17 replies to this topic

[Mad Mark]

I dont know anything about these kinds of motors. all I ever raced in the late 90s-00s was death stars and S16Ds. Any info would be great!

#1 engraved x12 arm

[Mad Mark]

#2 another x12 arm no engraving.

[Mad Mark]

#3 mura 20 on arm

[Mad Mark]

#4 RS??? 15 on arm

[mreibman]

I believe #1 and #4 are both RJR.

 

# 2 is mura

#3 is mura - and what I call the "champion hole pattern"

[Bill from NH]

#1 is a RJR C-can. Grp. 12, Mura?

#2 is a Mura C-can that replaced the "Green Can", maybe Grp. 7, if not tagged, Grp. 12 if tagged. The chassis it's in looks like an early GT-12.

#3 is a Mura (I think "Trinity") C-can that replaced #2, Mura Grp 20.

#4 is another RJR C-can, maybe for Int. 15. I forget who tagged their arms RSxxx.

[Mad Mark]

Thanks for the info! Are these built up from parts or are these something that could just be purchased as is and dropped in a car?

[Bill from NH]

Mark. these could have been bought both ways. They might have been complete motors &/or a bag of pars. I used to build my motors in the 70s & 80s from parts. That way each motor had my preference for bearings, magnets, arms, spacing, springs, etc.

[mreibman]

Thanks for the info! Are these built up from parts or are these something that could just be purchased as is and dropped in a car?

If i had to say, the mura with the white endbell is using an endbell from an older generation. I believe the "elephant ears" went out of style before this time period, but the can is a later style.

[old & gray]

If i had to say, the mura with the white endbell is using an endbell from an older generation. I believe the "elephant ears" went out of style before this time period, but the can is a later style.

 

Good bet, the end bell with the group 12 was usually tapered toward the bushing with a rectangular opening. This one has an inspection hole drilled on each side. 

[Bill Seitz]

#2 is Mura from the 90's used on all of their motors. Believe this is the last Mura can. Elephant ears were used circa 1980 on the G20/27/7 motors, and the white endbell and brush hardware are 80's or earlier vintage. Extra holes were added to the endbell top and bottom. A correct endbell for this can design would look like the black one in #1 with double overhead brush springs.

 

#3 is Mura from the 80's used on all their motors, but especially G15/20/27/7. Successor to the C-can with 2 round holes which was also still available on Wasp, G12/15 motors in the 80's along with this can.

 

Both the white and orange endbells have been shaved/filed on the bottom for more chassis clearance, not standard production. IIRC, white endbells were used with 2-round-hole cans, orange endbells used with the "slot" can referred to above as "Trinity", and the 90's can used black, double overhead endbells. 90's Mura used .500 long magnets, while the earlier motors came with .630 long magnets.

[Mad Mark]

#2 is Mura from the 90's used on all of their motors. Believe this is the last Mura can. Elephant ears were used circa 1980 on the G20/27/7 motors, and the white endbell and brush hardware are 80's or earlier vintage. Extra holes were added to the endbell top and bottom. A correct endbell for this can design would look like the black one in #1 with double overhead brush springs.
 
#3 is Mura from the 80's used on all their motors, but especially G15/20/27/7. Successor to the C-can with 2 round holes which was also still available on Wasp, G12/15 motors in the 80's along with this can.
 
Both the white and orange endbells have been shaved/filed on the bottom for more chassis clearance, not standard production. IIRC, white endbells were used with 2-round-hole cans, orange endbells used with the "slot" can referred to above as "Trinity", and the 90's can used black, double overhead endbells. 90's Mura used .500 long magnets, while the earlier motors came with .630 long magnets.

Great info thank you sir. #1 seemed pretty fast but already burned up. #2 while being the apparent hodge podge of parts is really fast runs nice and quite. 3 and 4 and quite underwhelming.

[Bill from NH]

Have the slow arms sent out for refurbishing (comm cut & rebalance), then reassemble the motors with new brushes & springs to see if they run better, The arms might be duds, or they might just have seen a lot of prior use.

[Bill Seitz]

The G20 (#3) appears to need a new set of brushes and might have a dirty comm as well. Cleaning and new brushes may restore most of the performance. I have some very old arms that have never been refurbed, and while they don't run like a brand new arm, they run well with good brushes and keeping the comm clean.

 

#4 is a Boxstock 15. The brushes look new, but the comm could be dirty which won't help performance a bit. Note that 12 and 15 arms are the same wind, 50T29, but the 15 has a longer stack so typically more wire. The 15 may not be as fast as a hot X12 arm. Usually they're pretty similar in performance. I15 is a different animal with a more refined arm.

 

I have Mura arms of various vintages starting with purchases made in 1980. Something I've noticed with these arms is that the older ones have longer stacks than the newer ones and none were at the USRA minimum length as you'd typically find with a Camen, Koford, or ProSlot racing arm. With X12, for example, the earliest Mura arms were nearly .400 long where the USRA spec is .350, the same as the Super Wasp. Mura Super Wasp arms were .360 long, and the X12 was eventually wound on that blank. The same holds for Mura G27 and G20 arms. My earliest arms have stacks around .490 with my shortest G20 being .460. The USRA spec is .440. Discovering these dimensional differences, I have a better understanding why older arms have less performance than newer arms, and particularly those from Camen, Koford, and ProSlot.

 

IIRC, racers were using 3.5:1 gears with X12's in the late 80's. That gearing will smoke a modern X12 arm in a couple laps. A modern 45 degree timing, .350 stack ProSlot X12 arm will need something at or above 4:1 to live.

[Mad Mark]

did some refurb on them cleaned/polished the tarnish off the brush hoods so brushs move freely and cleaned up the comms a little. Im not a motor builder so just very basic stuff. should help a little.

[Bill Seitz]

Yes, I did forget to mention cleaning out the brush hoods and making sure the brushes are clean and not gunked up. I've also had a few motors where clean brushes were very snug in clean hoods and didn't move freely. I had to work an alignment tool through the hoods a few times to get them loosened up so the brushes moved freely. Motor won't perform well at all if the brushes can't make good contact with the comm.

 

Another item to watch for, though I don't believe it's an issue with these motors, is that some springs have an overly long leg that touches the brush. The leg is so long that it can completely bridge the hood and hang on the far side.  The motor runs great on new brushes for some laps and suddenly loses speed and will eventually quit running altogether. The hung spring was initially causing loss of pressure (losing speed) and finally not enough for the motor to run.

[Bill from NH]

You can also radius the corners of the brushes & polish them on a piece of newsprint. Before all the diamond coated motor tools were available, we used square micro/needle files to deburr & slightly resize brush hoods after straightening.

[stoo23]

You can also radius the corners of the brushes & polish them on a piece of newsprint. ...........  we used square micro/needle files to deburr & slightly resize brush hoods after straightening.

 Me too,.. ... thats the sort of stuff that really shows our ages !!