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Resistance on 1955 R25/3 ignition coil

Dave -

I'm not very good with electrickery, but I'm trying to dig through some things. The singles were all battery-coil ignition, whereas the twins were magneto ignitions. I've found out that the coils on the R24-R26 were all basically the same, but things were different for the R27. I believe the generator was a Norris (or maybe Noris) L 45/60. Googling that doesn't help much, but I have a few feelers out for some info on the coil resistance.
 
Thank you

Dave -

I'm not very good with electrickery, but I'm trying to dig through some things. The singles were all battery-coil ignition, whereas the twins were magneto ignitions. I've found out that the coils on the R24-R26 were all basically the same, but things were different for the R27. I believe the generator was a Norris (or maybe Noris) L 45/60. Googling that doesn't help much, but I have a few feelers out for some info on the coil resistance.

Thanks again Kurt!

Sorting out the terrible wiring the PO did. All lights working along with neutral.
 
The info I got was that the primary resistance should be around 1.5 ohms while the secondary resistance should be about 6K ohms.

Interesting...those are about the numbers for a single coil for my /7! Also for VW coils as I recall.
 
Thanks again Kurt!

Ok I will double check. I believe it was right around there but not getting spark. 0 volts through the spark plug wire. I printed a couple manuals and have wiring diagrams but nothing specific on generator. Cleaned the contacts on regulator as well. Here are photo's of the unit.

EE79C125-496E-40D1-8C4F-1FECBAD29070.jpeg
571CB163-B7AB-410D-9647-E2D9F008221B.jpeg

Dave
 
Dave -

Have you run across this manual for the /2 system:

https://www.snafu.org/restore/uandm_bmw_v1.pdf

This tends to be more for the magneto systems of the '55-69 bikes. Vech at Benchmark Works sells Doug Rinckes' updated version with color photos, etc., and good wiring diagrams.

If no spark, are you sure the points are set up right, so that they open and close at the right time? If the points are too tight (ie, they never open) or too loose (ie, they never close), you will get not spark.
 
Thanks

Thanks so much for that manual!
Will read it thoroughly, the points are opening and closing (touching / not touching)
As far as being set up right , I will have to look into that.
The manual will definitely help!

Thanks again
Dave
 
Spark!

We have Spark!
Thanks for the guidance Kurt. Have the points cleaned and adjusted. Now onto the Carb. I put some clean fuel in, new hoses to give a shot at starting. No dice, but encouraged! Getting some gas leaking through the top seal on float chamber. So going to do a rebuild on the carb. Any suggestions on what I should be looking to replace ?
Thanks 🙏
Dave Manchester
 
There's not much to replace inside the carbs. Just be careful taking jets out, etc., as they are brass screwed into pot metal. One issue I had was a gasket that fits between the bottom feed port to the carb body. These are "bottom feeders" meaning the gas comes in from the bottom...that's where the seat is.
 
Compression

There's not much to replace inside the carbs. Just be careful taking jets out, etc., as they are brass screwed into pot metal. One issue I had was a gasket that fits between the bottom feed port to the carb body. These are "bottom feeders" meaning the gas comes in from the bottom...that's where the seat is.

Ok thanks!
Checked compression on the bike , measured a measly 54psi cold. Checked valves, set to .15 intake, .20 exhaust. Still same compression. Pulled plug dropped a little oil in cylinder and jumped to 95 psi. So would assume rings are in order. The bike has not been in years.
Thoughts?

Thanks!!
Dave
 
Dave -

My rule-of-thumb calculations reveal that the stock compression should be around 120psi. Certainly 54 is bad, 95 is better. I would try and do a leakdown test to really identify the problem. You get some kind of percent leak with that test...more than 10% is likely rebuild time. Plus you can listen to where the air is escaping to. If it comes out the exhaust, then it's the exhaust valve. Out the carb, then the intake valve. If you pull the dipstick and hear air rushing there, then it's rings.

My guess is you know little about the history of the bike. But doing the leakdown pinpoints what you need to work on. That said, if you go into the engine, likely you would need to just do it all. Slingers for instance...what's the status with those?
 
Slingers

Dave -

My rule-of-thumb calculations reveal that the stock compression should be around 120psi. Certainly 54 is bad, 95 is better. I would try and do a leakdown test to really identify the problem. You get some kind of percent leak with that test...more than 10% is likely rebuild time. Plus you can listen to where the air is escaping to. If it comes out the exhaust, then it's the exhaust valve. Out the carb, then the intake valve. If you pull the dipstick and hear air rushing there, then it's rings.

My guess is you know little about the history of the bike. But doing the leakdown pinpoints what you need to work on. That said, if you go into the engine, likely you would need to just do it all. Slingers for instance...what's the status with those?

Kurt,

Thanks again, yes I know nothing of the bikes history. Just have title and that is it. As far as slingers also unknown. I have been trying to find some info on the procedure. Or decent English repair manual. Any suggestions?
Dave
 
Procedure for what? Leakdown test is pretty straightforward but you need some gauges. Engine teardown to get to slingers? That's a pretty high "wrench count" if you ask me. Cycleworks.Net sells an engine top end DVD for singles and twins 1951-1969, but the bottom end DVD is for twins only. That was not something I was willing to tackle...both my vintage bikes with slingers were farmed out. I did all the top end and outside stuff removal, but I let them deal with the internals.

Vech sells a repair manual for the R25-R25/2 but I don't see one for the R25/3. Can't say as these are all that great...I think you have to have gone through BMW tech school to really get the details.
 
Thanks

Hey Kurt,
Thanks, yes the slinger cleaning procedure. Will do a leak down next and see where she blows.
Thanks T -foiler. Are you referring to the R25/3?
Thanks
Dave
 
Rebuilt the card with parts from Vech. Got her started up! Now have to compile a list of supplies starting with proper fluids. Have been looking online but figured I would ask here.
Thanks again for help!
Dave
 
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