Fuel Pump Eccentric for a cam sensor.

[TheSilverBuick]

On another forum a guy was talking about grinding down the fuel pump eccentric on a cam to be able to press on a toothed wheel of some sorts for a cam sensor that could be mounted through a fuel pump block off plate. This got me thinking, do you even need to do anything to the fuel pump eccentric? Could you not simply point the high spot of the eccentric towards the fuel pump openning and run a sensor through a block off plate towards the cam until it touches the eccentric then back off a hair? It would work like a half moon sensor (like the dodge 318 one on the EMC hemi) with only a shorter signal interval.

This of course may not likely work on all engines, but ones you could get close to the eccentric with some kind of hall sensor. Of course the clocking of the eccentric is probably important and changes engine make to engine make (or maybe even cam to cam )

I'm wondering about on my OHC Pontiac engine, for first round start up I'm going to use the distributor points contacts for the Tach signal, could I use the fuel pump eccentric for a cam signal and do sequential right off the bat? Originally I was going to start with batch fire until I figured out a crank sensor to make the distributor the cam sensor.

The fuel pump is right next to the distributor.


The shiny streak to the left of the gear is the fuel pump eccentric.


Thoughts? Would it work?

[TheSilverBuick]

As I'm thinking about this more, with the points contacts having six evenly spaced points for the MegaSquirt to reference, I would have to make sure the cam eccentric is picked up right before the true TDC point in the distributor. Or can I grind one lobe off the points cam to make it essentially a 5-1 missing tooth wheel? That I do not know if it could be programmed as a missing tooth, especially since the whole thing is moving at 1/2 the crank speed. More thoughts?

[STINEY]

Grinding a lobe off the points cam sounds good in theory, BUT.....

As long as you are still using the points as a trigger, you will have bad wear on the block of the points that rides on the cam. That surface is very smoothly polished from the factory to keep wear to a minimum. Can you duplicate that mirror finish?

I was thinking more of a stamped steel fuel pump eccentric (which does NOT appear to be what you are dealing with)

In that scenario (stamped steel) I could see cutting the eccentric to have one "tooth". Would probably work great.

What do you think of grinding the cast eccentric you have into a "tooth"?

[TheSilverBuick]

I want to run it round shape and all. With a hall sensor it will either detect it at some point or it won't. With a VR sensor I wonder if it would develop a sine wave or not, at which point the megasquirt figures out at what point it to call it a tooth.

[dieselgeek]

I would read the spec sheet on the sensor you intend to use. They are usually designed to read certain dimensions of "teeth" that will give you a clean signal. My worry about the cam lobe and a hall or VR sensor is, how accurate would the signal break be on each rotation, and would it overlap one of the crank position teeth if it's allowed to wander a bit?

[TheSilverBuick]

Excellent questions. At least on the OHC setup I can bench test it since it's on it's own shaft. The question kind of then becomes sensor selection.

[BKBridges]

Im sure Im missing something here, but doesnt your Pontiac camshaft have a big cogged pulley attached to it right out in the open? Could it not be used as a cam sensor wheel with some minor modifications? Not sure if the exisiting cogs (32?) could be used based on the hardware/ software issues and any new things that come to light, but might a window or two be easily added?

[dieselgeek]

I sure Im missing something here, but doesnt your Pontiac camshaft have a big cogged pulley attached to it right out in the open? Could it not be used as a cam sensor wheel with some minor modifications? Not sure if the exisiting cogs (32?) could be used based on the hardware/ software issues and any new things that come to light, but might a window or two be easily added?

I've been doing it this way on all the belt-driven cam engines I've tuned lately. Remove one cam pulley bolt, put a 90 degree tab underneath it so it sticks up above the bolt head, install a slightly longer bolt, and then mount a Hall sensor such that it reads the tab once per cam revolution.

[BKBridges]

Havnt completely lost my mind then... Whew! Going direct on the cam cuts out the middleman/men giving you maximum accuracy. Sequential MPI overhead Pontiac 6... That is cool. I gotta say a six barrel intake would really make it on that combo... Its an illness.
BKB

[TheSilverBuick]

Eventually I want to run a crank and cam sensor directly from the crank and cam, but I'm looking at something to get by before that happens. Also, I don't really want to ugly up the front of the cover with wiring if I can help it, so I have to figure something out still.





But I was also bouncing the fuel pump eccentric idea out there because there might be potential to be useful for other engine makes as well?

[dieselgeek]

I wonder if that timing cover is thick enough to thread so you could fit another Cherry sensor? I agree with the cover being nice and clean looking. but maybe you can hide a tooth and aim a pickup sensor while keeping the look clean.

[TheSilverBuick]

I have one that is thin gauge aluminum and one that is thin fiberglass. The one I go with will depend on which head I use as the mounting points are slightly different (2 bolts vs 3 bolts) and won't bolt to the wrong head.

[OldMachinist]

I'm not versed in sensors enough to talk about them but It looks to me like you could turn or grind the eccentric round. Then remove the timing gear and install something like the trigger wheel from an HEI distributor in the eccentric location. You should be able to find something that will work for a wheel realizing that said wheel might have to be bored to fit. I would try for a slight interference fit so the wheel could be tapped into position circumferentially and drill for a roll pin to keep it in place.
Of course this depends on the dimensions of the shaft and if the wheel could slip over the end and into position.

[TheSilverBuick]

I'm not versed in sensors enough to talk about them but It looks to me like you could turn or grind the eccentric round. Then remove the timing gear and install something like the trigger wheel from an HEI distributor in the eccentric location. You should be able to find something that will work for a wheel realizing that said wheel might have to be bored to fit. I would try for a slight interference fit so the wheel could be tapped into position circumferentially and drill for a roll pin to keep it in place.
Of course this depends on the dimensions of the shaft and if the wheel could slip over the end and into position.

Of course with enough time, money and equipment it can be completely re-engineered, but I'm notorious for taking what's there and either leave it alone or lightly modify it and make it work. This could be a dead end idea from me, but thought I'd through it out there.

I'm probably going to bench test with one of my spare cam sprockets grinding off the edge of one tooth (where the belt doesn't ride) and see if there is enough relief on the teeth for a sensor. That too is likely not going to work, but I can test that off the car easy enough.

[CDMBill]

What are the gears made of, they look like plastic? If so you could embed a metal or magnetic slug in one of the teeth and read it from below the underside of the cam gear. You only want one trigger per revolution anyway. Since the belt drive is external you don't have an oil impregnation issue. If the cam gear is metal, is there some gap to the cover? And, if so what if the tab was mounted to face of the cam gear and extended just a bit beyond the belts running circumference and again read from below between the belt paths?

On the crank sensor, why not a 36-1 wheel in front of or behind the damper? Like maybe one of these?