C-Can Motor Building Steps

Some notes about motor building: what follows, in outline form, are the steps I follow when building any given C-Can motor. And no, I didn’t think the list would be this long, either. After actually documenting what I did, I was surprised by the number of steps, checks, measurements, and general fiddling around I went through in what I had always presumed was a simple, straightforward process.

Not to worry. As it turns out, there’s a big difference between "complex," which is what this appears to be, and "difficult." None of these steps, taken by itself, is beyond the ability of an average slot car drag racer; there are simply a lot of them. Some may require tools you presently don’t own, some may involve procedures you may not be familiar with, and the point of some may escape you.

To paraphrase a note I include in my "Tools" presentation: what you end up doing is usually determined by the manner in which you end up approaching motor building. I figure it this way: if you have some idea about how you might do it, and a few suggestions about how you possibly should do it, you can make a more informed decision about how you will do it.

One final word about motor building: the best way you can learn about motor building is - surprise! - to build motors. Experience is a great teacher, not to mention occasionally providing those magic, humbling moments that can be described either as "Oops!" or "Oh, ****!," depending on their cost. Don’t be afraid of messing something up or building a motor that doesn’t perform up to your expectations.

Everyone does it. Regularly. Anyone who claims they don’t is either lying to you or suffering from some pretty low expectations. We all build dogs now and then, and you will, too. But when you establish a solid building method, you’ll have a better idea of what - and what not to - blame and/or change.

So good luck, and let’s get on with it, shall we?

Unca Frank

(What you see below is probably going to have to do for the time being; I estimate approximately 9,000 to 10,000 additional words are necessary to describe them, covering each meaningful step, even without illustrations. At these prices, figure on waiting a while for additional content. In the meantime, if you're curious about what some step may mean or entail, e-mail me.)

Motor Building Steps (by component area)

Can Work

1       Selection and Measurement

2       Bushing removal

3       Can Sizing

4       Interior prep

5       Exterior prep - "ear" evening

6       Bottom flattening

7       Bushing Hole centering

8       Seam soldering

9       Endbell screw hole cleanup

10     Bushing/bearing soldering

11     Mounting screw tapping (or)

12     Can mount tinning

Endbell Mounting                    

13      Alignment tool insertion

14     Endbell-to-can alignment

15     Screw hole drilling

16      Screw tapping & insertion by sequence - oiling

17     Disassembly

18     Endbell hole deburring

19     Reassembly & bushing alignment check

Magnet Installation

20      Selection, inspection, Gauss reading, matching

21     Insertion & measurement - thickness, centering, & configuration

22     Polarity/orientation check

23     Magnet Cleaning

24     Adhesive selection & prep

25     Final magnet installation

26      Positioning & measurement

27     Excess adhesive cleaning

28     Baking (if necessary

Magnet Honing

29      Hone & diameter selection

30     Hone installation

31     Clearance checking

32     Can-endbell assembly

33     First (or sequential) honing - heat

34     Disassembly & cleaning

35     Bushing/bearing cleaning & checking

36     Final dimension honing

37     Polishing

38     Disassembly & final cleaning - i.d. engraving

Armature Prep

39     Selection - Design, winding, balance, timing, commutator, length

40     Arm diameter measurement

41     Arm stack length measurement

42     Com diameter measurement

43     Timing check

44     Arm meter reading

Armature Spacing

45     Initial arm installation & can assembly - com & arm shaft spacer shortening, if necessary

46     Endplay inspection & measurement

47     Disassembly & preliminary spacer addition

48     Reassembly

49     2nd spacer measurement

50     Reassembly

51     Additional spacer measurement(s), as necessary

52     Disassembly & cleaning

Endbell Hardware Installation

53     Endbell inspection, internal/external deflashing, internal "radiusing," as necessary

54     Hardware checking & inspection - trimming & deburring - brush backplate flattening

55     Hardware cleaning & polishing

56     "Slug" or shaft installation

57     Brush backplate installation

58     Brush hood alignment tool installation

59     Endbell-to-can assembly

60     Brush hood and spring post assembly

61     Hood alignment & tightening

62     Alignment checking - com degrees vs. alignment tool degrees - advance/retard

63     Brush hood & back plate clearancing & honing

64     Hardware tinning/soldering

65     Internal screw facing - endbell cleaning

Brush & Spring Prep

66     Spring selection & matching - brush arm length matching & deburring

67     Brush selection

68     Brush honing - radius vs. break-in time

69     Brush shunt/spring slot prep- insulated vs. non- insulated

70     Brush deburring, cleaning, & polishing - brush orientation identification/engraving

Preliminary Assembly of Motor

71     Can & endbell final cleaning

72     Arm & spacer installation

73     Endbell attachment - final checking - installation of brushes and springs

Initial Motor Break-in

74     Initial oiling

75     Standard (nominal) break-in procedures

76         - 5 minutes @ 3 volts, temp check, cool

77         - 5 minutes @ 4 volts

78         - Disassemble, inspect brush face & commutator condition

79         - Clean, reassemble, reoil

80         - 5 minutes @ 5 volts, high-voltage checking

81         - Disassemble, inspect, clean can, endbell, spacers, brushes & springs

Armature Shaft shortening

82     Arm shaft measurement & marking

83     Shaft cutting & deburring

84     Motor reassembly & reoiling

Shunt Wire Installation

85     Shunt wire selection & construction

86     Shunt wire prep

87     Shunt forming, shunt & spring oiling, can screw removal, soldering, trimming

Gear Installation, Final Cleaning & Break-in

88     Shaft oiling & removable "barrier washer" installation, end cleaning

89     Shaft tinning

90     Gear prep & installation - tooth inspection

91     Brush & spring removal, final cleaning

92     Brush & spring reassembly, reoiling

93     Final break-in: 10 minutes @ 5 volts

94     Alternate break-in procedures

95     Motor data recording - amps vs. volts

96     Rezap magnets/motor

Motor Care, Storage, & Installation Tips

bullet  Avoid motor-to-motor contact. Whenever possible, use nonmetallic storage containers for motors.

bullet  Avoid shock and excessive heat, particularly when soldering a motor in.

bullet  Insure some free play (adequate gear lash) throughout the total rotation of both gears. Rotate the spur
    gear 5 or 6 times to check all mesh relationships. When in doubt, use the "plastic bag shim" method.

bullet  Clean the motor periodically. Pure naptha is less aggressive than motor sprays, less hostile than starting
    fluid (ether), and reasonably inexpensive. Make certain the motor has been dried and oiled before putting
    it back into service.

bullet  Periodically check bushing motors for wear between rebuilds. The can end bushing is subjected to the
     most side loads, and generally is the first to show signs of wear.

bullet  Disassemble, inspect, rebuild, and rezap your motor before it becomes necessary, either after X number
    of passes or X number of Races. It will perform better over a longer period of time if you perform
    "periodic maintenance" rather than "emergency repairs."

Maintenance/Rebuilding Guidelines

bullet  Disassembly & cleaning - parts segregation - shaft bearing/bushing surface inspection

bullet  Spring inspection, checking, & reuse

bullet  Brush replacement or reuse - temp hardening

bullet  Commutator turning & surface finish - minimum material removal - recording number of
     rebuilds/com diameter - minimum safe diameter

bullet  Rezapping after every rebuild

bullet  Replacing bushings/bearings - accurate motor "slugs" - avoiding heat

bullet  Rebalancing - when and what kind of arm

The Bottom Line

After all this, you may still be asking yourself "Why bother? I can just buy a motor off the wall and be done with it." Well, sure you can, but not just any motor.

Figure it this way: the parts alone for a good Grp 12 motor retail for between $55 and $60. At, say, $6.50/hr labor rate (not excessive by any means), and 5 to 7 hours worth of labor in a motor, you end up with a total cost of between $87.50 and $105.50. How many of those parts and how much of that precision labor do you suppose are included on the $28 motor you’re eyeing on the wall at your local shop? Uh huh.

To make it a little clearer, let me give you my estimates of just some of the improvements that make a "prepared" motor better than a non-prepared one:

Properly honed, matched, zapped magnets:          +7-10%

Low-inductance, well-timed, balanced arm:          +3-5%

Low-drag, well-sized brushes, matched springs:   +1-2%

Low-drag, accurate bushings, can alignment:         +½-1%

Can airflow characteristics, arm/shaft lightening:     +½-1%

Net result? a 12% to 19% improvement in the theoretical performance of the motor, or, to put it another way, approximately the difference between a Grp 12 and a Grp 20 motor. Is that clear enough? It goes a long way towards explaining why some 90-gram Grp 12 cars run the quarter mile in the .840/.850 range, while others run it in the .890/.900 range, doesn’t it?

Build or buy, you now have some information to base that decision on. In the long run, it’s still your money and your choice, so make the best of it!

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