LCGB Forums

Hi All,

I hope someone can help. On early and late LD models. Can someone tell me the Ohms reading expected from the stator coils please?

I'm trying to run some tests on determining if I have a faulty stator / coil and have conflicted information I have found online and as follows:

HT ignition coil on the stator is either around or just under 400 Ohms or between 400 - 500 Ohms?
Lights and electrics coil on the stator should be close to 90 - or between 100 to 120 Ohms?

Also,
1) When testing the HT coil on the stator, is it best to un-solder / disconnect the condensor prior to testing, or test from the condensor lead?
2) If readings are higher or lower than they should be (Which I understand that higher or infinite resistance suggests a break in either wire or a damaged low-tension coil & lower figure suggests either a trapped wire or a damaged low-tension coil), excluding checking the areas mentions in comma's, sourcing a new or second hand coil, or upgraded to a varitronic system, are there any other recommendations on repairing?

Thanks for your help.

There are no official specs for the coils. There are a series of test though. What exactly is your issue?

Hi,

Thanks for getting back to me. That would make sense given the readings I have from three other LD's. I have tested four engines so far. Two stripped / two not stripped and working.

This particular LD has no spark. I have found a number of issues in and around the stator and wires and currently have it in bits. Note: Spark Plug OK / HT Lead OK / Points dirty and marked but OK and will be replaced during rebuild of stator

Stator plate and coils in general are very dirty in and around the area and the cables (in this case Green / Red / Yellow) were very loose and fell off in some instances and will be replaced and re-soldered where applicable.

I suspect after I have cleaned it and replaced the cables that all will kick start OK. However, the readings from the stator plates coils are confusing, based on what I have read online and I am trying to understand if I have an ignition coil on its way out. My coil for the lights seem to be fine and readings seem to be within acceptable parameters. However, my primary coil readings are confusing me and I can’t find anything online, or in my various manuals about what it should be. I think what I have found online may be referring to later Lambrettas and not 1950 to 1958 models (/ without battery).

At some stage over the coming month’s, I intend to rebuild a primary HT ignition coil on one of the LDs, for the experience and need a base line of what readings I should expect at the end of the rebuild.

Summary of where I am on four of my LD’s:

Condensor Testing:
I can see that my Filso condenser holds a charge as follows:

Multi meter set at 20uf shows a new condenser registers 31uf and the old one as 35uf. The old one is therefore within acceptable parameters.

Ensuring that the condensor is discharged, when I recharge with a multi meter, I can see it holds it charge. When I drain it with a multi meter, the new condensor releases all of its charge fairly fast. However, I can see that the old condensor releases most of its charge very quickly and then slows down on releasing its charge. I’m not sure if this is a problem, so I am trying to figure out if this is a general problem with the condensor. I know I can just replace it for £7. However, that defeats me understanding if I have a problem in this area. Finding information on how a Filso Condensor (Or Marelli) works in regards to discharging has proved difficult at the moment and in particular, if a slow discharge towards the end of the discharge is acceptable. In theory, the condensor is releasing most of it's charge, so it should being doing it's job OK!

Stator Coils Testing:

Note: For Stator 1 and Stator 2 testing, I have by passed (un-soldered) the cable on the condensor and tested from the point that the cable is soldered onto the coil (After the cable fell off with the slightest touch!). My coil readings on four LD’s have a base line of:

Stator 1 (This is the one I have stripped apart)
• Primary HT Ignition Coil – 145 ohms
• Lighting Coil – 110 ohms

Stator 2 (This is another that is stripped apart and in my opinion, seems not to have enough copper wrapped around the ignition HT and will be stripped in the coming months. It is unknown if it works at present and will be tested on an LD prior to rebuilding the HT part of the coil. Looking at the ignition coil, it looks like someone may have already tried to build a new coil and not put enough wire around it)
• Primary HT Ignition Coil – 60 ohms
• Lighting Coil – 85 ohms

Stator 3 Working Engine
• Primary HT Ignition Coil – 110 ohms (Reading from exterior Green cable – not taken apart)
• Lighting Coil – 40 ohms (Reading from exterior Red cable – not taken apart)

Stator 4 Working Engine
• Primary HT Ignition Coil – 90 ohms (Reading from exterior Green cable only – not taken apart)
• Lighting Coil – 65 ohms (Reading from exterior Red cable – not taken apart)

Summary:
I’m trying to fault diagnose a condensor that slowly releases it charge (Is this a problem and if so why?) &

I,m trying to establish if there is a base line of any kind for LD's in regards to Ohms readings, that can be used for testing the HT Coil and Electrics Coil in a magneto ignition system environment. Then if it falls outside these parameters, I know I have a coil breakdown and can review further.

Any help gratefully received and of course, thanks for reading..............

John
LambrettaJourney.co.uk

Condensers need to be tested under very high voltages. Your multimeter puts out hardly anything. Haven't seen a condenser tester for many years. Had one in the first shop I worked in. Standard trick was to charge up a condenser and toss it to someone saying "catch". The shock delivered was quite pronounced! Generally the condenser is the first thing you change if there is any problems. It's cheap and, frankly, fails moderately often. By all means fix all the bad connections as well.

Testing involves seeing how far the spark will jump. The following is the the magneto ignition section from "The Lambretta Serviceman's Book":

https://jbcollier.smugmug.com/Scooter/i-NNhhrF7/A

https://jbcollier.smugmug.com/Scooter/i-CtJNqcJ/A

https://jbcollier.smugmug.com/Scooter/i-gdBnBKv/A

https://jbcollier.smugmug.com/Scooter/i-TjKgPvG/A

https://jbcollier.smugmug.com/Scooter/i-TKqTvRG/A

https://jbcollier.smugmug.com/Scooter/i-sZmWJG5/A

https://jbcollier.smugmug.com/Scooter/i-MnkLgPM/A

The position of the flywheel when the points open is very important. Once had a scoot with a very weak spark. By adjusting the stator position and point gap was able to get a nice fat spark that would jump 3x the gap.

Thanks for the info and snippet out of the service manual. I appreciate your time uploading them. I have a number of service manuals including the TLSB, but none of them have the detailed information I am after.

What I would like to do is create a base line for testing the actual pole coils and condensor, if it is possible, to allow me to use and confirm if either a condensor or a stator coil is either failed or on it's way out.

My understanding so far from another member who has worked on many LI's is that the coil readings will vary from between 0.3-0.4 ohms for lights and the ignition will be no more than 1.1 ohms. As also pointed out by him, what I did not take into consideration with my testing was that the metre reading was not zero when I crossed the meter wires over, prior to testing on the coil. It was 0.49, which needed to be deducted from my reading of 1.45. If I take my 1.45 reading, deducting 0.49 gives me a reading of 0.96 Ohms, which means it falls into the same category as an LI. However, this then makes my running LD readings I have taken from the green wire outside the magneto casing much lower as well.

NB: There is also a You Tube clip I have found of someone rebuilding a 2 Pole stator on an old bike (Not a Lambretta) and the reading coming out as between 1.4 and 1.2 ohms.

I guess moving forward, I need to review all my LD's and start to create my own base line for readings in this area. Then when I think one has failed in the future, confirm what the old readings were and if they have changed, rebuild the coil to prove the coil had failed.

If anyone reading this has what they believe to be a failed LD 2 pole stator ignition or lighting coil, that they are happy to part with, please let me know. Maybe put it on ebay with a starting bid of £1+ postage and advertising it as a possible failed coil and I will buy it, if you can let me know it's on there. I will then test, rebuild and confirm results, which may or may not aid others in the future with their diagnosing suspected faulty stator 2 pole coils

Thanks for reading.

John
https://www.lambrettajourney.co.uk

Additional Sources: My sources for the information so far are as follows:

Ignition system testing, Magneto coils, Points and CDI
https://www.youtube.com/watch?v=uggJMnuexMc

Rewind a Primary Ignition Coil
https://www.youtube.com/watch?v=632U6YPChQA

How to Test Stators for Motorcycle, ATV, UTV, Snowmobile & Powersports Engines - Review from time 12.15 in the video
https://www.youtube.com/watch?v=0o_beRly9iE

Test a condenser:
https://www.youtube.com/watch?v=DRD94arK964

Standard car environment, with a coil and battery – Not an LD environment, but I thought this was a good general intro for an ignition system with coil and battery that I came across during my research.
https://www.youtube.com/watch?v=W94iksaQwUo

Generally it is difficult to test low-impedance coils with a multimeter. Because the readings are so low, minor connection issues make a huge difference and the reading variance between different meters is high. In the old days auto shops had testers that applied a high voltage across the coil/condenser so you could check for leakage. You can get old Heathkit C3 condenser testers off ebay that will do this. The tester itself will likely require an overhaul but there are how-to sites on the web.

Another way to test a low-impedance coil is BRIEFLY hook it up to a battery and measure the current flow. Any internal shorts will show up as a much higher amp reading. I used this method to test alternator stators. Works very well.

Thanks again for the advice and reply. Seems to be a challenge in this area for coils and condensors testing on LD's. I guess this is why there is no information in the books.

For the condensor, it appears I do need to bite the bullet and replace condensors, rather than relying on the basic tests I am doing.

For the coil testing, I will look at your advice further and also continue to play around on each of my LD's, as I strip them down, including re-reviewing the working ones I have and there current readings (if I can get a stable one from them), to see if I can produce some sort of base line. Reading your reply, I'm not expecting to. It may aid me further down the line though, if my readings suddenly change and I have ignition problems! It's a real shame there are no obvious meter tests I can do to test the stability of them with ease.

I'm still also going to throw it out there: If anyone reads this post and thinks they have a suspected damaged 2 pole coil (In particular the ignition one) and your happy to sell it, please consider putting it on ebay with a notice, "suspect damage" and let me know. I remain keen to review a damaged one further and rebuild it. At some stage, I will probably strip one of my working coils down for the experience of rebuilding it and review the readings before and after, out of curiosity.

All the best and thanks for reading and your contributions.............

John
http://www.lambrettajourney.co.uk

It's very rare for the ignition feed coil on an LD to be faulty - the wire is fairly thick, and unless there's visible damage to the outer layer or the soldered earth contact is poor, it's unlikely to be the source of the problem. I've never attempted to measure the coil resistance, but I would expect it to be less than one Ohm, based on the wire gauge used. (Feed coil problems are common on the GP electronic ignition setups, but those coils have many turns of very thin wire to produce around 200 volts to feed the CDI module.) What does tend to cause starting problems on the LD is that the flywheel magnets tend to lose some of their magnetism over time. This reduces the electrical output, which makes starting harder and reduces the light output from the headlight. If your flywheels are the later types with the spring-loaded auto advance mechanism, make sure that the advance mechanism hasn't seized up, and the return spring is working properly.

Thanks for the additional feed back and information.

For the flywheel magnets I action as follows:

Using a demagnetised metal ruler, on some of my flywheels, via each magnet, I am able to lift the flywheel off the work surface a little, before it drops off.

On some, due to the make of flywheel, this technique is not possible and I hold the flywheel upside down and using a reasonable sized demagnetised screw driver (Or metal object), I hold it on each of the magnets and let go to see if it stays in place.

I also try to gauge the strength by hand when pulling a metal object off each of the flywheel magnets.

Fortunately, I have enough LD’s to swap and change parts from one to the other, to test and see if I think a part is faulty before sourcing a replacement.

That aside, non of these techniques can tell me for certain the strength or if the magnets are failing.

If you have any other techniques you have used or know of, it would be great to know.

All the best - John

I know it doesn't help if you can't get the engine to run, but the usual way that a loss of magnetism was detected was when the headlight was not as bright as it should be, or if the engine tended to stall when the lights were switched on. It was quite common for the early flywheels to gradually lose some of the magnetism, and the Lambretta dealers at the time would keep service equipment to remagnetise flywheels. There's a few of these machines still in use in the UK, but I seem to remember that most were for the 6 pole Series 3 flywheels, or possibly for the Series 1/2 four pole flywheels, which have a different internal diameter from the Ld. Testing the magnets by seeing which flywheel can lift heavier lumps of iron or steel will give an indication of which flywheels are better than others, but even the best may be partially demagnetised!

Hi Steve J

Update received with thanks and thank you for taking the time to post.

All the best - John