Interesting question this. On my old 1150 ADV, just a couple of years ago, the FD big bearing failed as I rolled off the train at Calais. I posted the story on here.
So while on the rest of that trip and after I fixed it, you'll understand I was left with a shade of paranoia. So I was often groping my FD to try and see how it was behaving. But having never done it before, I wasn't really sure how to measure it.
In Italy, in the summer, the FD got pretty bloody hot. But you could still touch it. I estimated this meant it was about 40-45°C.
Now with the 1200 that has a hollow shaft in the FD, I anticipated lower temps. And last year, sure enough, it was cooler, but still 'hot'.
So, I would guess, in high ambient temperatures, if you CAN'T touch it, then something is wrong. But if you can but its 'hot', then that's in the normal range
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