cam and crank trigger combo inside a distributor (megasquirt

[dorkie]

I was pre-reading the megasquirt manual and saw this:



So, I got to thinking about it and it just looks so simple. I need to know why it won't work. I need someone to look at what I plan to make and install in an old distributor (a barely used 009) and tell me what I am missing. I know what I am missing so far - a key or pin to time the trigger wheels to the shaft (easy to incorporate at this point). I have a 5-axis laser at my disposal for making the wheels. (I am just bragging about the "5-axis" part the extra axes are obviously not necessary for this project.)

http://images.thesamba.com/vw/gallery/pix/1105162.jpg

http://images.thesamba.com/vw/gallery/pix/1105161.jpg

http://images.thesamba.com/vw/gallery/pix/1105160.jpg

http://images.thesamba.com/vw/gallery/pix/1105159.jpg

http://images.thesamba.com/vw/gallery/pix/1105158.jpg

[sideshow]

I love your virtual mock up. Some packaging suggestion, it maybe easier to top load the pickups.

[dorkie]

ah yes, excellent idea. I will lay that out tomorrow and see how it looks. Thank you!

[miniman82]

My only question is: You're doing all this work, only to have timing scatter to still look forward to. Why? Put the crank trigger where it belongs, on the dagone crank! FWIW, this is not a new idea. I saw a setup where a guy used an EDIS system on the cam drive (1/2 crank speed means you need a 72-4 pattern and the teeth get really small), but never heard how it worked out. Again, the main reason for going with a crank trigger is spark stability, programmability and accuracy. When done the way you propose, you lose the biggest piece of the pie- accuracy.

[dorkie]

alright. that is the exact type of feedback I am looking for. the timing scatter is from the slop in the drive tangs/slots?

[Max Welton]

I think lash in the pinion interface to the gear on the crank also contributes as does axial movement of the crank itself.

Max

[MarioVelotta]

I have been working on a low profile cam sync myself Using the distributor drive gear for this is great. A cam sync is lazy and has a wide window it can be used in.



Tell me more about the laser you have access to

[dorkie]

Mario, your cam trigger is definitely going to be nicer than mine.

The laser I have access to is a Trumpf TLC Cut 5. A little more info here:
http://www.inconelco.com/e/3DLaser_e/EN_TLC_CUT5.html

I don't know the wattage, but it cuts through inconel extremely fast.

[MarioVelotta]

That's the most badass thing ever! What have you made with it?

Are you going to build an all one distributor to try for yourself?

[dorkie]

I don't get to play with this laser. In fact, not at all. It is usually tied up in cutting jet engine parts (sounds kinda cool to say that, but it really is cutting up pieces for jet engine parts). The older 3-axis laser, I used to program it so I got to play quite a bit.

I have done machining fixture, gage, and special machine design for the past 23 years, so if I was really cool, I would definitely design and build my own complete all in one distributor. I am not, so the plan is to modify an existing distributor and just make the trigger wheels and spacers. It won't be pretty, but I think it will work. If not, I am not out much.

[MarioVelotta]

so if I was really cool, I would definitely design and build my own complete all in one distributor.

Just do it

[dorkie]

got my trigger wheels lasered. i need to clean them up and make 'em look pretty. then i need to make spacers and a cap and knock some holes in the body for the sensors.

http://images.thesamba.com/vw/gallery/pix/1107984.jpg

[Devastator]

Looks nice! You might also drill a hole, roughly the same dia. as your single tooth, just behind the single tooth in order to counter balance it slightly. It could potentially see 3K RPM.

[dorkie]

I didn't even think about balancing this stuff. Good call. I will definitely drill a hole. Thanks, Devastator. I follow you (stalk?) pretty closely on the internet. I am definitely using you as inspiration for my current build (E85, Megasquirt, etc).

[dorkie]

Back to the timing scatter issue... I am looking at all of the components that make up the distributor drive. The crank gear, the drive pinion, the distributor tang (?). I measured everything, but since I don't have my engine together, I have to make an assumption. Or two. :~)> The distributor drive tang to distributor drive pinion has .002" slop. The manual calls for .0028/.005" crankshaft end play.
Assuming the crank will rotate the distributor 1 to 1 and then assuming .005" slop in the crank gear to drive pinion, .002" pinion drive tang to distributor clearance, and .005" crank end play for a total of .012" total sloppiness... and with my trigger wheel diameter of 1.75", I get a maximum of .7858° of timing scatter.

Am I completely lost and delusional? I understand the distributor doesn't rotate 1 to 1 with the crank as stated above. I only used that as a simplification. It actually makes the error worse, I think. I have always been under the impression that there is plenty of timing / spark scatter at idle. This doesn't bother me. I don't care about idle quality like the fella's over on the samba. If it will idle without me touching the gas pedal, I am good. Idles like an NHRA Pro Stocker? Even better.