GT300LC

GT300LC

300cc Liquid Cooled Development and Testing. GT300LC.


Granturismo have been developing a truly game changing engine for the Lambretta motor scooter since its first conception in 2015. The GT intercontinental engine cases that have been available since 2016 were designed to allow for the use of other larger barrels and larger crank shafts in regard to their casting. In standard format the cases have much more “meat” than needed, but when machined for use with the Rotax liquid cooled barrels and the Simonini air cooled barrel option which both also use the much larger purpose made GT crank it becomes apparent why the GT case is so “meaty”

This article refers to the Rotax liquid cooled variants which have a 76mm bore and 64mm stroke giving just over 290cc

More about the air cooled option at a later date when they have been ran and tested.

The barrel options are a non power valve Rotax 580 and a power valve Rotax 583, the numbers refer to the original engines that these barrels come from, the 583 is used for many applications including snowmobiles and light aircraft. These engines have proved to be extremely reliable, as you would expect for an engine used for flying. The 580 is primarily used in jetski’s.

The non power valve variant has been running in a lambretta for quite some time, to find out if the basic idea would be feasible the first time it ran it had a heavily modified JL exhaust which had to be cut and altered so that it would fit to the barrel as the exhaust stub is angled backwards and bares little resemblance to any existing lambretta exhaust stub. The engine ran like this but the exhaust restricted its performance hugely, so the engine and lambretta went to Charlie Edmonds for him to design and build an exhaust which would allow the barrel to “breath”. This exhaust development took several months to complete, but by early 2019 was ready to be road tested.

The exhaust is just one of the unique components, the mag housing and big crank taper is designed for the Aprilia RS125 ignition system. The crank taper will only accept the RS flywheel, this was intentionally done so that only the RS ignition could be used due to its proven reliability, power output and the quality of all of its components. There are also many aftermarket gadgets available such as the Zeeltronic programmable CDI/ECU which is widely used by RS 125 owners. Currently we are just using the standard RS125 ECU unit for road testing. The Mag flange is also designed to have its bearing lubricated by fuel/oil mixture rather than packed with grease, this means it only has one external oil seal. The RS pickup is external as standard and the generator produces 180 watts which is more than enough power to run a small town. The power of the generator meant that a new 16 amp loom was essential as a normal 8 amp lambretta loom will melt.

For road testing a standard width lambretta crank was needed as the decision to produce the big heavy new cranks was put on hold until it was known that the Rotax concept would be viable and work as expected, this also meant that a one off engine case was also needed for testing as the crankcase area had to be machined for a standard width crank but the mag area and barrel gasket face had to suit the ignition system and barrel respectively.

Once the Exhaust was created the first thing we did was take it onto a dyno to see if it was making the power we expected and more importantly, that it was making power where we wanted and expected it to, the results were promising and right where intended so the decision was made to put the engine into my GP and start road testing.

The first road tests were to jet the Delorto VSH 34mm carb, it was very obvious when I first took it out on the road that the carb set up was far too rich and needed leaning off. With that done the next step was to find out if the cooling system chosen was working. Too much cooling with out thermostatic valve would mean the engine would never get up to a reasonable temperature and too little cooling would result in the engine boiling over. To judge this I not only connected the standard thermocoupler which is at the top of the head which is the hottest location but also connected a second one to the system just before the water returns back into the barrel which should be the coolest point, the difference between the two gives an accurate account of how much heat the radiator is able to shed. Initial signs were that it was cooling too much but it later became clear that the position of the radiator mounted on a front rack on the leg shields along with the carburetion still being on the safe rich side was the reason for the low running temperatures. Once the radiator was mounted in the purpose made under legshield scoop and the carb was leaned off even more the running temperatures were where we wanted them. The radiator scoop threw up a problem though, it was acting like a huge airbrake creating a lot of drag but it also created downforce which kept the Lambretta much more stable at high speeds. The solution was to drill holes in the scoop to allow air to pass through with out being trapped, this reduced drag and didn’t noticeably reduce downforce at high speed.

June came around and I decided I was willing to risk road testing the engine all the way to Poland and back as the Euro Lambretta was taking place there. I was fully aware that it would be a huge risk, both in terms of being stranded a long way from home should one of the one off components fail but also a risk that if that did happen it wouldn’t put the project in a good light in the eyes of the lambretta fraternity. I wasn’t so much worried about the top end as its a proven cylinder, the thing that concerned me was firstly the crank we had used as it was standard width webs at 64 stroke with 125mm conrod, secondly i was worried about the bottom end being able to cope with the torque, but again I was willing to risk it because from riding it over about 1000 miles before I set off, I knew the power delivery was very smooth so the bottom end wasn’t being suddenly hit hard with a harsh power band every time it accelerated. I also knew by then that cruising at 70mph+ it wasn’t breaking sweat, with the 3.9 final drive 4 speed gearbox 70mph only requires the engine revolving at 5500 rpm so it would be ticking over riding with my riding partners, that would at least be until we met up with Mr G who was riding his BSG305 motor, more about that later.

GT300LC prototype. This video is quite long but im uploading all of it because it shows how at home it is cruising at car speeds on the motorway. I'm not sure if the video shows how effortless it is for this motor to do this, it starts just before i get past the 30mph speed limit roadworks, it then shows roll on in top gear from that speed, bare in mind i had been plodding along at 30mph for maybe 10 miles? so it doesn't pick up that well as it needs to clean its self up, it also has a bigger main jet I'm testing the last couple of days which needs knocking back down a little. now and again you get to see how it picks up from 70+mph when the throttle is opened. Bare in mind that at 70mph its revving at around 5800 rpm

Posted by Eden Bakewell on Monday, May 6, 2019

Outbound journey to Poland

It was a pleasure to ride the GT300LC to Poland, below is a gallery containing images showing the route for each day along with miles covered each day.

We didn’t have a backup van with us for the trip so the Lambretta had to carry all of the luggage as well as an array of spare parts and tools. The only issue the GT300LC suffered on the outward journey was loss of current to the water pump which was due to me cramming my 2 stroke oil bottle into the legshield toolbox at one of the fuel stops in Germany, I had inadvertently dislodged the live terminal on the battery. This resulted in the water temperature sky rocketing not long after leaving the fuel station. A quick stop to reconnect the terminal rectified the problem.

pics below from the outbound journey.

Returning from Poland.

The return threw up a couple of problems which were all related. We met up with G before leaving Zakopane which gave the opportunity to compare how the GT300LC fared with his BSG305, not that either of us rode anywhere near flat out as we were a long way from home, but we did have a couple of instances while heading back to the UK when we left the others behind.

The GT300LC and G's BSG305 did a few days riding together, we didn't go silly racing one another being so far from home and because I had a hole in my case but we did have the odd time we left the others behind. This video shows one of those occasion. Note I'm in top gear for the duration of this video as i'm unwilling to rev it high and throw more oil over my back wheel. G's 305 has much shorter gearing than the LC. We are both carrying weight too, I weighed my luggage yesterday when i took it all off the scooter. 72 kg so same as carrying a passenger with no luggage. Somewhere in the Czech Republic.

Posted by Eden Bakewell on Sunday, June 23, 2019

We decided to ride north to Auschwitz to pay our respects on the first day before heading west. the first problem happened about 10 miles before we got there, my chain broke. It was pretty obvious that was the problem and I had a spare new Iwis chain with me, however while changing the chain I noticed another problem. The chain had wrapped around the rear sprocket and clumped up above the sprocket puncturing the engine case quite badly. This gave two things to worry about, the main one being that with a huge hole in the engine case above the rear sprocket how would the gearbox oil not escape, and secondly, if the crack grew while ridding, the engine case although unlikely could crack in half.

Sealing the hole was achieved by filling it with gasket sealant, this worked to an extent but hot oil will and did escape through the makeshift repair. The other issue just gave me something to worry about while riding thereafter. The video above was recorded the day after the chain broke, you can see I’m choosing to not knock down a gear to accelerate but rather just winding on the throttle in top gear.

the video below shows the moment the chain broke.

When your chain brakes in Poland the morning after a heavy night out on the town 🙁 i was mistaken, I was actually in 3rd gear and just as the power kicks in it brakes. doesn't look scary, just lose drive, so much weight on the scooter it didn't have a chance to lock the back wheel as it smashed over the rear sprocket taking the case with it.

Posted by Eden Bakewell on Sunday, June 23, 2019

No problems for the next few days over the trip back, I even gave up checking the gearbox oil after a couple of days. It was loosing enough to cover the rear tyre with oil but not so much that I would need to top up often. Luckily we didn’t get much rain on the way back so the oil on the tyre wasn’t too much of an issue, the odd few times I did find myself on a wet road it was frightening but using a little common sense, slowing down and not leaning far to the right, made it manageable.

When we arrived at Spa a few days later I decided to take the side case off while at the hotel and have a look to see how things were in there, the reason i decided to have a look was because during that day the drive had become snatchy when pulling away and it felt like the cush was riding over when accelerating hard. I found that the chain tensioner had moved making the chain very slack and more than that, the cush spring had broke in two, this meant that the cush wasn’t doing its job at all. it must have been like it for quite a few miles as the ramps on both the cush and sprocket were both very worn. As i didn’t have a spare cush spring all I could do was put it back together and take it easy. We did put an SOS out on facebook asking if anyone in the area could supply a spring but that night we had only offers that were either the wrong direction or too far away. Next morning some good news came, a guy about 40 miles away had one, strangely I don’t know his real name but he goes by the name of Far Far on Facebook. We went to his house and him and his family were fantastic, lovely coffee, shelter from the rain while doing the fix and a good laugh. It was very much appreciated.

The chain and cush problems were all due to the chain tensioner moving resulting in a very slack chain. Since then a new chain tensioner design has been added to the LC.

Euro sos Anyone near Spa who has a cush spring. Just took side case off to check the chain and found the cush spring broken, that's one spare part I dont think i have.

Posted by Eden Bakewell on Thursday, June 20, 2019

Random photos from the return trip

Strip down once back home

Once I got back home I stripped the engine to see how the other parts had coped during the 2780 miles covered during the Poland trip. I had ran the engine on a 2% oil ratio as the induction is dirrectly over the big ned bearing. While away the engine had been very economical, at most fuel stops I was putting less fuel in than the other lambrettas riding with me, Russel Baker on his “Brig me sunshine” TS1 powered LD mutant, Nige Hadley on his TS1 powered LI black special and Adrian Donnelly on is TS1 powered series 2. Great riding partners as usual. also the pair who also rode part of the way back with us, Grahame Fowler on his BSG305 powered LI special and Nick Jordan on his Avati powered GP.

When it all came apart it all still look brand new as you can see from the image gallery below.

Production build testing

Now the concept had proved its self the big wider cranks could be made along with other upgrades for the production runs of the engine. Upgrades include the crank specific engine case, big crank, mag housing and cover, upgraded chain tensioner, new rear sprocket with higher teeth to align front and rear sprockets to name a few.

the gallery below shows the build using the production parts.

Road testing of the non powervalve production engine will begin during October 2019. More info will follow, including a full spec sheet.

Once testing is complete for each version of the engine, non power valve LC300, power valve LC300 and aircooled 300, the engines will be released for general sale. People who have already reserved the engines will be supplied first but don’t worry if you have not yet reserved one yet, due to the interest so far production has been increased in the hope we can keep up with demand.

As full testing is yet to be completed the finalised price for the engines has not been set. There will be options for plug and play units and options for the supply of the key components where the buyer will source their own generic parts.

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2 Replies to “GT300LC”

  1. re.gt240 engine service I booked with you.
    I’ll leave that for the time being,with the intention to have one of the liquid cooled engines when available.
    Thanks.Roland.

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