Hi,
I started my engine up for the first time after my rebuild and re-phasing and am real happy so far. A couple of nights this week, I re-torqued the heads and adjusted the valves. I wanted to do some more research on the valve over laps and what is a good compromise for setting clearances, performance, noise and avoid burnt valves!
I have a 1979F so have set my valves to the latest specs of 0.0024"(0.06mm)...0.006"(0.15mm). I notice that 5twins said to use, though but earlier in this thread mentions using .003" for the intakes,
"Bigger is better as far as oiling goes. I wouldn't recommend .002", not much oil will get in. Try at least .003". My '78 recommended .004" for the intakes but they clattered at that setting. Closing them up to .003" got rid of the noise."
I pulled up an old article that I saved a while back written by Bob Bertaut,
http://www.650motorcycles.com/isky.html. He has some great actual measurement data and is biased toward larger clearances, maybe even using the original XS650 factory specs of .006" and .012" for intake and exhaust respectively.
Looking at the actual measured data that I edited a bit, not the values though.
XS 650 Intake Cam Actual In Motor Specifications
Acronyms:
Intake valve opening = I.V.O., Intake valve closing = I.V.C.
Exhaust valve opening = E.V.O., Exhaust valve closing = E.V.C.
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. Intake Lobe 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. exhaust Lobe 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" = 238 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
I also put together the chart below doing an overlap of the curve from Doug Meyer,
http://www.muzzys.com/articles/lobe_centers.html
My other concern with opening up the gaps too much would be the impact and wear potential when the adjusters close with the valve stems. The ramps are gradual though and this is probably not a big deal for the XS cams. I can deal with the noise it I get noticble performance improvement. I wear ear plugs anyway ;-))
So any constructive XS650 experience based comments?