Which cam is this?

[Merlin]

I thought my XS2 was standard, and runs just fine, but when I measured the cam timings I got:
Inlet: opens 58deg BTDC, closes 90deg ATDC
Exhaust: opens 65deg BBDC, closes 50deg ATDC
These are the times at which the rocker contacts/releases the valve (clearances 6 and 12 thou), so may not be accurate to a degree, but the open times seem very long.
Is this a hot cam (that I don't really want) or have I screwed-up somewhere?
Thanks in advance for any info.

 

[TwoManyXS1Bs]

Hey, Merlin. Let's start with this service bulletin:

 

[TwoManyXS1Bs]

Ok, after you've reset valve lashes to 0.012" and reacquired the cam open/close events, compare them to this spec:

 

[Merlin]

Hi,
Thanks, but that is the standard cam. My valve lashes are at 6 and 12 thou (as per book) and its hard to see how any lash-setting could increase the open times to the values I have:
inlet open for 328 degrees, exhaust for 295. I notice that the full-open positions on my cam are fairly close to the standard, but I suspect that position may be common to all cams.

 

[TwoManyXS1Bs]

Then, you can reset the valve lashes to ZERO, and record the open/close events at 0.040" lift.
Also, note the total lift for each valve.
See how they compare to the Megacycles Cams chart:

 

[TwoManyXS1Bs]

... My valve lashes are at 6 and 12 thou (as per book) and its hard to see how any lash-setting could increase the open times to the values I have...

Your inlet lash must be set to 0.012" for the timing values.
Being larger than 0.006" will reduce the recorded duration...

 

[Merlin]

Thanks. I think that you have the answer. I assumed (wrongly) that figures were relative to "when the lash is at zero". If the figures are quoted at 40 thou lift this will almost certainly reduce my values to something more sensible. I will need to get a dial-gauge to check that, but I'm pretty sure that I now understand my values - which was what I wanted.
Many thanks for your hep and expertise.

 

[TwoManyXS1Bs]

...Many thanks for your hep...

Always glad to give hep when I can.

Yeah, you gotta watch the measurement method used by cam grinders. Not all are the same.

Your current numbers sound interesting.
Please update when you get new numbers.

 

[chizler62]

Yeah, you gotta watch the measurement method used by cam grinders. Not all are the same.

This is true. Some cam grinders measure degrees in Celsius while others Fahrenheit

Lots of good info here. Thanks!

Posted via Mobile

 

[Merlin]

True, 40 is a special number: -40F = -40C that's why they chose 40 thou.

 

[Brian902]

Some more numbers from a Web Cam;

http://www.webcamshafts.com/mobile/motorcycle/yamaha/yamaha_xs_650_twin_(68-85)_4v.html