Posts tagged Engine
Selecting the proper final drive ratio for the XR650R is important for optimum performance and comfort on your selected terrain. The stock gearing is a 14 tooth on the front sprocket and a 48 tooth on the rear sprocket.
Many owners dual sporting their bike will run a 15 tooth front sprocket and will drop a tooth or two on the front. Riders doing mostly tight technical trail work will drop to a 13 tooth front sprocket and possibly go up a tooth or two on the rear.
The stock ratio of 14/48 is pretty versatile.
A one tooth adjustment on the front sprocket is equivalent to approximately 3 teeth on the rear. So 14/48 gearing is roughly the same as 15/51.
If you would like to calculate the optimum gearing for your bike based on your average and max speeds you can use this Honda XR650R Gearing Calculator. It is an Excel spreadsheet (*.xls) file and will require Microsoft Excel to open. If you do not have Excel then use Open Office – it is a free download (and better in my opinion).
I have preset all the inputs for transmission gearing, chain size, RPMS, and swingarm lengths. Just change out the 14/48 combo for other values and watch the speed calculations change.
Note: Changing to a 15 tooth countershaft sprocket on the XR650R will require your XR650R to have a Case Saver that fits.
The top end of the Honda XR650R is very robust and long living. However, if you push it too hard you can eventually hit a wall. The pictures below are from a motor that was running a stage 2 cam. This cam puts the valves VERY close to the piston when fully open. When the cam chain stretches a bit then Kablammo!
The XR650R is a fairly smooth running motor but is known to have a variety of rattles and ticks. If your motor seems to be making a little extra noise lately the cause could be one of the below:
notes from JM-2008
Worn Cam Chain
Historically larger XR,s (old 350’s/400/500/600/650) use a ‘Morse Hy-Vo’ type cam chain.
Looks like a series of gear teeth as opposed to a conventional roller chain.
When new and in good condition they run very quiet.
As the chain wears noise emanates from the rear of the cylinder near the cam chain tensioner.
Usual sign of a worn chain is the noise will diminish as engine rev’s increase.
Strange as this may seem it is due to the chain riding up on the gear type sprockets and taking up the slack.
Suggest checking your chain is not worn and tensioner is not stuck.
WEAK CLUTCH BASKET DAMPENER SPRINGS
(at rear of clutch basket) – If these have sagged or lost tension the clutch will be noisy at idle and low revs, the noise will usually diminish when you pull in the clutch.
Have not had one out of an XRR but suspect it’s the same as with all previous XR variants. These traditionally have a ‘spring loaded split gear drive’ to dampen drive line lash and subsequently noise when not under load.
One of the gears will be spring loaded and appear not to line up with the adjacent gear when not installed.
Should this item lose spring tension the resultant noise will be caused by clearance/back lash in the drive gears.
AUTO DECOMP CAM
(item #7 on the camshaft – http://www.honda-xr650r.com/honda-xr650r-cam-shaft-rocker-arms-and-valve-assembly-parts-fiche/)
Not much to do with this other than remove it.
Unless the clutch hub is notched from wear I wouldn’t bother replacing it, same applies to the balancer & decomp cam, very little to be gained throwing wads of money at the motor to find it’s still noisy!
From time to time it’s a good idea to inspect your clutch bushing for wear. Wear can create slop in the clutch and over time significant damage to the basket. These parts aren’t known to wear at any accelerated rate, but next time you replace your clutch plates make a point to pull off the basket and have a look. This is what you’ll see when you remove the XR650R clutch basket.
Follow the directions in the service manual available on this site.
A couple manufacturers make a magnetized oil sump plug for the XR650R. The factory plug is not magnetized, however many competing bikes (such as the KTM) come stock with a magnetized plug. The magnetization picks up any small metallic debris from your bikes oil – and can be used as a great indicator of troubling times to come. Seeing a nice clean magnetized plug when you change your oils is always a delightful site. I’ve never heard of anyone who bought a magnetized plug who didn’t like it and wouldn’t recommend it.