Hi lads, new to KTM and to the 640. I took it for a spin today and at 120 kph it was revving at around 7000 rpm. I got off the motor way as soon as I could as it didn't fell normal. The lad that sol it to me said he change the sprockets on the bike dropping a tooth or two. Would that have this effect on the revs at motor way speeds. If so by fitting an original chain and sprocket would it return to normal. What is normal for these bikes?
Yes, if you fit the stock 16/42 ratio your bike will show revs between 5500-6000 at 120 KPH... With the gearing you have now I bet the bike is a tractor...
Even a 17 tooth front sprocket (w/+_42 rear) is not too much for these bikes. I liked the way it "calmed down" my old 640Adv. You do have to slip the clutch a bit more at low speed w/ this arrangement, but booking along at 70 is more relaxed.
If it's rattling like a paint shaker and sounding like a bucket of hammers falling down a flight of metal stairs then it is running right.
Eric, Try this if you travel.... http://www.advrider.com/forums/showthread.php?t=649629 A smaller tire makes the higher ratio less. My favorite tire for dual sport travel is the Kenda 270 510X18, my guess is that the diameter is smaller. On very steep climbs fully loaded you need to keep the rpm's up with the 5.10/17T combo but the engine is more than willing bill
Thanks for the input so far lads. Would driving at 120kph 7000rpm for mileage damage these bikes. I could happily sit at 120 if it wasn't harmful to the bike. Also what's the service intervals on a 640 adventure where oil changes are concerned?
To find MPH from KPH multiply by 0.61 So 120KPH = 73.2MPH To find KPH from MPH divide by 0.61 So 100KPH = 61MPH
Hi Bill, no 120 Kph is just 120 Kph but I'm not used to a bike that Rev's like this one. If its driveible with out damaging it in the current gearing then I'll leave it as is. Might as well get the use out of the chain and sprockets that are on it. I found the service interval in another Thread. If I ready it right it's every 5000 for oil and filters. Thanks again lads.
http://josh.wild3d.net/KTM/400-660 LC4 ENGINE SERVICE '98-'03 (ENG).pdf http://www.manualslib.com/manual/90446/Ktm-640-Lc4.html?page=5#manual This should do it. bill
I recall seeing somewhere on here that someone monitored their valve clearances whilst trialing different rpm at cruise. They came up with 6500rpm as the point where they saw increased valve wear. How accurate their testing was I have no idea, but it gave me a target to aim for. I try and cruise at 6000rpm now, its a nice comfortable speed where the engine makes good power without reving itself silly. I find 17/42 good for cruising at 110km/h-ish.
I get the conversion SRG, it's why someone would want a motorcycle to turn 7000 rpm's at crusing speed under 90-100mph is beyond me unless you are running a woods racer or hare scrambles racer. bill
My 640 came with modified (lower) gearing. It has 15-44, so quite low. While excellent in the dirt, it doesn't like to go much over 60 mph / 100 kph! Not sure what rpm (can't remember) but it is revving high and some vibration is more noticeable than normal. I primarily ride it from home on backroads, searching gravel and dirt, but wouldn't mind a little less buzzy on the pavement (running DOT knobbies and won't change until they are worn out - already have two of the same waiting to go on). I might have to ride 100 KM's one way to get to the dirt / gravel goodness... One day I hope to ride the Divide (portions thereof) from Calgary AB to Moab, then backtrack to join up with the TAT heading west to Oregon, then home through WA / ID / BC. It would be nice to do it all at once, but life dictates this to be done in stages. Might try to transport bike part ways or heaven forbid, ride more pavement than desired to quickly get to the starting point / hurry home at the end. With these parameters in mind, what say you inmates in the know? Should I go to a 16 or 17 tooth front if I keep the 44 (being frugal... the 44 is a supersprox and in great shape. The front is starting to hook so will need to be replaced this spring. Need to check the chain.) Sounds like I will have to either modify or replace the chain guard if I go up to a 17; will I need to also get a longer chain / flip the blocks? Thanks for your help / opinions in advance. Dean
I run a 17/45 on one of my bikes... This is just a very slight lowering of gearing over stock... With a 17 tooth counter sprocket you either need to grind the hook out a bit on the case guard or order the part # guard for a 640 Duke... The larger sprocket combo offers a few small advantages:1- The chain touches the swingarm less so the rub block will last longer..2- The larger sprockets will mean less bend on the chain for smoother running and possibly longer chain life... If you go with the 17 front you will be geared a minute {unnoticeable} amount higher than the stock 16/42... I would of gone for the 17/44 combo if a 44 tooth sprocket was easier to find... I ride my bike everywhere with my decided gearing and in the tight stuff slipping the clutch becomes my low gear... LC 4s have very strong, long life clutches...
