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Cam info

How to Degree a Cam

Discussion and questions related to the course How to Degree a Cam


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Hi

I’m building a motorcycle race engine in a BMW S1000rr. I have a pair of Alpha stage 4 race cams .

i have attached the cam info given to me by Alpha

please can you confirm that I’m correct in thinking that my opening and closing event happens at 1mm of lift? That’s the way I’m reading the sheet.

Also would am I correct in thinking that I set my valve clearances before I dial my cams in?

Attached Files

Uh, no.

Because the method of measuring the opening and closing points can differ between manufactorers, or even between cam's from the same manufacturer, a 'standard' point for measuring effective duration was established. In the US, this is at 50 thou of lift and, it would appear, a European (or just that manufacturer) uses 1mm.

The pdf shows the spec' opening and closing points - you will notice the exhaust has two different figures, for the two different timing recommendations.

The pdf gives all the information you need for timing, although it could be clearer - the inlet is timed for full lift at 111 degrees AFTER TDC and the exhaust to 112 degrees BEFORE TDC for the OEM pistons and 109 degrees BTDC for their race (and I assume all high compression pistons).

The minimum valve to piston clearance, and where to check is to the bottom left - with some camshaft suppliers they will give a clearance at TDC but that is not always where the clearance is least, as the degrees at which to check illustrates.

What I am a bit surprised about it that the clearances don't specify hot or cold (I assume the latter) - you can set them during assembly and, if the engine uses shims, as many performance engined do, it is usually much easier to do before doing the timing, etc, as the camshafts may need to be removed to adjust the clearances. Make SURE the crank is rotated away from TDC (I usually use 90 degrees), as if the pistons are near enough to the top of the bores it is possible to bend the valves when rotating the camshafts and checking the clearances - you can do them all this way and establish any adjustment needed.

TBH, if you didn't know this, you may be advised to get help from an experienced builder as it is easy to make a mistake and bend a valve, or worse.

First thing I would do is ask the manufacturer (check their website or call/email) what their preferred procedure is for installing their product and setting the clearances/lash. Also, check the service procedures from BMW for the stock bike on stock cams.

And yes, the duration is 1mm (hence the opening and closing timing). So for the intake side, if you add 17 (nominal opening angle) + 180 (crank angle degrees in a stroke + 59 (nominal closing angle) = 256 degrees, the nominal opening duration at 1mm listed in the sheet.

Thanks for confirming the 1mm opening / closing event.

I will ask alpha whether they recommend hot or cold for setting the clearances . Cheers

Oh, if you're a bit confused, the duration (and timing) is given in CRANKSHAFT degrees, not camshaft degrees - confused the heck out of me as a youngster.