SLUK is the world’s first scooter publication to try one of the new Pinasco 251cc engine kits on the road. Sticky reckons it delivers the performance that many riders are now looking for. After reading his article I think I’ve just decided which engine I’ll be fitting to my troublesome PX… Super T5 anybody?
Flexible is the new fast
I know tons of riders, usually of a certain age, who would love a fast scooter that came without all the usual associated drama of tuned scooter ownership. I’m talking about tooth-rattling vibration, ear-splitting noise and wallet-draining fuel consumption. Most of us have been there, got the T-shirt, grown a bit too large for the T-shirt and cut up the T-shirt for rags by now.
How much more appealing as a daily driver – to sit alongside the little-used warp-factor weapon in your garage – would be a standard-looking large-frame Vespa that makes 30hp while running a relatively quiet box exhaust? Maybe something with a power-spread as wide as the Amazon so you don’t need anything more than a 4-speed gearbox to enjoy it?
How about one that has the good manners of a standard scooter at low rpm but will lift the front wheel in first gear at will? An old Vespa that will dust any GTS rider silly enough to challenge your well disguised 2-stroke superiority…
If this sounds like your sort of scooter riding, then read on.
Pinasco 251 by name and 251 by nature…
As Pinasco’s design guru Vittorio Zitun explained, their new 251 engine is going to be an affordable (comparatively) self-build motor kit in the true sense. The kit will contain all the main elements you need to assemble just such an engine in a plug-n-play stylee…
What comes as a surprise, but shouldn’t really, is that the 251 is not based on the PX125/150 or the 200 casing. This is in effect a ‘super T5’, based on the casing layout of easily the best large-frame 125 motor.
‘The main elements of the basic Pinasco 251 kit’
The T5 layout was chosen for the more modern (in the mid-80s) square stud layout and centre spark plug layout of the cylinder. These advantages carry over into the 251, but only in massively oversized versions.
Rather than the T5’s usual 52mm stroke, this engine comes with a purpose-made 60mm stroke crankshaft.
Where the T5 has a modest 55mm bore, the 251 sports a massive 73mm diameter piston.
‘This is not a PX. It is a T5 super-big’; said Vittorio.
Mr Big Stuff
All of this makes perfect sense when you see the barrel and head layout. The kit looks like a massively oversized T5 kit, but the barrel not only has a massive central exhaust port, but also 2 smaller sub-ports (‘boosters’ as the Italians call them).
Due to the engine maintaining the standard T5 cylinder stud pattern, these booster ports have to maintain a long route that flows around the outside of the cylinder studs before joining the main exhaust duct.
The cylinder does not use a cast-in stub like the PX cylinders, instead there is a flat gasket face with 2 studs to which you bolt a steel flanged stub onto which the Pinasco box exhaust (extra to the kit price) slips.
The flat stub is not supplied with a gasket and with only a small sealing area, which Vittorio said should be sealed to the barrel with high-temperature silicone sealant. Having seen the relative weaknesses of all the Lambretta kits with exhausts mounted this way, I’d like to see a bit more gasket area and a thicker flange on the steel stub to prevent leaks if the exhaust is ever grounded-out.
One aspect that I did like though is the head fastening. The four standard studs are augmented by an extra four M8 bolts into the barrel and there is a brass (not copper) gasket used between the two parts that Vittorio says massively reduces any prospect of damaging detonation.
Crank it to the max
Core to all of this are crankshafts designed from the ground-up to work with a 73mm piston. Standard T5 crank webs – and this crank – are wider than the PX so far less liable to suffer twisting at the crankpin.
Unlike a normal T5 crankshaft, which has a much smaller diameter flywheel side crank web, the 251 webs are both 98mm in diameter and the flywheel side casing of the dedicated Pinasco engine casings are opened out to accommodate it.
Two versions of the 251 will be available shortly, either with rotary inlet system (‘Master’) or a huge hole for Pinasco’s downdraft reed valve solution (‘Slave’).
In order to balance the rotary valve crankshaft for the huge 73mm Asso piston, there are two tungsten weights pressed into the webs. The crankshaft for the reedvalve version is more of a bell-shaped design with plain webs.
Clutching at straws
One of the chief weaknesses of the large-frame engine design is the heavy clutch being mounted directly onto the end of the crankshaft. Not only does it act like a second flywheel but the mounting system of a parallel shaft with a woodruff key being required to transmit all the torque is hopeless for really powerful engines.
Pinasco’s solution, after much testing and many failures using Woodruff keys, has been to machine both the crankshaft and the clutch centre with a broad spline. This offers the advantage of an un-twistable joint that still allows the clutch to be removed without need for special tools. The clutch is based on the Cosa style with 4 friction plates. Various spring strengths are offered.
Price and other parts needed
The basic 251 kit consists of casing, crank, clutch and cylinder kit and the 2019 target price for the ‘Master’ (rotary) version is €2,340 (£2012) and the ‘Slave’ version – including the reed-valve inlet is €2440 (£2,098).
On top of that kit price you will need a full gearbox, primary drive and shafts, but these can be taken from a donor PX or T5 engine. Vittorio says that genuine Piaggio gearboxes have so far proved strong enough in testing.
The other vital element is an ignition kit, but since this engine is based on the T5 layout then you can fit a normal T5 flywheel and stator – if you can find one. Alternatively, other manufacturers make ignition kits for the T5 including Pinasco’s own Flytech advance/retard system; which is available either with a plastic or aluminium fan.
For the ‘Master’ version you can use a standard type SI carb box, but Vittorio advises a big carb inside, such as their 28mm to allow the engine not only to breathe, but also to take in enough fuel and air to keep itself cool.
For the ‘Slave’ reedvalve version Vittorio is happy to use the classic round-slide Dellorto PHBH 30mm carburettor because it is easy to set-up and isn’t too big to fit under the panels of most large-frame Vespas.
This engine configuration – the ‘Slave’ reedvalve 251 with 30mm carb – is the one that Pinasco used to win their class in the recent Magny Cours endurance race, and would also be the one that I’d get to try in a moment…
I couldn’t wait…
In order to get a flavour or the 251 Vittorio let me try his road scooter which he’s recently been using for mountain tours as part of the company’s testing regime.
With their own box exhaust developed for the 251, Vittorio says that there is 29hp on tap in the road scooter, but the peak power is not the important aspect of this engine. It is the epic power spread.
A beast of a T5 like this takes a bit of kicking, so Vittorio recommends doing so on the stand. when it fires into life it sounds like what it is – a T5 motor on steroids. The most important aspect of the € 200 (£172) box pipe they’ve developed for this motor is that it’s not too loud. I’ve always preferred the look and sound of an expansion chamber, but when you have a box pipe that delivers the best part of 30hp and retains the excellent ground clearance and tyre-change-ability of a standard exhaust then I’d be willing to sacrifice the yobbish appeal or an expansion chamber.
VIDEO | On the road - Pinasco 251
The front wheel of Vittorio’s Vespa hovered controllably above the tarmac as I set off enthusiastically outside Pinasco’s HQ. The power delivery is amazingly progressive, linear and tractable. Even as low as 3,500rpm it makes 10hp so you can potter around in city traffic without working the clutch or gears too much.
The harder you rev it the faster it goes, with peak power and torque of around 30hp being reached at below 7,500rpm; which means the engine shouldn’t wear out too quickly, nor will it need a fuel tanker to follow you offering in-flight refuelling to make it between petrol stations.
For the past few years I’ve run a Cyclone 5-speed gearbox in my tuned Lambrettas and it leaves you spoiled as there is a gear for every occasion. I’d forgotten quite how widely spaced the gears were on a P-range motor, but the lovely part of this ride is that there is no lag between the gear-changes. You never have to wait for power. Change up and it always pulls.
I’m not surprised that this was a perfect engine for Pinasco to win endurance races because riding it fast is almost as effortless as riding it slowly.
There was no opportunity to test this scooter for top speed, but to me it felt like an engine that would hold 80mph (130 km/h) for long periods without sniffing. In the real world, very few classic scooter riders ever travel distances much faster than that.
I was less impressed with the clutch in Vittorio’s scooter which, though easy to pull in due to using the lighter spring options, still dragged a little. Vittorio simply rides around this. He explained that this clutch drag was due to the lever arrangement in the trapezium-headlight Vespa headset not pulling the clutch cable as far as later headsets.
On a Vespa PX he assured me that the clutch frees-off when pulled in and behaves impeccably due to a different lever ratio. Certainly, the lever pressure did not require a python-like grip unlike tuned scooters of yesteryear.
You want more?
This is a motor conversion that has been developed to do exactly what Pinasco wanted from it. They have already proved the reliability of this motor over 10 and 24 hours of racing, in the same way that Vittorio has proved it in development rides through the Alps and the Dolomites.
I come from a country where large-frame Vespas are traditionally used more for touring and rallies than for turning into street racers, so I think this motor will be massively popular in the UK. Compared to similar conversions for Lambretta, the price is certainly a bargain.
For the rest of the world – Germany and Austria in particular – where the Vespa Street Racer was always the default custom style, then the Pinasco 251 engine represents a blank canvas for further tuning.
I would expect a purpose-built expansion chamber for this motor to add at least 5hp if not more. I’m sure that 40hp is well within reach, if that’s what you want, but I feel that’s missing the point a bit.
What you have here is a well developed plug-and-play solution that will fit almost any classic large-frame Vespa, without attracting attention from the police or dragging a fat exhaust on the floor on every corner.
For me, it feels like a standard T5 only with three times the power output. Given that I already love the T5 motor, then I regard this as three times as good, so it’s a motor that I really would love to own and use…
Words and Images: Sticky and Pinasco
Video clips: Christiaan of PLC Corse
Thanks also to Piergiorgio Bettella and Vittorio Zitun
It’s fair to say that Pinasco have been the team to beat in both small-frame and large-frame classes on the European scooter endurance racing scene for several years now. As we explained in our article on Team SLUK’s class victory in the first UK scooter endurance race, this is a cruel sport where victory is lost when within reach more than it is won.
To win consistently requires military-like organisation and planning, but Vittorio assures us, it does not require special engine tuning. The team’s victories usually come with engines built entirely from Pinasco’s extensive production catalogue (which can be downloaded here).
Many rivals imagine the Pinasco team use specially-prepared parts but Vittorio explained that it’s often the opposite case and they race using ‘seconds’. For instance if they spot a kit in stock with a few pin-holes in the plating, they will use that one in preference to selling it to a customer who might reject it because it doesn’t look 100% perfect.
They know that there is no difference in use because even the imperfect barrels are good enough to win a 24-hour race…
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