Yamaha Confirm Overrevving Was Cause of Mugello Engine Problems

Yamaha have issued an official explanation for the problem they suffered at Mugello, which saw Valentino Rossi's engine blow up during the race, and Jorge Lorenzo's engine blow up during warm up on Sunday morning.

The cause given is exactly in line with the reasoning in MotoMatters.com's Mugello Sunday post-race round up: the engine overrevving as the rear wheel lifted at the end of the Mugello straight. At that point in the track, with the bike hitting 350 km/h and nearing peak speed at top gear and at full throttle, when the rear wheel lifts over the crest at the end of the straight, the engine spins up too quickly for the rev limiter to catch.

Yamaha MotoGP project leader Kouji Tsuya acknowledged they had been caught out by the new unified software package: they had used similar settings to last year, but the rev limiter with the 2016 electronics had not reacted as quickly as Yamaha's proprietary software was capable of in previous years. That caused engine damage at the end of the straight, eventually causing the engine to fail completely with piston and valve damage.

Because of the nature of the damage, and the difficulty in locating the precise nature of the problem, Yamaha were unable to put in a fix for both factory Yamahas for the race at Mugello after Jorge Lorenzo's bike had blown an engine on Sunday morning. The engine which Rossi blew up was his third engine, a relatively fresh engine, as was Lorenzo's engine that blew. Lorenzo eventually raced his second engine, which had been in action since Qatar, and had 25 practice sessions and 2 races on it. 

Yamaha's statement says that they have identified the problem and have a fix in place from now on. In part, the risk is lower, as there are no other tracks coming up with such unique conditions as Mugello. But it is entirely possible that part of the fix is lowering the maximum revs on the engine a fraction (perhaps just 50 or 100 revs) to avoid a similar problem. That should not have a material effect on the performance of the bike.

Below is Yamaha's press release:


Barcelona (Spain), 2nd June 2016


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.


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And Lorenzo's 2nd engine made it to the end of the race. I am not a mechnical engineer, but something seem to be missing in this explanation. While plausible, I find it odd that Lorenzo's engine was able to endure the few seconds of "overreving" for 20+ laps, specially as it wasn't a new one.

Oh well...

I came to say the exact same thing, how did Lorenzos 2nd engine make race distance if the software was still facing the same issue? I guess just luck? OMG   CAN WE ACTUALLY SAY LORENZO'S WIN WAS BASED ON PURE LUCK??

Survey says Yes. Let the hate begin.

In the post-race press conference, Lorenzo acknowledged that he was lucky to have his engine blow up in Warm Up, while Rossi's blew in the race. So the first person to say that his win was based on luck was Jorge Lorenzo himself. 

My same thought exactly. David has anyone managed to ask Yamaha engineers that question? How can JL bike take almost 3 times more "overrevving " than VR and not blow up?

Both Lorenzo's #3 engine and Rossi's #3 engine blew up. Lorenzo was lucky, because his blew up during Warm Up. Rossi was less lucky, because his engine blew up during the race. The more interesting question is what would have happened if Rossi had raced his #2 engine. 

The odds are that Yamaha did something with the #3 engine to prepare it for Mugello. Presumably, they turned up the revs to hold off the Ducatis at Mugello. Why the #3 engines blew up and the #1 and #2 engines did not blow up is a mystery. But the fact that both Rossi and Lorenzo used the #3 engines very little before Mugello, and both had engines blow up on them suggests that something was going on there. 

The press release says, "There were no special mapping settings used for Mugello". Yet you're saying "they turned up the revs to hold off the Ducatis at Mugello". Hmm, aren't you having cake and eating it, too, by believing the overrevving part of the press release and disbelieving the no-special-settings part?

What the press release says is that they did not use special mapping settings, but I interpret that to mean within the context of Mugello. They said they used the same settings as last year, but that the spec rev limiter did not work the same as the rev limiter in their proprietary software. It is conceivable they have turned the revs up at Mugello for at least the last couple of years, but that the rev limiter in their proprietary software prevented the overrev. If they plugged in the same parameters as last year, then maybe that is what went wrong. Perhaps that is having their cake and eating it.

Then again, the press release may be an elaborate cover for a mechanical issue. But we have to take Yamaha at their word.

So, Lorenzo was running a tired No#2 engine, and Rossi a crisp new No#3?  Kind of brings the idea that Rossi was just biding his time to pass Lorenzo on riding ability, since he was running the stronger of the two Yamahas..


I remember reading a story regarding the auto maker GM and testing the Camaro Z/28 on the Nurburgring. There was one section that was causing the car to over rev at WOT when going over a hill. They programmed a setting to allow the engine to rev freely over the hump but not over the limit. Yamaha needs to find a similar solution. 

I'd like to see the speed and sector times from both VR#46 and JL#99 during the race. I'm just wondering why Rossi's engine gave up the ghost during the race, while Lorenzo's made it all the way to the checkered flag. Lots of data to examine. I wonder if there is a way to overlay each riders exact path on track lap by lap using the bikes transponder signal. Maybe Lorenzo had a different line than Rossi going through Mugello's "problem area". A very intriguing and mysterious situation, indeed.

I have seen evidence that there is a lot more going on here than meets the eye. There is proof that Marquez & Lorenzo have engaged the same team that faked the moon landings...


Obviously Jorge´s side of the garage or Jorge himself did something different not just in the race but all week. In the warm up the average top speed of his best 4 runs (Dorna data) for Rossi was 342.2. Jorge averaged 338.7, but blew his motor.  Lower speed equals less revs n sixth gear with these 81 x 48.5 bikes. In the race on his best 5 laps Jorge averaged 340.5 to Vale´s 342.52. 

But that is only along the top. What load was each rider putting on the valve gear in other corners? If Yamaha are saying the overrev came from the little jump over the hump at the end of the straight then it seems hard to establish that without seeing the full data...and we ain´t gonna see that. 

All we can really say for certain is that both the factory Yams put valves through piston tops and the satellite Yams, faster at the end of the straight on many, many laps, did not. The Honda, with pneumatic valve closing like Yamaha, didn´t either. And the booming Ducati desmos, faster that anything out there at least at the end of the straight, didn´t blow up. 

I don´t buy the Yamaha explanation. I think it was not just a flash of overrev in a single place, but a weakness in the Yamaha distribution and/or electronics at high revs all around the track or at some specific part of the track. if I am right, Yamaha, inspite of the win by Jorge, will be turning down the revs a bit at Catalunya, although that may not show up in top speed....but maybe they have been overrevving at other places on the track to avoid short-shifting or shifting at all. 

I like it when technical problems take us back to the basics. Maybe the boys need a red line painted on the tach! I knew if I took the 250 Ducati over 10,800 something was going to come out for air and I remember pulling out of a race on the Aermacchi 350 because I missed a gear. Those puppies didn´t forgive and my mechanic heard that false neutral on the Snetterton home straight and was already packing up when I came cruising home...if I had kept going he would have been rather cross. 

It´s nothing like that now......is it?





"And the booming Ducati desmos, faster that anything out there at least at the end of the straight, didn´t blow up."

That comes down to the Desmo valvetrain though, doesn't it? Valves are pulled shut mechanically - of course you can't rev them infinitely, but a valve on even a pneumatic engine is surely going to bounce on a piston before a desmo GP valvetrain would give out

It may only be one lap on each bike, but on the Motogp youtube channel you can see an on-board lap from each factory bike.

It was only on the Yamaha video that I could hear a definite hard "cut" when the rider crested the hill. The Honda didn't make a noticeable noise, and neither did the Suzuki or Ducati. It does make me wonder if they were designating engine 3 as the hot engine for the fast tracks, and just every lap, hitting that harsh cut over the hill was just enough

The problem with skeptics is that even if you tell them what happened they will want additional information to back up the findings. When you show them those findings they will want additional information in an endless cycle of "....well I don't believe you what about this".  A 'PROTOTYPE' engine blew up, Yamaha says it was from the new software package being less efficient than the previous software, why all the skepticism?

Given these are prototype engines I am sure they are running very little piston/valve clearance. The design of contemporary four stroke engines and the need for maximum valve area means you need to close these gaps as much as possible to get more flow in and out of the engine. If you allow uncontrolled over rev then you may be exposed to a piston to valve collision. Read: DO NOT allow over rev.

Mugello really throws a curve ball at the engineers. The bike is at maximum load/WOT and then free wheels as it jumps. I am not sure how you’d catch that in the software. You can not actually brake the motor. Some pretty simple logic would be, 6th gear full noise, RPM at 95% = limit the motor. But that will screw you when you hit a wall of no power. Bad for trying to overtake some one, damn right dangerous really.

Throwing in the draft is another really interesting parameter. If your slip streaming not only is your engine possibly under less load, but your going quicker and that means higher RPM. The more you draft the more you are likely to over rev the engine. Unfortunately Rossi was chasing Lorenzo for 5 laps doing just that. And then bang!

I am wondering if Lorenzo’s team had turned the RPM down slightly for the race. Rossi’s race pace appeared faster than Lorenzo’s, then again his practice pace was quicker also. If Lorenzo’s team had a suspicion that his engine broke for that very reason possibly he was shutting off before the bike gets airborne.

I don’t think there is much to be suspicious about who’s engine went bang and when the engines when bang. I am more suspect that there is something else they are not letting on!

Once a Honda blew up on the straight and Randy Mamola was quick out of the box...he was retired then and working with Toby Moody and I. We were in the booth and Randy was pit reporter. The Honda smoked big...it was Nicky´s bike. I could tell you the track but I´d have to look it up. Anyway Randy comes up to me before I go into this Honda technical briefing and hands me a rag with some very gnarled unobtainium bits and says, "This is what Nicky´s Honda puked. Have some fun."

So I sit thorugh the talk...Nicky was there and so was Yamada, and finally somebody asks what the problem with Nicky´s bike was and the Japanese tech who was there says, "Not sure yet. Maybe a water leak, or oil on pipe." And Nicky looks out the window, and so I open my rag and say to Nicky, "Or maybe it was this?" 

Nicky blinks and says, "I did hear something kinda tingy."

Before I could get out the door, Yamaha had me. I gave them back their bits. Randy made me tell the story two or three times to different people and everytime he laughed like it was the first time.

So that is why I don´t believe every word they tell us.  




It wasn´t Yamaha who got the bits back off me at the door it was Race Director Yamada....and I can´t even blame that on spellcheck. 

Perhaps the rider briefly closing the throttle (partially even) over the bump is what is necessary.

Do TT riders not do this at the few points on the circuit when briefly airborne? I doubt they sit there WFO.

Since they're not submitting design changes for the remaining engines, and their fix is software only, then they're either telling the complete truth, or saving a little face (and their company's rep) by blaming the rudimentary (by implication) spec software to cover up the fact that they asked too much of the engines at Mugello.

As always, the truth is probably somewhere in the middle.