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Pitted Points
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NONORT



Joined: 26 Apr 2012
Posts: 55
Location: Southampton

PostPosted: Sun Jun 30, 2013 9:02 pm    Post subject: Pitted Points Reply with quote

Hi Guys,
I have a question for you. Have you ever come across a problem with Pitted Points. I am involved with a 20hp Rolls. Which continually pits its contact breaker points. Having done all the usual things condenser, points, HT leads and rotor arm. Thing is I have just spotted that the Distributor has a gallery between the crankcase and the points area of the distributor I am wondering if any oil mist from the crankcase is fouling the points. Any help greatly appreciated. If any one knows if there should be a felt filter or anything else please step forth as my brain is about frazzled. Confused
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Kelsham



Joined: 18 Jan 2009
Posts: 349
Location: Llandrindod Wells Powys

PostPosted: Mon Jul 01, 2013 8:15 am    Post subject: Reply with quote

I have seen pitted points caused by one of the coils that use a resistor to drop the voltage to use 9 volts.
In the case I am writing about the two wires feeding the coil had been crossed ove causing the 9volt coil to continuosly run at 12 volts.

Not sure if this system is on a 20 hp rolls? otherwise try another condenser? some of the modern offerings can be suspect from new.

Kels.
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Farmer John



Joined: 18 Feb 2010
Posts: 181
Location: Manawatu NZ

PostPosted: Mon Jul 01, 2013 9:08 am    Post subject: Reply with quote

The point faces will be black when contaminated by oil or fumes but the points still perform better than you might expect from their appearance.
We were taught by an auto electrician that a condenser needs to have a rating appropriate for the rest of the primary circuit. The circuit must be balanced. There is a calculation to perform which will tell you the required number of micro farads the condenser needs to be, then you wander into the parts department and test all their condensers to find the right one.
The sad thing is that I can remember no more than that. If you can find a helpful old auto sparky you should be able to find a condenser that will help your points last much much longer.

John
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Mon Jul 01, 2013 9:08 am    Post subject: Reply with quote

I have seen a condensor incorrectly fitted, so that it was effectively shorted out, if the Rolls has a low compression engine, the reduced energy in the coils secondary may still be enough to fire a plug, but the points will burn out.

Otherwise I'd go with Kels suggestion and look for reason why the points are having to switch too high a current.

With ref to Johns comment about the condenser size; yes it condenser and coil should be matched, (its about creating an oscilating circuit) but if they are not it would not cause excess pitting, and in practical terms most condensers are fine with most coils.

If you can get the car to an engine scope it would take all the guess work out.

Dave
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NONORT



Joined: 26 Apr 2012
Posts: 55
Location: Southampton

PostPosted: Mon Jul 01, 2013 9:35 am    Post subject: Reply with quote

Many thanks for the info so far. The Rolls has a ballast resister much like an old electric fire. I believe that this is to aid starting and seems to be working in so far as it gets very warm when operating. One theory that has been mentioned is that if the manual charging circuit is left on the battery can over charge and send more than twelve volts to the coil? I understand that the condenser has to be matched to the system but how many micro farads are required 22 seems to be common and 17 for ballasted circuits. The Rolls compression ratio is about 4.5:1. I am going to ring one or two of the Rolls restoration people and see what they say. And will post there reply in due course. Having removed the points from the car they have a grey/white burnt area and a deposit of a waxy substance which I wiped off with white spirit this morning. I tried to take a picture of this but failed.
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Mon Jul 01, 2013 5:49 pm    Post subject: Reply with quote

Hi

If the voltage is greater than it should be, then the points will switch a lower current, so would actually last longer, I'd check that the coil and ballast are correct and wired correctly and that the condenser is ok and wired correctly, in fact I'd be tempted to pop down to Maplin purchase a 22ufd 400v working, capacitor and wire it between the coil an earth, the RR compression is so low that it won't take much to fire a plug,I still think you may have a faulty or s/c condenser.

Dave
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Kelsham



Joined: 18 Jan 2009
Posts: 349
Location: Llandrindod Wells Powys

PostPosted: Tue Jul 02, 2013 8:10 am    Post subject: Reply with quote

The ballast system I had problems with had two feed wires. One wire fed full twelve volts to the coil when starting. then switched over to run through the ballast resistor once running.
It's a long time ago, but I seem to recall the wires had been switched so the coil had twelve volts while running.

Kels.
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petelang



Joined: 21 May 2009
Posts: 442
Location: Nottingham

PostPosted: Sun Jul 14, 2013 12:52 am    Post subject: Reply with quote

It could just be that the points are coated in a preservative to aid long term storage (common on modern copies) clean them off and try again. Note, higher voltage makes for lower current, that wouldn't cause burning.
Peter
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NONORT



Joined: 26 Apr 2012
Posts: 55
Location: Southampton

PostPosted: Mon Jul 15, 2013 10:33 pm    Post subject: Reply with quote

First of all many thanks for the info so far, great bunch of presumably guys out there? I have thought about jury rigging a normal coil next to the posh Rolls one and just trying it out. The Rolls coil gets so hot you cannot touch it may be the voltage drop across the ballast resistor is causing the larger current and making it run hot, ending in a self destructing circle. I presume that if I by-pass the ballast resistor and run a 12volt coil using the original points and condenser it would do as a test rig to take the Rolls coil out of the equation. Any more ideas greatly appreciated.
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Kelsham



Joined: 18 Jan 2009
Posts: 349
Location: Llandrindod Wells Powys

PostPosted: Tue Jul 16, 2013 10:05 am    Post subject: Reply with quote

When the car is running, is the supply going through the ballast resistor?

Remove the other feed wire. to check.

Is the ballast resistor short circuiting?

You could do as you suggest and fit a twelve volt coil and feed to test the rest of the system.
The coil seems to be getting too hot and I am still thinking the ballast is either incorrectly connected or shorted out.

Regards Kels.
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NONORT



Joined: 26 Apr 2012
Posts: 55
Location: Southampton

PostPosted: Mon Jul 22, 2013 8:49 pm    Post subject: Reply with quote

Many thanks for all your help I think I have traced the fault to the coil. We ran the car for short while the other day and the fault re occurred switched off had a cup off tea restarted the car and it ran OK for fifteen minutes then the fault showed itself again. Other possible causes that have been forth coming are tappets closing up when hot. Unleaded fuel does run hotter and the Rolls only has three thou clearance? Partially blocked vent in filler cap, meaning that the engine runs weaker after after a while?
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NONORT



Joined: 26 Apr 2012
Posts: 55
Location: Southampton

PostPosted: Thu Aug 01, 2013 3:58 pm    Post subject: Reply with quote

I have acquired a new coil it measures 3.2 ohms. The old Rolls coil was reading 1.5 ohms. I don't know enough about the electronics involved and can't really check the current flow through the points with the new coil when the engine is running. The real con was that in fitting the new coil I scratched the paint to reveal that it is a Lucas DLB100 costing £20 stick a fancy end on it and charge £140. Shan't be making that mistake again. All seems OK now will let you know if the gremlins Have been laid to rest in due course. Many thanks for your help.
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Kelsham



Joined: 18 Jan 2009
Posts: 349
Location: Llandrindod Wells Powys

PostPosted: Fri Aug 02, 2013 9:26 am    Post subject: Reply with quote

Sounds like a six volt coil? Are there any markings on the coil to confirm?

Kels.
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NONORT



Joined: 26 Apr 2012
Posts: 55
Location: Southampton

PostPosted: Fri Aug 02, 2013 9:46 am    Post subject: Reply with quote

Hi nothing as fancy as 6 volts I'm afraid. It is listed on a website as a 12volt coil with the Ht lead connection as being of the Acorn type. Which is exactly what I received. Still you live and learn.
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NONORT



Joined: 26 Apr 2012
Posts: 55
Location: Southampton

PostPosted: Sat Aug 03, 2013 3:59 pm    Post subject: Reply with quote

All went well yesterday got the bride to church on time and got home without bother. Just need to have a look at the exhaust system now as we have gained a slight backfire I think the gasket between the main down pipe and the silencer a small hole in it.
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