Technical Zelmot distributor advance

[smart51]

I have a Zelmot distributor on my car. It has points but no rotor arm and uses a twin coil to make sparks for each cylinder.

I've recently bought a strobe to check the timing. The static timing is right and it starts to advance if you blip the throttle. But if you sustain revs above about 2500, the timing seems to go back to 10 degrees. It could be that the cheap strobe can't do high advance on 2 cylinder engines.

Today I had the bright idea of running the engine with the distributor cap removed and shining the strobe on the insides. The return spring for the weight stays in the same place so using the strobe seems like a valid test. Off idle, the spring moves a bit but goes no further as the revs advance. It doesn't seem to stretch at all. Do you think I'm right in diagnosing that as it not advancing properly?

 

[bugsymike]

I have a Zelmot distributor on my car. It has points but no rotor arm and uses a twin coil to make sparks for each cylinder.

I've recently bought a strobe to check the timing. The static timing is right and it starts to advance if you blip the throttle. But if you sustain revs above about 2500, the timing seems to go back to 10 degrees. It could be that the cheap strobe can't do high advance on 2 cylinder engines.

Today I had the bright idea of running the engine with the distributor cap removed and shining the strobe on the insides. The return spring for the weight stays in the same place so using the strobe seems like a valid test. Off idle, the spring moves a bit but goes no further as the revs advance. It doesn't seem to stretch at all. Do you think I'm right in diagnosing that as it not advancing properly?

It's probably well worth checking and oiling the advance and retard mechanism, note on some they have different strength and length springs so on some can look slack a little. With the points plate removed you should be able to see the bob weights and springs so if you turn the rotor a little you should be able to see if it moves all the way. I am assuming your electronic system doesn't control advance electronically?
In the old days we always ran a little engine oil down the centre spindle under the rotor arm, this lubed the shaft as some seize there.
I assume yours doesn't have vacuum advance as well, the reason I ask is that the affect of appearing to back off the advance slightly can be caused by a change in vacuum, but probably not applicable.
I would have thought the strobe would react to the spark impulse regardless of price. The fancy strobes can alter spark advance on timing mark checking, but personally I prefer the basic version.
Incidentally if you have timed it statically, it is not unusual to see the advance a little further on at idle.
So does this system use the points to trigger the twin spark system using the wasted spark principle, if so it does seem a slightly convoluted idea, neither one thing or another.
Perhaps another Forum member can tell me the advantages of this set up, as if you are still using the points and condensor, is it just a fatter spark and possible cleaner exhaust due to the wasted spark on the opposite cylinder to the one on the power stroke?

 

[smart51]

It's probably well worth checking and oiling the advance and retard mechanism, note on some they have different strength and length springs so on some can look slack a little. With the points plate removed you should be able to see the bob weights and springs so if you turn the rotor a little you should be able to see if it moves all the way. I am assuming your electronic system doesn't control advance electronically?
In the old days we always ran a little engine oil down the centre spindle under the rotor arm, this lubed the shaft as some seize there.
I assume yours doesn't have vacuum advance as well, the reason I ask is that the affect of appearing to back off the advance slightly can be caused by a change in vacuum, but probably not applicable.
I would have thought the strobe would react to the spark impulse regardless of price. The fancy strobes can alter spark advance on timing mark checking, but personally I prefer the basic version.
Incidentally if you have timed it statically, it is not unusual to see the advance a little further on at idle.
So does this system use the points to trigger the twin spark system using the wasted spark principle, if so it does seem a slightly convoluted idea, neither one thing or another.
Perhaps another Forum member can tell me the advantages of this set up, as if you are still using the points and condensor, is it just a fatter spark and possible cleaner exhaust due to the wasted spark on the opposite cylinder to the one on the power stroke?

The Zelmot is all mechanical, there are no electronics. There's no vacuum advance either. The distributor housing has the centrifugal advance mechanism and points, but with no rotor arm above. The HT leads go direct from the coil to the spark plugs. All it does is replace a single coil and a rotor arm that distributes the HT with a twin coil and no rotor. I guess it is one fewer part to wear out and go wrong.

I think it's worth taking it apart, cleaning it and oiling it. Maybe it is sticking a bit.

 

[bugsymike]

Thanks for that. My thoughts were that in the old days as an apprentice etc. it was points and condensors that I frequently had to change rather than distributor caps and rotor arms, but I suppose it removes some potential troubles.
Have you found any differences/benefits from a standard set up, just curious?

 

[smart51]

Thanks for that. My thoughts were that in the old days as an apprentice etc. it was points and condensors that I frequently had to change rather than distributor caps and rotor arms, but I suppose it removes some potential troubles.
Have you found any differences/benefits from a standard set up, just curious?

It was fitted to the car when I bought it. I can see why Fiat would change it in production, it's bound to be a bit cheaper. I'm not sure I'd have gone to the trouble of swapping it out unless the old one broke. Now if the contacts were replaced with a transistor, that would seem worth it.

 

[the hobbler]

It was fitted to the car when I bought it. I can see why Fiat would change it in production, it's bound to be a bit cheaper. I'm not sure I'd have gone to the trouble of swapping it out unless the old one broke. Now if the contacts were replaced with a transistor, that would seem worth it.

I have been looking into just such a system, only with no 'base-line' to go from I had to source what I thought would be a suitable coil--I used a coil designed for classic 2-cylinder motor-bikes (Norton, Triumph, BSA etc) and for use with points. Just for interest, what coil are you using on your set-up?

 

[smart51]

I have been looking into just such a system, only with no 'base-line' to go from I had to source what I thought would be a suitable coil--I used a coil designed for classic 2-cylinder motor-bikes (Norton, Triumph, BSA etc) and for use with points. Just for interest, what coil are you using on your set-up?

One of these

 

[the hobbler]

View attachment 428213
One of these

Thank you for that information---appreciated. Would I be correct in thinking that as you are using 'points', you are still fitting a condensor into the system?

 

[smart51]

Thank you for that information---appreciated. Would I be correct in thinking that as you are using 'points', you are still fitting a condensor into the system?

Yes, that's right. For all the world, it looks like a standard distributor with the rotor taken off and a flat blanking plate instead of the cap.

 

[the hobbler]

Yes, that's right. For all the world, it looks like a standard distributor with the rotor taken off and a flat blanking plate instead of the cap.

View attachment 428214

View attachment 428215

Thank you for that info---much appreciated. As a little piece of (hopefully) useful information, I have found a source of WELL made condensers in the UK. The company is "Distrubutor Doctor" and their '484249' condenser, with a bit of tweaking of its 'long' mounting bracket, fits the Fiat distributor very well. Yes,it is a bit more expensive than the current 'pattern' condensors, but it will last a LOT longer.

 

[bugsymike]

Do any of the "old school " mechanics agree with me after looking at the inside of the distributor, that when you check the advance and retard mechanism as you mentioned, it could benefit from a clean and lubrication, especially around the cam area which looks devoid of high melting point grease, this can result in rapid wear of the fibre heel that opens the points causing the gap to close, at least retarding the timing slightly and at worst a breakdown.
Also the bush in the moving contacts pivot point appears to be worn off centre, so could benefit from a new set of contact points and HMP grease on the pivot there also.
The reason I mention the cam side is I have seen where not lubricated the cam has actually worn down, on one or all the lobes, resulting in varying point gaps on different lobs. For some reason very common on earlier Mazda.
I don't claim to know much , but having fitted literally thousands of contact points when servicing vehicles since 1969 until the advent of electronic ignition, I always had the expectation that any car I serviced would still be running well when next due for a service.
Another thing always done was a few drops of engine oil on the little sponge in the centre below where the rotor normally fits, along with checking that it can be moved along with the advance mechanism, usually by working the rotor arm.
All this and much more whilst labour intensive is what kept cars of the past going reliably, modern cars are much more forgiving for longer, it's just when they do die it usually involves a recovery vehicle and a much bigger bill.

 

[fiat500]

Do any of the "old school " mechanics agree with me after looking at the inside of the distributor, that when you check the advance and retard mechanism as you mentioned, it could benefit from a clean and lubrication, especially around the cam area which looks devoid of high melting point grease, this can result in rapid wear of the fibre heel that opens the points causing the gap to close, at least retarding the timing slightly and at worst a breakdown.
Also the bush in the moving contacts pivot point appears to be worn off centre, so could benefit from a new set of contact points and HMP grease on the pivot there also.
The reason I mention the cam side is I have seen where not lubricated the cam has actually worn down, on one or all the lobes, resulting in varying point gaps on different lobs. For some reason very common on earlier Mazda.
I don't claim to know much , but having fitted literally thousands of contact points when servicing vehicles since 1969 until the advent of electronic ignition, I always had the expectation that any car I serviced would still be running well when next due for a service.
Another thing always done was a few drops of engine oil on the little sponge in the centre below where the rotor normally fits, along with checking that it can be moved along with the advance mechanism, usually by working the rotor arm.
All this and much more whilst labour intensive is what kept cars of the past going reliably, modern cars are much more forging for longer, it's just when they do die it usually involves a recovery vehicle and a much bigger bill.

I can't claim to see as much as you have noted about that distributor, but I will echo that it is very important to have smooth movement of the overlooked, internal, mechanical parts of the distributor. I have found distributors that looked OK from above, but where the weights were were seized on their pivot;. occasionally you find a missing or broken advance-weight spring.

When you have a distributor in good order, with (ideally) genuine replacement wearing parts, and where all is well lubricated, it can make a big difference to your confidence in the machine that you're driving and into the smoothness of the engine.

 

[smart51]

Can you double check a couple of things for me please. The arrow on the oil pump case is TDC, the line to the left of it is 10 Degrees before TDC and that the red line on the pulley being in line with that line means my timing is set correctly.

Also, is the red line bouncing around so much normal or abnormal? I thought it might be a little more steady.

The timing strobe is set to 0 degrees. When set to 10 degrees, the red line is closer to the arrow.

 

[fiat500]

Can you double check a couple of things for me please. The arrow on the oil pump case is TDC, the line to the left of it is 10 Degrees before TDC and that the red line on the pulley being in line with that line means my timing is set correctly.

Also, is the red line bouncing around so much normal or abnormal? I thought it might be a little more steady.

The timing strobe is set to 0 degrees. When set to 10 degrees, the red line is closer to the arrow.

View attachment 428220

I have useless internet and these embedded videos play badly for me.
You have two ways of doing this and it can be confused by the fact that some timing-cases have additional factory timing marks.
The factory line on the pulley being aligned with a line approximately 13mm to the left of the arrow mark is 10 BTDC and with the engine stationary you should loosen and rotate the distributor so that the points are just opening at this point.
I find this easier to understand if instead, you make a mark on the pulley that is 13mm to the right of the factory TDC alignment mark. In that case, you turn the engine until this new mark aligns with TDC and adjust the distributor.
There is no point testing this with the strobe because once the engine is underway the timing automatically starts to advance and the marks won't necessarily align.

To use the strobe,you need to check that you get full centrifugal advance at high RPM; there is an actual range at which you test this, but I just go for "quite fast"

The standard, maximum advance is 28 BTDC, which I think equates to 36mm to the left of the arrow on the crankcase or to the right of the factory TDC mark on the pulley. The 28 degrees is total advance and therefore includes your existing 10 degrees or the 13mm measurement.
Depending on which way you approach it, what you are looking for is that your new, 28 degree mark, painted white, should align with either the TDC mark on the pulley or with the TDC arrow on the timing case. You carefully tweak the slightly loosened distributor one way or the other to get the marks spot-on; they may falter a little, but not very much at that speed.

Any adjustment will put the original static-timing out, but unless it is by a serious amount (in which case the distributor needs looking at), this is not a problem.

 

[Goldnrust]

The bounce might be because the distributer is just about to start advancing and so the actual timing firing is dancing a little. If this were the case then you'd expect a more stable reading at a slightly lower idle speed.

It's also possible that as you're running a wasted spark set up, your timing light will be firing for both cylinder 1 & 2. If the points cam is worn or a little off centre (mine was, but I've no idea if this is common) then the timing might be slight different on each side of the cam which might account for your bounce.

Either way, while things to look into, that bounce is not enough to be causing the kind of issues you've mentioned you're chasing.

From your video the timing looks ball-park correct at idle, it's hard to see the exact sight lines on video but close enough that you'd not expect any problems. It also makes sense when you say that turning your timing light to 10 degrees aligned the red line with the arrow, and suggests the advance feature of your timing light is working correctly.

As @fiat500 mentions, you would expect to see 28 degrees advance at high RPM if your distributer is working correctly. So if you set the timing light to 28 degrees you'd expect to see the red line come in to line up with the arrow when you rev the engine hard.

If that's not the case then I suspect you might need to strip the distributer down and give it all a nice clean up and oil / grease as the advance mechanism might be sticking/

 

[fiat500]

There bounce might be because the distributer is just about ot start advancing and so the actual timing firing is dancing a little. If this were the case then you'd expect a more stable reading at a slightly lower idle speed.

It's also possible that as you're running a wasted spark set up, your timing light will be firing for both cylinder 1 & 2. If the points cam is worn or a little off centre (mine was, but I've no idea if this is common) then the timing might be slight different on each side of the cam which might account for your bounce.

Either way, while things to look into, that bounce is not enough to be causing the kind of issues you've mentioned you're chasing.

From your video the timing looks ball-park correct at idle. it's hard to see the exact sight lines on video. It also makes sense when you say that turning your timing light to 10 degrees aligned the red line with the arrow, and suggests the advance feature of your timing light is working correctly.

As @fiat500 mentions, you would expect to see 28 degrees advance at high RPM if your distributer is working correctly. So if you set the timing light to 28 degrees you'd expect to see the red line come in to line up with the arrow when you rev the engine hard.

If that's not the case then I suspect you might need to strip the distributer down and give it all a nice clean up and oil / grease as the advance mechanism might be sticking/

I just notice that I'm talking rubbish as regards points and setting this up; as you say, it's a wasted spark with no points. Your assessment is good.

 

[smart51]

I drove to the end of my street and back timed as shown on the video. It was terrible. Massively down on power and just wouldn't rev beyond half way. I've timed it up against the other mark, so 10 degrees more advanced. It will now rev now but it is very rough. I'm confused. Which is the correct timing mark on the 594 cc engine?

I had stripped the distributor yesterday to inspect the movement of the weights. They move freely if you grip the gear at the bottom and turn the shaft at the top.

 

[fiat500]

As a rough check, l

I drove to the end of my street and back timed as shown on the video. It was terrible. Massively down on power and just wouldn't rev beyond half way. I've timed it up against the other mark, so 10 degrees more advanced. It will now rev now but it is very rough. I'm confused. Which is the correct timing mark on the 594 cc engine?

I had stripped the distributor yesterday to inspect the movement of the weights. They move freely if you grip the gear at the bottom and turn the shaft at the top.

As a rough check, loosen the distributor so that it still has a bit of "gription", rev the engine fairly high whilst strobing and turn the distributor slightly anti-clockwise and see if the pulley mark retreats to the left. When high in the rev-range it wants to be approximately 23mm to the left of that 10 degree BTDC mark on the case or 36mm from the arrow on the case.

 

[Goldnrust]

Dare we mention the C word? Condensers seem to be a common source of random ignition related weirdness and loss of power that goes with it? As discussed in various threads recently, even if a new one has been recently fitted it's no guarantee of reliability.

You could run the car with the distributer cap off, and look for any sparking at the points. If there's a lights show in there, its a sure sign the condenser is at fault.

 

[smart51]

You could run the car with the distributer cap off, and look for any sparking at the points. If there's a lights show in there, its a sure sign the condenser is at fafault.

Yes, yes there is. One more thing on the shopping list.