Hey all, its been a long time since i have posted anything thing on here. My last posts I would have to look to see where I was at! Anyway Im back to square one with my pony motor. Previously my issues were that it would run on one cylinder at a time, but not at the same time with both plug wires connected?? Finally the mag failed and I had no spark. So i replaced the condenser no help, cap no help, the points and then all was good!!!! Along with rebuilding the carb before hand. Fast fwd to now with one successful season of starting and driving the dozer and tweaking and greasing etc. only burning approximately 15 gallons of diesel over the summer the same problem returned Any input I'll gladly take. What I have done and checked below. 1) good blue spark at both plugs ckd gaps 2) cleaned carb no help 3) put gas in both cylinders no difference 4) swapping plug wire no help 5) cleaned mag cap noticed some carbon erosion at one of the carbon pickup. Cleaned and coated with silicone just to see if any difference, none. 6) cleaned points,looks geat. No help. Spent six hours and got nowhere covered it up and will get back to it in the spring due to winter coming. The coil is original along with the rotor disk. The only thing I didn't check was timing which not sure would be off since i never messed with it. Again any advice greatly appreciated. I think whats frustrating is there is not much to it. Two cylinders with a carb and mag. Jeff 1949 CatD4
You don't mention a compression check on the engine cylinders. You could have a valve either hanging open, or carboned up precluding compression in the proper amount to burn the fuel.
Ask yourself how important it is to you to retain the original integrity of the tractor. The single best change I ever made to an early Cat dozer was to scrap the pony motor and convert to direct electric start. Cat built amazing equipment back in those days, and then started them with washing machine engines! It isn't that hard or expensive, and I can't emphasize enough how "worth-it" it was to me to do!
Yes you are correct haven't done that yet but was and will. I forgot to swing by and pick a compression tester up the day before i went to the tractor site. Last time i checked it was last fall or early spring when i got it running and it was about 70psi per side. The only thing i could do yesterday was use my thumb and they both felt the same amount on the compression stroke. I will take a reading the next trip.
I've briefly thought about it and then thought I wouldn't have ever got this dozer running without the "pain in the ass" pony motor. Reason being, once I broke the main motor loose and everything else prepped it took me approximately 40 minutes to finally get the main started. Since then, usually the first start takes a few before it goes. The only time a direct start would work on " this dozer" is after the initial start and has been driven and all warmed up. I watched Matt ( Pacific Northwest hillbilly) start his for the fist time and it instantly popped off and started with direct start! Mine would have never or ever do that. When I saw that I was in disbelief.
Try taking off the rotor and covering the shaft end in insulation tape .
I could try that. Has that worked for you? What would cause the need for that to be done?
On direct electric start, mine only starts unaided on the warmest summer day. However, with a small shot of starting fluid, it takes off immediately in any conditions. I bet yours will surprise you too!
Mine won't run unless its taped , the tape wears after awhile and needs to be done again . My rotor leaks . Does yours have a switch to turn it off ? Suggest you remove the wire from the mag . First start ups after winter usually had the dozer (D7D , D47U's not much better ) started just in time to turn it off and go home for the day , alright following days though . You can set up the mag on a board with an electric drill driving a socket at slow speed to test it .
Maybe,just maybe. She is a cold blooded machine that much I know. so your able to slide the rotor on no problem with tape? Do you have spark without the tape? Cause I have spark, just doesn't want to run on both cylinders at the same time. This was the same symptom at the first time I had to get the pony running. Was only able to fix it after the spark finally quit. Then I was able to get it fixed by replacement of the points. With very little time on the points and a good spark Im at a loss.
In mine there was a little brass clip that holds the rotor firm , that needs to be removed , the tape holds the rotor firm . There was no spark till it was taped . Frustration till the penny dropped , all the other things had been checked over and over . The condenser and points were replaced , the condenser was darker than it should have been , I have been told its a crook condenser that causes the points to pit / burn , been told to thats its the coil . A cracked cap will leak as well , crook leads won't help either .
I don't have a clip on mine and have a spark. Compression and timing are all thats left.
Unless there is no compression that should be alright . You should be able to hear if a cylinder has nothing when the motor is turning over . Timing is easy depending on what drives the mag , if its the key and slot type you can change your leads over to test , while the cog driven one there are dots on teeth to find . I like the big key drive one , if its dark and the x can't be seen its a 50 / 50 chance of getting it right with a simple lead swap and its away . The jets in the carburetor need to be clear and enough flow to the carb needs to be sorted as well . Sometimes it looks like enough petrol is getting there but its just enough to flow to fill the carb while its sitting , check that by allowing the flow through it . Catch that fuel , as its a serious fire risk . Check it for rust . Sometimes one side can have a weak spark but once the other cylinder gets the motor going it drives the mag fast enough to fire up both
I swapped the leads and when i did that it would run at all. I can't believe the points could be bad already after only a few months of use? But its the same game as last time and that is what fixed it.
It takes more power to create spark under compression so you might have spark when the plug is out but not under compression
Well that would make sense according to what im experiencing.If thats the case what is your best guess? Condensor, coil or points? Coil I have not replaced yet. Now remember that I can run each cylinder one at a time but not together. Go figure.
You have the timing right if its the key type fitting . If you have had a few months of starting you have done well and I'd be back at the points . Very fine wet and dry paper folded so both sides done at once and it'll be right .
Yeah the timing is key type Bosch mag. Im thinking of just buying a new set and eliminate that before i replace anything else for that fact. Its doing exactly the same as before so I just feel its a mag issue even though I got spark.
C Cat starting engines are not washing machine engines, far from it, I have started Cat engines in -20f with the pup, where the the direct start machines fell flat on their face, Starting engines where designed to heat the main engine and build up oil pressure for easier starting , it also puts less strain on the main engine. A properly setup and maintained starting engine can’t be beat, used them to load dead machines onto lowboys. Don’t forget these machines are 60- 70 yrs old, now days most people don’t understand these engines. They are very simple If you know what to look for. Do you have a service manual?, Did you put a little oil in the cylinders to bring up compression, is there compression when you turn the engine over by hand?, put your thumb over the spark plug hole while turning the engine over by hand. Are the sparkplugs wet or dry. Do you have electric start on the starting engine. Matter of opinion on the direct start isn’t expensive, horse m**** in my opinion . I would check the spark plugs, I had a lot of problems with Champions, I switched to NGK AB-6 , no more problems, also had problems with the magneto coil , would fire outside the cly, not inside. Sorry for the rant about starting engines, it just makes me mad at people that don’t understand these engines.
Its alright to clean them rather than replace , mine have had two layers and once the top layer has been cleaned too many times I then replace them . Usually with Lucas parts that I adapt .
I've had a Black Rhodesia do a service on a wheel tractor of mine , while yacking to him he told me Russia gave South Africa several D7G's with pony motors on them . D7G'S would not be a late model dozer anymore but still a front line dozer . The oldest Caterpillars are going still because of the pony start .
Thanks for your input!!!!! I believe I can answer yes to all your questions. Its a electric start. Left cylinder #1 is and always more wet where the right #2 is always dry more hot. I know these machines are very old and Im truly amazed that they can still do after all these years. Im very thorough with maintenance on this machine. Is was rotting away when I got to it and it took a lot of TLC to get it to where it is today. I treat the pony motor well knowing without it the dozer ain't going anywhere. I always change the oil constantly. As I stated before to the previous post I know direct start isn't for this machine and the pony as temper mental as they can be by design, its the only way. Maybe start by replacing the coil as a precautionary and clean the points? Thanks much.
A side note; I currently have champion plugs.
I understood mine well enough to know it belonged in a scrap tub. Sorry if I offended you. I know all about the pre-heating, using it to move the machine, etc. To each his own. My 9U is direct electric and I wouldn't look back...even in the western NY winters. If the pony were mine, I'd check compression, fresh plugs with copper core wires, clean and coat the fuel tank, and completely go through the carb and mag. That all can get expensive too. Good luck.
Thanks. And no worries, all opinions are welcomed, you take it all in and go with your gut and see what happens. The pony is where they maybe needed to save money so you pay for it 70+ years later. Lol!
Well, on the big engines, if you have to replace both the 8D batteries every few years, the pup engine will start to look better
Oh yeah for sure. I believe its a lot of work and a few bucks to convert. I would have never got that dozer started without that pony. I can't say that enough. I even shot starting fluid into the intake. Approximately 40 mins later it took off.She is a stubborn cold blooded beast. Not saying all dozers are like that, i only know this one.
No worries guys. There are "pony guys" and "direct-start" guys, and that is ok. Whatever works for you. It was simple for me to grab a used 40mt starter from the junkyard, grab (2) group 31's and fab up a battery box. Again, not a huge investment compared with rebuilding all that fails on the pony. Maybe yours is in better shape than mine was. Fuel tanks get rusty and constantly plug up the carb. Mag's need frequent attention. Be careful that the gas doesn't dilute the oil- that was a problem with mine. Run them dry on fuel after each run, making sure you have a good working gas valve.
Yep i know. I run it dry with a in-line shutoff and filter. Check and smell the the oil before start and change as soon as it gets a tad dark. It ran awesome all summer until it started to act up.
It might be worth it to send out your mag to have it looked at/freshened up. I can't remember the name of the place, but the guys over on ACMOC will definitely be able to steer you in the right direction, and maybe have some other advice we haven't thought of.
I will look into that. Maybe not a bad idea
I like the pony motor on my D7E, but I also have a lot of experience working with old gas motors so its easy to keep it running. I start it, let it run a minute then crank the diesel on high speed with fuel turned off for a minute or so, the turn on fuel and it starts immediately.
That is about what i do but it never pops off right away. It takes a couple of minutes. Then as it starts to pop a bit it kick out the pinion gear and i have to reingage it a few more times. I adjusted the counterweights a half turn I been meaning to go another to see if that helps.
Update Okay so im doing a follow up to my temperamental pony motor. So with our very unusual warm winter with no snow I was able to get back at it this February. With a totally rebuilt mag. I installed it to only have the same problem with only running on one cylinder at a time with both plug wires hooked up. But will run on either cylinder with one plug wire off either one. After checking and rechecking every possible scenario swapping plugs, wires, gaps compression and timing etc,etc. I discovered that while starting it with the number 1 cylinder only then connecting the #2 cylinder it would run on both for a few seconds only So after a few more tries while seating the plug and it started to run on both I stopped and with the plug cap not fully seated it runs just fine. Go figure? I stumbled across a fix that Im not understanding completely. Just as I was at the end of my rope! It doesn't get much simpler then this pony motor but it sure can throw a curve ball. I may try a different brand of plugs and see if it resolves. Currently using Champions. So if anyone ever has a problem like this hopefully my agony can help someone. Jeff
There used to be a fiddle around for motorcycles, pull the cap away from the plug just a little, it makes the voltage build a little higher before it jumps across the gap. Sometimes it would help if one plug was fouled, just pull the plug boot off a fraction until its fired a few hundred times then it was fine. Maybe it needs a little more plug gap?
Maybe. I will try that along with another brand of plugs and see. Never the less Im just happy as hell I stumbled across this anomaly.
Do you still have the original points? I often find points in mags that are far better than any you can buy today. I f you can see layers of tungsten or whatever it is they are worth saving. New points nowadays are plated crap and won't last. Good points take them out and reface with Dremel.
I don’t know if anyone mentioned it, but you may want to use stabilizer in the gas you’re using, especially if it sits all winter because it will likely go stale. I use stabilizer all the time just because some of my gas powered equipment sits for extended periods. Stale gas even though its clean, in a pup motor can cause issues
I’m on my second set. I replaced them fall of 2022. Not sure if I have those. Will have to check. But it doesn’t seem as if that was the problem. These were new again when I rebuilt the whole mag this year.
I have put some seafoam in every so often. But I drain all the gas out during the winter
I quit using Seafoam. I feel there are better products for stabilizing
My secret is my F250 swills gas during the winter so if the gas is off color but not stinky, I'll run a couple gallons of that per tank. Stinky or looking like motor oil I run it to the guys that recycle waste oil into fire for heat.