crankwebs were black in appearance.
The crankpin was solid to the drive side crankweb, unfortunately the machinist under cut around the crank pin building in a fault and did they go wrong!

The next smaller batch was introduced with a 22mm crankpin, pressed in both sides as normal, these used .5mm big end crank shims and these cranks were OK.
Scooters Indian introduced their own uprated crankshaft, this used a 22mm crankpin with no shims either side of the con rod eye, it used a copy of a Yamaha rod that we had used previously, but as usual it wasn't done well enough and some failed!
They are still available today! They look a mess but are very tight on their crankpins and stay in line, it's a shame they didn't use a good con rod!

Another batch of race type cranks came but this time the webs were too brittle and the crank split from the crank pin scrapping the crankshaft!
Some of this batch still exists but mainly in the 60 and 62mm type, this type is very difficult to assemble and either crack if too tight or spins out of line if to loose.
Welding was the only cure as these cranks are used for high-powered motors.

As time went on another batch was introduced these were basically the same but black in appearance with polished race con rods.
These had their faults too, most came from the manufactures assembled out of line and some were also loose on the interference fit with the pin.

A similar crankshaft is still available much cheaper through Europe beware! MB Developments have stopped using them!
Some are out of line from the factory, when realigning them you find that they are very loose and spin out of line. Some when reassembled with oversized crankpins don't line back up!

Then finally at last 13 years on the race crankshaft is available, this is now the only off the shelf race crankshaft that we sell, I must say it is very nearly perfect!
(I would have used 1 mm crankshims not .5mm as I have seen a number of failures of these shims in both Lambrettas and Vespa engines).
MB Developments recommend changing the supplied small end bearing to an INA or Japanese type, as these never go wrong.

Update July 2001, it has come to our attention that some of these crankshafts have been supplied to us out of balance and need realigning!
Some are so obvious that copper hammer marks are present on the crank webs. Some of these crankshafts are also loose on their crank pins!
MB Developments policy is: we like the crankshafts best of all, each crankshaft supplied to us is checked for alignment and any faulty ones are realigned!
If a crankshaft is found to be faulty and loose then we reassemble them using retainer and, or high strength retainer to make the pins tighter with less chance of spinning out of alignment.
Any very loose ones would be rebuilt with special MB Developments over sized crank pins.

MB DEVELOPMENTS CON ROD CONVERSIONS

MB Developments have, since 1985, been at the forefront of conrod conversions in Lambretta and Vespa engines.
As a brief history I'll explain what I did.
After the con rod incident in 1985 when my TV175 rod let go with out warning at 70 mph and shot myself and passenger straight over the handle bars I thought it's time I did something about improving the con rods!

Lambretta in their wisdom used very strange sizes apparently to stop people copying their designs.
Their sizes were not normal to the rest of the world!

Given this basic information it was apparent with out finding a totally odd ball rod or having one remade (which I did get prices on, but was beyond a joke for experimental purposes) that this was not going to be easy!

Over the years Lambretta have used various crankpin widths, all being smaller than 40.5mm.
MB Developments started at 40mm but in an effort to improve the conversions the width was increased to 41 mm.
This increase in surface area in the crankwebs made the cranks much tighter on assembly.
Originally MB Developments used 2 magneto gaskets otherwise the crank would foul the mag housing.
Now all MB Developments rebuilt engines have the mag housing internal face machined down. It was found that 2 mag gaskets over time would become loose and would leak.

COMMON CON RODS USED BY MB DEVELOPMENTS

Manufacturer of con rod Model of con rod Con rod length Big end pin diameter Big end width Gudgeon pin size
Yamaha RD125/DT175 110mm 22mm 16mm 16mm
Yamaha RD400 115mm 22mm 16mm 16mm
Rotax MB Special 115mm 22mm 15mm 18mm
Rotax Microlite 115mm 24mm 14mm 18mm
Rotax/Fantic 120mm 22mm 15/16mm 18mm
Piaggio Ape 110mm 22mm 15mm 18mm
Kawasaki KDX 106mm 22mm 17mm 16mm
Kawasaki KDX 108mm 22mm 17mm 16mm
AF Race cranks 107mm 22mm 15mm 16mm

There are a number of conversions suitable in all Lambretta applications, there are more but the ones listed are good reliable conversions.
For example most racing Japanese pistons that could fit and work in a Lambretta cylinder had 18mm gudgeon pins, 2mm larger than a standard small end.
There are ways around this by sleeving down using piston bushes but they go wrong with disastrous results.
To over come this, con rods were found with 18mm gudgeon pins and made to fit a Lambretta crankshaft.
This was not as straight forward as it seemed as these pistons used different compression heights and the conrods used different lengths so it was not uncommon to either machine the cylinder or pack up the cylinder.
So basically the improved con rod conversions were invented to make better pistons work with in a Lambretta engine.
Most con rods donít just fit straight into Lambretta crankshafts. Crank webs need machining to suit the special crankpins, rods and bearings used.
NOTE: Any engine using an MBD eccentric pin to take the stroke to 60mm or higher needs to have groove machined into the crank case to allow for the con-rod. This involves welding to your casings and makes the conversion expensive.
For years the cranks were copies of the Innocetti GP200 crankshaft, but as the race crankshafts were developed the crankpin was reduced from 22.9mm down to 22mm the same as most high performance Japanese engines, this then made my job easier when converting to Jap style con rods.

th_crank1.jpg - 10550 Bytes This photo shows three new race cranks.
Top crank is the AF road/race crank.
Middle shows the excellent, long lasting Yamaha 110mm rod converted crank for use with all Lambretta pistons. This requires a 3mm packing plate.
Bottom is the famous rotax microlight 115 rod conversion with the virtually indestructible 24mm big end pin and 18mm Small end, as used on many Japanese piston conversions.
th_crank3.jpg - 10477 Bytes Left - the standard race crank big end area.
Right - the Rotax big end area.
This picture shows the Yamaha 115mm, 16mm wide big end area, 1mm wider than a race rod, 3mm wider than a standard rod.
This crank uses an MBD eccentric pin to take the stroke to 60mm and give a 240cc engine.
The massive 24mm crank pin of the Rotax 115mm microlite conrod for piston conversions using 18mm gudgeon pins. With the work required to the casings this makes it a very expensive conversion but this crank is one of the only ones we can use on the really high horsepower engines.
Others include Vespa Ape, Fantic and other Rotax rods.
A view of the 58mm stoke AF road/race crank.
Beware of cheap European copies, we have stopped using them.
Our only gripe with the AF cranks are that we always have to check them for alignment.
Sometimes we have to overhaul the cranks and use loctite to tighten the pin up.
Top crank is the AF road-race big end area.
Bottom crank is the Yam con-rod big end area with much improved big end pin, bearings and shims.
The rod is excellent, long lasting and very strong. 2 lengths are available 110mm and 115mm to suit different conversions. Sometimes a loose cylinder pack plate is needed.

IDENTIFYING A GP STYLE CRANKSHAFT

Firstly you need to identify the crankshaft being used.
A lot of time and effort over the years have gone into perfecting these conversions.
These conversions do not come cheap, as there is a lot of work involved so you need to identify an excellent GP crankshaft.
There has been various crank manufacturers the most common being Omega in the 70's and early 80's these were good to work with and offered 58 and 60mm stroke items, unfortunately that company went by the wayside and cranks dried out.
These were identified by an Omega symbol on the con rod.

MDP were and still are a common make but are now called MEC, only 58mm stroke cranks have been available from this manufacturer.
Identified by a MDP Innocenti 'I' emblem.
A lot of these crankshafts were loose on their crankpins. (This makes no difference with MBD conversions.)
Another common manufacture is Mazzucchelli these have made 58 and 60mm crankshafts and again are very good.
These are identified by a MMC on the con rod.
For years the cranks were copies of the Innocenti GP200 crankshaft.
but as the race crankshafts were developed the crankpin was reduced from 22.9mm down to 22mm the same as most high performance Japanese engines, this then made my job easier when converting to Jap con rods.
Today most crankshafts are bought though MEC but they subcontract this work out and it is difficult to pin point their suppliers, some are good some are bad.


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