72-2 Toothed Wheel

Patriq · Post by **Patriq** » Fri Sep 07, 2007 11:08 am

[quote="aarc240"]

More precisely, the sensor mounted in the distributor will be positioned at half the usual angle BUT ....
you would check the true firing point against a reference pointer and a degree wheel (or tape) on the nose of the crankshaft.

quote]

That's a good idea. I didn't think of that first.That's off course how I'll do it.
Only problem - my crankshaft doesn't have any markings what so ever. I've checked many times.
But I'll sort that out.

alexander · Post by **alexander** » Sat Jan 19, 2008 12:18 pm

hi, just adding to this older thread, i have fitted a 72-2 wheel in the case of the old distributor. the wheel is a slice of gearstock which is 36mm in daimeter. the teeth are 1mm thick, separated by <1mm, and the valley between them is <1mm deep. i used a vr sensor from a 90s mazda rx7 crank angle sensor.

the car is up an running today. it certainly revs out high enough, but i have not put that to any rigorous test. still having an issue with missing under acceleration, which could in theory be to do with poor signal quality due the tiny teeth. i have, however, only driven the newly fitted car about 4km. these parts were suggested to me by someone who had successfully used exactly the same parts.

so, bottom line.. yes 72-2 wheels in the dizzy can be done, and they can be very small indeed.

regards
alexander.

Patriq · Post by **Patriq** » Sat Jan 19, 2008 10:04 pm

That's good news !

I'm not having much time at the moment to work on the car. Babies and family taking time, and all that....

But... since last I tried to manufacture the trigger wheel myself. It is 90mm in diameter. I gave up because of poor tools and teeth varying too much in size and position when I tried.
But a collegue at work has a friend that works as a watchmaker. And he has now been put to the task !
So I hope to have that part quite soon. Everything else has been installed in the car.

Patriq · Post by **Patriq** » Sun Mar 30, 2008 2:50 pm

Just to follow up on the thread. Here are some images of the converted dizzy.

alexander · Post by **alexander** » Mon Mar 31, 2008 12:14 am

nice work, patriq!,
just watch your fingers when you hand is in the engine bay - it might be a good safety precaution to add a cover over the wheel (realising of course that you may have already done so...)

it is a neat solution, particularly, in that it uses the stock vr sensor, which comes almost for free with the used EDIS units. i note that www.trigger-wheels.com sell wheels down to 2.5" diameter. for the benefit of those reading this thread regarding their future project, i suspect you can go even smaller than 2.5" and still use the ford vr sensor. that would usually allow a distributor to be converted and still have the moving parts hidden under the cap. you can then cut the top off the cap, and glue in a flat piece of acrylic sheet so you can see in, and amaze your friends

.

anyhow, those are all just some additional thoughts, and not to take away from your very neat work, patriq. well done, and great to see people being inventive when the need presents itself.

regards
alexander.

Patriq · Post by **Patriq** » Mon Mar 31, 2008 8:40 am

alexander wrote:nice work, patriq!,
just watch your fingers when you hand is in the engine bay - it might be a good safety precaution to add a cover over the wheel (realising of course that you may have already done so...)

it is a neat solution, particularly, in that it uses the stock vr sensor, which comes almost for free with the used EDIS units. i note that www.trigger-wheels.com sell wheels down to 2.5" diameter. for the benefit of those reading this thread regarding their future project, i suspect you can go even smaller than 2.5" and still use the ford vr sensor. that would usually allow a distributor to be converted and still have the moving parts hidden under the cap. you can then cut the top off the cap, and glue in a flat piece of acrylic sheet so you can see in, and amaze your friends .

anyhow, those are all just some additional thoughts, and not to take away from your very neat work, patriq. well done, and great to see people being inventive when the need presents itself.

regards
alexander.

Thanks !

Yes, the thought has crossed my mind about a cover. Haven't really done anything about it yet. (Haven't had spark yet either....)
I was in contact with trigger-wheels.com, to see if they would manufacture a 72-2 wheel. But it was to expensive for them to do.
This wheel was done by an enginer who manufactures parts for helicopters. So you could say he had the tools for the job !

Your solution with the smaller wheel - I would rather have done that. But when I had mine done, I wasn't sure that the size of such a small wheel and small teeth would work with the sensor. But were I to do it again - I think I'd gone your route.
(or maybe an upgrade of this dizzy later.....)

Dean924s · Post by **Dean924s** » Sun Nov 09, 2008 5:46 pm

Patriq wrote:Bump !

Does anyone know ?

'But - since the wheel is 72-2 toothed. Should the sensor be mounted at half the degree BTDC that you would have on a 36-1 wheel ? Since 1 revolution of the distributor axis equals 2 revolutions on the crank.'

I am going to try to reason my way through this question.

My first thought (as others had implied) was that you would decrees the offset of the sensor. However, after thinking about this further, I think that offset angle and tooth count are getting confused here.

I believe the answer to this is: If you are using a 72-2 wheel you would mount/align the sensor using the offset as determined by a tooth count. Setting it by the # of teeth depending on the EDIS unit / cylinders you are using. (As per the installation instructions here on this site).

Now to clarify / confuse things

By setting it up as I have just said you ARE actually reducing the angle/offset from the missing tooth by fifty per cent. This is due to there being 2x the teeth on a 72-2 wheel (each tooth is at 5 deg) as opposed to 10 degree on a 36-1. So on a 72-2 wheel you are only mounting the sensor at half the offset from the missing tooth had you mounted a 36-1.

Lets use a EDIS 8 set up as an example as the offset is 5 teeth making the math very simple

With a 72-2 if you offset by 5 teeth (each equal to 5 deg) the total offset is 25 deg on the cam but because it moves at half the crank speed it is equal to 50 deg of crank movement. and since one revolution of a 72-2 wheel mimics two revolutions of a 36-1 you have to mount the sensor by the tooth count not the off set angle.

So the answer to the original question is "technically" yes. You are actually mounting the sensor at half the offset angle as compared to the same mounting at the crank but this is not really how you determine the mounting location. It is the tooth count that offsets the sensor and determines the mounting location.

So have I confused you yet ?

Dave Pruit · Post by **Dave Pruit** » Fri Jan 16, 2009 5:40 pm

Hi I am new here but has anyone tried running two ignition system on one megajolt lit jr. I have a lycoming 0540 on an airboat with dual mags. Would like to run dual ignition with map sensor, will the megajolt provide input on saw to both edis systems.

alexander · Post by **alexander** » Fri Jan 16, 2009 11:38 pm

hi dave, i dont have the answer to that question, but may i suggest you ask the question in a new thread in the Q&A section? just because it can be a bit confusing to the history of threads if an old one is reactivated into essentially a new topic.

regards
alexander.

Dean924s · Post by **Dean924s** » Sun Apr 19, 2009 3:23 pm

my cam fired porsche with a 72-2 wheel. What I learned was that the width of the wheel has to be wider than the pickup on the sensor. The diameter and tooth size can be very small.

http://www.autosportlabs.org/viewtopic. ... 6&start=90