Some manufacturers preferred to skip the homologation for the new OK/OK-J non-shifter engines, the new open bet in karting; but a leader like TM could not miss the great opportunity
The new OK engine concept aims to bring back the simplicity and compact nature of the old direct drive 100cc engines that so many kart lovers are nostalgic about. Compared to KF and KF-Junior engines, which had been coinceived and built in line with the TAG (Touch and Go) concept, the new OK and OK-J engines do away with the battery and related cables, the electric starter and relative wiring, and the clutch.
In addition, the water pump is again external, like it used to be in the 100’s, allowing for quick intervention and replacement if necessary - another important element of simplification. All things considered, then, the OK “revolution” seems to be driving a valid goal: return to simpler engines, that don’t need a huge number of expensive high-maintenance components to perform well, able to offer greater reliability and significant cost reduction. Even so, skepticism continues to run high on several grounds, beginning with the argument that it will take some time for these new engines to acquire the tried-and-tested “status” of today’s KFs. Another hot-button issue is the elimination of the electric starter. The polemic here is that having to push-start the kart makes things tougher and requires the more petite and inexperienced drivers to rely on help from a mechanic.
Finally, doubts have also been raised regarding the removal of the clutch: if the kart ends up off track, the engine will easily come to a halt, forcing the driver to either push-start his vehicle again or withdraw (in case of a competitive race).
All caveats considered, let’s see how a successful and important company like TM has interpreted the CIK-FIA guidelines for the new non-shifter classes.
For starters, TM’s OK and OK-Junior engines look very different compared to the KF and KF-J models, precisely because there is no starter and clutch and the water pump is external. Second, they are much lighter.
In fact, one of the major goals of the new class specifications was to enhance performance by cutting the regulatory weight limit (of kart plus driver): while for the KF minimum weight was set at 158 kg, for the OK it is set at 145 kg.
Now, the major factor of weight reduction is precisely structural simplification, which accounts for a loss of 3.5 kg (5 kg if we also consider the battery and its cables). The other “lightening” factor is the elimination of the front brakes, which brings the new OK in line with the old 100 cc class. Along with stark simplification, the distinguishing feature of the new engines is the decompression valve.
The introduction of the component has been discussed far and wide, but in this sense TM was facilitated, because it had been using it for years on other products, relying on external providers. In terms of details, technical regulations call for a small and precision-finished valve to ensure a perfectly tight hold (when shut) and prevent the formation of incandescent pockets in the combustion chamber that could lead to detonation and seizure.
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