Valve Clearance Question

pa23driver

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what's the deal with different intake valve clearances on various years?

on my 1977 the factory manual calls for an intake valve clearance of .002.

on my fathers 1978 the manual calls for a clearance of .004.

I thought the valves and cams were pretty much the same from 1974 on.

any ideas?

and what are the appropriate valve clearances on a 1981? i don't have a manual for the girlfriend's 1981 special and i set the clearances at .002 and .006.
 
...XS1-B.....0.003"(0.076mm)...0.006"(0.15mm)
...XS2-650..0.006"(0.15mm)....0.012"(0.30mm)
...XSB........0.0024"(0.06mm)...0.004"(0.10mm)
...XSC-on...0.0024"(0.06mm)...0.006"(0.15mm)
 
^^^ that's what i thought too, but i've seen .004 on the intake recommended for later models on this forum
 
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 have no idea why Yamaha changed their specs so often. As you mentioned, the motor wasn't changed much, if at all, after '74. The general consensus is bigger is better for the clearances. It allows better lubrication of the valve stem top and adjuster screw contact patch. Even so, those 2 parts do wear, especially the screw tip. No sense speeding that up by running the clearances too tight.
 
I run mine at .0024 and .0060. I hear a little clatter, but I want better oiling and less wear as 5twins said and it's stock. I got the tappets from mikesxs with the hex head and they are freaking great!!!! Talk about making minor adjustments and ease to adjust.
 
sounds good, thanks for the replies. i set the valves so that .002" feeler slides in with very little drag so they're probably set at .002+ a couple tenths. next time i got the covers off i'll go with .003".

i was wondering how well the mikes adjusters worked. when it comes time to get a new set i'll pick those up.
 
Good tip to try the next size up feeler gauge as well. Just a double check of where you're at on the clearence. Example: .0024 fits, but .0025 doesn't, then you know you're at a solid .0024. Sometimes the size you need works good and drags just a bit, but then the next size fits too.
I also set the clearence, then rotate the engine back to that valve and re-check it. I've noticed that sometimes it's off and the next size fits real easy, so you need to readjust again. It's a bit of a pain, but when you think about it, you adjust the valve, then rotate it once, and it's off? So now your valves are not the correct clearence. Not good. I've set it and rotated the engine several times to make sure it's a true setting. Try it, you'll see what I mean.
 
I think they used the tighter spec in an attemp to quiet the noise. The EPA did more than messing up the carbs.
 
Hey guys. How critical is a thousandth here? My feelers are .102 & .152 (70 XS1). Is that enough to totally bugger the adjustment up?
 
Right I know the conversion, curious about tolerance? If the clearance calls for .10/.15, is the extra .02 on my fender gauges going to be an issue ie: do I need EXACTLY .100/.150 gauges?
 
On the 70 the specs were .003/.74 Intake .006/.15 exhaust.
The .004/.10 may be a bit noisy.
Leo
 
...XS1-B.....0.003"(0.076mm)...0.006"(0.15mm)
...XS2-650..0.006"(0.15mm)....0.012"(0.30mm)
...XSB........0.0024"(0.06mm)...0.004"(0.10mm)
...XSC-on...0.0024"(0.06mm)...0.006"(0.15mm)
This almost answers my question. I'm not sure which of these is my XS though. I'm pretty sure I have a Special II. It's a 1981 (See my pictures). Can you clarify which of these are the proper adjustments? Be as detailed as you can. I'm new to this and I'm doing my tuning myself! Any help is great.
 
Use the last one in the list. It's become pretty much the accepted practice to use that one on all the models. You probably don't have a .0024" feeler gauge, most people don't. Just set the intakes to a snug .003".
 
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?
 

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