Several times I have recommended putting the starting batteries in the engine compartment and cabling them directly to the starter. Low voltage at the starter results in the death of the starter and probably the batteries as well. The timeline of the failure is that when you press the starter button the solenoid pulls the starter drive gear into mesh with the engine flywheel ring gear and in the last part of movement makes the electrical contact between the battery cable and the starter motor. If all goes well the engine cranks and when you release the start button, solenoid reurns opening the electric contact and moving the starter gear out of mesh.
If there is insufficient voltage at the starter motor for the engine to crank, the starter gear is under pressure and can't release. The pressure is caused by the cylinder pressure trying to push the piston back down, that you got almost to the top before the starter couldn't crank it any further.
When you release the start button the starter stays engaged and since it is in a locked rotor state it draws infinite current. The starter smokes, the batteries overheat from having a short circuit across them and you are within seconds of serious failure.
Thee is no way to 100% guarantee that this will never happen but the best preventative measure is to always have good batteries good cables and run the cables directly to the positive and negative terminals on the starter. From the negative terminal, run a cable to the engine cradle bolt and from there to the chassis ground bolt From the positive terminal on the solenoid run a cable to the junction bolt that has the cable feeding the rest of the bus.
Corrosion of battery cable connections is always a problem because of dissimilar metals and battery acid. A good method at the battery end, is to use marine type connectors wihich have a bolt and wing nut connection. Put news ones onto new batteries and leave them there for the life of the battery The cables are easy to remove by taken of the wing nut and you don't put any strain on the battery post as when trying to remove the cable clamped directly to the post. All connections should be liberally coated with anti corrosion paste (or just palin chassis grease) before assembly
Stan
I have always wondered when you use the wing nut connectors if there is enough surface contact to carry the necessary current.
It would seem like that would be the bottle neck
What has your experience been????
Melbo
Melbo: I have them carry enough current to make 0000 cable smoke and that is way more than we should be using on a bus. That occurred when I hit the rear start button after installing a rebuilt starter. I had a lot of argument from a young employee in the rebuild shop that there was supposed to be a connection to frame in the starter. Eventually the boss confirmed that there should not be a connection to frame and I stood there and metered it, piece by piece, as the young man dismantled it. It turned out that one field coil had been put in backwards and made a direct short to frame.
Voltage drop and overheating occur because of the resistance in the circuit. Resistance is a function of the length of the conductor. When the cable is clamped tight under the wing nut, the length of the conductor is virtually zero, hence very low resistance. The good quality marine terminals use a 3/8" bolt on the positive lug and a 5/16" bolt on the negative.
I have wondered as to why the bus engineers located the batts up front, almost as for away from the starter as they could. But I know that it works, has worked, and will continue to work. I also wonder as to why I would want the batts next to 144 gals of fuel in case of an accident ????
Relocating the batts to the engine comp makes sense, but I think that the radiant heat will take a toll on the batts. I agree that the elimination of corrosion on the ends of the cables, Including that which gets within the crimped on lug will allow the Batteries to preform well in the upfront location.
I am checking info out about the newer trucks using a 12 V starter with two lesser size batts in parrallel.
I put a Delco 39MT on my 8-92 this summer. We've burnt out 4 starters in 3 years so this will be a good test. Quote from Delco's site:
"The 39MT MxT (Maximum Torque Technology) Heavy Duty Starter is the next-generation starting solution for today's demanding heavy duty applications."
http://www.delcoremy.com/Starters39MT.aspx
Gary 79 5C: If you look at your 5C the battery location is obvious. They are in a space that was not really good for anything else at the end of the A/C compartment They are close to the big motors that ran 24 hours a day when it was a commercial bus and the starter was only used once a day when it was shut down to check the oil.
There is no question that it worked fine for what it was designed for but we have changed the design. Just count the number of cable and bolt connections between your batteries and the starter and tell me how often you check and clean every one. I have helped hundreds of busnuts with electrical problems and I can tell you that almost none of them did any maintenance on the battery system until it failed. When it fails, it frequently costs you a starter, if not more serious damage, but if you have a V drive just changing the starter is bad enough.
Bobofthenorth: That is a really high rate of starter failure. Did anybody figure out the cause? If you are using rebuilt starters, do they have Delco solenoids or the aftermarket imports? Even field coils and armatures can be obtained aftermarket. If you still have the factory cabling system, I would have serious look at all the connections, especially the ground side as there is no negative cable between the batteries and starter. If the ground bolts are not welded to the frame they are very suspect. Double check the ground bolt on the cradle and the cable from there to the main frame ground bolt.
As you have probably gathered by now, I think you are getting low voltage to the starter motor. The only place to check it is right on the two terminals on the strater motor. not the terminals on the solenoid and not using the frame or engine block as the reference ground.
I agree Stan - its a really high rate of failure. Its also a really expensive rate of failure. :(
We thought we had the problem solved 2 years ago which is when I last changed starters but evidently we didn't completely solve the problem because I had a couple of hard starts this summer. It didn't actually let me down but I went ahead and changed the starter anyway because I would rather do that at home than on the side of the road. I agree with you that the ground side is a potential source of resistance but I don't think that is the problem. I have double cables to ground in the batt comp and two ground cables in the engine comp (one from the block to the frame and the other from the starter to the frame) - should be overkill. I've never taken a voltage reading while I was cranking - it always lights up with less than a full revolution - but I guess I could figure out a way to check the voltage while cranking. I'm not sure what that should be. I've got a 12V system which is certainly part of the problem.
Its a really frustrating problem because you never really know whether or not it is solved. I went 18 months on the last starter so I was getting to thinking that it was fixed and then one blistering hot day there I was with a growly starter. All I did that time was open the engine doors and have a half hour nap while everything cooled off but now I have to wait 18 months before I will know whether I have made any improvements. I put the 2nd ground strap in the engine comp this time. I've already got a double run of 4-0 cable for the positive side. I'm running out of ideas. My starter rebuilder told me that the 39MT has bearings and that should help my hot start problem. The only time I ever get a draggy start is when everything is piping hot. His theory was that bushings tighten up when they are really hot but the bearings shouldn't. We'll see.
Bobofthenorth: Do you have a rear start panel in your bus. If you have, just clip a voltmeter to the positive and negative starter bolts, hold the governor in the stop position and crank the engine. Or with the switch (key swith or master switch) turned off, you can attach the meter and then use a jumper wire from the battery terminal on the solenoid to the small bolt. On a 12 volt system, you need 10 volts, absolute minimum when cranking and preferably above 11.
If you have low voltage, move one meter lead at a time back to the next connection and repeat the test until you find the connection with the high resistance. Use this same method to find a bad battery. hold the meter leads directly on the battery post while someone cranks the engine. If the voltage drops at the battery posts, then the battery is bad. If it doesn't drop on the post, then it is a connection. Since most mechanics are used to starters with the case being the ground connection, they commonly clip their meter to the engine block or the battery negative and this completely overlooks the negative side of a DD starter which is insulated from ground.
That's the first time anyone has told me what voltage to look for. Its 30 below here right now so I won't be checking this until it warms up but I will give it a whirl come spring. Thanks
Bobofthenorth: Wait until the temperature gets warm enough to take the big mitts off long enough to hook up your meter (+20 F) and cranking a cold engine will give you a good starter test.
I'm not an electrician/mechanic, so this is a question not advice! Why cant you use a infrared tempature gun to check for a faulty terminal/connection?
jrbus: I don't see any reason to not use an infrared temperature gun to find bad connections. It is just that I am from the old school and I was using a meter for forty years before the cheap infrared guns came on the market.
Us young people use them for everything! When I stop with the bus, I go around and shoot all the tires, brakes, bearings on bus and toad. I also check the radiator, if I get a low reading at the top, it is low on coolant. I should start a thread "Uses for temp gun"!
Beauty JJRBUS - a perfect excuse reason to buy an IR thermometer. Just what I've been looking for!
Thanks.