Part 1: Disassembly
Having recently fixed our 1990’s vintage Kenwood Chef mixer, my wife and I were inspired to have a go at restoring an original 1950’s “Chef”. In the process I discovered that there’s not a lot of in-depth or freely available technical information on these machines out there, and so have decided to share details of this project in the hope that it may help others who are attempting or would like to attempt a similar restoration.
The Kenwood “Chef” was designed in the late 1940’s and first sold in 1950. US patent 2584887, for a “domestic mixing apparatus”, filed in May 1950 and assigned to the Kenwood Manufacturing Company Limited, specifies the inventor as Roger Laurence. It also mentions the original British patent, filed on May 24th 1949. In 1946-47, Roger Laurence and Ken Wood started a company called Woodlau Industries (from Wood and Laurence), which produced an electric toaster (model A100), and the “Kenwood Electric Food Mixer” (model A200). The A200 was a stand mixer design copied from the popular Sunbeam Mixmaster (admitted to by Ken himself in this video). I don’t know if Ken got into trouble with Sunbeam, but the A200 was quickly replaced by the more sophisticated “Chef” planetary mixer model A700. At some point before 1950, presumably after designing the “Chef”, Roger Laurence left the business, whose name was then changed to the Kenwood Manufacturing Company Limited.
The “Chef” we obtained for this restoration, pictured below, is an early example of the first A700 model, as indicated by both its serial number (91831), and the name “Kenwood” printed on the mixer body. Later A700 models have “Kenwood Chef” printed on them. This mixer would have been manufactured no later than 1951.
There are two variants of the original A700 design, the A700.A and A700.B. The B variant is easily identified by its having two short motor vent slots on each side instead of the single long vent slots of the A variant. The Kenwood Chef Restore website states that the A700 A&B models were made between 1950 and 1957. They were followed by a revamped model, the A700.D, made between 1957 and 1960.
Before I get into the details of disassembling the machine, let’s have a closer look at it in its pre-restoration condition:
Ok, now I’ll describe how to completely dismantle this A700.A model Chef. Note that you will end up with a lot of small parts and screws, so before you start I suggest that you get a supply of small zip-lock bags and a marker pen to label what they are and where they came from. Also, take plenty of photos as you go to remind yourself how things go back together!
Remove the plastic bowl stand from the base, and, whilst there, unscrew and remove the two metal spring supports that the stand sits on.
Remove the mincer retaining screw (the knurled knob in the photo above) and the round plastic mincer drive cover from the front of the machine.
Remove the large chrome screw and washer from the juicer socket on top of the machine.
Remove the chrome nut and washer at the centre of the planetary hub.
Remove the planetary hub by pulling downwards whilst gently jiggling it back and forth. It can be a bit tight, but it will come off.
Remove the pin and washer from the exposed planetary drive shaft.
Removing the Top Cover
The top (gearbox) cover is secured by 7 machine screws (size 4 BA thread) as described:
Remove the three recessed screws and washers from around the front edge of the planetary ring gear. At this point you can also remove the ring gear by removing the four other screws that hold it in place. Note that these screws have a rubber washer to seal against grease – these will need to be replaced (we cut our own from a sheet of nitrile rubber).
Remove the two outer screws under the middle of the arm (behind the planetary ring gear), leaving the larger centre screw in place for now.
Remove the black plastic rear cover to expose the blender drive.
Remove the six screws and washers from the raised inner metal locking-ring.
Remove the inner-ring and the circular metal plate to expose two more screws. Note that the inner-ring has a felt washer in a recess in its base – this will need to be replaced.
Remove the two exposed rear screws. The top cover should now lift off to reveal…
Removing the Gears
Lift off the large gear made of red reinforced resin and collect the metal washer from underneath.
Use a 1/16” hex wrench to loosen the set screw in the top of the motor shaft (protruding through the pinion gear at the rear). Push the pinion gear down and remove the pin. Lift off the pinion gear and spring. Note that there is a small metal washer on top of the spring, and a larger metal washer sitting on top of a felt washer under the spring.
Remove the split pin and washer from the top of the gear with the holes in it.
Lift both the final (planetary drive) gear, and the gear with holes at the same time. Collect the washers from under both gears (the final gear may have more than one washer/shim)
Pull out the mincer drive gear from the front of the top cover.
Removing the Motor Assembly
Unscrew the four screws on the front of the mixer that secure the sliding latch to the mixer body. Remove the sliding latch by pulling the locking pin and moving the latch rearwards out of its slot. The mixer top part will need to be tilted back enough to allow the latch to be pulled clear.
Remove the locking pin itself by unscrewing the small set screw that holds it in place.
Remove the speed control knob by unscrewing the centre screw. Collect the spring from under the knob.
Cut the electrical flex beneath the motor.
With someone supporting the motor underneath, un-bolt the motor from the body by using a 5/8” (or 8mm) socket to remove the two bolts located in the gearbox above the motor (hidden under the grease in the above photo). Note that these bolts can also be accessed with the top cover on, which allows the motor to be removed for maintenance without taking the gearbox apart.
Tip the top back and slide out the motor assembly. Note that there is a wide cork gasket between the motor and the mixer case – if it doesn’t come out with the motor it will be stuck in the recess at the top of the motor compartment.
Unscrew the saddle clamp that clamps the electrical flex under the mixer base and discard the old flex.
Taking the Motor Assembly Apart
The motor assembly consists of the universal motor itself, bolted to a metal shroud which houses the electrical and speed control components.
On the outside of the shroud, remove the guard for the speed control cam (two sheet metal screws), then slide the cam off the shaft.
Remove the main vented cover at the bottom of the shroud (fixed with a single screw and nut) to expose the electrical components.
Cut away all the wires near their soldered connections and pull the free wires out of the compartment. These are the three mains wires, the two wires to the motor, the two wires to the resistor on the outside, and the two wires to the on/off switch. I’m going to include a wiring diagram in the next part of this blog, so don’t worry about exactly where the wires connect.
Cut off the capacitor (upper silver can in photo) and resistor (green component near top of photo) which are soldered to the pivoting board (what I will call the governor switch assembly).
Unscrew and remove the narrow electrical board with the solder tabs (where the mains wires connect).
Remove the capacitor which is clamped to the shroud behind the governor switch.
On the outside of the shroud, unscrew the governor switch hinge (two nuts with screws through to the inside, and the one screw and three nuts holding the base of the hinge). You can now remove the governor switch by pushing it back out through the hole on the hinge side so that the hinge can be folded up, then back as far as it will go through the hole on the other side, rotating the hinge end down and out of the shroud.
Slightly above, and to the right of the apex of the shroud opening there is a round hole (photo below), possibly covered with tape. Shine a light in here and turn the motor shaft until you see the set screw which holds the fan assembly to the motor shaft. Use a 3/32” allen (hex) wrench to loosen the screw. Reach up and pull the fan assembly off the shaft.
Inside the shroud you will now see the two nuts which attach the motor to the shroud. Use a 11/32” socket and extension bar to remove the nuts.
To remove the motor from the shroud, pry the shroud down by putting a flat bladed screw driver between the top edge of the shroud and the motor and twist. Work your way around until it comes free.
Un-bolt the 450 ohm wire-wound bypass resistor from the outside of the shroud. It is sandwiched between two mica sheets.
Pry up the tabs holding the paxolin board which is insulating the on/off switch from the shroud (critical: this is essential electrical insulation and must go back!) Remove the two screws holding the on/off switch in place. The left-hand one protrudes down to act as a stop for the cam. Note its position for reinstallation. Remove the on/off switch.
Taking the Universal Motor Apart
The motor consists of two end bells and a central section (the field coils) held together with two long threaded rods and nuts.
Before you take it apart, I highly recommend using a paint pen to make reference marks to show the alignment of the end bells to the field coil section. Take a photo of this too, as cleaning or painting may remove your marks. Of particular importance is the relationship of the end bell with the brushes to the field coil, as this determines the angular relationship of the magnetic fields in the motor. Once this bell is correctly aligned, the other bell is aligned such that, looking straight down on it, a line between the two screws is perpendicular to a line between the protruding brush housings. Getting this right is important for correct re-fitting of the motor to the shroud.
Remove the two nuts with the 11/32” socket (or spanner) and carefully pull the motor apart. Before you can completely remove the end bell with the brushes, you need to reach in with a pair of long-nose pliers and pull the brush wires out from between the plastic housing and the brass brush holder sleeve.
Note that there is a metal washer that fits over the commutator end of the armature shaft. If you can’t see it on the shaft, it may be stuck inside the bell (in a later A700B model that I have since restored there were two washers, one over each end of the armature shaft).
If you have difficulty removing the armature shaft from a bell, tap the shaft with a rubber mallet.
Separate the top and bottom halves of the mixer body by removing the hinge pin with a 6mm pin punch.
Remove the remaining chrome screw and washer from the grease filling hole under the arm of the mixer.
Dig out the degraded o-ring from around the gearbox. You will need to buy or make another one of these.
Remove the rubber feet from the mixer base.
And that’s about it! In part 2 I’ll discuss restoring the motor and electrics, and in part 3 cleaning and finishing the body parts and reassembling the mixer.