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Mura archaeology & restoration/rebuilding/rewinding


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#1 havlicek

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Posted 02 March 2018 - 07:02 AM

While going through an old Mura Green Can "C" in preparation for restoring/rebuilding/winding, it occurred to me that some might find it interesting to look at how these things were done. The motor seems to be "nothing special" (although they're all "special" to me), a typical example. Like most of these, it shows signs that it was run hard and run fast by its owner. No doubt it provided hours of fast fun. Maybe it saw the podium, maybe it never did but tried real hard, but it's for sure the motor saw action.  :D

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As was the case with these things, the lamination profile made it impossible to do the kind of super neat coils we're used to seeing today on both machine and handwound armatures. At least, if you were going to hit a "target" wind, you just had to "make it fit." That meant having the coils spill over the end of the winding leg and onto the outside crown (see arrow). So, whatever "shmooshing" you did to get your first pole done... you had to do the same "shmooshing" on poles 2 and 3. Plus, you still had to make it as neat as you could within the constraints of those difficult lams. Think about it, hand winding a bunch of these things would be enough to drive a man to drink. This may look sloppy to you, but try doing better yourself with those lams. Actually, try doing even nearly as well! Metering the arm without cleaning the comm to get a more accurate reading, shows the arm is a Group 20 wind. The comm has been cut... several times from how deep the shoulder is (see second arrow)

Interestingly, the comm tab connections may look like they were soldered (see second arrow), but they were done with some sort of hard solder/brazing metal. Scraping them with an X-Acto blade proves them to be much harder than any solder I'm aware of. Whatever they were done with, it held up. Also, you can see that the tabs are still wide open and filled with the metal, as opposed to flattened closed and welded. Something a little different going on here.

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Using a Q-tip and some alcohol to try and read the barely visible tag, it has a hand-written "NCC 20" on it. Maybe for a while this is how factory arms were done? Maybe someone was winding arms privately and they were allowed? The powder coating that's visible looks like the same color as other Muras. Beats me, but racers from the period would know better. Whoever wound the arm is unknown, and other than the tag, there's no engraving or other identification visible. So, whoever did wind it, did a fine job and most likely wound so many that this one was "just another armature." By today's standards, the armature is anything but "ordinary." It represents skill and real effort on the part of the winder. It may not look as pretty, but I have no doubt it ran just great.

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So, it's worn way beyond any further usefulness... but that's a good thing. That means it did it's job, and well! "Pretty," no, but to me it's a beauty in its own way. One last note: the drill balancing uses what looks like a regular type drill bit instead of the wide/shallow type that shows up on so many Muras. Maybe they went to that type drill later on?
 
h4.jpg
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John Havlicek




#2 zipper

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Posted 02 March 2018 - 07:20 AM

Looks pretty neat compared to those NCC20 (machine wound) Mura arms we used late '70s/early '80s. And Camens were mostly the way to go after our rules permitted handwound arms.


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Pekka Sippola

#3 havlicek

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Posted 02 March 2018 - 07:24 AM

For sure, Pekka. Some of those Muras were really ugly (although they ran well, too). The tag and the comm connections here were most interesting to me, aside from the good job whoever it was did.


John Havlicek

#4 Bill from NH

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Posted 02 March 2018 - 08:24 AM

A few thoughts. I never saw handwritten tags used on Grp. 20 arms from a major manufacturer. The early Mura arms had printed tags. Steube's were printed also. Camen used a printed purple script on theirs. I've never heard that tags from that period were being replaced either.

 

The wide, shallow, balance holes were used by Mura before they went to HSS drill bits. These shallow holes were often off-centered on a pole's crown.

 

The arm pictured above probably came from the '70s, a time when individual comm lathes were not commonplace, like today. This could probably mean that the multiple comm cuttings you see were done by an arm refurbisher, such as Thorp, Rocket, or Camen. This could also mean that not all the current balance holes were placed, or sized, by the original arm winder.

 

IIRC, Mura placed a dots of yellow and blue paint on the tail end of one pole. Camen placed a purple paint dot on the comm end of one stack. These dots were used with strobe lights when balancing. I don't notice any such paint markings in the photos shown above. Does it have any?


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#5 old & gray

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Posted 02 March 2018 - 08:28 AM

 Since there has some discussion of Group 20 motors  on a different thread, can you give some more information on this motor please?

 

"I" would be interested in the timing, magnet gap, magnet length, and can thickness.


Bob Schlain

#6 havlicek

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Posted 02 March 2018 - 09:21 AM

Hi Bill,
 

A few thoughts. I never saw hand-written tags used on Grp. 20 arms from a major manufacturer

 
Me either, which is why I found that interesting.  I guess (but doubt it) that it could be that a manufacturer... Mura or other... could have "run out of printed tags," but I tend to think this was an individual's work.
 

The wide, shallow, balance holes were used by Mura before they went to HSS drill bits. These shallow holes were often off-centered on a pole's crown.

 

Makes sense, but I would think they were all HSS bits, regardless of tip profile right?.
 

The arm pictured above probably came from the '70s, a time when individual comm lathes were not commonplace, like today. This could probably mean that the multiple comm cuttings you see were done by an arm refurbisher, such as Thorp, Rocket, or Camen. This could also mean that not all the current balance holes were placed, or sized, by the original arm winder.

 
The period seems certainly to be about right (even though "periods" then could be defined by a single year or even months!). It's also possible, likely even, that the refurbishing was done by others than whoever originally made the arm, but all the balance holes were done with similar drill bits. Then again, that doesn't mean much because I've never seen anyone other than Mura use those weird wide shallow drill holes!  :)  As for the comm cutting, it was done on lathes then, too... just bigger ones from what I've seen here.  :)
 

IIRC, Mura placed a dots of yellow & blue paint on the tail end of one pole. Camen placed a purple paint dot on the comm end of one stack. These dots were used with strobe lights when balancing. I don't notice any such paint markings in the photos shown above. Does it have any?

 

I've seen plenty of Mura and other arms with no dots at all, but that could just be because they wore off (?). Then too, I've seen plenty with two dots. This one has none.
 

Since there has some discussion of Group 20 motors  on a different thread, can you give some more information on this motor please?
 
"I" would be interested in the timing, magnet gap, magnet length, and can thickness.

 

Hi Bob,

Timing is low by today's standards. I haven't measured it, but it looks to be around 15 degrees CCW. I have some "Puppy Dog" arms here that are over 30 degrees! The gap is generous... around .5375", and the magnets are the typical (and more difficult to source nowadays) long type... better than .630" long. All these cans are formed of the same general thickness mild steel... around .025" or so, within a few thousandths of modern formed/folded/welded cans.


John Havlicek

#7 B.C.

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Posted 02 March 2018 - 09:21 AM

I would guess, john, that you look at how well an arm is wound not only from an appearance standpoint but also how it is wound.

 

I would compare it to someone looking at a car that had some bodywork done and thinking that looks good. But to a body man/painter they would see the waves, orange peel, etc. Point is for me, I have numerous hand wound arms from the '70s and '80s that used this blank and to me they are works of art. Bill Steube, Bob Green, Joel Montague, Dan Debella, Carl Ford, and various others that I have arms from all look and run like a scalded ape.

 

I even have a couple of newer arms from someone who goes by H-Power; they look pretty good also.


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#8 havlicek

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Posted 02 March 2018 - 10:07 AM

Hi Brian (and thanks). 

 

Yeah, I look at all of that stuff. These lams were about the worst design you could imagine from a winder's standpoint, worse than the Mabuchis that predated them (not talking about the lam thickness of maybe the "lamination steel" used). I have to guess that, after spending big time to have them produced in industrial quantities, they weren't going to invest in having new ones developed (?).  Interestingly, I did get to use some of the last .007" lams Mura sold and they were bizarre in the extreme other direction. Somewhere in the middle would have been nice.  

Anyway, maybe this particular winder went on to become more well known, and this was one of his early arms. Maybe he was just another anonymous winder who eventually burned-out. Whoever he was, this arm was definitely not his first rodeo, and he did one fine job!


John Havlicek

#9 Foamy

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Posted 02 March 2018 - 12:40 PM

Looks like a Camen arm due to the comm welds and the thread.
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#10 Steve Okeefe

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Posted 02 March 2018 - 01:35 PM

For a point of comparison, here is an NCC20 arm left over from 1971:
 
1971 NCC20 Arm 01.jpg
 
Printed tag, welded tabs, later rebalanced by Camen.
 
1971 NCC20 Arm 02.jpg
 
Probably .007" lams, green Hysol, (cracked epoxy), red and orange paint dabs (IIRC, this is a Thorp arm).
 
1971 NCC20 Arm 03.jpg
 
Almost certainly machine wound, nevertheless it ran just fine. :D
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#11 havlicek

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Posted 02 March 2018 - 03:14 PM

Thanks, Dennis and Steve.  Your arm looks like it would still be a runner, although the cracked epoxy might let go! The comm welds are markedly different (note how closed the tabs are on the above arm). It would make sense if it's a Camen, because it's an awfully nice arm!


John Havlicek

#12 blue&orange

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Posted 02 March 2018 - 05:11 PM

I'm not an expert on this, but National Competition Committee (NCC) rules stated all parts had to be NCC approved. I seriously doubt a handwound arm with a written tag would have been considered legal for NCC sanctioned races. The six NCC20 arms I have all have printed tags, and the two 22 arms have printed script "GRP22" tags.


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#13 Alchemist

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Posted 02 March 2018 - 06:19 PM

Hi John,

 

Thank you - as always - for taking the time to share the details of your motor building/dissection.

 

I find it very interesting and educational - always!

 

Thank you again John!

 

I appreciate it.

 

Ernie


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Ernie Layacan

#14 havlicek

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Posted 02 March 2018 - 07:42 PM

I'm not an expert on this, but National Competition Committee (NCC) rules stated all parts had to be NCC approved. I seriously doubt a handwound arm with a written tag would have been considered legal for NCC sanctioned races. The six NCC20 arms I have all have printed tags, and the two 22 arms have printed script "GRP22" tags.


Actually, I've never seen any tag that wasn't printed, but I haven't seen everything!  Whatever the reason, it's a pretty thing.  :)


John Havlicek

#15 GE53

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Posted 02 March 2018 - 08:37 PM

Great subject, I've got two examples of pre-C-can Champion 20 arms that originally came in 16D motors. Both were reconditioned before selling on eBay. The red tag is from arm dye applied years ago.



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#16 Mike Patterson

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Posted 02 March 2018 - 10:39 PM

IIRC, the original NCC Group 20 rules specified a Champion stamped steel chassis and a Mura motor.


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#17 old & gray

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Posted 02 March 2018 - 11:38 PM

Champion chassis and a Mura Armature (Champion and Mura motors).
 
We quickly found out the armatures were great; the frames, not so much.
Bob Schlain

#18 havlicek

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Posted 03 March 2018 - 08:38 AM

Great subject, I've got two examples of pre-C-can Champion 20 arms that originally came in 16D motors. Both were reconditioned before selling on eBay. The red tag is from arm dye applied years ago.

 
Nifty arms! In general, this wind on various stacks in set-ups is pretty great for all kinds of things. Still today, in a spiffy C-can, it makes for an impressive powerplant. Heck, you can even stuff one in a minican... if you're nuts!  :D
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#19 havlicek

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Posted 04 March 2018 - 11:07 AM

On to the nasty/scary/difficult part, it's time to get busy on cleaning-up the can and removing as much of the considerable pitting on there. Usually, there's some pitting above the rear can notch from soldering the motor into the chassis. On this motor, the bottom was pitted worse than the usual place... and it's deep pitting. 

First step is to strip most of the paint, and then run some sandpaper on the can to see where the pitting really is and how much of it there is. Then I slide the can onto a mandrel and go to work with a small plastic mallet, tapping the can on all sides to get it as straight and flat as I can.

IMG_2553.jpg

I have my work cut out for me on this one. Still, the can has "good bones." The bushing strap is OK, even with the pitting and the mounting holes seem unused thanks to the heavy soldering that was originally done. Time to chuck the can up in the lathe and start turning-down the radiused sides until I'm too frightened to go any further.

IMG_2554.jpg
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#20 havlicek

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Posted 04 March 2018 - 11:09 AM

After getting the curves done, I cleaned them up with some sandpaper and I was glad to see I got almost all the pitting off without making the sides paper-thin.
 
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John Havlicek

#21 havlicek

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Posted 04 March 2018 - 11:15 AM

On to the upper and lower flats, I moved the can to the mill.  

IMG_2557.JPG

One flat wasn't too bad at all, the other was... well... pretty bad

Taking the can out of the mill and hitting it with some sandpaper, I was relieved to see that, again, I got out almost all of the pitting on both flats.

IMG_2558.JPG

 

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Now, the bearing strap was really pitted looking, and of all the other sides, I wasn't going to remove more than a bit there so as not to weaken this critical area. Surprisingly, I only had to remove about three thousandths to be able to finish sand it to an almost totally clean surface.

So now the outside of the large can areas are done. The can lost a fair amount of weight in the process, which is probably never a bad thing. All the edges still have to be done, but a mini-file and some sandpaper is going to take care of that. Then I still have to clean the inside... gak!

 

IMG_2561.JPG


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John Havlicek

#22 havlicek

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Posted 04 March 2018 - 11:20 AM

Things are looking up for this old Mura.

IMG_2562.JPG

With a little more elbow grease on the edges and inside, I can dig in to the endbell and then clean up and reinstall the magnets so they can get a fresh zap. 

They say "the longest journey starts with but a single step" and, the way I see it, I've taken some pretty big steps already. Funny thing, making and winding an armature for these things is the least of it!
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#23 dalek

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Posted 04 March 2018 - 12:27 PM

Hey John,
 
I'm curious how you pronounce your last name.
 
Is it:  
 
Hav – pronounced "have"?
li  – as in "list"?
cek – as in "section"?
or
cek – pronounced "check"?
Dale King
 
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#24 havlicek

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Posted 04 March 2018 - 12:45 PM

Hi Dale,
 
It's a Czech name, and the common "cek" suffix (the diminuitive) is pronounced as "check." Many Czech names take the form of the diminuitive and for instance "Havel" (as in the famous writer/dissident/Czech leader Vaclav Havel) could be morphed into "Havlik" and then too as "Havlicek." These names are often family-related, so people with any of those surnames names are more than likely related back in time. 

More than you probably wanted to know.  :)
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#25 havlicek

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Posted 04 March 2018 - 03:47 PM

So, the actually important stuff is done (even the magnet clips are heavily pitted!?). The inside is all cleaned up, although there is still a bit of pitting in there, too! 

I dug through my "bottle of bushings" for a replacement here. The original was in far better shape than about anything else on the motor, no doubt at least partly because of how long these bushings are, giving them long life. Surprise, I found one that was actually still a snug fit for an armature shaft! 

As this "rescue" has evolved. I wanted to rebuild the motor close to its original state. I do so many of these that my conscience makes me want to do at least some restorations so future peeps can experience these great motors more closely to how they were. That means, this one will get a "20" wind. It won't be NOS, but I gotta do something here that's "all me."  :)

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