My trusty 2008 XTR . Been running it for 2 trouble-free years now as a go to work hack. It gets used fairly hard as we have lots of open roads around here. It regularly has a sprint to over 100 and I usually sit at 80 to 85mph on my 15 mile commute.
Last week I glanced at the clock as I slowed down from speed to see the red temperature light was on, and tick over was very fast. After stopping I found the hose from thermostat had come off due to a loose jubilee clip. I don't know how long it had run without water . I replaced hose and all seemed well for the rest of the week. At the weekend I fitted a k&n panel filter and removed the snorkel, I was so pleased with the way it went (especially with my loud Arrow cans) I even polished the bike!
Slowing down last night from an indicated 100 it sounded odd on the over-run, kinda vibey too. It now seems very noisy and vibes can be felt through bars, pegs and seat. The only time it's quiet is when it's hard under power. I'm struggling to pinpoint noise but I'm starting to suspect big end bearing is going. Perhaps I've been too hard on it. Is the motor worth stripping as it's only done 16500 miles and most second hand engines seem to have covered more?

Nobody ever replied since 2015 ?:O:O

I'm really curious how you fixed the problem..

if it was my bike I would deffinately open it and see if you can fix it.

To my knowledge, high displacement single cylinder engines & the 660 engine are not designed for sustained high revs work (motorway work). If you want to move around at over 70mph for relatively long periods, get a 2 cylinder engine

More than happy to be proved wrong BTW, as i love my 660Z, but i have to forcemyself to keep speed in check ... & replace engine oil frequently.

PS : would be good to hear from original poster what the outcome was !

i did a 30km run at 6000rpm and the engine seemed happy ,doing well...
i did find alot of il in the airfilter box.
could i run a straight tube up with one breather filter on top instead of the whole setup with the box in between?
it is offcourse better to stay below 5500-5000 rpm for long travels, but i don't really worry if i go over... engine is bullit proof they say :-p

I sit at 80 - 90 mph most days on my return journey from work (25 miles) never had any issues, even when opening up to 100 for short blasts on overtaking.


Would it be worth returning your bike back to a 'standard' condition (snorkel and filter) to see if the noise still remains?

just yesterday i notice a slight more vibey engine (or i imagined).
got the engine warmed up and fiddled a bit with the home made 'kev mod' and the vibes i felt, got more smooth as it was before.
as myself, you also might have imagined it?
maybe check your kev mod too if you have one?

cheers, hannes.