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MotoGP, Yamaha: over-rev caused the double failure at Mugello

Kouji Tsuya: "the failures were caused by the malfunctioning of the limiter at the hill crest at the end of the straight"

Yamaha: over-rev caused the double failure at Mugello

It was obvious from the start that the Yamaha engine failures at Mugello were down to a problem with the head, caused by over-revving. We spoke about it at length, and seeing as over-revving in acceleration is almost impossible with the current technology and limiter intervention times, we'd hypothesised about other causes.

Over-revving caused by drag effects in braking. Or engines particularly 'suited' to the characteristics of Mugello. A track that allows for significant top speed, to which they needed to respond if they didn't want to be humiliated along the straight. Yamaha has revealed that we were, indirectly, right: it was an over-rev, or perhaps repeated over-revving to cause the Iwata engine to fail.

The story that engine engineer Kouji Tsuya tells does not totally convince us though. A rev limiter that doesn't work, or rather that didn't intervene quickly enough at the hill crest at the end of the Mugello straight before San Donato, is a really rare occurrence. And then, if it were that, how is it that the technicians, during practice, with the telemetry data in hand, didn't notice the problem and take action?

They're probably right, but seeing as it was impossible not to notice some over-revving during the tests, it's highly likely that they decided that the engines could cope with the forces. In the end it worked out for them: thanks to a 'superengine' they won the Grand Prix with Jorge Lorenzo. Beating the Honda. A priceless result.



After the technical problems in Mugello the two defective engines were returned to YMC for investigation. Following our detailed investigation of the engines, telemetry data and related systems we found the cause of the failures. The failures were caused by an electronic issue related to the rev limiter which ultimately resulted in valve and piston damage. The cause for both Jorge‘s and Valentino‘s engine failures was the same. To be clear, there was neither an engine component nor a structural failure, it was purely an electronic control issue.

Valentino‘s failure was caused by an accidental over rev in acceleration that occurred jumping over a crest with full throttle at the end of the straight. This failure was not in any way related to the mistake made by Valentino at the San Donato corner on the lap before.

There were no special mapping settings used for Mugello; we used the same precise mapping as always. We have now withdrawn both engines from the allocation for the season.

We have a strong history of engine reliability and this fact does not change after this incident; the engines had no problems, but we were not aware of the different behaviour of the standard ECU software, that made the rev limiter work in a different way compared to last year. We set the rev limiter using last year‘s data in exactly the same way as we did last year, but we could not be aware that the software worked in a different way.

Valentino‘s engine was the freshest of the three that were sealed so far from his allocated engines, therefore after Jorge‘s Warm Up engine failure there was no reason to consider replacing it. Furthermore we couldn‘t find out the electronic issue in Jorge‘s engine in such a short timeframe.

Mugello is one of the most critical circuits because of jumping over a crest with full throttle on the straight, and engine RPM becoming higher. We have learnt from this incident and already modified the rev limiter setting, so it will be OK in Catalunya. As a precautionary measure, the other engines used by both Valentino and Jorge in Mugello will be used only for practice sessions, until their life cycles are completed.

We understand an electronic issue caused the failures in Mugello, therefore we do not need to intervene with our remaining engines that are not yet sealed. We still have enough engines for the remainder of the season. We have already devised a countermeasure, so we are confident that the failures in Mugello will not recur.

Translated by Heather Watson

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