Largest cc

[AL BARKER]

Conversion with a mate...... What's the biggest cc that can be achieved WITHOUT reed valves? AF seem to have run out of 250 Rapido kits. Just pub talk lol

[Scooterslag]

Old school iron 240cc ? Paul

[Adam_Winstone]

All depends on how far you want to go and whether you're talking 'off the shelf'.

My piston port Mugello is 293cc on a CasaCase; 72mm bore and 72mm stroke crank. My bigger spigot will allow me to go 72.5mm (297cc) or 73mm (301cc).

[Cgt75b]

What’s it like on fuel Adam?

[Adam_Winstone]

It's amazing on fuel!!!

Because it pulls 4.12:1 top gear, the low revs = fewer combustion cycles, with fewer combustion cycles = better MPG.

I'm running what are basically SIL stage IV port durations, meaning that the low RPM is happily making very useable power, whereas a more 'tuned' barrel would need higher rpm, which would knock fuel economy again.

[AL BARKER]

Adam, is that a 225 barrel over bored or something special with a larger spigot. Sounds like it's fun to ride, slow revving with grunt

[Adam_Winstone]

Started as a 70mm 225 that was extended with extension welded to top of barrel, new alloy spigot welded into the barrel, then bored to suit 72mm piston. All of the above done by Paul Baker (lovely job) at SRP to my spec.

Loose base packer cut circular (by Steve Rowe) to my specification, transfers cut and shaped by me, along with porting by me.

The Casa casing mouth was cut to my spigot size, transfer feeds cut in by me.

AFR heavy cast head machined by me for spigot fit into bore. Squish profile and combustion chamber by me.

Once happy with the configuration the top end went off for ceramic plating with Wossner piston from AF.

Motor assembled with bits from CamLam, MB and Readspeed. Then dynoed by Readspeed.

Over a development period the bike went back to Readspeed a couple more times more, each time with different exhaust, ignitions (advanced/retard and/or static), 2nd head, carb swaps and different exhaust configurations. Jerome's dyno observations and expertise giving me food for though and a bike that I've been confident to rally on.

The gearing I've dialed in with real-world road miles, matching gearing to pipe delivery and Anthony Tambs AC tacho feedback (a huge help for appreciating how these factors influence one another).

Last big change, other than further exhaust swaps/tests, was taking the plunge and investing in an LTH clutch from Darrell Taylor, with his modified centre. This change was necessary as even the uprated 6-plate was struggling with the low RPM torque but, whilst I have never been able to justify the price of an LTH clutch before, I'm now an absolute convert and appreciate the class above any clutch that I've used before. Ok, there are plenty of other clutches over £450 that I've not tried, but there really is no comparison to any of the other 5, 6 or cassette clutches that I've used (and I've tried all sorts over the decades).

The motor is a personal project to deliver the performance that I'm looking for, at the RPM that I'm comfortable with. It only makes just over 28bhp but it rides beautifully, cruising at high speed and low RPM. In a world of Subarus mine is an old school V8; not a performer by today's standards but a tree stump puller.

My engine, to my spec, with the help of a lot of skilled people that have helped me to realise what I was looking to create (thanks and sorry to anyone I've overlooked).

I continue to try different configurations and the keep learning as i do so. The project teaches me about all sorts of 2-stroke issues that I've not really had to consider before (e.g. primary compression ratios, etc) so it's a project that keeps giving

[AL BARKER]

That's impressive Adam. Sounds like it's a ongoing project still.... there are some really clever people out there. The amount of work involved to go from 70mm to 72mm bore!!

[GRTDKAD]

Mind blown by that Adam. Impressive development and with the likes of Jerome involved you know it’s going to work, he’s like the oracle!

[Solid Air]

Inspirational stuff Adam! You obviously have a very active and curious mind to take this route, but I imagine that's all part of the fun for you.

I think the idea of riding on the torque rather than revs is the way to go for a mile-munching tourer, hopefully giving an an easy but fun ride and a longer lasting engine that doesn't guzzle fuel.

The parts that are now available open up all sorts of opportunities to us, especially when paired with the experience gained through mile upon mile of road riding and the wealth of knowledge held by some amazing engine builders in the world of the Lambretta.

I'd be very interested to hear where you end up in the development of your engine.. if it does ever end?!

[Adam_Winstone]

^... it doesn't ever end (lol)!

Is it a blessing (keeps my interest) or a curse (always other options to explore)? My mid has already started considering options of a GT Case with 76mm stroke, barrels without cylinder stud holes (to allow a bigger bore), utilisation of Casa Case SSR fixing points to allow me to utilise a Quattrini style spigot less cylinder at 76mm (can't recall what 76 x 76 results in), etc.

When does obsession become lunacy? However, I like the engineering challenge of making ideas become a viable reality. Sadly, my limited skill set requires the input from others to bring it to fruition... but it also allows me to realise my own limitations, improve some of my skills, and make some valued working relationships (to the point of friendship) along the way.

I consider myself lucky to be part of a communal scene that actively encourages development.

Thanks for the nice responses.

[Solid Air]

It doesn't ever end.... tell me about it! Something going wrong is just an opportunity to develop something else and bringing together the people with the necessary skills for a project to reach fruition is perfectly acceptable.

I've wondered about the SSR type cylinder fixings too, more for ease of fitting rather than to increase cc though. From my own experience I wouldn't go spigotless, like the Quattrini, unless the casing could be utilised as a spigot (dont think that would be feasible?) or the gudgeon pin to piston crown was a decent distance to keep the piston stable in the bore maybe? I know lots of people use the Quattrini with no major issue, but with wear and / or hard riding that area becomes the weak point from what I have found.

Keep up the good work!

[Adam_Winstone]

^... like.