XS 650 Stock Camshaft Specifications
Actual Camshaft specifications from a 1980 XS 650 OEM stock motor with 330 miles on it, it has a perfect original cam chain, cam sprockets, and chain guides.
Stock timing mark was off only 1 degree.
Dial indicator mounted up to check the number 1 cylinder intake cam specifications measured at the valve at zero lash.
Positive stop Top Dead Center Indicator made from a 3/8" stud, a couple of 3/8 std. nuts and a 14mm automotive spark plug oil firing adapter.
I checked the stock early and late model (256 / 447) cams "cam lift" with a dial indicator in a head thats off a motor. The 34 tooth 256 cam has .300" lift at the cam and the 36 tooth 447 cam has .314" at the cam.
The stock XS 650 rocker arm ratio is 1.24 to 1.
Both cams have a 1.270" base circle.
So the early 256 cam will have .372" lift at the valve minus the valve lash. I can see it has a little more duration, have not checked one yet.
XS 650 Intake Cam Actual In Motor Specifications. I.V.O. @ .002" @ 95 degrees B.T.D.C. I.V.O. @ .004" @ 70 degrees B.T.D.C. I.V.O. @ .006" @ 50 degrees B.T.D.C. I.V.O. @ .040" @ 11 degrees B.T.D.C. I.V.O. @ .050" @ 8degrees B.T.D.C. Max. Lift @ .000" lash = .388" I.V.C. @ .050" @ 43 degrees A.B.D.C. I.V.C. @ .040" @ 46 degrees A.B.D.C. I.V.C. @ .006" @ 78 degrees A.B.D.C. I.V.C. @ .004" @ 98 degrees A.B.D.C. I.V.C. @ .002" @ 124 degrees A.B.D.C. ------------------------------------------------ Stock Intake Cam Lobe Center = 107.5 degrees Intake Cam Duration @ .002" = 399 degrees Intake Cam Duration @ .004" = 348 degrees Intake Cam Duration @ .006" = 308 degrees Intake Cam Duration @ .040" = 237 degrees Intake Cam Duration @ .050" = 231 degrees |
XS 650 Exhaust Cam Actual In Motor Specifications. E.V.O. @ .002" @ 127 degrees B.B.D.C. E.V.O. @ .004" @ 120 degrees B.B.D.C. E.V.O. @ .006" @ 91 degrees B.B.D.C. E.V.O. @ .040" @ 44 degrees B.B.D.C. E.V.O. @ .050" @ 41degrees B.B.D.C. Max. Lift @ .000" lash = .388" E.V.C. @ .050" @ 11degrees A.T.D.C. E.V.C. @ .040" @ 14 degrees A.T.D.C. E.V.C. @ .006" @ 53 degrees A.T.D.C. E.V.C. @ .004" @ 71 degrees A.T.D.C. E.V.C. @ .002" @ 88 degrees A.T.D.C. ------------------------------------------- Stock Exhaust Cam Lobe Center = 105 degrees Exhaust Cam Duration @ .002" = 395 degrees Exhaust Cam Duration @ .004" = 371 degrees Exhaust Cam Duration @ .006" = 324 degrees Exhaust Cam Duration @ .040" = 238 degrees Exhaust Cam Duration @ .050" = 232 degrees |
Note the camshaft duration at the valve lash settings of .002", .004", and .006"!
Setting valve lash to the stock cam specs just contributes to reversion and lost compression with these old design dead slow cam lobe opening and closing rates.
For Example: setting the intake valve lash at .002" versus .006" means you have lost 91 degrees of time (45 degress on the intake opening side and 46 degrees on the intake closing side) the intake valve is just hanging around the valve seat but is still open when it could have opened 45 degrees later, and shut 46 degrees sooner and trapping mixture to burn, there is no flow or other advantage with the slow opening and closing rates that leaves the valves open for 91 degrees a few thousandths off the seat except burned valves, lost mixture and compression. The very small lash settings also leave little time or physical space for oil to get to the cam lobes and rocker arm friction surfaces, and contributes to early wear. Modern camshaft computer designs have changed these opening and closing rates and take into account valve train weight and operating design parameters. (the rocker arm pad radius, forked followers, pushrods etc.)
The Yamaha OEM specs are .006" and .012" for the intake and exhaust respectively on the early motors on the OEM Yamaha micro fiche I have and the OEM Yam service manuals. That's why people think that the early cam works so well. It is because it is another of the ancient old slow opening and closing ramp design cams that waste valve event time to actually open and close the valves. Engines are designed to do work after all. In fact they had to have a compression release when used with the proper lash settings to relieve the much more efficient engine cranking compression gained because of it on the earlier model 650's.
I profile stock and performance cams from the opening to the closing in thousandths per degree every 10° at the crank to check cam profiles at the cam every 5° from opening to closing. Most of the newer design (non symmetrical) cams open the valves faster than they set them down and both speeds are much faster than the old fashioned degree and efficiency eating slow designs of the past. (Some of them are still sold as performance cams today) Only a few companies still sell the same old designs, with their specs changed only by base circle size.
The late XS650 cams set at .002" int. lash are a pure gamble. The stock base circles have runout. Many ask why when turning the motor over the narrow lash setting keeps changing once they have set it, that is why. Base circles get sloppy when cam grinders do not let them spark out on the final passes. So a possible .001" inch or less is not enough open lash in an instant on the long slow sloppy base circle ramps for oil. Not much time to get oil on the valve tips either. People complain of wear there as well. Some cams have slots around the base circle to allow for oil, and others have a hole in the base circle to supply oil directly at that point of lash. Especially important in these low oil pressure ball and roller bearing engines.
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