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The D4 actually started around 1937 with a G4 Series then evolved into the 7U Series of the 1940s and 1950s. The Caterpillar Company continued to build new D4s right up till now and they are a great machine. The smaller D2 was a bit underpowered for the weight but the D4 was another machine and solid as. The Pony motor started the machine then the diesel engine kicked in once primed by the petrol -powered motor. The Pony motor carb kit: CAT part number or better yet the Zenith carb number should be a Zenith K2067 kit. The older D-4s have the same carb kit as a John Deere JD 720 and 730 pony motor

Note in the above picture: the tap at the bottom turn 1/4 turn only to release any water if sitting on both sides of the pony motor. Check dip stick & use SAE30 grade oil to replace or top off. Drain plug is on the right side if in the drivers seat. If access to air line take the plugs out both sidse & blow air when you crack 1/4 turn taps to release water etc. Make sure spark plugs are free of water

The D4 can give you problems especially when sitting a long time. Clean the bowl & blow the air thru the carb line and bowl if sitting. Makde sure you have fuel flowing thru the fuel lines to the carb bowl. Either water or the points get stuck. With us we had intermitten spark problems and it turned out to be the magneto shaft not centred & the condenser which although we gor spark we only just got it. If you have problems with spark check each of the 2 plugs once the motor starts but also start the pony with spark plug arcing against metal to check for spark. In our case it we had one spark plug good and the other cold-- tried leads & switching spark plugs as we didn't have any spares at the time (this machine was in the bush). We got spark in the magneto and set the timing OK (bit hard to see timing marks so make sure you have a strong torch to see and try to mark if you dismantle). You will see the timing marks once the magneto is out. One plug was hot the other cold but we found the problem in the magneto & points @ .20. Still the pony motor once started was running on 1 cylinder but then we stripped the magneto again and saw the offset shaft which caused the problem & then the condenser being the main cuplprit so check these as its normally the magneto or fuel you will have the problem with. We then managed to fire the Pony motor up OK


The Caterpillar D4 -JU Series

Remember this bulldozer does not use a battery as the magneto does the work of the normal distributor and spark etc. Once awake you need to keep the Pony running until the water heats up to the main motor and the head at the rear of the main motor is warm. Especially when starting in real cold weather this is important. The pull rope start is a headache-- you start it clockwise. We will change to auto start this machine and show you how to do. Remember we are back yard bush mechanics!!!


D4. 7U. 1947 7U1-7U1797 D4. 7U. 1948 7U1798-7U4257  
D4. 7U. 1949 7U4258-7U8027 D4. 7U. 1950 7U8028-7U11887
D4. 7U. 1951 7U11888-7U16008 D4. 7U. 1952 7U16009-7U20836
D4. 7U. 1953 7U20837-7U26193 D4. 7U. 1954 7U26194-7U30583 
D4. 7U. 1955 7U30584-7U35569 D4. 7U. 1956 7U35570-7U39596
D4. 7U. 1957 7U39597-7U42012 D4. 7U. 1958 7U42013-7U42725
     D4. 7U. 1959 7U42726-  


Magneto in the pony motor Caterpillar D4 Bulldozer-- easy to get out and easy to check but make sure you line up the timing marks (you normally need a good torch to get TDC). Check coil & condenser in the magneto and test for spark before you put back as this and the carb are normally the headaches in the Pony motor



Magneto number made by Bosch in Massachusits, USA very rarely you have a problem with but still check. To time check points @ .20 Open cylinder head drain bolt at the rear of the magneto and below it & turn flywheel [pully where you start it]. Take out spark plug & check piston is coming up on the compression stroke. Continue until the mark or [MAG] is even with the mark on the start engine crankcase cover. Crank on No1 is now 25 ahead of TDC on compression stroke -firing point. Take magneto out & plate & rotor off then rotate magneto drive gear until rotor contact in line. Breaker points will begin to open, Install.

Spark plug gaps= .025" Contact points = .20"

The sediment bowl sometimes you can use an old pill bottle but the problem can be the top of the bowl housing has corroded over the years. The spark plugs D16 are the same as the seagull outboard motors for boats and readily available in NZ.

Overview with the breather off the Pony motor. The oil pressure gauge will register oil pressure and the fuel pressure gauge (on the front left side of the engine) will go to the green. Now start the main engine by simply opening the throttle. Fill the ;ony motor gas tank with regularf petrol only. The diesel should kick in and when it does the pinion will kick out, so release the starting engine clutch and shut the gas off on the pony motor.Try to use all the petrol in the pony motor up before you fire the main engine but no worries if not. When you start the main motor check your guage on the front left side for fuel pressure. Open the tap to make sure diesel is coming thru OK. When D4 not in use you can turn the diesel off at the square nut under the tank.

We have a mobile truck with petrol compressor so we can clean the carb, magneto etc, gas tanks in the bush and assist anyone in the lower North Island of NZ who are stuck in the bush.

THIS IS AN ELECTRIC START pony motor using a starter with pre start ignition and beding the starter arm to engage the flywheel pulleys. You can also use a Briggs & Stratton lawnmower motor with pull start to make it easy as the old pull start is a pain.



If you wish to share any CatD4-7U info please send us email. We are happy to add information for you on our website especially parts comments, problems, pics of your machines ---etc. For Kiwis with Cat 7U tell us what serial number you have and where in NZ you live as we wish to index machines. [ D4-7U bulldozer Forum ad ]

[ D4-7U pony motor & add Honda starter ] [ D4-7U pony motor & magneto continued ] [ D4-7U bulldozer latest Oct-Nov pics ] [ D4-7U work next on steering clutches 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17] [ D4-7U bulldozer USA parts ] [ D4-7U backend installing ] [ D4-7U brakeshoes ] [ NZ suppliers of CAT & Komatsu parts ] [ D4-7U bulldozer pics ] [ D4-7U bulldozer hyster winch ] We are also suppliers of NEW Komatsu spare parts for PCs up to 4 tonne as well looking for agents to buy our [ retread truck and bus tyres ]. RUBBER EXCAVATOR TRACKS FOR SALE all models : [ RUBBER TRACKS ] [ Kiwi bulldozer parts links ]

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