fifth gear fear (FGF), will it ever go away? it seems every tenere rider lives in fear of the german dive bombers visiting their gearbox...
still, i suspect that it is more bark than bite, and to paint with too broad a brush is misleading.
a mate of mine and myself recently completed an overlanding trip from london to cape town, and FGF was our main concern to start with. we had heard so much about it before we left, we had even been told that pretty much every tenere will get it over 30,000km, and that it was almost inevitable.
as my bike already had 50,000km on the clock BEFORE the trip, i was a little alarmed about FGF. so when i had to replace my countershaft in rome en route, i was rather pleased to have the opportunity to inspect my gears.
imagine my surprise to see that they were absolutely fine, no different to any of the other gears. i had considered replacing the fifth gear, but the italian yamaha workshop (who know the bike about as well as anyone, the tenere is much more popular on the continent than it is over here in the uk) told me that there was nothing wrong with my fifth gear and there was no point in replacing it. and this is on a 50k engine (the original engine too by the way).
my experience of FGF was further tempered in egypt, where i had the good fortune of befriending and staying with raed badder, who was egypt's top motorcross rider in the 80's and 90's - and mostly on the 1VJ yamaha tenere. raed knows the bike better than anyone i have met - with very little technical support during his racing days he had to in order to compete with the sponsored european riders of the day - and the fifth gear issue did not even feature in his list of the bike's weaknesses (which, for those interested, he listed as a CDI unit prone to breakage, a ppor cooling system, and a resulting engine prone to overheating). so long as the bike was ridden correctly, the gears should wear the same.
and this is really the issue - riding the bike properly. teneres are not meant to be ridden in high gear/low rev ratios; doing so will place unneccessary strain on the gears, and obviously they will encounter metal fatigue. and naturally, it is the higher gears that are going to show it first, as they are the ones which take the most strain due to this mistreatment.
the "correct" range to ride the tenere is supposedly between 3,000 and 5,000 revs, and to be on the safe side i tend to stay in fourth at high revs rather than go to fifth and strain the engine at lower revs. and by doing this i managed to do 17,000km in 3 months on a 14 year old 1VJ which started the trip with 50,000km on the clock - and the main problems at the end of the trip were in the top end of the engine, not the gears.
i do not doubt that the fifth gear doesn't give problems in a tenere, but the more i learn about it, the more it seems to me that the problem lies with the rider, not the bike. if you change the oil regularly (and that is OFTEN in an old bike) and the oil filter, and use all the gears as they should be used (i hardly ever use fifth around london for instance, there just isn't the opportunity to get the speed or revs up high enough to justify it), then you might consider yourself unlucky to have FGF coming to reality.
in reality, most teneres are going to have been previously owned, so if you do not know how the bike had been previously ridden, then you might do well to inspect the gears to start with, and if there is damage replace them - but once that is done, provided you ride the bike sensibly, you should be ok.
or get a 3AJ, where the gears are meant to be strengthened to counter the effects of poor riding. either way, keep the revs up and have fun.