Anyone fab up an external crank trigger?

[donk_316]

I have a bored and stroked 2.8 which i wanna go gen3 topend.

Instead of losing all the work done to my shortblock I would like to run a external crank sensor but im having a hell of a time... so much that im thinking of just swapping to the 3400 shortblock (which im also having a bitch of a time finding up here)

Shaun sent me a pic and an email addy of a guy who had his dad or something build one for him and it looks like what i would like to do....typical crank sensor bolted to a L bracket pointed at a disc behind the crank pulley.

Its that disc that im having issue with...mainly the diameter....once i have that then im flanged.

Anyone point me in the right direction? or have a 3400 shortblock? lol!

[bszopi]

I built one.. .lemme find a pic!

[Guest]

I also have one, it was my grandfather that built it, since he's the machinist, soon he will be teaching me. :0

Anyway here's some pics:

Test fitting, before notches.


Another pic before notches.


In the truck, after it was running, with notches.


I don't remember the diameter of the disc, and it didn't seem that important, what did seem important was the spacing and length of teh notches. We estimated the size/spacing based on the OEM crank trigger wheel on teh crank, using degrees of crankshaft rotation to find this. although IIRC we made the notches the same width as factory, even though this wheel is larger in diamater. We figured it would be easier to remove more material if need be, than to add it back in. My research since then also supports the idea of the importance being on where the leading edge is, not nessisarily how long the notch is.

The entire wheel is also turned in relation to teh OEM trigger wheel, due to the location of the pick up, I don't recall the exact difference, but it was somewhere around 20 degrees counterclockwise. We also made my pick up adjustable, which I have used a little to my advantage, but have yet to completly dial it in.

[donk_316]

Your the guy i emailed cause i have that last pic! You never answered me!! Bastard!! LOL!

I appreciate the information. Maybe building one would be alot easier than anticipated.

[geoffinbc]

Why not use an MPFI system instead of SFI then? There is no need for a cam or crank sensor and you can then use any aftermarket cam of you choice because you do not need a cam sensor.

Just a suggestion.

[donk_316]

Why not use an MPFI system instead of SFI then? There is no need for a cam or crank sensor and you can then use any aftermarket cam of you choice because you do not need a cam sensor.

Just a suggestion.

im not using SFI....still need a crank sensor to run the DIS though....nothing to do with a cam sensor at all.

[geoffinbc]

All you need is a crank sensor that goes in the side of the block. You do not need the high resolution sensor on the balancer.

[RacerX11]

He doesn't have the block-mounted sensor. His engine is a bored-out Fiero engine without the crank pickup, thus the need for an external crank trigger to fire the DIS.

Marty

[geoffinbc]

Ahh ok I see the problem now.

[Guest]

Your the guy i emailed cause i have that last pic! You never answered me!! Bastard!! LOL!

I appreciate the information. Maybe building one would be alot easier than anticipated.

Sorry, I don't remember getting an e-mail about my crank trigger.

To make the crank trigger, it's not overly difficult, but requires a lathe and mill, or at least that's what we used.

The trigger wheel itself isn't all that involved of a design, basically a flat wheel with notches on the outside, and 5 holes drilled, 4 for the pulley and one for the center crank pulley. Also there is a centering tang on the back of the disc, that fits into the balancer, like the factory pulley does, plus a receiver groove in the front for the pulley.

I think it was more difficult to design and make the sensor bracket, since I wanted it adjustable, I think I have something like 25 (maybe it was 35) degrees of adjustablility, LOL since we really weren't sure how well thsi was going to work before I installed this engine. I believe the break down was 10 degrees retard and 15 (25) degrees advance ability.

If need be, I could get some dimensions for you, since the truck is sitting for teh winter while I upgrade the turbo and a few other key parts *coughspraycough*.

[donk_316]

Well I appreciate the offer! I would think the sensor bracket would be the easy part and the wheel would be the iffy part but you have the experience with this and i dont.

What i would like is maybe a few measurements such as dia / circ / notch spacing and so on.

So you have this between the balancer and pulley? This didnt offset your pulley at all? I think thats all im worried about.

[bszopi]

All mine was made out of was a 1/4" slice of a 6" aluminum stock. Then I used a drill press to drill out the holes for the magnets.

[RacerX11]

All mine was made out of was a 1/4" slice of a 6" aluminum stock. Then I used a drill press to drill out the holes for the magnets.

I think the main difference here is that you were using the Perfect Power ECU that used hall effect sensors, with both a synch and home signal, and requires magnets mounted in a non-ferrous trigger wheel. The GM DIS uses a variable reluctance (VR) sensor that requires a ferrous metal timing ring with missing notches.

The thing you need to be careful of when working with the VR sensors is that several things affect the quality of the signal. (thickness of the timing disc, the width of the notches, and the diameter of the disc). The critical dimension is the diameter of the pole piece in the sensor. You can see this by looking at the end of the sensor?.there is a metal cylinder.

The width of the notches must be equal to the pole piece diameter for best performance. Any bigger, and the signal will flatten out (the ICM triggers off the middle of the notch). Any smaller, and the signal amplitude will decrease.

The thickness of the disc must be at least as big as the pole piece diameter?.anything larger is good.

The smaller the diameter of the disc, the slower the speed of the notches past the sensor, and the lower the amplitude of the signal. If it gets too low, you may run into starting issues.

Based on this, my recommendation is to use a disc that is the same diameter (or larger) then the stock crank disc, with the same sized notches. Using a thinner disc (maybe ¼? or so thick) as long as it is thicker than the pole diameter will be sufficient. I would consider drawing up the timing disc in CAD and having a shop laser-cut it out of 1/4" thick steel plate, or something similar. This would ensure a pretty accurate wheel.

Marty

[donk_316]

Ahhh ok. that makes alot more sense to me now knowing that last little bit of info. Thanks.

[RacerX11]

I've been busy the past week, but I have a spare crank I could get the measurements for you. If you don't have access to a CAD program, let me know, and I can draw something up.

Marty