| Author | Message | ||
| Chuck Lott (Chuckmc8)
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On a road trip today, I stopped for lunch,and when I restarted the engine,the starter bendix stayed engaged. (8V71)I rapped the starter with hammer a few times and got it to free up. It took several times of engaging the starter to finally get it running. This is the first time I've had trouble with it. Of course,this happened at the furthest distance from my home. (don't it always?) Anyone had this problem, and what to do to fix it? Thanks | ||
| Pete/RTS Daytona (Pete_rtsdaytona)
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Had the same thing happen to me - you need to replace the starter solenoid - or replace the solenoid contacts I welded mine together by trying to start the bus with batteries that were not well charged - I held the start switch as it turned over slower and slower - that causes the current to go way up and weld the contacts closed - well know problem for big diesel engines Pete RTS/Daytona | ||
| R.J.(Bob) Evans (Bobofthenorth)
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I did the same thing with too long a run of 4-0 cable on 12 volts and a long crank on a cold morning. I took out two starters in 3 months before Prevost in Mira Loma (Nathan Parker actually) figured out what was happening. | ||
| Phil Dumpster2 Rating: N/A |
Actually, the longer the cranking and the more the batteries get discharged, the current drawn goes down. What kills contacts is resistance. The formula for heat in this context is the current squared multiplied by the resistance. Since all switch contacts have some resistance, they heat up when electricity flows through them. As they heat up, the resistance increases, which makes the problem worse. More resistance makes more heat, until the resistance gets high enough to reduce the current in the circuit. If there is no means provided to dissipate this heat, it can build up to the point where it welds the contacts together. Take the solenoid/bendix assembly apart and check for binding in the linkage. It's likely that it just needs to be greased a little. | ||
| Tom Caffrey (Pvcces)
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Phil, I don't think the current falls as the batteries become discharged unless they go nearly flat. I agree that a hot spot in the solenoid will increase the resistance, worsening the temperature at the contacts. In a given series wound motor, such as a low voltage starter, the back EMF increases with the speed of the motor. To me, this means that current will increase with loss of cranking speed, whether it is caused by low batteries or low temperatures. Our coach starter draws 400 amps at 10 volts if the temperature is around 50 degrees. If the system resistance is around .01 ohm, that means a stalled starter could draw in the neighborhood of 1,200 amps. A 400 amp draw is telling me that the back EMF amounts to 8 volts at normal cranking speeds. Cut the cranking speed in half and the back EMF drops to 4 volts and cranking current roughly doubles. Using your formula for heat production, the change in current could have more effect than a similar change in resistance. I figure the welding of contacts is to be expected under slow cranking conditions. It seems to me that if you try to crank your engine and find that it doesn't turn very fast, the cause should be corrected rather than trying to continue cranking. That what I try to do, anyway. For what it's worth. Tom Caffrey PD4106-2576 Suncatcher Ketchikan, Alaska | ||
| Gus Causbie (Gusc)
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Tom, I don't agree with Phil either. Just feel those battery and starter cables, they are really hot and only high current will do that. The starter is a certain HP motor under the starting load and is demanding a certain number of Watts. If it can't get enough voltage it demands more amps. | ||
| Chuck Lott (Chuckmc8)
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In this case, the run of the battery cables are extrememly short, since the batteries have been relocated to the rear, about 20" from the starter. There is no dragging or weak batteries, the cranking speeed is excellent....(always)The bus starts in about 2 revolutions of the engine. Also,when the bendix stuck, the bus had just been 100 miles and then shut off for 20 minutes while I went inside and had a sandwich.Probably still 150 degrees. Weak batteries,long crank times or long cables aren't the culprit here.....I don'thave either of the three. here's look http://groups.msn.com/July2004Busphotos/shoebox.msnw?action=ShowPhoto&PhotoID=141 I should have provided more info, Sorry. So is it the bendix or the solenoid? Thanks, Chuck | ||
| john w. roan (Chessie4905)
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If that is your engine in the pics., it's the dark grey paint; Detroits only work properly in the green or silver.  | ||
| Geoff (Geoff)
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If the Bendix is staying engaged my experience is that it is worn out, and my further experience in the repair business is that it is not worth just replacing the Bendix-- the starter motor is next so you might as well just replace the whole unit with a new or rebuilt starter/solenoid. I say new because there are some aftermarket starters (RH-11 tooth) that are just as cheap as rebuilt units. --Geoff '82 RTS AZ | ||
| Chuck Lott (Chuckmc8)
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We'll, I removed the solenoid-and after dissecting it, the contact plate was badly arced and the contact points on the bolts were also. After cleaning the solenoid up where I could read the numbers, they are 1115556 and the bottom number is 12V6A28. So, this is a 12V solenoid.....On s 24volt bus. Wonder if it's a 12v starter as well? Anyone know how to tell? Would this be a Delco 40MT or 50MT starter? | ||
| Chuck Lott (Chuckmc8)
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OK- Sorry for the multiple post- I thought I had everything in my bus tool box that I might need....but noooo.....I didn't have a 12 point 9/16" socket to remove the starter bolts. I had to scrounge one up this afternoon at home. If you do your own work, you need the said socket, a 6" extension and some grunt to get the bolts loose. All I came up with was some 3/8" drive stuff,but I will retool with a new 1/2" drive socket before I reinstall. I removed the starter, (heaveee) and the tag on the starter housing reads- Series 40MT Serial 90G Rotation CW Model 114987 24 Volts. Thanks to those who have emailed me off board to help. I'm sure glad to play with this at home rather than in the Waffle House parking lot in Annistion, Alabama! | ||
| Tom Caffrey (Pvcces)
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Chuck, it sounds like you're well on your way to getting it sorted out. Sears sells a manifold wrench that could make your job a little easier. With a 4106, one of these is a must. Tom Caffrey PD4106-2576 Suncatcher Ketchikan, Alaska |