Trials Australia Forums

Continuing with electric problems, had had my Primary Ignition coil (magneto) rewound. There was a short.
The fellow who done this observed the amount of turns to the wire gauge used and ended up similar to my original resistance of 2.0 ohms.
He said it cant possibly be 4.5 ohm (as below) as the winding would be twice as big etc.

Now contrary to this measurement is the info found in the TY175B manual (thanks to PA), says 4.5 ohms for this item. Also the service data for specs on the Yamaha Parts web page came up with 4.5 ohms.

But the DT175 being similar, and having a such coil, is 2.1 ohm.

What is the correct resistance and what have others measured in their bikes?
I have taken the bike to them now, after trying 2x other secondary coils and condensers and checking the points, even tried a new wire directly to the secondary coil, checked for shorts in wiring - still no spark.

I've only the information you have posted to go on so don't laugh or be insulted at what I ask. I have seen all these things wrong with various bikes over the years:

About the no spark:
Is the secondary coil properly earthed to the frame? (suggest measuring resistance from secondary coil laminations to the motor casing - should be almost zero resistance)
Is the primary coil properly earthed to the backing plate, backing plate earthed to motor casing/motor casing properly earthed to frame? (suggest measuring resistance from primary coil laminations to motor casing)

Do the flywheel magnets have a strong magnetic effect?

Is the flywheel touching the primary coil laminations? May be due to surface rust, worn crankshaft bearings, loose coil screws, coil screwed on too close to flywheel magnets, misaligned flywheel due to the key not having top clearance.

Is the wire from the points to the primary coil broken?

Is there any conducting dust on the points ie graphite or other powder?

Is the points cam surface on the flywheel smooth?

Is the flywheel tight on the taper?

Has someone fitted a different primary coil mounting plate or a different flywheel to standard ie with a different number of magnets or with the magnets not in the right place to match the location of the primary coil at the point where the points open?

About the primary coil resistance:
How are you measuring the primary coil resistance? If you are measuring it with the coil fitted to the bike, you will get a false low resistance due to the capacitor being in the circuit.

How did you diagnose that the primary coil had a short before you had it rewound?

Thanks David for your thorough point reply, I like how you can raise more questions, this is exactly why this forum works, I like another viewpoint.

David Lahey wrote:I've only the information you have posted to go on so don't laugh or be insulted at what I ask. I have seen all these things wrong with various bikes over the years:

Non taken, I will laugh with relief if it goes, I didnt detail too much as I didnt want to bog the post just yet.

David Lahey wrote:About the no spark:
Is the secondary coil properly earthed to the frame? (suggest measuring resistance from secondary coil laminations to the motor casing - should be almost zero resistance)

Yes, good bond, but not tried to laminations. Did try 2x other coils.

David Lahey wrote:Is the primary coil properly earthed to the backing plate, backing plate earthed to motor casing/motor casing properly earthed to frame? (suggest measuring resistance from primary coil laminations to motor casing)

Was evidence of water and surface coating, did spend some time cleaning this area up. Good bond now.

David Lahey wrote:Do the flywheel magnets have a strong magnetic effect?

Seem to, used a hacksaw blade on each magnet, and compared to the DT175 magnets in that flywheel, seemed to be similar.

David Lahey wrote:Is the flywheel touching the primary coil laminations? May be due to surface rust, worn crankshaft bearings, loose coil screws, coil screwed on too close to flywheel magnets, misaligned flywheel due to the key not having top clearance.

Have a good bottom end, flywheel not touching, coil ceaned up laminations since rewind. Key original, does not seem to be not aligning flywheel back on taper.

David Lahey wrote:Is the wire from the points to the primary coil broken?

Wiring was burnt by cooked lighting coil, have replaced and repaired this.

David Lahey wrote:Is there any conducting dust on the points ie graphite or other powder?

Cleaned with contact cleaner after a quick file to deglaze anything.

David Lahey wrote:Is the points cam surface on the flywheel smooth?

Yes, no corrosion

David Lahey wrote:Is the flywheel tight on the taper?

Yes, as answered above.

David Lahey wrote:Has someone fitted a different primary coil mounting plate or a different flywheel to standard ie with a different number of magnets or with the magnets not in the right place to match the location of the primary coil at the point where the points open?

No original. This bike was running, but has been hard to start and would breakdown at higher revs.

David Lahey wrote:About the primary coil resistance:
How are you measuring the primary coil resistance? If you are measuring it with the coil fitted to the bike, you will get a false low resistance due to the capacitor being in the circuit.

How, cardboard between points, and unscrew condenser. Measure to ground with poits open - reads Pri coil, then with points closed - good contact. Check condenser with Fluke meter on Capacitance at 0.25 or .03 uF depending on which cap is used.

David Lahey wrote:How did you diagnose that the primary coil had a short before you had it rewound?

I didnt, I took it down to be rewound on lack of direction, the rewind guy said it had a short.

I used a torch across the points, upon points opening, it just dims as it loads via the Pri coil, then brightens when closed. I did the same with a moving iron meter, did spike ok when points open on resistance, but not show open circuit.

Have since solved this. Replaced stator plate with another one of a "B" model. It has 2x large coils, not like my original that has 3x smaller ones, and no it is not a DT one, as they are different again. Main thing is that is going again!