Mep 002a Starter Issues

[dangier]

I picked up 2 002a's in a private sale. Both units run, but one has starter issues. I found the flywheel ring gear and starter drive trashed. Repaired starter and replaced flywheel/ring gear combination. Now when I start the unit, the starter bangs in and out constantly until I let up on S1. Guess that is why flywheel ring gear is trashed. Tried following manual troubleshooting guide. Didn't help much. Traced wiring and found K3 relay opening and closing A1-A2 contacts. Replaced K3 with a known good one. Drew out S1 wiring to right side of diagram and down to last line with K3 and S7 controls. Diode between A1-5 and A1-6 checks out. S1 switch seems to be working correctly. Circuit looks good between TB4-10 and TB4-3.
OK, I am out of ideas now. Put two auto headlight in series to mimic starter action so I do not kill this starter and the circuit still has a load. Bulbs work as they are supposed to.
I can push in K3 manually and it pulls in K6 and turns over starter nicely. There is not much between S1-27 and S7. Just can't put my finger on it. Maybe staring at it too long.
Anyone faced this before?
David

 

[Triple Jim]

The starter solenoid on the motor should have a contact that makes it go from pull-in (high current) to hold (lower current) once its core pulls in. If the hold coil or connection is broken, then it would pull in, and with nothing to hold it, release, then the contact would close and it would pull in, over and over. At least I believe it's made that way.

 

[gimpyrobb]

I'd try a different starter.

 

[dangier]

Hmmm, never thought of that. Guess I am trying to make things harder on myself.
Always pays to have a different set of eyes.....
Thanks,
David

 

[dangier]

Well, that one flopped. Jumped starter solenoid with 24 v. Starter runs as long as I hold the wire on it. Spins at a good rate.
In my original post, I held in K3 which energizes K6 and the starter will run with no problems. Back to somewhere in the control circuit....
What's the purpose with the diode between A1-5 and A1-6? Diode checks out last time I checked it...
David

 

[Guyfang]

Have you tested and adjusted the Starter lockout Switch? If not, go to TM 5-6115-585-12, page, (PDF reader page)144. read and perform the starter lockout switch test and adjustment before you get in a lather. Then, when you are done and it still is screwed up, we can proceed to the next step.

 

[Triple Jim]

It looks like it prevents backfeeding relay K3 through R1 (on diode board) when the generator is running. I woudn't have thought that could happen though.

I wonder if the starter disconnect switch has something strange going on. Try shorting out its terminals and cranking the generator. Obviously when you do that, the starter will keep running as long as you hold S1 in the start position, so treat it like a car's starter during this test.

Edit: While I was looking at the schematic and typing, Guy posted, hence the same idea as he posted.

 

[Guyfang]

Great minds think ALIKE!!

 

[dangier]

Bypassed K3 negative circuit by jumping TB4-3 around S7 to battery negative. Starter runs like it should. I had taken the speed switch out and looked at it before. Will pull out again and check it out. Also wiring could be suspect.
Got to run for now. Many thanks for the support.
David

 

[Triple Jim]

If you jumper just the terminals on the switch, it should tell you if it's the switch or the wiring.

 

[Guyfang]

Read the procedure for adjusting S7, starter lockout switch. Its simple, you only need a feeler gage. Don't jump it, adjust it.

 

[dangier]

Well, I am back into it this AM.
Jumped S7 contacts and starter runs correctly every time I tried it.
With TM in hand, cleaned S7 contact and set to just closed (w/continuity). Started unit and disconnected circuit. Checked with .040 feeler gauge and only had to adjust point gap 1/8th of a turn to get as directed in TM. Shut down and connected everything back up. Started unit several times and it still has the pull-in and drop out action.
The only thing that stopped it was the jumping of the S7 contacts. Is the pushrod internally in the switch a wear item? This unit has around 3k hours showing on the hour meter.
David

 

[Triple Jim]

It would seem that there is something mechanically wrong with the speed switch or the mechanism that's driving it.

 

[Guyfang]

Well, I am back into it this AM.
Jumped S7 contacts and starter runs correctly every time I tried it.
With TM in hand, cleaned S7 contact and set to just closed (w/continuity). Started unit and disconnected circuit. Checked with .040 feeler gauge and only had to adjust point gap 1/8th of a turn to get as directed in TM. Shut down and connected everything back up. Started unit several times and it still has the pull-in and drop out action.
The only thing that stopped it was the jumping of the S7 contacts. Is the pushrod internally in the switch a wear item? This unit has around 3k hours showing on the hour meter.
David

Let's take this slower.

Jumping the S7 contacts was good. But it just tells us the problem in in the S7 AREA. Doesn't mean S7 is bad. Have you tested for 24 volts at the P16/J16 plug? Jumping at the TB, doesn't say you are getting voltage at J16. If for example, the wires to P16, or going out of J16 are broken, the S7 can not function. So disconnect P16, and so if you have 24 volts at pins A&B. Then reconnect the plug. Go down to the switch, and see if you have 24 volts, AND the ground return. If you do, then I would say you need to look at a new S7.

Yes, S7 goes bad. I have replaced more then several. Just because the hour meter is low hours, doesn't mean the S7 is new. After an engine replacement, normally a new hour meter is installed. When engines are tested before rebuild, the S7 would be checked for FUNCTIONALITY, nothing more. An old switch, if it works, is a good switch. TRUST NOTHING! Test first. The S7 was a part commonly available.

And personally, I think the S/ is the culprit. But TEST the circuit.

 

[dangier]

Guyfang,
Appreciate the comeback. My unit does not have the cannon plug (P16?) to disconnect the S7 switch. It has been cut and replaced with crimp-on butt connectors. I have direct continuity from tb4-3 through S7 to ground when genny is off. When starting, it acts like the S7 contacts are bouncing and causing the starter to drop out and then kick in.

I have gone through the TM's numerous times and settings are right on. The contacts do not have the stability to stay closed while starting. I have cleaned the contacts and they are clean. When I get a chance, I will pull the S7 switch and look it over.

Can't look at it until tomorrow afternoon. Will post back if I find anything.

Thanks,
David

 

[Guyfang]

David,

Its been a long long time since I held a switch in my hand. But I seem to remember there being a spring back there. If ist not in place, or not serviceable, that may be it. But I wold still check for voltage at the S7. Continuity can lie.

 

[dangier]

Guyfang,
The only way there would be voltage at S7 would be the switch is open and S1 is in start position? Correct?
David

 

[Guyfang]

If the switch is open or closed, dosnt make a difference. The main thing is for the S1 to be in the start position. The S7 is what opens and closes. There will be always voltage there coming in on pin A.

Something else to check. You said the canon plug is not there. Make sure the wires were hooked up right, and tight.

 

[dangier]

guyfang,
I do have 24 volts on one wire that was attached to P16. Compared this S7 to another from a donor machine. The copper strip seems stiffer on the donor S7 (contacts have more "snap"). Everything else on the switches looked the same. Both plunger's were the exact same length. Cleaned up the donor S7. Switched S7's and reconnected wires. Checked contact adjustment. Started unit. Seems to start well each time I have tried it. I'll get back to this machine later. Got to get another one checked out.

Many thanks to all who contributed!

David

 

[rustystud]

So it was the S7 switch. Good call Guy !