72-2 Toothed Wheel

EDIS and Megajolt installation related topics. Be sure to review the <a href="http://www.autosportlabs.net/MJLJ_V4_vehicle_installation_guide">Vehicle installation guide</a>

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Nigel
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Joined: Mon Aug 08, 2005 9:40 pm

72-2 Toothed Wheel

Post by Nigel »

Hi

Now that my V3 MJLJ is working I'm taking another look at the toothed wheel.

I'm running a 2L Pinto which has very limited space to mount a 36-1 wheel on the crankshaft. The most accessible option would be to mount a 72-2 wheel on the oilpump/distributor take-off wheel (this wheel is the same size as the cam shaft wheel). This would also be more convenient position for mounting the sensor.

My question - has anyone tested a 72-2 wheel? What diameter wheel did you use?

The only potential problem that I can see is that for a 140mm diameter wheel the tooth and gap size will be half of that of a 36-1 wheel with the same diameter. On a 140mm 72-2 wheel the pitch of the teeth would be 140*PI/72 = 6.11mm so each tooth would only be 3.055mm and the gap between teeth would be the same. Is this big enough? The sensor (although inductive) must have a "focus spot" so at some point when the teeth become small enough it would see a tooth and a gap at the same time, so would only ever see the average of a tooth and gap.

Asking what the smallest diameter wheel is that you can use with a 36-1 wheel is would also answer the same question.

Your comments and suggestions would be much appreciated.

Thanks
Nigel

Oliver Sedlacek
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Location: The Chalfonts
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Tooth size

Post by Oliver Sedlacek »

I'm using a 36-1 wheel with a 90 mm diameter (approx), so the tooth size isn't that far off. If you check out my photos at http://community.webshots.com/album/187745001srPbmU you can see that the VR signal is still pretty big.

Patriq
Posts: 161
Joined: Sat May 26, 2007 12:56 pm
Location: Oslo, Norway

Post by Patriq »

I'm thinking the same. I'm having no where to mount the sensor - and no pulleys seems to be able to fit the trigger wheel too.
So, I thought I could just as well use a distributor I have that is faulty.

So, can one make the trigger wheel smaller than 90mm diameter as mentioned here ? Or would one get trouble with the pickup area on the sensor being too large so that the teeth overlap when passing the sensor? 90mm seems abit large on top of the distributor that I would rebuild.

And, does one really use 72-2 toothed wheel ? Doesn't the distributor make one revolution when the engine makes one revolution ? And hence the engine makes two revoultions in one cycle - same with the distributor? Or am I wrong here?
Last edited by Patriq on Mon May 28, 2007 9:09 am, edited 1 time in total.

MartinM
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Joined: Sat Aug 27, 2005 12:08 pm

Post by MartinM »

Distributors rotate at half engine rpm so you need a wheel which is 35-gap-35-gap to fool the EDIS into thinking it is measuring engine revolutions

(a special 72-2 wheel, as being discussed here, should not be confused with a 60-2 Vauxhall trigger wheel which is 58-gap-gap i.e. the gaps are together)

brentp
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Post by brentp »

You'll need to meet the requirements of the EDIS module- that means 36-1 on the crank, or 72-2 on the distributor shaft.

In principal it should work fine- the only thing is in a small space you may not generate a signal with enough voltage to satisfy the EDIS module. An amplifier could help, or; you could go with an optical wheel with the necessary circuit to feed the EDIS module.

So, Patriq, would you like to take on this challenge? :)
Brent Picasso
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Patriq
Posts: 161
Joined: Sat May 26, 2007 12:56 pm
Location: Oslo, Norway

Post by Patriq »

Sure !

Is it easy to source an optical wheel and sensor ? My distributor has a 4 toothed wheel which is treaded down on the axel. The centerhole of the wheel has a "star" shaped hole with many teeth. I was thinking I would have made a trigger wheel with a centerhole that would fit this shape. It would then stay firmly in place, and at the same time be easily adjusted - and at the same time the whole thing could be adjusted as when timing the ignition with an ordinary set up.

Is the problem with a small wheel that the circumference is so small that the distance between the teeth is so small that the voltage never manages to rise high enough? Maybe an amplifier could work just as well then?

And I see that I would need a 72-2 wheel with the two gaps at 180 dgs from each other on the wheel. I thought wrong about the relationship between the rotation of the distributor and the crank.

MartinM
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Joined: Sat Aug 27, 2005 12:08 pm

Post by MartinM »

Sourcing an optical wheel - almost certainly not, you will have to make one yourself :(

Sourcing an optical sensor - sounds like you may have one already? If not, they're reasonably easy to get hold of - how experienced are you in purchasing electronic components? You probably need one something like the ones on
http://www.mouser.com/catalog/630/1552.pdf
- but preferably a 'C' shape one so that it can be base-mounted and your wheel can pass through the middle. I know you can get them, but I can't find one quickly.

Will it work - probably, but you will need some electronics knowledge, an interface circuit and probably need to prototype it outside the car first with just an EDIS module and a coilpack. The electronics problem is that you are replacing the passive VR sensor (ie ferrous metal passes in front of it and it generates a voltage) with an optical switch that has to be powered and then send the switched signal to the EDIS down the same two VR sensor wires. The EDIS VR sensor processing expects an ac voltage with a 'kink' in it at the missing tooth - see
http://www.bgsoflex.com/mjl/mjl_edis_summary.html
and you need to turn your on-off output from the optical sensor into something close enough for the EDIS to think it's processing a VR sensor ouput.

You may have to slightly negatively bias your switched output so that the EDIS sees the -ve to +ve voltage transitions

If you haven't a clue what I'm talking about, then it might all be a challenge too far. If not, I'd say go for it - this would be a great addition to the MJLJ capability and I know of a number of people that would love a MJLJ but need this facility to make it feasible.

I'm sure you'll get a lot of help here if you try - there are some good electronic circuit designers here

Let us know if you're going to take this on :D

EDIT: Will an optical circuit be fast enough - definitely. You could probably (not done the calculations) sense tens of thousands of distributor rpm 8)

Patriq
Posts: 161
Joined: Sat May 26, 2007 12:56 pm
Location: Oslo, Norway

Post by Patriq »

I'm partly with you on the details. I'm an architect, but I've done my part of reading on the subject. I've built a MSII with ignition for another of my cars.
I also have a friend who is an electrician whom I bug when I get stuck.

First hand, I'm going to try to use an ordinary wheel with the default VR-sensor. I've been measuring - and I might be able to use a 90mm wheel on the distributor. I only need to manufacture it. But if it doesn't work out - I'll either try the amplifier or the optical wheel. I always like a good challenge!
But if it is not necessary, I'll off course not do it more difficult for myself than I need to.

Cheers !

capri_turbo
Posts: 122
Joined: Tue Jan 10, 2006 8:17 pm
Location: North Yorkshire, UK

Post by capri_turbo »

pinto install is easy using a 36-1 from a Sierra CVH and an alloy bracket for the VR sensor.

Here's mine on my Capri:

Image

Image

Image

Patriq
Posts: 161
Joined: Sat May 26, 2007 12:56 pm
Location: Oslo, Norway

Post by Patriq »

Yes,

unfortunately - there is not enough metal to either weld or screw a wheel on my pulley......
All those who believe in telekinesis, raise my hand now !

capri_turbo
Posts: 122
Joined: Tue Jan 10, 2006 8:17 pm
Location: North Yorkshire, UK

Post by capri_turbo »

ah, you must have the pressed pulley rather than the cast one. Could you not swap the pulley for the meatier cast one as above?

aarc240
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Joined: Mon Dec 18, 2006 10:54 am
Location: Mid North South Australia

Post by aarc240 »

Only go for 'in the distributor' if there is absolutely NO way to get the 36-1 onto the crankshaft.
If you are really stuck on the nose of the motor, consider a drilled or milled flywheel to simulate the arrangement Ford used on some 4 cylinder motors.

I have tried a 'drilled' flywheel where we put 35 holes each 12.7mm diameter and 6mm deep in the rear of it (each on the usual 10 degree spacing with effectively one missing hole).
Provided the VR sensor was accurately aligned with that ring of holes it worked perfectly.
As an added bonus it lightened the flywheel too!

One of the main reasons for going to crank trigger is to eliminate the spark scatter caused by backlash in the gears etc driving the distributor.
Don't throw that advantage away unless there is NO other solution.

Patriq
Posts: 161
Joined: Sat May 26, 2007 12:56 pm
Location: Oslo, Norway

Post by Patriq »

aarc240 wrote:Only go for 'in the distributor' if there is absolutely NO way to get the 36-1 onto the crankshaft.
If you are really stuck on the nose of the motor, consider a drilled or milled flywheel to simulate the arrangement Ford used on some 4 cylinder motors.

I have tried a 'drilled' flywheel where we put 35 holes each 12.7mm diameter and 6mm deep in the rear of it (each on the usual 10 degree spacing with effectively one missing hole).
Provided the VR sensor was accurately aligned with that ring of holes it worked perfectly.
As an added bonus it lightened the flywheel too!

One of the main reasons for going to crank trigger is to eliminate the spark scatter caused by backlash in the gears etc driving the distributor.
Don't throw that advantage away unless there is NO other solution.
Well. My existing crank pulley is in cast iron. I don't belive welding will be a good option. I don't think I'll get it hot enough, or precise enough. There is no metal what so ever to screw a toothed wheel on and into. The flange is to thin - and further towards the center of the pulley it is in profile so much drawn back that the distance from the toothed wheel - if mounted - would be to long - and bolts would be so close toghether because the radius is so small. So I don't think it would be stable enough.

I have thought about cutting teeth directly on to the flange of the pulley - but then I would have the belt running almost free, because of the shape of the wheel. Also the flange is as I mentioned too thin.

I'm now in the process of manufacturing a 72-2 toothed wheel for my distributor and a bracket for fastnening the sensor to it as well. I think and hope this will work out fine. This way I can also finetune the positioning of the sensor in regards to TDC - like you would with a distributor.

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.
All those who believe in telekinesis, raise my hand now !

Patriq
Posts: 161
Joined: Sat May 26, 2007 12:56 pm
Location: Oslo, Norway

Post by Patriq »

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.'
All those who believe in telekinesis, raise my hand now !

aarc240
Posts: 65
Joined: Mon Dec 18, 2006 10:54 am
Location: Mid North South Australia

Post by aarc240 »

Depends on where you are referencing the BTDC angle :)

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.

When checking at the crank the degrees BTDC will be exactly as for a 'normally' mounted wheel and sensor.

Think it through - if the crank rotates twice for one revolution of the distributor (or cam) then there is going to be twice the angular deflection at the crank as there is at the distributor for any given movement.

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