Choose the language.
TKART magazine Under Review | S3: the latest evolution of TM Kart direct drive engines
Exclusive Content


Giacomo Mantovani
01 April 2024 • 10 min. read

The TM Kart S3-Senior and S3-Junior engines are a 2-stroke engine, like the vast majority of racing-type kart engines.

125 cc

The TM Kart S3-Senior and S3-Junior engines has a bore of 53,95 mm and a stroke of 54.40 mm for a cylinder volume of 124.36 cm³.


Starting is manual: to start the kart engine, you need to rotate the rear axle manually or push when the kart is on the ground. All this is facilitated by the presence of a decompression valve on the engine head, which makes it easier to push the kart itself.


There are two "big families" of kart engines: Direct Drive and Shifter. The TM Kart S3-Senior and S3-Junior are a Direct Drive engines, therefore non-shifter, and without a clutch, therefore with direct drive: when the kart stops, it doesn't stay running, but switches off.

041-ES-03 & 041-EJ-01

The engine was designed and built by TM Kart for the Direct Drive FIA Karting, OK and OKJ classes. Its international approval (which you can find here) is valid for 6 years and ensures that owners can take part in all types of events that adopt CIK-FIA regulations. There is only one engine, the one designed and built for the OK-N class, but simple technical interventions can also turn it into the version for the OK Junior class, the OKJ (read more here Dossier| FIA approvals: what they are, what they are for, how long they last... The ultimate guide!).


March 2024 article update

On the occasion of the FIA Karting 2023 homologation cycle (dedicated to engines, carburetors, ignitions and intake silencers), TM Kart has updated its Direct Drive powertrain offer, launching the new OK-S3 Senior and OK-S3 Junior models, intended for the CIK-FIA OK and OKJ direct drive categories, respectively. These engines have immediately shown excellent performance in all international competitions (WSK and FIA Karting) in which they have been used. With no doubt, however, the pinnacle - in terms of results - was reached at the FIA Karting World Championship OKJ 2023 in Franciacorta where a chassis equipped with an OK-S3 Junior engine triumphed (for more, read "Must Have | The accessories of Forza Racing's Exprit Noesis RR, winner of the FIA Karting World Championship OKJ 2023, in Franciacorta").

We went to TM Kart's new headquarters to find out what new features the Italian company has introduced with the OK-S3 Senior and OK-S3 Junior engines, which compared to their S2 predecessors represent an update rather than a revolution. The biggest novelties, in fact, are refinements in the thermal part and tricks to improve cooling. How, here's what we found out.



As of 2023, the historic TM Racing company-co-founded by...

Read all
At first glance, the new OK-S3 Senior and OK-S3 Junior powerplants are distinguished from their predecessors by the new TM Kart logos placed on the sides of the cylinder, engine crankcases, countershaft cover, and the new ignition assembly (PVL ones have been replaced with the new Selettra-branded supply). Further novelty is the head, which has been completely redesigned.
alt alt
alt alt
alt alt
The crankcase, made of lightweight aluminum alloy, is designed with a focus on reducing weight and improving structural rigidity. The ribs present ensure greater mechanical strength, optimally distributing stresses, while the lightening millings are designed to eliminate superfluous material without compromising durability.
alt alt

The production of TM Kart engines, apart from the casting of raw materials (a process entrusted to external foundries selected for their ability to work in close synergy with the specifications provided by TM Kart) and some specific treatments, is a completely internalized process. In fact, the Italian company has a production facility where it handles the design (entrusted to the research and development department), robotic machining (through CNC machines capable of working on 5 axes), manual machining (press operations and through manual milling machines), assembly and finishing of the engines. The design of S3 engines combines TM Kart's decades of experience with the latest innovations in mechanics and fluid dynamics.

Continue reading the article by subscribing for only 0.96 € / week
Explore these and many other
premium contents
Go to Magazine