Lotus Elan

ignition coil resistance

PostPost by: rdssdi » Fri Mar 23, 2012 10:24 pm

I have a hot staring problem with my +2. This problem began at the end of last season. I had the car out for a drive today and again it was hard to start when hot. It does not happen every time and if I wait around 10 minutes it will start.

I was thinking it could be the ignition coil. I have a "new" (4 years old) Lucas gold coil. I do not know the impedance. I am running 12V without a ballast resistor.

I have a pertronix ignition and was wondering which coil I should purchase. What ohm coil will be the correct choice.

The car is also running hot. Providing the gauge is correct the car will get to 100C or a little higher. That is hot.

I have a custom alloy rad with a large pusher electric fan.

Bob
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PostPost by: UAB807F » Sat Mar 24, 2012 6:30 am

Hi Bob,

I have a Pertronix set up on mine and the instructions said that it must have a coil with at least 3 ohms resistance for 4 cylinder engines. That's pretty much what my existing Bosch coil had that was being used with the old CB points. If your Lucas one was designed for a 4cyl. setup then I would think it's the same range.

There is also a comment in the Pertronix notes that 6 & 8 cylinders coils must have 1.5ohms resistance, which did make me wonder if 6cyl coils are normally rated lower and hence possible to buy the wrong resistance. I think there was a thread recently where someone had bought a 1.5ohm coil and was having trouble. There have certainly been threads on Pertronix before and a search in the archives will bring out both praise and some unexpected failure tales.

As far as hot starting goes, the other thing you could check is the carb/fuel set-up, incorrect fuel supply can also give a hot-start problem.

For the general hot running, is your +2 running webers, dellortos or Strombergs ? I'm not familiar with the +2 arrangement but it seems to be generally held that strombergs run hotter than the others. The two problems may not be connected, running hot has been a common topic over the years with answers ranging from the simple "fan belt" to worn pumps, ignition timing, etc. Again it would be worth a search in the archives to see what's already been covered.

Brian
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PostPost by: DavidLB » Sat Mar 24, 2012 8:53 am

As the car is running hot maybe it's fuel vapourization. I had the same trouble on an elite, try leaving the bonnet up when hot and see if that does the job, if it does you need to to either get the electric rad fan to run on after the engine has been turned off or use a small fan to push air into the engine bay, this is the route I took on the elite
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PostPost by: RogerFrench » Sat Mar 24, 2012 11:42 am

Your coil sounds like the Lucas Sports Coil which is OK for Pertronix Ignitor 1.

Why do you think the problem is with the coil? It doesn't much sound like it from the problem you've described - more like carburation.
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PostPost by: mikealdren » Sat Mar 24, 2012 1:42 pm

Bob, I wouldn't rely on an old gauge being accurate. You can easily test its accuracy at 100C in boiling water but you can also get cheap and accurate electronic thermometers on the internet nowadays and that would allow you to calibrate you car gauge.

Mike.
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PostPost by: promotor » Sat Mar 24, 2012 3:48 pm

Sounds like it could be running lean - is the timing set too far advanced? Have you cleaned the carbs recently?
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PostPost by: rdssdi » Sat Mar 24, 2012 7:23 pm

I felt it was the coil as the car has always run hot and the hard start problem only recently appeared. I wonder if the heat soaks into the coil and reduces its output. It is also a Lucas which is probably made in China.

The carbs are Zenith Stromberg and were rebuilt as part of the restoration. I have never liked them and added the adjustable "pre emission" mixture needles and pistons. It very well may be that they are now in need of a rebuild. Will wear cause a propensity to vapor lock? I now use another carb rebuilder who I believe does better work than the one I used years ago when I restored the +2.

Last season I had a problem with a small leak from the water pump. At that time I decided to install the Dave Bean cassette pump conversion. Upon disassembly of the front cover it was discovered that the timing chain and gears had worn significantly. Upon closer inspection it was found that a small oil hole and a water passage hole were clogged from excessive gasket sealer use. The timing chain,gears and adjuster were all replaced. The mechanic who did the job was able to replace the pump and covers without removing the head. A task I thought was impossible.

As the car has always run hot I would like to get a test gauge to determine the accuracy of the temperature gauge readings. Then if found accurate as I feel it is, I want to run through all the reasons for a hot running engine.

I must assume the timing was done once the pump and covers were replaced. It is possible the carbs are too rich but a colortune shows a blue flame, which could still be rich.

I have my doubts about the custom alloy radiator I purchased. The fin spacing seems so tight that I feel it becomes impervious to air flow except at high speeds. I have a very high output electric pusher fan.

Any recommendations for the test temperature gauge? Where would the sender be attached?

Bob
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PostPost by: mikealdren » Sun Mar 25, 2012 7:55 am

Bob,
probably the easiest check to start with is to take the rad sensor and put into some boiling water to check if it reads 100C correctly.

I've not looked at thermometers myself although there have been earlier threads on infra red thermometers which UK?s Maplins (radio shack type stores?) sell cheaply.

I?m tempted to buy one of these to control my garage dehumidifier so that it switches off when it?s below about 4C.

http://www.autospeed.com.au/cms/A_112617/article.html

Mike
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PostPost by: UAB807F » Sun Mar 25, 2012 8:59 am

Hi Bob,

I bought a cheap digital thermometer from Ebay, only a couple of quid and it does seem to be accurate at least in the 20-100C range. I bought it to check the calibration on my gauge, the probe & sender in water as it warms up, cross checking the readings.

For my money though the easiest and most reliable check is to pull the sender and drop it in a kettle of boiling water, assuming you have an old electric kettle lying around. Even if you have to buy a cheap plastic one for a fiver it's probably easier than any other way of testing.

Brian
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PostPost by: Galwaylotus » Sun Mar 25, 2012 8:08 pm

Alternately, just boil water in a saucepan and drop in the t-stat! Nothing to buy and it's easy to clean a saucepan before you-know-who gets home!!
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PostPost by: rdssdi » Sun Mar 25, 2012 10:33 pm

Very good suggestions.

I would like to be able to determine the temperature at the inlet of the radiator and the temperature at the outlet. That way I can calculate the difference and see how well the rad is working. Then replace as required. That would include the possibility of a full width unit and repositioning the ancillaries that attach to the radiator supports.

I would then be able to know whether or not the rad is functioning as it should. If not I have a piece of the puzzle.

A friend has an infrared thermometer. I wonder how accurate they really are.

I guess I should start with that and proceed to a digital gauge with a sensor that can be attached to the rad or placed in the coolant stream through the hose / radiator joint.

Bob
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PostPost by: stugilmour » Mon Mar 26, 2012 6:11 am

Bob, I can't recall if you can just open the rad cap while idling the car to get a temperature reading of the coolant, or is it too low? You may have to raise the front of the car while idling to get the rad cap to the highest point in the system. I was able to check my system this way, but I have the Clivey Boy thermostat housing with the extra cap located right next to the sender and a few inches higher than the rad. I used a candy thermometer, which are readily available at the grocery store and cover the range needed with sufficient accuracy.

Based on comparing the coolant temp from the candy thermometer to the dash gauge I determined the gauge was reading high by about 10 degrees C over the critical centre portion. By measuring the resistance in the sender at various coolant temperatures I was able to calculate the value of additional resistance to add in series to the circuit to trim the gauge response. I believe I needed around 7 ohms or so in my case. Two Radio Shack resisters in parallel got me to the correct value. I am now completely confident in the gauge. I had already changed the sender out, but it was the gauge movement that was at fault.

I don't have my notes to hand right now, but I recall it made sense to me at the time that the 40 year old gauge would be expected to read high as the spring wears out. Based on my experience and a few posts here, it is quite possible the car is not running hot at all, rather the gauge movement is out a bit.

HTH
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PostPost by: Robbie693 » Mon Mar 26, 2012 9:47 am

Bob,

If you know the temperature that the rad fan switches on and off at, presumably through the otter switch or whatever controller you have fitted, then could you not compare these points to what the gauge is reading at the time to see if they are the same?

Just a thought

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PostPost by: rdssdi » Mon Mar 26, 2012 2:17 pm

I do not remember the sender "on" temperature. I will take a look. Possible it is stamped on the part.

I would really love to create a chart of the coolant inlet and outlet temperatures to get a picture of the radiator efficiency or lack of. I will try this with an infra red thermometer and see what results I get.

Any suggestions on using an infrared thermometer.

Bob
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PostPost by: Galwaylotus » Mon Mar 26, 2012 2:53 pm

If you use one with adjustable emissivity, be sure to set it for the surface you are measuring. If you don't, the temperatures will be inaccurate. It will still show the relevant differences however.
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