Birth of a cylinder kit – SSR 250 | FEATURE
What is involved in making a new cylinder kit from scratch?
SLUK joined Casa Performance at their base in Italy to follow progress of their new SSR 250 kit as it makes its way from drawing to running prototype in record time.
Things have moved on a great deal since Terry Shepherd drew a Lambretta cylinder for Ray Kemp and sent the drawings off to Gilardoni to produce the TS1 kit. Much of the laborious hand-drawing and prototyping work can now be eliminated by use of modern technology.
Casa Performance – the spin-off performance arm of Casa Lambretta operated by Rimini Lambretta Centre – have used various high-tech shortcuts to get the prototype up and running in only a few months. Here’s how they did it.
Casa Performance have an in-house tuner/designer in Lorenzo, but also used a specialist 2-stroke engineer not only to map the cylinder in CAD but also to perform Computational Fluid Dynamics (CFD) testing on the port layout in advance. The cylinder was a joint effort by Lorenzo and Tommy.
The advantage of starting from a clean sheet of paper and inputting all the data into software means that it is possible to simulate the output of the engine in advance, which is where they got their target figure of 50hp+.
The relatively high output of this 250cc engine for its capacity comes from the fact that it uses short external studs to bolt the barrel to the engine. This in turn frees up the design of all of the internal ports by removing the limitations of the oddball Lambretta stud pattern.
Casa Performance also ordered a custom 70mm forged piston to their design based on the CAD drawings.
The team have recently upgraded their in-house 3D printing machine to a larger unit capable of producing a complete engine. It melts a reel of plastic wire onto a model, layer by layer to build-up a three dimensional model of a part in solid plastic. Depending on application, certain simple non-stressed parts – i.e a carb bell-mouth – could actually be tested live.
Obviously a plastic cylinder and head will not function, however they are perfectly good for bolting to a demo casing and using to check for sizing of ports, clearances to the frame and even making prototype cowlings.
- Rapid Prototype Casting
The use of 3D printing technology is going to revolutionise the world. It is not only being used for modelling. Already printers exist that can actually print testable parts in layers of molten metal.
In the case of the SSR 250, the barrel and head were cast as usual in aluminium, but the modern shortcut was to use 3D printing to produce the sand-cores used for the casting. Ordinarily producing inter-locking sand cores and aligning them by hand is a laborious and technical business which can result in misaligned port-heights and timings if not done correctly. The 3D printed sand cores eliminate that variable and produce a cylinder casting that is far more likely to work as predicted first time.
The two rapid prototype cylinders were sent off to Gilardoni for plating with only a week to go before the promised unveiling at Bridlington scooter rally 2016.
- Exhaust design
The plastic models and predicted power characteristics are enough information to design a suitable exhaust system. Their exhaust builder, Protti, actually designed the first prototype pipe using a plastic cylinder bolted to a new CasaCase. The plastic prototyping material has perfect machined faces and stud dimensions, so is good enough to build an exhaust from. The cone layout evolved from a mixture of experience and computing, but the belly diameter is actually far smaller than I was expecting. Shallow cone angles usually offer a wider power spread at the cost of maximum power, so there is certainly more power to come.
- Engine assembly
The external stud SSR barrel will not fit onto a normal Lambretta casing unless the gasket area has its face built-up more than the make-up of an overly-enthusiastic killer clown.
Instead, it is designed to fit on the new CasaCase with its unique vertical split to load the crankshaft. The crank in this engine is 64mm stroke, but the casing and the length of the barrel with its stepped head permit stroking to 70mm in the future.
Plastic models of the cylinder base were used to carve out the transfer port cutaways by hand, but in the future this will all be carried out by CNC.
VIDEO: first start of the SSR 250
- First Start
The plated cylinder only arrived back from Gilardoni one day before the scooter had to be packed in the van to show at Bridlington. However the design process using 3D modelling meant that everything went together quite smoothly and the engine was assembled and running by lunchtime.
Even with rich carburetion, guessed ignition timing and using the first prototype exhaust it produced just shy of 42hp (at 9,300rpm) with a wide power spread on the first run on the dyno. That’s a very encouraging figure for a first run and makes the 50hp target seem perfectly achievable.
We at SLUK will follow the progress of the SSR 250 project and will be the first scooter publication to give you a full road test once it’s been dialled-in.
SSR 250 Q&A with Dean Orton
Why make this kit now?
This is one of the reasons behind making the CasaCase in the first place. The idea was to produce an affordable replacement Lambretta engine that makes over 50hp.
What do you mean by affordable?
Affordable meaning much cheaper than the low-volume billet alternative. The cylinder kit itself should be around the same price as the current SS225 kit for Lambretta casings which is under £700 retail.
When will it be available?
There is still a lot of development and road-testing left to do. The plan is to have it on sale by summer next year.
Do you really think that many scooterists need 50hp?
Everyone likes power and having personally toured long distances across Europe with a 50bhp Lambretta engine, I can vouch that once you have tried it, you’ll only wonder how you ever did without it until now.
We are also developing a Touring version, the SST 250, in tandem with the SSR and that will be will a lower-revving torque-monster engine kit specifically designed for rallies.