helical gear as a trigger wheel

[andrew_mx83]

Running through cam sync options for my next ms3 install, was wondering if i ground off one (or ground off all but one) tooth of the helical gear on the exhaust cam, which used to drive the distributor, if this would work ok with a hall or vr sensor?
Crank has a 36-1 VR setup


Thanks in advance

[Matt Cramer]

As long as (1) the gear is steel or iron and not something like a copper alloy, and (2) the gear does not drive an oil pump, that should be workable.

[billr]

Further my education here:

Would the OP need to grind of all-but-one teeth, or can the MS cam detection work with the "missing-tooth" config of just grinding off one? Would "missing tooth" work for "polling"?

[Matt Cramer]

With current firmware, you would need to be sure the sensor is triggered when lined up with a particular crank tooth on one engine phase but not another. This may or may not work with an unmodified helical gear if the gear has an odd number of teeth and you have a small enough sensor point, but it will not work with a gear with even numbered teeth.

[billr]

Sorry, I'm even more confused now. Will "missing tooth" work at all, or does it have to be a single tooth or some specific tooth pattern? That even vs. odd tooth bit, does that only apply to polling, or only to missing tooth, or only missing tooth with polling? Talking only about the cam sensor here. At least I understand the need for the gear to be "magnetic"!

[andrew_mx83]

Thanks for the replies guys.
The gear is cast iron so no worries there. I cant remember how many teeth it has, but it must be an even number so i dont think 'polling' will work.

So finally, would single tooth or missing tooth be more appropriate? The gear is fairly small (under 2" dia) and the teeth are closely spaced.
Any reason to choose hall over VR?

[Matt Cramer]

If you're using a 36-1 crank trigger, I'd just grind it down to a single tooth; that's the easiest option to handle.

Hall effect sensors tend to be a bit less "fussy" than VR.

[andrew_mx83]

Thanks for the info Matt, will now try and find a hall sensor i can fit inside the head in the hole once occupied by the distributor drive shaft. Will be nice and neat plus one less rotating joint to leak.