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im a huge fan of the offset keys. the best bang for buck you can get on a 944 engine.
would it help your inner engineer to know the 944/928 offset camshaft keys offered are in fact Genuine Mercedes-Benz parts that happen to fit the Porsche engines?
Really? I have a hard time believing that my crude looking keys are oem MB. Are yours crudely v-ground on the ends?
+1 on that. The off set key also moves the ignition rotor relative to the cap which doesn't seem ideal.
Given the shape of the rotor covers 30 or so degrees I don't think 4 degrees changes operation any unless you are running an incredible amount of advance or retard.
Yes, I have heard the spark is advanced or retarded separately.
The DME still sees the same firing points since the speed and reference sensors read the crank. The ignition timing doesn't change with the position of the cam, just the relative point of the rotor edge to the cap post. If it had a very small edge on the rotor, it could be an issue.
Really? I have a hard time believing that my crude looking keys are oem MB. Are yours crudely v-ground on the ends?
i havent owned a key for a few years since i got a good deal on an adjustable cam gear, but have since gotten out of 944 engines so i dont have much of anything
but yes the offset cam keys came to the 944 by way of the 928 guys, who were the ones who figured a MB factory offset key would fit their engines.
I had another idea. Mount the cam gear in a lathe with the new slot location at 9 o'clock. Grind a boring bar bit to the correct width and clamp it in a 90º boring bar on its side. Set the cross-slide to a cut depth of a couple of thou. Use the carriage as a manually operated shaper ram to drive the boring bar through the gear and repeat.
Maybe... a lot of force though that might give the ways and carriage a test. How about an end mill on a vertical machine? Either cut past the required depth and leave the radius or stop short and finish with a file.
I had considered using the vertical mill, but it sounded like a lot of (imprecise) filing. But what about both? Hog out most of the metal with an end mill and then just take out the corners with the lathe/shaper hack....
I had another idea. Mount the cam gear in a lathe with the new slot location at 9 o'clock. Grind a boring bar bit to the correct width and clamp it in a 90º boring bar on its side. Set the cross-slide to a cut depth of a couple of thou. Use the carriage as a manually operated shaper ram to drive the boring bar through the gear and repeat.
Thoughts?
sounds like a lot of work to not be as useful as a $300 adjustable cam gear
@jeyjey : This is a twofer, fer me, since I have no idea what you're discussing (but would like to learn) and love me some successful machining stories. Please post what you do, I'm interested to see.
Jeff,
First off... your approach is very unique & one I never considered (I have a scheme kind of similar, but not flipping it nearly 180 like you did). I like this because it's strong & looks factory. Plus one can always set it back to original if they wanted. I also really am impressed with the quality of the cut... looks factory!
It's a bit tricky with the advance-retard because rotating the cam gear clock-wise on the cam retards the timing, but that's always my impulse to do, which is wrong.
...unless one was to bump the belt a tooth, which would give you about 5 degrees cam advance, which works if the head is shaved but don't know if the valve clearances allow for that. This is one reason I finally got the adjustable gear is I can use it as a testing tool to check clearances valve-to-piston much easier.
05-02-2021, 06:08 PM
