There’s a lot to love about the GT kits. Back in our pre-SLUK days I did an extensive multi-test on a selection of GT engines and every owner I ever speak to seems delighted with them.
The problem with the GT kits is that Richard has always favoured pragmatic over machismo. The original GT186 is a great small-block kit, but now all the high-end rivals have gone to 195 or 198cc. The same is true of the big-block GT200 kit. It works a treat, but there are people who won’t have a 200 when they can have a 225 because bigger sounds better.
Especially down the pub.
A true 240 – out of the box
Bowing to human nature, Richard Taylor has finally created a big-capacity bolt-on* version of the GT kit. Various dealers are now offering the GT240 as an over-the counter conversion for any large-block Lambretta, but this a not a massively over-bored wafer-thin cylinder. There’s more than one way to skin a cat.
The 240 uses a normal cast iron GT200 cylinder casting, but left longer and bored to 70mm – which is the same piston size used on all the popular 225cc kits. The chosen piston is an all-time classic of ’80s ‘Jap’ piston conversions; the ever-popular Suzuki TS250ER.
The additional capacity comes from a 62mm stroke crank, as opposed to the standard 58mm stroke or the popular 60mm stroke upgrade crank. Unlike most other 62mm stroke crankshafts, the big-end of Richard’s con-rod barely pokes out beyond the webs of the crank, so while full-on ‘trenching’ of the crankcase isn’t required, *you do still need to open a standard Lambretta casing a little for more clearance. Richard explains that this can be achieved quite easily with a drill and a flap-wheel.
If you use the GT casings then there is already enough clearance for plug-and-play assembly.
The clever thing about the GT crank is that it can take both 16mm and 18mm gudgeon pin pistons due to interchangeable small end bearings, so there’s no problem fitting the 18mm-pin TS250ER piston straight onto the crank.
Pros & Cons
The GT kit has numerous advantages:
- Reborable cast iron construction
- Dedicated cylinder head supplied
- Reed valve with left or right hand manifolds available – will fit with any tank or battery tray configuration
- Reliable piston with lots of oversizes
- Cast iron really could do with running in a bit and careful set-up
- Only 2 exhaust studs and only 4 head fixings (some newer kits have double that)
On the dyno
By far the greatest influencer on 2-stroke engines is the exhaust, but luckily we’ve managed to dig up three curves for engines using exactly the same Franspeed Race pipe and the same 30mm PHBH carb size.
In the Red corner, we have a standard bolt-on GT200 kit (23.6hp 19ft-lbs)
In the Green corner we have a Taffspeed-ported TS1 engine from a previous magazine exhaust test. (25.2hp 20ft-lbs)
In the Blue corner, we have Gary Dickenson’s GT240 (25.7hp 21ft-lbs)
Graphs are very pretty, but what are they telling me?
The important areas to look at in any dyno graph are the parts of the rev range that you use most.
Around town, you need a crisp 3,000-5,000 for the scooter to pull away cleanly and not waste tons of fuel. Despite the label Race the Franspeed exhaust is actually a pretty decent all-rounder. The 10.6 horsepower of the GT200 at 5,000rpm is good for round town, but the 14.6 of the GT240 is more than 35% better.
On acceleration, you’ll be using the 5,000 to peak power range. Here, the extra capacity of the 240 continues to make its presence felt. It betters both of the other motors in torque and also power, holding 2hp more over the whole acceleration phase.
Over-rev only here, in the rev range you use the least (unless flat out) does our TS1 kit, with slightly extended exhaust timing, start to win out thanks to peak power being at 7,100 rpm.
On the road
The graphs don’t tell the whole story. I’ve ridden two GT240 motors now (Gary’s with the Franspeed and the Disco Dez demonstrator with a Clubman) and both pull cleanly from 2,000 to 8,500rpm without a cough. That’s a wide spread. It is a pleasure to just wind the throttle on anywhere and for the engine to pull so strongly.
The GT240 has characteristics that I think a lot of Lambretta riders want: a torquey, easy-to-ride engine that works with an expansion or a box pipe.
Neither of the GT240s were bad on vibration either. Gary’s felt slightly more noticeable at low revs and smoothed out the faster it span. This will be due to the relatively light piston and the revised balance factors that Richard Taylor used for his 62mm stroke cranks.
Gary – who built this SLUK feature scooter – reports that the fuel economy is on par with other GT kits and better than TS1s he’s been riding with.
VIDEO | GT240 on the dyno
Will it last?
Here’s the 6-million dollar question.
In terms of the kit, the current Japanese-made Suzuki pistons are strong and reliable and there are at least 4 oversizes available. Supplies however were dwindling, which has forced Richard to get the manufacturer to re-start production.
As far as the crankshaft goes, longer strokes with the crankpin closer to the perimeter of the crankwebs is riskier in terms of twisting problems, but Richard had the ends of the 62-stoke crankpins blasted to improve grip on the webs. So far only Eden has managed to twist one in a frantic high-rpm missed gear escapade.
To ride the GT is a pleasure, and because it is reedvalve it seems happy to be set-up with a hose and filter without encountering the starting/flooding problems that piston-ported kits sometimes suffer from in the same configuration.
My only real bone of contention is the use of two exhaust studs when having four (and being able to make use of the four fixings on a BGM Big Box exhaust) removes an inherent Lambretta weakness. The same applies to the head fixings, though blown head gaskets do not seem to be so much of a problem with Richard’s dedicated ‘Porcupine’ head.
As a complete bolt-on kit including the head and crankshaft, the GT240 comes in at just over £800 including a choice of inlet manifold. To me, that seems like pretty good value for the performance you end up with.
Where do I get one?
Well, this has been an issue in the past with the GT kits, hence lots of people using them from the Birmingham area – where they are made – but little distribution further afield.