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Tuning options for 125/150/175cc engines using the SRP kit

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The 175 Asso/Vertex pistons are back in stock so we are now in a position to be able to offer the SR 175 kits with all stages of tune again.


Having kept an eye on the SR pistons we can report some good news and some bad.
One piston was fitted to a standard cast 190 cylinder and did 10,000 miles no trouble!
Great but on the other hand some only did 300 miles and the peg came out! Not so good.

No decent pistons have turned up! We have been given a delivery date of March – April 2003 for Asso / Vertex pistons but we were told that last year.
So time will tell.

As a fill in gap we have used the 3-ring Italian GOL piston in standard or stage 3 175 kits to good effect.
Guess what?
We have used up all the pistons we can find.
The Suzuki 190 kits slowly sell and Wiseco have been supplying us with pistons all year with no problems.
Our chosen kit for the moment is the GOL set up when we get pistons, the SR 175 standard kit is good and gives performance that equals or beats a standard Italian GP 200 so something must have been done right in the first place, we just need pistons.

September 2002. SR PRODUCT UPDATE.

It is with great regret that, in our opinion, the SR piston has turned out to have too many problems to make it worth using.
We have had problems with noisy pistons and ring pegs coming loose - this then damages the cylinder.
For this reason we have stopped using the SR piston.

We have kept the information below as it is still of interest to Lambretta owners.
We have had no stocks of the Vertex piston this year, which could replace the SR piston in the 175 cylinders.
So unfortunately we can not use the 175 cylinders.
Slight casting problems with inlet port heights make using the 190 cylinder very difficult to set up using the Suzuki piston and standard con rod.
So the only kit that can be safely offered is the Suzuki 190 using a Yamaha 115mm con rod, these are proving to be excellent!
The only problem here is expense and we only recommend it if you are adamant that you still want to keep your original casing and engine number.
If you are not bothered about swapping the engine casing then we recommend a new 200 casing with a stage 4 factory kit, it's much cheaper, see the cast iron 200cc tuning page.

MB Developments were involved with the design of the Scooter Restorations kit from the beginning, we spent 2 days reworking a cylinder as a casting pattern.
We spent many hours in discussion about different ways of doing the kit and supplied some of the information towards the piston design.
What you will now read is our explanation of the kit, its pros and cons and where we are now with the kit.

This kit is new for 2001. The kit is basically a modernised and beefed up 175 cylinder now made in aluminium with an iron liner and using the newly designed SR 2-ring conversion piston.

Two kits are available, 62mm - 175cc and 64mm - 190cc. The cylinder is aluminium with a cast iron liner cast into the alloy. In standard form the cylinder has been manufactured and modernised to a stage 2 or 3 spec.

The kit can be fitted to standard 125 and 150 engines with no upgrading of crankshafts etc but we always recommend up grading to GP components.

No tuning work is required in standard form if using standard carbs and exhausts. The cylinder was beefed up and designed to be able to take the tuning spec to very nearly a full 200cc stage 5 and even designed to be easy to liquid cool it if required.

MB Developments are offering stage 3, 4, 5 and stage 6 tunes as extras to the bolt on kit, including cylinder head skims.

Early tests are proving all the hard work over a 2-year period is worth it! And good things are expected from the kit.

The SR pistons are a cross between Japanese and Lambretta pistons and are possibly the best piston for using in any Lambretta cylinder, the rings are drawn wire making them difficult to break!


MB Developments originally remade the 1st cylinder as the pattern to be copied by the manufacturers. We took an Italian TV 175 cylinder looked at it in terms of remanufacturing it!

The TV cylinder has been a very good cylinder for many years, this cylinder is now very difficult to obtain even second hand. There has been over the years various batches of cast iron pattern cylinders made these have been inferior in casting quality and were usually made from soft cast iron, this meant that they wore out easily. We looked at the port timings and other limitations of the cylinder. We considered that the original cylinder had slightly large transfer timings, the inlet port we were happy with but considered the exhaust port to be a little on the small size!

Given that the cylinder was now over thirty years old it needed modernising to suit to day’s traffic and to suit what a Lambretta is used for!

We decided that a new design could be done to cover nearly all possibilities.

It had to cover;

With these facts in mind, the cylinder ports were modernised and tuned to stage 3 ideal for standard carbs and exhausts giving a good power to keep up in towns and still keep up with modern traffic on dual carriage ways and motor ways.

The out side of the cylinder was thickened up around the inlet, exhaust and transfer ports. This allowed the choice if required to tune the inlet, exhaust and transfer ports to a full 200cc stage 5 tune! The area around the cylinder studs that are normally exposed was blanked off in the event of any one wanting to liquid cool one. The cylinder was made in alloy for good heat dissipation.

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Standard SR cylinder, from inlet port side.

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Standard SR cylinder, showing the thickened
up area around the transfer and inlet area
and also around where the cylinder
studs go through.

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Standard SR cylinder, showing the exhaust port
and the thickened up transfer area.

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Standard SR cylinder base gasket area.


We considered our options here, it was a toss up between an iron liner or Nicasil plating. The chosen manufacturer didn’t do any kind of plating. Sending it elsewhere was out of the question so we went for the old trusted iron lining method, which also kept the manufacturing price down.

There are usually two trusted ways to liner a cylinder.
1. Bore out the alloy cylinder, machine a groove into the top of the cylinder then fit a straight liner with a top hat shape to locate into the groove. This is the method used by MBD when repairing alloy cylinders in the UK.
2. Manufacturers when using the older designed alloy cylinder with iron liner would cast the alloy part around a pre shaped iron liner. The pre-formed liner would be of a shape where the liner would not move once cast.

We went for the second method, this method has been used from the early beginnings right up to modern day mass-produced bikes made by the Japanese.

The advantage for the iron liner method is;
1. Price, it was much cheaper to produce a cylinder kit his way.
2. Allows rebores when required.


We had a choice, use an existing piston i.e. the Vertex one or make a completely new one.
Paul deemed the Vertex piston too expensive for the kit, now looking back we should have gone down that route as to date MB Developments has not had any the problems at all from a Vertex piston.

Lambretta pistons have always had their problems.

  • Cast iron rings wear out and break very easily.
  • The skirt was not strengthened below the gudgeon pin.

If a new piston was to be made then it would have to do a variety of jobs!

  • Have the Lambrettas crown height from the centre of the gudgeon pin to the start of the dome which was 39mm.
  • Have the same dome height to suit all Lambretta cylinder heads.
  • Have the same skirt length to suit all Lambretta cylinders, whether it was standard or tuned.
  • Have a ring peg spacing to suit all known Lambretta cylinders, including Imola and TS1’s.

Again we looked at the piston design based on over twenty years of using various different pistons. We came across good and bad points from manufacturer to manufacturer. All put together we came up with an amalgamation of a number of pistons.

  • We decided that the piston rings were to be the drawn wire type, these tend not to break and you can actually tie them in knots and they don’t break.
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    SR piston rings. Yes, we tied a
    nice knot in the ring and it didn't snap!

  • The ring design and thickness was designed to be interchangeable with a ring already manufactured in Japan.
  • The alloy material and taper was chosen to suit the expansion required in a Lambretta engine.
  • The internal bearing area was designed to use a standard width small end bearing requiring no shims but also centralising the con rod if required.
  • The area at the top of the piston surrounding the rings was recessed to help the rings not to stick, in the event of a seizure.
  • The pistons weight was reduced above the pistons gudgeon pin.

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The new SR piston.

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The new SR piston.

We believed it could have been the best piston ever used or manufactured for the Lambretta engine, unfortunately this has turned out not to be the case.


We did machine up a 175 cylinder head to suit the kit and it was sent to the manufacturers, only to find that they already manufactured a cylinder head.
Our cylinder head was machined with the squish cut to suit the Lambrettas dome, giving a perfect squish clearance. Our head had the compression lowered to suit modern day fuels used.
The manufacturers head used the internal shape of a 200 head but used the fins and stud arrangement of a 150 engine. This head could be used as it is or could be reprofiled to suit the piston and gain a little extra power.

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Left - Reprofiled head, with the compression raised.
Right - Standard, very low compression 175 head machined to suit a 190.


Engine casings vary in height where the base gasket goes, this tells you if a base gasket or head gasket is required. Early set ups appear to show that no base gasket or head gasket is required! Silicone sealer would then be required to seal the base gasket and studloc would be good to seal the head.
This should give a correct squish clearance of around 1mm but this should always be checked.


The basic cylinder kit comes with an alloy cylinder, race / touring piston, cylinder head, gaskets, studs, nuts and washers. Our kit comes with fitting, running in and jetting in procedures.


  1. The kit can be supplied as a standard kit.
  2. The kit can be supplied as a standard kit with a reprofiled head.
  3. The kit can be supplied as a blue printed stage 3.
  4. The kit can be tuned to stage 4 or 5.
  5. The kit can be supplied as a big brother tune i.e. tuned to as near to a 200 cylinder as possible.

It is a little early to predict horsepower out puts, time will tell we expect the standard set up to be 7 – 8 HP, tuned kits could exceed 15 HP!

PROS: Aluminium cylinders will reduce heat build up. The Iron liner is very hard, ideal for a long lasting cylinder kit. The iron liner is reborable and has a large amount of oversizes available from 62 to 64.5mm, in .50mm increments.
The standard cylinder kit is a direct replacement for 125 or 150 engines and can be used with standard carbs and exhausts. The piston was designed to be the most perfect piston available for a Lambretta standard or tuned. The cylinder head has a lowered combustion chamber volume ideal for unleaded fuel.

CONS: Non apart from the kit is new and has yet to prove its self. The porting is a little on the rough side, as the factory didn’t copy the original cylinder. The ports resemble a standard TV 175 cylinder not a stage 3-tuned cylinder. The cylinder would possibly be better off with a blue print to a stage 3 as it was originally designed for. The alloy casting is done in a sand-cast method and may appear a little rough this is not detrimental to the running of the kit and actually could aid cooling through surface area! Reprofiling the cylinder head would be a good idea for more power.

Mark Broadhurst, Oct 2001,

SRP 175 and 190 cylinder update Nov 2001.

The kits have arrived, at last. The cylinders appear to be very well machined around all gasket faces, the bores are machined well and within manufacturing tolerances, on some cylinders the stud holes could create a problem latter on in life especially with rough big handed Scooterists. Basically some of the threads do not seem deep enough, but this leaves a conversion to drill and tap further into the cylinder to get more thread area. All studs will be loctited into position before sale to prevent any latter problem.

The piston varies very little in size, less so than Vertex, Honda or Wiseco pistons. So hopefully this creates a very good piston as we hoped it was. Just to be correct MBD will match a piston to a cylinder bore before sale allowing for correct piston to bore clearance.
We took ten cylinders and measured the bore and piston sizes, the pistons were with in 0.0004’’ (4 tenths of a thousands of an inch) very close indeed.
The cylinder measurements varied a little more, 0.0013’’ between the largest and smallest size, but given the large amount of pistons available MBD can match a piston for every bore.
The worst case would be a tight bore with a large piston, this would still give a piston to bore clearance of over 0.001’’ (normal for motor cycle alloy cylinders) a small piston in a large bore would give 0.00279’’ normal clearances for Lambretta iron cylinders. MBD will try to send out cylinder kits of 0.0015’’ to 0.002’’ clearance.

Careful setting up of the squish clearance by removing either or both cylinder head or base gasket could result in a quicker engine. Cylinder fitting instructions come with the MBD cylinder kits, squish clearances are explained in here in depth.
All the piston skirts are the same length as an original 200cc Borgo piston, this helps the Rapido, GT/TV 200 cylinders in terms of port timings, they make no difference to standard SX/GP cylinders except they should last longer. In terms of tuning, 2mm needs removing from the inlet side of the piston especially in 150 – 175/190 conversions and 200cc Indian cylinders or an extra 2mm could be lowered on the port.

The ports look rough and vary in size from cylinder to cylinder. This could mean one cylinder is quicker than an other in standard form! It seems the manufacturing process has allowed for some liners to be slightly moved around, this shows up in the transfer passages, but should make little or no difference to how the kit works. The 175 cylinder seems better than the 190 kit here.

Cylinders set up on our timing jig with no base gasket showed the approximate port timings to be,

Exhaust 165 degrees, close to our pattern stage 3.
Transfers 126 degrees, close to our pattern stage 3.
Inlet 134 degrees, a little too small compared to our pattern stage 3.

The exhaust width varies from 42 to 46mm, this is possibly where one cylinder varies in speed over another. (With these rings it could be possible to tune the exhaust port width to 50mm!) The exhaust port has been lowered 1mm by the factory more than our pattern, this should make no difference at all but we normally like the exhaust port flush to the piston at bottom dead centre.
There is a casting gap between the liner and the exhaust port on some cylinders, again looks rough but would not be detrimental to its running.

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Standard exhaust port.

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Standard exhaust port.

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Standard exhaust port.

The transfer ports are the roughest of all both inside the cylinder and along the passages. Inside the cylinder the ports have been widened to suit a 200-cylinder size. Around the out side of the transfer ports the casting is beefed up so tuning a transfer passage to near 200cc ports is possible depending on what casings you have.

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Standard exhaust port with standard transfer port.

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Standard exhaust port with standard transfer port.

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Standard transfer feeds.

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Standard transfer port.

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Standard transfer port.

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Stage 4 tuned exhaust port and cleaned up transfer port.

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Tuned exhaust port with cleaned up transfer port.

The inlet port has been reduced in size compared to our pattern cylinder and a standard TV175 cylinder. The port gasket face matches a standard 175-inlet manifold but the port then becomes much smaller, more like a 150 port, but then inside the cylinder it reaches the size of our pattern cylinder. This is very obvious, as the factory has done a little cleaning up work inside the port. The inlet port timing is a little low to match the transfer and exhaust port timing, removing 2mm from the inlet side of the piston would put the cylinder ports similar to our original modernised pattern.

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Standard inlet port.

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Standard inlet port.

The 175 head for some reason comes with a very low compression ratio, larger than a 200 head. Not what we designed! This will impair power. Ideally these need machining quite a lot and will still work with unleaded fuel. We would expect all 175 kits to need the head machining, standard or tuned.

The 190 cylinder head has come from the factory machined wrong, typical! And in standard, off the shelf form is useless. But once reprofiled they should be perfect for power and for using unleaded fuel.

Having said all this, it's not to slag off the kit and it is not to say it is perfect! It has good points and bad points. As a standard kit it is good value for money in every aspect, it will reduce heat build up, it gains cc’s, gain horse power and help in modern day traffic, it should prove to out last any kit as the liner is so hard.

Now the kits have landed and we have seen the production versions compared to the early prototypes we can set the exact kits available by MB Developments.

  1. Standard 175-cylinder kit. Not available due to lack of Vertex pistons
  2. 175 or 190 with a Stage 3 blue print tune with reprofiled cylinder head.
    (In this case the stage 3 tune consists of a quick rough clean up of the inlet, exhaust and transfer ports, 2mm removed from the inlet side of the piston) this kit could use either 18, 20 or 22mm standard carburettors or even 24, 25 or 26mm modern carburettors.
    Could use standard or Clubman exhaust systems.
    Not available in 175 cc version, only available in 190 when used with 115mm con-rod.
  3. 175 or 190 with a Stage 4 tune and reprofiled cylinder head.
    (In this case the stage 4 tune consists of all ports enlarged, cleaned up, squared off and polished) designed to use 24, 25, 26, 28 or 30mm carburettors.
    Could use a Clubman or touring type expansion systems.
    Not available in 175 cc version, only available in 190 when used with 115mm con-rod
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    Stage 4 tuned exhaust port.

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    Stage 4 tuned inlet port.

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    Tuned and flowed transfer ports.

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    Stage 4 tuned inlet port.

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    Stage 4 tuned inlet port.

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    Stage 4 tuned exhaust port.

  5. 175 or 190 with a Stage 5 tune and reprofiled cylinder head.
    (In this case the stage 5 tune consists of all ports enlarged, cleaned up, squared off, polished and matched to 28 or 30mm carburettors.
    Could use Clubman, touring or racing expansion systems.
    Not available in 175 cc version, only available in 190 when used with 115mm con-rod
  6. 190 with Big Brother tune.
    (In this case all the ports are increased to the maximum size to suit what would normally be done to a Stage 5 200 cylinder kit, the only difference is that the piston is 2mm smaller in diameter), expect to use 30 – 34mm carburettors and expansion chambers.
    For the money you are better off getting a stage 4 200 kit and some new 200 casings.
Spares are available separately. Contact us for a quote.
  • 175 cylinder 62mm,
  • 190 cylinder 64mm,
  • 175 standard cylinder head,
  • Cylinder heads reprofiled,
  • Pistons shortened,
  • .5mm standard base gaskets,
  • 1mm base gaskets,
  • .5mm standard 175 / 190 cylinder head gaskets,
  • Standard exhaust gasket,
  • Big bore stage 4, 5 or 6 fibre exhaust gaskets,
  • Big bore stage 4, 5 or 6 copper exhaust gaskets,
  • Standard 125 / 150 inlet gaskets,
  • Big bore 28 / 30mm inlet gaskets,
  • Inlet and exhaust studs are available in different lengths,
  • Helicoil or steel timeserts fitted to be safe,
  • Various inlet manifolds to suit various carburettors,
  • 25, 28, 30 or 32mm Dellorto carburettor kits,
  • Standard, Clubman or expansion chambers,
  • GP 200 race crank shafts,
  • Uprated bearings, seals and gaskets,
  • ETC, ETC
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Our preferred exhaust system for touring tunes is the AF clubman.
We cannot buy the parts to make our Clubman exhausts at the price we retail these exhausts.
They give good performance up to 15 HP.
They fit well and look good.
They come epoxy coated black or grey.
We supply them with a chrome exhaust clamp and one of our exhaust gaskets.

Please E-mail us with any questions or comments.