Almost two years ago SLUK was the first scooter publication to test the Pinasco 251 engine.
Essentially, the 251 is a kit of parts which you can use to build your own ‘super T5’ engine, because it is based on the T5 layout rather than the PX. Back in our original article we said it was a lovely engine to ride; which is a statement we stand by. It has a broad spread of power – even with a relatively quiet Pinasco box pipe fitted – but it’s not too powerful that you can’t use full throttle in the lower gears. For me, it seems like a nice compromise engine: like standard but much faster.
Dyno results
One thing we don’t stand by is the dyno curve supplied by Pinasco at the time, which showed 30hp with the box exhaust. Every other Pinasco 251 and box exhaust engine we’ve seen dyno tested since has made between 23 and 25bhp.
If you are buying one and expecting 30hp then you might be disappointed, but too much emphasis is placed on peak power figures and not how well the end result rides on the road. In the real world an easily accessible 25hp is plenty for most riders in a PX chassis.
Iggy had the casings, selector box and T5 flywheel cowling masked and powder-coated in crackle glaze black by Trevor at Midas Touch in Leeds prior to assembly. It looks great but coating is a brave move on an untested motor.
What’s the point of this series of articles?
This series of articles and videos will be useful beyond the Pinasco 251. It’ll contain real-world tips and tricks useful to anyone building large-frame Vespa motors.
A bit rusty
It’s been a long time since either Iggy or I concentrated on large-frame Vespas. My last radical project was Dreadnought – the hub-centre-steered Malossi 172, built to win various European Cannonball runs. It was later fitted with SIP’s Nitrous Oxide injection kit for a series of articles in Scootering Magazine in the early 2000s. I’ve still kept my hand in with Vespa, both building our 6-hour race-winning Quattrini endurance smallframe and another Pinasco 251.
In the mean time the Vespa world has gone mad with radical new developments, like the Lambretta one, while at the same time the quality of main-market spare parts has plummeted. It feels like there was a lot for us to learn, or re-learn, about the big-bummed Vespas.
Making replacement casings – not as easy as it seems
Pinasco are now one of many firms producing brand new upgrade engine casings for various classic scooter models. These replacement casings allow manufacturers to beef-up around known weak areas of the original engines. They also allow owners to start with a clean casing to build that isn’t battered like a ginger step-child, through years of abuse.
What has become increasingly apparent, from all of the replacement casings, is that it’s not easy to completely re-draw and redesign a scooter engine casing from scratch. What we are seeing from the majority of manufacturers of replacement Vespa and Lambretta casings is that they’ve overlooked one small dimension, or missed one small detail and as a result you have to develop work-a-rounds to use their products.
Such examples include:
- Replacement Lambretta casings where the gearbox end-plate studs and dowels are not perfectly aligned
- Upgrade smallframe engine casings where the gear selector wheel is offset causing the gear cables to rub and fray
- Lambretta performance engines that are not compatible with certain makes of ignition flywheel, or feature baked-in inconveniences with regards to fitting the rear brake arm for instance
- Vespa upgrade casings which rapidly wear out oil seals due to increased shaft diameter
- Lambretta engines with revised cylinder orientation that vibrate like a jackhammer
Plug and play?
All this points to one truth: it’s not as easy as many people think to redesign an engine, so engine builders will encounter compromises and must develop solutions to overcome these issues. For me, that’s part of the fun. For anyone who expects any of these engines to go together like Lego will be bitterly disappointed and should really have their performance engine built by a dealer.
As you’ll see later on the Pinasco 251 engine presents its own set of challenges to overcome, and some of these stem from repeating problems that Piaggio made in the original T5 engine casing.
The ‘Slave’ version of the engine uses this funky reedvalve with a flexible rubber 90-degree inlet manifold and 30mm PHBH Dellorto
Getting Started
The first step for anyone looking at a 251 is to decide which inlet type to go for. Essentially Pinasco make two versions of many of their engines:
- ‘Master’; which is a rotary-valve crankshaft and casing to be used with the original SI-style carb in a box. The advantage of this set-up is cleanliness, possible improved fuel economy and quieter induction noise. Sadly these casings will not run an autolube system, so that advantage is deleted.
- ‘Slave’ is the reed-valve version. In the 251 edition the reedblock bolts straight to the casing and comes with a manifold and jetting instructions for a 30mm PHBH carb. This should be the more powerful version and uses a specific ‘bell’ crank.
Iggy chose to get the reed-valve Slave version for his PX; which is the same configuration that we originally tested and the same as I’d built previously.
The 251 kit has quite a big bore for the available cooling fin area
Eight-point head fixing, utilising location dowels on the bigger holes
What’s in the kit?
- Casing (with engine mounts and reedvalve block to fit
- Crankshaft
- Cylinder kit including head
- Carburettor (30mm Dellorto PHBH)
- Clutch (Pinasco Bull clutch)
- Ignition (Pinasco Flytech for T5)
- Exhaust (Pinasco box for 251)
- Cylinder studs
What you can see from that list is that there’s also a lot of missing parts. These must be purchased, either as new (Pinasco make most of what is needed) or pinched from a donor engine.
The bell-shaped crank of the Slave version has a splined fit for the clutch
The Pinasco Bull clutch is a 4-plate derivative of the Cosa-style clutch
The Box exhaust supplied with the kit is quiet. Iggy expects to fit something sportier in the future…
Missing from the list are all the following:
- Output (lay) shaft
- Complete gearbox
- Primary drive gears and shaft
- Rear brake plate, cam and shoes
- Crankcase studs
- Engine bearings and circlips
- Clutch cover (requires grinding to accommodate Bull clutch)
- T5 cylinder and flywheel cowling (not always easy to find)
- Gear selector box (KR Automation one fitted)
- T5 gear selection box cover
Doner kebabed
For most of the parts we robbed bits from Iggy’s previous Malossi 210 engine. For the remainder, Iggy obtained parts like the primary drive kit and brake shoe kit from BGM and an engine revision kit (bearings/seals etc.) from SIP.
Pressure-testing Iggy’s old 210 motor. It was as leaky as a torn rectum…
Let’s make a start on the strip and build
One really useful tip when rebuilding or stripping any engine is to use a leak-down pressure test to test BEFORE DISASSEMBLY. This can be useful in diagnosing what, if anything, afflicted it.
In the case of Iggy’s old Malossi 210 motor, which we were salvaging for parts, this was very revealing. It wouldn’t hold any air pressure at all.
VIDEO: Pressure test
We hunted in vain for the source of the leak from all the usual places, but eventually tracked it down by replacing the gearbox oil drain and filler bolts and checking for bubbles at the clutch cover breather bolt.
Essentially, any pressure you add in a leak-down test should not leak into the gearbox at all. The drive-side crankshaft oil-seal should keep any pressure inside the crankcase, but since this wasn’t happening then that component was clearly at fault. You can see quite how knackered that oil-seal was on the accompanying video; primarily because the drive-side main bearing had, like a poltergeist stool pigeon, completely given up the ghost.
Soapy water spray was used to try locating this Scarlet Pimpernel of an air-leak
Buy or build one
If you’re stripping or building a scooter engine don’t bother unless you’re using a leak testing kit. You’ll be surprised at just where casings, old or new leak! We showed you how to build one on the cheap here.
Alternatively, Darrell Taylor makes and sells a leak down kit for Lambretta (he can also add Vespa bungs), his kit costs £59 and can be bought on eBay here. Tell him we sent you though.
Images and video: Igg
Words: Sticky
NEXT TIME: We start the engine build process in Earnest. Ernie finds this very uncomfortable and suggests we use a shed.
Read Part 2 here.
