Hi, I have recently acquired a 955 - 12A model Cat Track Loader. It had been barn stored for the past 6yrs, but previous owner had said that it was put away running. obvious thinks I am doing, gas, gas lies/filter, etc... I am also checking switches... I found the push button switch for the PUP/Pony engine sticking, so replaced it.. there is also a On/Off switch on the left panel that I believe is used to ground the mag to kill the pup.. While connected to the mag, it seemed to be shorted to ground, regardless of the position. I then checked it, not connected, it worked fine... That brings me to my question.... the mag terminal that this switch was connected to appears to be shorted to chassis ground all the time.. while not turning. I took the mag off and tried to check for spark on the bench.. nothing.. i also connected my ohm meter to the terminal and to chassis of mag and spun the gear... resitenace goes from 0 to infinite when spinning.. is this correct?? am I checking it correctly?? any thoughts or comments are appreciated.... thanks rod
Welcome to the forum rditz. :usa The only test you make to the output terminal with the mag turning would be a voltage output test. The only tool required for that is a known good spark plug. Have you checked the breaker points and condensor? I haven't worked on one of these old Cat pony engines, do they have an external mag like a Fairbanks or Wico? Need a little more info of your mag setup.
ATCOEQUIP, thanks for the welcome.... i will probably post a lot here as i get familiar with this old Cat... I have tried a known good plug, but no spark... Yes, it is an external gear driven mag... i have opened it up and found that the wire from the magnate is shorted to the mounting points of that magnate... i will have to have the unit tested next week.. another question though, i wanted to know how the mag was timed to the crank?? the mag has a timing mark, but have not seen an obvious mark on the gear that drives it.... there has to be a mark somewhere to let you time this thing.... HELP !!! lol i am getting close to firing up this PUP, once i sort out spark and fuel (still flushing tank.... YUK!... then i can move on.... thanks rod
Back in those days some of the cat mags had a little tiny rotor in them and inside the rotor were two metal tangs that would break off and allow the rotor to wiggle on the shaft and not allow the spark to transfer to the cap properly. The timing marks were sometimes a dot and sometimes an X. Got to be a mark on the drive gear, some times they missed the tooth a little when stamping the X and this is all u will see /. Clamp the mag in a vise so you can manually fire it with the cap off and short directly to the coil when firing it. If no fire at coil than problem is deeper than cap. coil, points etc.
grandpa, thank you for your input... I found the timing mark on the mag, but have not yet noticed any marks on the gear in the engine... will keep looking. I have opened up the mag from both sides.. under the cap (the back side) there is a rotor, like you mentioned. the tangs are still both there. points apeear to open and close. on the gear side there is the magnate, when removed i have a dead short from the black lead (which is connected to the terminal) and the mounting bars. the tab that is connected to a lead on the cap has a potential of 7ohms... it is all put back together now and I will be taking it into a shop tomorrow and see if they can test/repair. I am finding this all very interesting as i believe that the pup serves more than just a starter purpose... it appears as though the exhaust runs through the diesel instake,probably for the purpose of heating up the air for the big motor... it also appears as though there is a belt driven water pump on the pup and it is connected to the diesel's cooling system, presumably to warm up the big motor's coolant .. all for cold weather starting.... very neat. thanks rod
Keep us posted as to what u find just to quell our curiosity.
Some of these old magnetos that sit for a while, especially if they are outside and the cap gasket is not perfect, will develop a bit of corrosion on the points, usually it can't be seen. If you get no spark, file the point surfaces lightly, or use some garnet paper to freshen them up. Check your rotor, as mentioned before, as some models on Cat equipment, the small odd firing magneto, used a rotor with a clip inside that broke. You can add a shim, with some silicone, to make these last a surprising long time. As I recall the cap has spring loaded 'terminals", check that they work. If the impulse does not work on the bench, it will not spark when installed unless you possibly can get the pup cranking very very fast. The main shaft should lock with the impulse drive as you are turning it on the bench, and release, just as you feel you can't turn it any farther without a wrench. If you take the impulse apart, note very carefully where the spring and other parts are located. Sometimes just penetrating oil will free it up, as they do get gummy if the engine oil is not kept fresh. It's not good for a magneto not to be grounded on it's high tension lead(s), when rotated. Rarely is weak magnets or a coil a problem. I believe your condenser can be checked by disconnecting it, but that may not mean it's okay. I never had one of the original ones fail. Use solid wire in your plug leads with a magneto. I think the plug gap is .025". Best not to use Champion plugs. There is a mark on the camshaft gear to match up with the impulse drive. If you get the timing wrong or think it's wrong(a lot of backfiring), just remove and rotate 180, and try again. Yes the ground wire from the mag remains grounded with the dash switch off. Not unusual for the pups to be idled for 5- 10 minutes in very cold weather to heat the main engine. Use 10-30 oil in pup crankcase, not #30, as this oil rarely gets warm. Phil
Phil, thank you for your reply, some very helpful comments... I am going to take the mag to a local place and see if they can test it... Still have to check for timing mark on the cam gear... This Cat was stored in a barn, so not weathered at all from sitting... will definitely update the thread on my progress.. thanks again rod
update, I have had the magneto rebuilt and got it installed this weekend... I had some trouble getting it timed, but with the help of a neighbour, we got the little pony running.. and it runs good.. now I have to figure out how to engage it to the big engine.. when i pull out the lever, it grinds gears... my assumption it that i need to engage the clutch and then pull out the lever.. can anyone confirm this?? also, there seems to be no feel to the clutch when i try to pull the lever... a lot os play in the linkage, which I will have to take care of... any direction on clutch adjustment would be much appreciated??? thanks rod
Rditz one lever is the clutch lever and the other lever is your starter pinion engagement lever. When you get your pony motor going take your clutch lever and go the opposite way with it. This will ingage your clutch brake so you can easily engage your starter pinion. Then move clutch lever the other way to engage clutch and the big motot should start to turn over. Should have the decompresser lever pull at the beginning and then when the big engine has oil pressure dump the decompression lever and she should start. When it starts the speed of the big motor should kick out the starting pinion. Make sure it disengages. If it doesnt automaticly than youll need to adjust your pinion tension. GOOD LUCK. LOL, Dont adjust your clutch just yet, there is alot of play in in but when its engaged it should feel better to you.
Hi rditz, It's been a long time ago to remember but I would push the bottom lever in as far as it will go and pull out the top lever easy, feeling for the teeth to mesh and then fully engage the clutch lever by pulling it all the way out. When the diesel engine starts push the clutch lever toward the main block to be sure the clutch isn't dragging. On a real cold start you might have to reinguage the starting engine a couple times or hold the clutch lever out until the diesel will continue running.
955 with a pony motor? Any photos would be interesting...
well, gave it a try tonight and got the old girl fired up, thanks again for your thoughts/comments... it is not charging at the moment, so I have been advised to polarize the generator.. hope that works.. next is to replace guages and once charging system works, wire up some lights as there are none... thanks again rod
If memory serves me right( thats scary in itself ha)that has an external regulator on it , big old box with removable cover . They had alot of problems with them, have u full fielded the gen to see if it works then?
well, i tried to polarize the generator last night.. I had done some research and asked around and the basic instruction was to take a wire and connect to bet power and the other end to the armature terminal, do it quickly and you will see a spark. i did this, but still not getting voltage from armature or field terminals to ground... here are a couple of pictures I had read that the larger of the two termials on the generator would be the armature, so that is the one i tried to polarize... it is the far left one. the middle is the field terminal and the far right one is ground. I guess the next step is to pull the generator out and the other test i read i could do is to connect battery voltage to the armature and ground and the generator should turn on its own.. if it does not, time to dig deeper.... thanks rod