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1975 DT250 Contact Breaker Assembly Replacement

  • arch75250
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Hello,

Does anyone have feedback on the 1M1-81321-20-00 set of points available from Niche Cycle for $5.90? The price seems awfully low. I went ahead and ordered the part and it looks spot on. I made the mistake of ordering a NOS part from an online retailer for more than $50.00 and it ended up being a mirror image of the correct part . Fortunately they're okay with a return.

The price of the Niche Cycles replacement seems almost too good to be true. It looks pretty good though. Just trying to decide if I want to stick this on or not. I don't technically know if my old set is bad as the electric stuff is still just magic to me.

I'm trying to understand how to test my old set. The stator assembly is on my work bench, not on the bike. When I use a continuity test light I can't break the current on my stator by opening the points when I clip to the stator plate and touch the other lead to the top of the points, with the points open. Should I be able to? I can break continuity with the new part, not mounted but I can't break continuity with the original part mounted to the stator. What am I not understanding? Does this indicate that my points are bad for sure, or maybe that something is getting grounded to the plate that shouldn't or am I just a dolt?

Thanks in advance (no timing pun intended).

Mike
23 Jan 2021 11:43 #1

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Hi arch75250, l can't really help you regarding your query on the quality of points you are considering purchasing other than to say there is a vast difference in the quality available. Here in the UK I bought a set from a very well known supplier (no names as they do supply many good parts too) and they were so flimsy they may as well have been made of chocolate..!! In the end I stuck with the original very robust Mitsubishi set and dressed the contacts carefully to remove pitting.
As far as testing your existing points in situ on the stator plate it sounds like the problem could well be your test equipment and/or your expected results. Obviously when your points are closed they are directly earthed to the stator plate and your continuity tester indicates 'continuity'. Remember however when you open your points there will in fact still be continuity showing but it will be via the source coil because it too is earthed to the stator plate. A continuity tester will not pick up the subtle difference between points closed i.e. direct earth 0 ohms and points open which gives a very small resistance path through the source coil of 1.65ohms +/-10%). What you need is either a very sensitive analogue meter set to lowest resistance setting or better still a digital one. When you get to setting up your timing 3.2mm BTDC this resistance measurement is handy to know because your multimeter will change from 0 ohms (i.e. points CLOSED) to give you your coil resistance value (i.e. points just OPENED) . Hope this all helps, Andy L
23 Jan 2021 16:23 #2

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Replied by arch75250 on topic 1975 DT250 Contact Breaker Assembly Replacement

AndyL,

Thanks for the reply. The real issue here is my lack of full understanding of where the electrons come from and where they go. I have a general understanding of how it all works but when it comes to specifics I get lost pretty fast.

I have borrowed a digital multimeter and I’ll see what I can find based on your description.

The main problem is that the bike hasn’t run for 30 years and sat outside for 2 years under a janky tarp without the stator cover. I’m not able so far to get a spark anywhere. As a rank amateur my tactic has been to replace things I don’t understand or if I think I understand based on resistance readings noted on this forum.

Right now I’m down to points and condenser, and then maybe taking apart the ignition switch and kill switch to see if there’s some issue there. My intuition tells me I should be able to track down any issues there with a test light so I’ll try that first.

I’ve just replaced the condenser thinking that could be my issue but haven’t put it all back together yet. Already mounted a new ignition coil. Based on your description, maybe I should have some confidence in my original points before I replace them with the $5 ones.

I’ll report back with resistance reading when I get a minute. The other thing I haven’t ruled out is the primary coil but I read somewhere that it’s a “lifetime part” and shouldn’t ever need to be replaced. Any thoughts on that? It doesn’t look too bad visually.
23 Jan 2021 18:43 #3

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Most of the time after a bike has been sitting just cleaning the point contacts is all you need to do. "Give em a scratch" is what RT325 says if I remember right.

Some fine wet/dry sandpaper... contact cleaner... and strips of white uncoated card stock are helpful. Pull the strips of card stock through the contacts until they come out clean. I like white business cards.

Digital meters often suck at the measurement you are trying to see. They jump all over and never settle down. Meter needs to be on the Rx1 scale or it won't show anything. Some auto-ranging digital meters just won't work at all.

But yes, Point closed should get you a solid "0" reading and points open meter will read between 1 and 2 ohms... with a powered test light in a darkened room you might see a very slight dimming of the bulb when points open.

Best way to rule out switches is to run a jumper from black points wire out of stator directly to ignition coil. Nothing else connected. That should give you spark.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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23 Jan 2021 20:39 #4

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oh... you're not trying to "break current" when the points open. This is an ET magneto.

Battery ignition charges up primary winding creating magnetic field in transformer (aka ignition coil). Points opening suddenly collapses magnetic field which induces high voltage in secondary winding of ignition coil... and SPARK!

Kill on battery ignition is disconnecting battery from points/primary winding.

ET Magneto spinning magnets are generating AC voltage in primary stator coil. Points closed the voltage goes to ground. Everything is mechanically timed so when points open the AC voltage spike is very near maximum... that brief spike of voltage goes to primary winding in transformer (ignition coil) when points open. This quickly creates a magnetic field in primary winding which induces high voltage in secondary winding of ignition coil... and SPARK!

Kill on magneto simply grounds wire from points to primary winding on ignition coil.

Summary:

Battery points ignition needs outside power source to charge up primary winding in ignition coil. Points open suddenly collapses the magnetic field in ignition coil creating spark.

Magneto ignition uses a stator winding and spinning magnets to create power. Points open allows voltage spike from stator to suddenly create a magnetic field in ignition coil creating spark.

Hope that helps.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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Last edit: 23 Jan 2021 21:09 by MarkT.
23 Jan 2021 21:01 #5

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Replied by arch75250 on topic 1975 DT250 Contact Breaker Assembly Replacement

Excellent description MarkT. That helps a lot. The readings I get from testing between black lead on stator and stator plate or top of condenser fluctuate between 0.7 and 1.1 points closed and about 2.2 points open. Will reassemble and start tracking things down and eliminating possible snafus. I like the idea of jumping from the stator to the coil. That sounds like a winner. Do my readings seem anywhere close to what I should see?
23 Jan 2021 21:56 #6

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What do you get with meter leads shorted together? Digital meter on Rx1 might have a reading (the resistance of leads) that you need to subtract.

Other than than, it sounds like you may need to clean the points as I described. Even brand new points that have been sitting often need to be cleaned to work. An invisible film of "corrosion" forms on the contacts.

You should have a zero reading with points closed. Also hold the leads in place for a bit when points are open.... the meter might be trying to charge the capacitor (condenser) and that might affect the readings.

Another place to test is the black wire coming out of the stator that plugs into the main wiring loom. You should get the same points open and points closed readings there. Important to test because if that wire is broken or shorted you'll never get spark.

It's no secret I much prefer the old fashioned analog meters with an Rx1 scale for these tests... just much cleaner solid readings. But you can use what you have.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
Last edit: 23 Jan 2021 22:15 by MarkT.
23 Jan 2021 22:14 #7

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The strip of business card part of the cleaning is particularly important.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
23 Jan 2021 22:17 #8

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how toasted were the original points?
If the original ones are high quality and not burnt up, then perhaps there's value in dressing them with a points file?
23 Jan 2021 22:18 #9

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Replied by arch75250 on topic 1975 DT250 Contact Breaker Assembly Replacement

I saw a BRIGHT BLUE SPARK! I’m so excited! Thanks to you both and everyone who has commented on my other posts! Hopefully my next post will involve smoke and noise!
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23 Jan 2021 22:28 #10

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