# Replacing obsolete ignition module w/ generic?

#### jbtvt

Joined Feb 27, 2012
7
Hello, I'm trying to get an old but awesome Craftsman Brushwacker with Robin (Subaru) engine running again after spark failed and new plug didn't change anything. Although it uses the same engine as the Robin NB04 trimmer, unlike that model it has an ignition module, which is $200+ on the only site that still lists it, AKA more than half the cost of a brand new Honda, and this company doesn't actually carry any stock so I suspect they may not be able to get it regardless and just haven't updated their parts availability. I would like to use a generic like the Nova 2 and have it running for ~$15 but all the information out there suggests that this is only possible with a coil/points/condenser setup with only one wire to the coil, whereas this module has 4 wires, including the kill switch/ground wire. So I'm not sure if it's even possible, and if it is, which wire I should be attaching the positive lead from the Nova to. Can anyone offer guidance?

Alternately, I'm considering getting an NB04 ignition coil and trying to adapt that to my machine while using either the points or a generic like the Nova, but at \$75 even that isn't a risk I'm keen on taking for this old machine, unless the chances of success are high. Any thoughts there? Thanks.

#### debe

Joined Sep 21, 2010
1,148
If you want to try a Nova or Atom ign module. I would cut the wires & re wire the module as the diagram. If no spark or weak spark reverse the module wiring polarity.

#### jbtvt

Joined Feb 27, 2012
7
Thanks, I'll give that a shot.

#### jbtvt

Joined Feb 27, 2012
7
No luck. According to the diagram the body of the Nova should also be grounded. Not sure if truly necessary, but in any case I wired it up like this

Continuity from transistor body to all metal on the motor (including the OEM coil ground). Tried polarity both ways but still no spark. Never used one of these transistorized modules before. Am I missing something?

#### debe

Joined Sep 21, 2010
1,148
Did you cut this wire & ground it?

#### jbtvt

Joined Feb 27, 2012
7
I hadn't, assumed it was grounded internally. Tried this morning, polarity both ways, but still no spark. Resistance between the two leads is 155 ohms which seems reasonable. Suppose it could be something with the plug wire, also no longer available, but the symptoms really seemed like a coil the way it stopped running when hot a few times, restarted later and finally stopped altogether.

#### shortbus

Joined Sep 30, 2009
7,236
It looks, from the pictures like there is a lot of rust on the pole pieces of the coil. And from that I assume also the magnets will have rust on them. Rust on either one of those places will really hamper the ignition. Sanding to remove the rust and then regapping the distance between the poles of the coil and the magnets will give the highest output from the coil.

#### ldent100

Joined Jan 14, 2019
2
Hello - I seem to be in the same boat as you. I have the Sears/Craftsman labeled brushwacker model 636.796234 (37.7cc). It is showing the same symptom of not firing.
Have you come to any successful resolution for your coil?

#### jbtvt

Joined Feb 27, 2012
7
Never did. I bought a Honda. Will likely try splicing the plug wire at some point as I can't think of anything else it would be, assuming the aftermarket module I have works.

#### Tonyr1084

Joined Sep 24, 2015
3,895
The goal is to make the engine run AND to be able to shut it off.

My approach would be to find a coil of the same flywheel radius and mount that up. Then the wiring is straight forward from that point on. Grabbing a coil off of a free lawnmower or other similar sized part may offer up a coil that is ready to go. Would come complete with ignition wire and ground wire. And if memory serves - it would only require the installation of the coil and the ground for shutting it down.

Of course I'd have to have the machine in hand to do some testing.

Question: How do you know you don't have spark? Is it because the engine won't run or are you observing the presence or lack thereof for spark? If you're depending on whether the engine starts up - keep in mind those piston to cylinder wall tolerances are quite close. With wear and tear they simply reach a point where they don't want to run any longer. Especially so with the engines you have to mix gasoline and oil.

#### wayneh

Joined Sep 9, 2010
16,126
Never did. I bought a Honda. Will likely try splicing the plug wire at some point as I can't think of anything else it would be, assuming the aftermarket module I have works.
The plug wire is what has failed - I think - on the magneto on my McCulloch chain saw. It has visible cracks in the insulation.

Having to buy a new chainsaw due to a failed spark plug wire - which is built in to a magneto that you can't find anywhere - is what makes me crazy. Why the hell can't magnetos be universal, like nuts and bolts? What would you need, maybe 10 models for the entire small-engine universe? My chainsaw is in parts in a box because I was too mad to continue.

#### jbtvt

Joined Feb 27, 2012
7
Having to buy a new chainsaw due to a failed spark plug wire - which is built in to a magneto that you can't find anywhere - is what makes me crazy.
You can splice the wire -

#### wayneh

Joined Sep 9, 2010
16,126
You can splice the wire -
I had thought about doing that but dismissed it for some reason. I think I was hoping to find a new replacement part and just got so disgusted with the whole thing that I gave up. Anyway this video had some good tips (like using heat shrink) and I may reconsider it now.

#### ldent100

Joined Jan 14, 2019
2
Never did. I bought a Honda. Will likely try splicing the plug wire at some point as I can't think of anything else it would be, assuming the aftermarket module I have works.
Looking around I See this is a Sachs-Dolmar BC37.7 label or the Robin NB04
I wonder if the one listed below is getting close..

https://ebay.us/H6F2LF

#### Tonyr1084

Joined Sep 24, 2015
3,895
@jbtvt Nice video. Probably will never personally need to do that, but one thing extra I think I would have done was to use a drop of superglue between the two wires to glue the insulation together just to give it a bit more strength than just the shrink sleeving.