This article was originally written in mid-2018 to address the problematic 56 × 46 mm V-FORCE* 3 reed valve used in KTM SX/EXC motorcycles. In December 2022, the article was updated to present additional improvements introduced by CompoTec. These improvements are intended to increase the service life of all V-FORCE 3 and V-FORCE 4 reed petals offered by our company.
Our full range of reed petals is available here: https://www.ebay.com/usr/compotec.pl
Original 2018 article concerning V-FORCE 3 reed valves in KTM SX/EXC motorcycles:
In this article, I would like to briefly present a solution to the recurring problem of the lower V-FORCE 3 reed petal cracking in KTM SX/EXC motorcycles. When we started manufacturing replacement reed petals in 2016, we were quickly faced with a large number of warranty claims.
Interestingly, at that time we were manufacturing more than a dozen different types of reed petals (today we offer several dozen!), and it soon became apparent that the only complaints concerned replacement V-FORCE 3 reed petals measuring 56 × 46 mm, currently designated in the CompoTec range as RV-No.9-VF3-MIX (original Moto Tassinari reed petal designation: 3P602H). It took us a little longer to realize that the 3P602H reed petals are used almost exclusively in KTM SX and EXC motorcycles.
Eventually, we discovered that out of the four reed petals making up the V-FORCE 3 reed valve, in 99.9% of cases only the lower reed petal located closest to the engine crankcase was cracking (Fig. 1). According to our customers, there were cases where the lower reed petal failed after the very first full-throttle run and did not even last one engine operating hour.
Fig. 1. Typical damage to the lower 56 × 46 mm V-FORCE 3 reed petal in KTM SX/EXC motorcycles.
The problem described above caused us considerable trouble and forced us to look for a solution. We succeeded thanks to several KTM SX/EXC owners from across Poland who agreed to cooperate with us in testing, in exchange for receiving successive replacement reed petals free of charge. It quickly became apparent that failure of the lower V-FORCE 3 reed petal was a common problem with this application — regardless of whether an original reed petal or an aftermarket replacement was used.
It appears that the V-FORCE 3 performance reed valve was not particularly well designed for KTM SX/EXC motorcycles. As a result, the lower reed petal is located very close to the crankcase and may strike against it, leading to rapid damage. Due to manufacturing tolerances, every motorcycle is slightly different. In some motorcycles the problem becomes noticeable only after a longer period of use, while in others the lower reed petal may fail almost immediately.
It is worth noting that the problem was probably recognized by the manufacturer of the V-FORCE reed valve, the US company Moto Tassinari. V-FORCE 3 reed valves do not have reed petal travel limiters, which under unfavorable conditions allows the petals to strike the crankcase. In the newer V-FORCE 4 series, however, travel limiters were introduced (Fig. 2).
Fig. 2. Comparison of the V-FORCE 3 reed valve with the newer V-FORCE 4, which incorporates reed petal travel limiters.
Through extensive testing, we managed to develop a solution to the problem described above. We have been offering this solution since mid-2018, and it has proven effective for the vast majority of our customers. For KTM SX/EXC motorcycles equipped with a V-FORCE 3 reed valve, we recommend replacing all reed petals with what we call a “mixed set”, available in our range as RV-No.9-VF3-MIX.
This set consists of reed petals with different stiffness levels: 3 carbon-fiber reed petals, 0.35 mm thick (lower stiffness) and 1 carbon-fiber reed petal, 0.45 mm thick (higher stiffness). The thicker/stiffer reed petal must be installed on the crankcase side, while the remaining three petals should be installed in the middle and upper positions of the reed valve.
This combination means that the stiffer lower reed petal opens less, reducing the likelihood of it striking the crankcase. In addition, when installing new reed petals, make sure that they are held tightly and securely in the reed valve housing.
This is particularly important for the lower reed petal. If there is any play, our customers have dealt with it either by making a small shim from an old reed petal or by carefully heat-forming the plastic reed valve body, for example using a heat gun.
The solution described above has worked successfully for hundreds of our customers, although there have been a few cases where it did not solve the problem. This may be due both to manufacturing tolerances of components in a particular motorcycle and to the skill and care of the person replacing the reed petals. One thing is certain: the problem results from the combination of the V-FORCE 3 reed valve (using 56 × 46 mm reed petals) and KTM SX/EXC motorcycles, not from the quality of the reed petals manufactured by CompoTec.
If anyone has doubts, we strongly recommend buying original reed petals and seeing for themselves! 😉
Based on our experience to date, installing our RV-No.9-VF3-MIX mixed set according to the instructions above significantly extends the service life of the lower reed petal in KTM SX/EXC motorcycles. Some customers have ridden for several dozen engine operating hours using these sets, with the reed petals still remaining in perfect condition.
December 2022 update concerning all V-FORCE 3 and V-FORCE 4 reed petals offered by CompoTec:
After several years of gaining additional experience with various V-FORCE 3 and V-FORCE 4 reed valve models in motorcycles with engine capacities of 125 cc and above, our conclusion is clear: all of them show a tendency for the lower reed petal to crack or wear faster than the other three petals. The problem is most severe with the 56 × 46 mm V-FORCE 3 reed petal described above, used mainly in KTM SX/EXC motorcycles, although other reed valve models are not completely free from this issue either.
The reed petal travel limiters used in V-FORCE 4 reed valves improve the situation, but they do not completely solve the problem. Although the lower reed petal no longer cracks as a result of striking the crankcase, it may still deform relatively quickly and lose its sealing ability. In all cases, varying the stiffness of the reed petals helps. This is achieved by using a mixed set consisting of one 0.45 mm thick lower reed petal and three 0.35 mm thick reed petals in the remaining positions.
The thicker lower reed petal must be installed on the engine block/crankcase side, regardless of the motorcycle make or model!
For the reasons described above, starting from January 2023, CompoTec will offer only mixed reed petal sets for all V-FORCE 3 and V-FORCE 4 reed valves in our range intended for motorcycles with engine capacities of 125 cc and above. At the same time, individual replacement reed petals for these sets will also become available. This will allow customers who have previously purchased our mixed sets to service their reed valves at a significantly lower cost by replacing only the worn reed petals.
At the same time, due to occasional problems still being reported by customers concerning the 0.45 mm thick No. 9 lower reed petal, we have decided that WE WILL NOT PROVIDE A WARRANTY FOR THIS PARTICULAR REED PETAL. Too much depends on the quality of installation and the manufacturing tolerances of the components in the individual motorcycle. We would rather not sell the product than later have to explain — often in an unpleasant atmosphere — that the reed petal itself is not the problem, but rather the specific combination of the V-FORCE 3 reed valve and KTM SX/EXC motorcycles.
Currently available mixed sets:
V-FORCE 3, size 56 × 46 mm, CompoTec part number RV-No.9-VF3-MIX: https://www.ebay.co.uk/itm/226856741370
V-FORCE 3, size 64 × 47 mm, CompoTec part number RV-No.10-VF3-MIX: https://www.ebay.co.uk/itm/226856813497
V-FORCE 4, size 64 × 45.5 mm, CompoTec part number RV-No.36-VF4-MIX: https://www.ebay.co.uk/itm/226858696464
V-FORCE 4R, size 58 × 44 mm, CompoTec part number RV-No.89-VF4R-MIX: https://www.ebay.co.uk/itm/226858896194
*V-FORCE reed valve is a registered trademark of Moto Tassinari. All other trade names and/or brands mentioned herein are the property of their respective owners and are used solely for the purpose of indicating compatibility.