156 replies to this topic

[dc-65x]

The only soldering left to do on the chassis (besides soldering in the motor) are the little pan downward stops and plumber rail upward stops.

 

To avoid having to wash and dry the chassis again for soldering in such a small area, I broke out the painters tape. It looks goofy      but worked great and only took a minute to do:

 

 

The pan stops:

 

 

The stops installed, the tape did its job and made cleaning up the small exposed area easy:

 

 

The setup for the unusual plumber rail stops. To hang onto the little .032" L-shaped wire stops while soldering they were slid into a long piece of pin tube and lined up with the jigs pins:

 

 

Kapton tape keeps the solder out of where I don't want it:

 

 

The same setup on the opposite side:

 

 

With a final polish the chassis will be done.  

 

Time to build the motor.   

 

 

 

 

 

 

[Pablo]

Perfect surgery   

[dc-65x]

Hi Pablo.       

 

Time for some surgery on my Mura 2-hole C-can:

 

 

I used a cut off wheel and files to raise the axle clearance for the tall 1" tires:

 

 

Added extra clearance for motor bracket bracing:

 

 

 

I decided to make this can a "big hole" version. I enlarging and aggressively chamfering the vent holes as shown on the top can in the photo:

 

 

It's finished off with some VHT black wrinkle finish paint:

 

 

The area on the can for soldering it in the chassis was tinned and masked off:

 

 

 

[Bill from NH]

Enlarging the vent holes was a common practice in the day. Those Mura C-cans were some of the straightest cans that came from a factory. A can straightening mandrel was hardly ever needed.

[Brian Czeiner]

I'm assuming chamfering the holes is for better airflow like a set of heads?

[dc-65x]

That's an interesting theory on the chamfering and air flow. I've seen it done on period motors and I liked the way it looked. 

[Bill from NH]

In the day, we chamfered the holes on Green cans just to remove any burrs left from enlarging the holes. The larger holes seemed to change the magnetic flux. Airflow wasn't a concern, but the Champion C-cans did run cooler with open arms.

[Mark Onofri]

Didn't think of that Billnh,interesting. I remember seeing c-cans hacked up and still be allowed as box stock in the 80's.I assumed it was for weight.

[dc-65x]

I grabbed a pair of Champion Blue Dot magnets for the motor:

 

 

They had a low 600 gauss reading after sitting around for 50 years:

 

 

They got a good ZAP in the "big dog" zapper:

 

 

That woke them up a bit:

 

 

Installed and the can is ready to go:

 

 

 

Time to dig up an armature.

[Bill from NH]

Just as tip shape is important, so is tip strength. You can match the tip strength on the leading edges of the magnets & that of the trailing edges too. That can prevent two "alike edges" from opposing each other.

[Pablo]

I always wondered what those orange donut holes were for 

[Martin]

You mean there not ear plugs 

[SpeedyNH]

hi Rick, 

love your expert build threads!  

do you know what type of steel you use to make your magnetizer slugs from? 

 i have some that work and some that don't (poor permeability). i'd like to make some more, but i don't know what type they're made from. i've seen 1010 low and 1018 medium carbon mild steel.  

says online that i need something called "soft magnetic steel", high permeaility. but they don't give practical examples.  

do you know what yours are? 

thanks! 

Speedy 

[Jay Guard]

Steve:

Without getting too technical (and expensive) 1010 low carbon steel is your best bet, it's widely available and inexpensive,  In addition I believe it's what most of the good zapping slugs are made from.

[dc-65x]

Thanks Jay for the explanation about steel for magnet zapping slugs.   

[dc-65x]

I've decided to use this Mura armature:

 

 

It's got the later thin laminations with welded comm wires but it's still using the fiber lamination endplates instead of the green powder coating:

 

 

It's a single wind and the wire looks to me to be thinner gauge that a S24 or S25. It looks very similar to a couple of S26 arms I have that the original owner engraved as such:

 

 

Here the armature has been scrubbed clean with brake cleaner, shaft and laminations polished and the comm trued:

 

 

 

[Bill from NH]

The off-centered balance holes with a flat bottom on each stack indicate it's an early one also.

[SpeedyNH]

thanks Jay! much appreciated. 

[dc-65x]

Endbell time:

 

Mura "big bearing" endbell with frame half rail clearance cut and cooling cutouts under the brushes.

Mura solid state buss bars and and deburred brush hoods.

Reproduction Parma elephant ear heat sinks.

2-56 stainless steel machine screws:

 

 

My favorite setup for a brush spring post vs the Mura spring post setup on the right:

 

Mura brass spring post cup reversed and a machine screw inserted.

Fiber armature washer to insulate the brush spring from electrical current and heat.

 

 

The finished endbell:

 

 

 

[Bill from NH]

I would bend the ends of those Murs buss bars 90 degrees. Then I could solder leadwires to a flat horizontal surface rather than to a vertical one. It would save time when doing a motor change.

[dc-65x]

Sounds like a good trick for most racers Bill but my motors never blow up and need to be changed in a race.

 

 

...........well.........almost never blow up!        

 

I'm using these Certus brush springs. They are not super heavy:

 

 

Stock spring on the bottom and cut and bent to fit my motor on the top:

 

 

Vintage 36D brushes shown with a screw slot file from Brownells used to modify them:

 

 

On the right the brush spring slot is filed larger to fit brush spring insulation and shunt wires:

 

 

The shunt wires are 2 strands of TQ lead wire twisted together:

 

 

The brush spring insulation is Teflon tubing I bought years ago before Small Parts, Inc. was gobbled up by Amazon. This size works well with the .014" springs:

 

 

Here's everything ready to install and get this motor running:

 

 

 

 

 

[dc-65x]

The finished motor. It runs cool and smooth drawing 1.2 amps at 3 volts:

 

 

9T Fass pinion gear will be mated to a Fass 45T spur:

 

 

I really enjoy the Mura A, B and C motors. They are fun to build up.

 

 

The "big hole" can gives a nice view of the arm and the cool flat bottom drill balancing:

 

 

Shunt wires and brush spring insulation are doing their job. You can touch the power supply leads to the brush spring and the motor will not run. 

 

[Brian Czeiner]

Where do you get the armature heat sink or is it something you make? I have seen it before on builds.

[Bill from NH]

Those were originally sold by Parma in the early '70s. Today, I believe they are user-made.

[dc-65x]

Years ago Steve Okeefe and I had comm coolers made Brian:
 

Thanks Tex
 
Good deal Tony, that's what I did. I used epoxy on the magnets and shims. Magnet clips held everything in place while the epoxy cured and I just left the clips in.
 
Thanks for the insight on the arms of the day Steve. Less turns, more timing....MORE POWER!
 
I most often see comm coolers in the old newsletters starting in '71-'72 as you mentioned. But I found this 1970 Thorp ad showing their comm cooler on a B-motor:
 

 
I have a 1969 ad for comm coolers from another maker whose name escapes me but I can't find it right now. Anywho, we had a small lot of them repoped so I use them whenever I get the chance:

 

 

Parma is probably the comm cooler ad I mentioned above that I couldn't find Bill.