Camshaft gears. Myth vs observation

[silverbullet]

Camshafts on wbx have a number stamped on the shaft side of the gear wheel, usually in the range -5 to +5
Rebuild manuals state that if replacing the cam, you should replace like for like. The myth in flat four building circles is that this is because the gears are cut in subtle over and under sizes to compensate for variations in case machining and crankshaft/camshaft centres.
I while ago I measured some low-mileage and new gears of various numbers and guess what? The gear forms are all the same, showing near-identical amounts of running clearance*
What does vary is the position of the fixing rivets...
I believe that the cams were machined and profiled, then the pre-cut gears were rivetted on. However, this introduces room for rotational error as there is no reliable datum on the camshaft to "zero" the timing relative to the gear.
So the +5 to -5 number is (probably) degrees of crankshaft rotation, stamped on by inspection after assembly, to allow the engine builder to achieve correct valve timing.
If you have ever driven a car with a mis-timed cam, you'll know how bady a few degrees can dent the performance or affect fuel consumption.
As ever, happy to be proven wrong but VW only supply un-numbered replacement gears part number 025109111 for the later 4- bolt cam in suffix B engines.

*There is also an alarming amount of variation in the radial clearance between the cam flange and the gear, which can result in eccentricity. This is well known and usually remedied by tapping the gear around while rotating the crankshaft, to achieve even blacklash clearance.

[sarran1955]

Hello,

Yes...always been backlash not clearance for me...

Cordialement,