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Author Topic: Lister CS 6/1 Start-o-Matic Won't Turn Over  (Read 134 times)

Steve Roberts

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Lister CS 6/1 Start-o-Matic Won't Turn Over
« on: April 15, 2021, 02:59:19 PM »
Hello,

I'm a new member of the forum, based near Tavistock, Devon, and hoping for some advice to solve a problem.

Three years ago a friend and I rescued a SOM 6/1 that was destined for the scrap yard, supposedly with a broken crankshaft. The crankshaft wasn't broken (probably a ploy to sell the previous owner a new generator) and my friend soon had the engine running while I did some re-wiring of the control and alternator boxes, which were in a sorry state. The machine was restored to working order (functional, though not pretty) and was installed to provide power on demand to an off-the-grid building belonging to my sister. All was well for two years and then, with no warning, the wires associated with the battery charging circuit suffered a severe melt-down. I re-wired these a couple of months after the problem occurred and we flicked on a light switch, expecting the machine to burst into life again.

Sadly, this didn't happen. Though the detector circuit sensed the 100W lamp and the starter began to turn, it was unable to turn the engine sufficiently to start it and soon stalled. The two 12v truck batteries were good (and charged), connections between the batteries and to the alternator module clean and the starter contactor was pulling in with a healthy 'clonk'. I inspected the commutator of the starter winding, which was fine though I gave it a light clean anyway. One of the brushes wasn't under as much tension as I'd have liked it to be and so I wound it up a couple of notches on the spring pre-tensioner. Still the starter wouldn't turn the engine. The engine can be started by hand by turning it up to speed with the handle and then manually operating the fuel control solenoid to introduce compression & fuel. It runs well and if decompressed soon picks up again from a very slow speed.

I don't have the instructions for the 6/1 set, though I do have the circuit diagram from inside the control box. I'd hoped that I'd find a means by which the starter would run the engine up to speed and then activate the FCS and introduce compression/fuel, but I was surprised and disappointed to read in a posting on this forum that the starter should turn the engine whilst under compression. I don't see any way that our engine will (or ever would) have done that unless the starter can be persuaded to produce a tremendous amount more torque than it does. Using the starting handle, it is all but impossible to turn the engine on the compression stroke.

Any suggestions would be welcome. I'm puzzled as to why there should be an issue with the starter purely as a result of not having been used for a couple of months. The carbon brushes appear about half-worn and whilst replacing them would do no harm, I don't see why a period of disuse would have affected the starter's operation.

Any suggestions would be appreciated. My only thought is that a closer look at the field winding cables/connections might be worth a shot, but again, I don't see why anything should have changed.

Thanks very much in hope and/or anticipation!

Steve

Hugh Conway

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Re: Lister CS 6/1 Start-o-Matic Won't Turn Over
« Reply #1 on: April 15, 2021, 05:37:00 PM »
Hello and welcome Steve
I don't have the answer to your problem, but I can send you a PDF of the 6/1 start-o-matic manual. It includes wiring diagrams and parts.
PM me if you are interested.
Cheers
Hugh
JKson 6/1  (Utterpower PMG ) Off-grid
Lister 6/1 Start-O-Matic engine......running with PMG
1978 Royal Enfield (glutton for punishment by Indian iron)
1963 BMW R-27 project

mihit

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Re: Lister CS 6/1 Start-o-Matic Won't Turn Over
« Reply #2 on: May 05, 2021, 12:45:23 AM »
Just thinking out loud...
Could batteries be suffering low internal resistance? IE voltage good at rest but drop volts when starter is in the circuit?

Can you get an ammeter/clamp meter on the battery lead while trying to start?

Could starter be shorted internally so the circuit is being made across only half the windings? Can you find another starter to swap in and test?

Has the alternator (?) lost it's field/sense circuitry?

I would be keen to know -why- the wiring melted in the first place... is there a short in the alt? Try taking that out of circuit and starting.

oldgoat

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Re: Lister CS 6/1 Start-o-Matic Won't Turn Over
« Reply #3 on: May 05, 2021, 01:13:15 PM »
On page 11 of the S.O.M. manual there is mention of a wedge which is on the valve lifter mechanism which I assume is some sort of compression release. It appears to release compression until the fuel solenoid is operated according to the book. On page 33 it shows a fuel cut off and exhaust valve lifter mechanism I have no idea how it works not owning that machine but this might be the place to start looking.