125 KZ Engines: the Survivors

Contrary to the remarkable (r)evolution with the direct drive KF engines, mechanical gear class engines follow traditions, keeping faith to its original simplicity. This is why Marco Natoli named it the Survivor.
Report: M. Natoli – Photos: C. Avolio

With the KZ engines we have the respect of tradition, natural balanced development of protagonists of a class with several positive aspects, like the number of drivers attracted by an engine which is now perhaps the simplest one available on the market.   

The factory, which has always stood out for its craftsmanship now presents the CRS P1, a natural successor of the S1. In looks it is very similar, while some changes have been made inside, timing diagram is different and expansion design so as to get a more fluid response on accelerating. Always looking to overall improvement on track, gear ratios have been revised, 2nd and 3rd gear now shorter. Continuing in the drive section, there’s a dry multi-disc clutch that goes from 6 to 5 lined discs. The P1 has a round upper part with a clear head cover line seeing that to take apart all you have to do is take out 3 grub nuts housed on the outskirts. In the front part there is the reed pack characterised by 2 single flap reeds made of carbon fibre, layout is horizontal. On the left hand side there’s a curved cooling circuit sleeve that connects the base to cylinder base.

Maxter MXV
Maxter too has decided on improvements and specific operations carried out especially to improve engine breathing. The main difference lies in the reed pack, now vertical, no longer horizontal, and important changes have been made to gear selector. It is stronger and engages accurately. Then there’s the version with the horizontal pack, now denominated MXO, but which was homologated for 2004-2009. In this case too, appearance is basically the same. The thermal part, which comes out o a very clean base, is roundish and in the front part there’s an interesting innovation, vertical reed pack. The clutch has an external plate, which is anodised in black, like the head cover.


Pavesi 25° Evolution
Looking at it, you don’t see any difference compared to the Pavesi 25° from which it derives. A lot has been done inside though. It has been refined looking to improved balance between running performance and reliability. That’s why the driving shaft is balanced differently, however maintaining the same mass, in order to get improved acceleration and corner exit pull. The five different gears have a different ratio, there’s a 6th gear that is now a bit shorter. Different design for the muffler, which manages to maintain a full delivery even at maximum revs. 

SGM G.A.207
As for the others, there are few differences, but it has been modified inside. Therefore the driving shaft is heavier, and balanced with a tungsten insert so as to get better acceleration. Head and cylinder, including ducts and ports are all new. On request, you can get tear-protectors on the clutch, minimum difference in cost. This is a manufacturing difference that gives better than average results; official retailers get a better chance of dealing with their respective customers, but then you mustn’t forget that it is a product made for racing. 

Backed by a long series of success, this is very probably the factory to beat in the KF classes, first with the KV, then with the K9. And in honour of the tradition mentioned at the start, there’s the K9C. Special attention has been given to fluid mechanics, for which the induction duct is tilted upward more immediately after the reed pack so as to shorten the flow of fluid drawn in towards the transfer. Innovated transfer ducts too, especially that of the TT and exhaust, whose end has an oval in section for a certain tract before the port, and profile and tilt is different too. There’s an absolutely new cylinder . To get a complete job done, the muffler is different too; the cones in the end part are different. Gears and crank mechanism have remained the same. On request, you can have different degrees of preparation concerning driving shaft, timing case, reeds, ...  

VM M 02/B
Perhaps not so well known in Italy, but VM is a successful trademark from abroad, known for its reliability and performance. It started out in 1993 with Vladimir Vàcha. The 125 m 02-B is the third model made and takes over from the previous 125 o 2. It maintains the same gears, while the cylinder has been changed and also the transfers, The driving shaft is different too just like overall weight. All the changes applied have resulted in improved delivery power. The line of the 02-B is compact and at the same time elegant, based on the flow of the casing, perhaps a bit robust in the rear part. On the right hand side, according to the most common design, you have a dry multi-disc clutch. The characteristic sizes are standard, with diameter and stroke measuring 53.99x54.50 while the conrod is 110 mm and ignition is Pvl.

Vortex RVX
The new 125 with mechanical gears made by Vortex for the KZ1 and KZ2 is RVX sealed, and with it the factory in Pavesi is trying to repeat the brilliant success of its KF RAV. The main innovation lies in the tilt of the thermal group, now almost vertical in order to improve fluid load drawn in. For this same reason, the base is nearly completely new, more compact and lighter. The reed pack is fully developed and the new thermals, together with a careful study of cooling liquid flow, according to Vortex experts, have improved overall yield. Details are fine finished. Clutch cap is lighter and closer fitting so as to protect the mechanical parts, the clutch cable is easier to reach for adjusting, suction pressure intake from left to right hand side of the casing to install petrol pump on appropriate brackets. Airflow passage has also been improved thanks to a new opening under the reed pack.

Read the entire article with technical tables for each engine on Vroom International July 2007 issue (n.75)

Created by: admin - 01/10/07

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