yamchop
XS650 Addict
is there a easy way to tell if i got my cam 1 tooth off?? its a 72.
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cam 1 tooth off??
- Thread starter yamchop
- Start date
Yep. Set the left intake tappet to the inspection (not running!) clearance--for 256 motors like yours that's .012". With the plugs removed, rotate the crank CCW (from the left side). When the piston starts to rise into the exhaust stroke, start turning in very small increments, checking for play in the intake tappet; when the tappet gets close to closing use a .001" or .0015" feeler gauge to judge where you are, and rotate just to the point at which the small gauge is a no-go. There's no lift specification for degreeing XS650 OEM cams; valve opening is measured at initial lift, and this gets you close.
Next jam-fit the smallest wall anchor you can find in the hole in the end of your crankshaft and use it to mount a clear plastic protractor from an office supply store. Look through at your timing marks. For your engine, intake opening should occur at 47*BTDC, so your rotor mark should be sitting ~7* to the left of the advance timing mark on your stator.
This isn't an exact procedure, but for your purposes (checking stock installation) it doesn't have to be. Since the cam turns at 1/2 crank speed, 1 tooth error on your 34-tooth cam sprocket yields >21* error at the crank, and this method will put you well within that range.
Next jam-fit the smallest wall anchor you can find in the hole in the end of your crankshaft and use it to mount a clear plastic protractor from an office supply store. Look through at your timing marks. For your engine, intake opening should occur at 47*BTDC, so your rotor mark should be sitting ~7* to the left of the advance timing mark on your stator.
This isn't an exact procedure, but for your purposes (checking stock installation) it doesn't have to be. Since the cam turns at 1/2 crank speed, 1 tooth error on your 34-tooth cam sprocket yields >21* error at the crank, and this method will put you well within that range.
Last edited:
Sundie
Jabroni
Whoa. There's a much easier way. I just can't remember if it's the ATU side or the Points side - but take off your alternator rotor inspection plate, put the motor to the TDC mark, then remove your points or atu - one of the sides has a scallop cut into the cam that is the same as the mark on the cam internally. It should be facing up. If it's on the bottom, rotate the crank through 360 degrees to come to TDC again, and it should be at the top, pointing directly up.
I'm thinking it's the ATU side.
I'm thinking it's the ATU side.
To get close to valve opening, you can also insert a piece of cellophane between the tappet and the valve stem and rotate just to the point where it can't be pulled out.
Whoa yourself. A lot of guys have set these things a tooth off using their eyeballs.
Whoa yourself. A lot of guys have set these things a tooth off using their eyeballs.
yamchop
XS650 Addict
thanks guys i'll check it out and let u know
yamchop
XS650 Addict
would it run 1 tooth off???
yamchop
XS650 Addict
did a quick check the way sundie explaind and the line is at about 2 o'clock. i'm gussind i got the cam a tooth off. bummer pull the motor again!!
Sundie
Jabroni
Yeah, i can believe that if they don't have the tensioner installed, or have put their finger through the hole to tighten the chain. But once they do that, it's always obvious.
I don't deny that your method is the definitive test, and will tell you how stretched your cam is, but for simple "am i off a tooth" it's overkill.
You're right re. overkill, Sundie; to check for 21* of error you could just eyeball the timing marks and be close enough.That brings the procedure down to pulling one tappet cover, readjusting one tappet, pulling the inspection plate on the left motor cover, and finding a piece of cellophane. I think I'd rather do that than pull down the ignition.
For those who don't like to consult manuals: the inspection lash and valve opening numbers given above are for 256 motors and don't apply to 447's.
For those who don't like to consult manuals: the inspection lash and valve opening numbers given above are for 256 motors and don't apply to 447's.
yamchop
XS650 Addict
alright so i got the motor out and apart. when i line the mark on the ATU straight up when the left cylinder is at tdc but the cut out on the cam doesnt match. wtf???
I don't know if Yam changed the design later, but I just pulled an XS1 cam out of the stash for a look-see. Unlike later 447 camshafts, it had one hole for the ATU pin, in the same alignment as the notch on the points side of the camshaft and the timing notch on the sprocket. All you want to look at is the camshaft notch, the sprocket notch, and the crankshaft center, all on the left side. Jam-fit a line into the hole at the end of the crankshaft and pull it up across the camshaft center at TDC. If you can't get the chain on the camshaft in a position that aligns the camshaft notch and the sprocket notch together with the line crossing the shaft centers, the sprocket may have been moved; degree the cam.
