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MG MGB Technical - runs cooler wirh points

Some of you have read of my travails with my pertronix melting much of the ignition system. Have now cured those problems and switched back to a points system. With the pertronix unit my car usually ran with the temp guage a bit to the right,as viewed, of the N, now with the points the needle is only 3/4 of the way over from the C to the N, i.e. she is running a bit cooler. I did change the Lucas sport coil (was fried) for a Blue Bosch coil, but can't see how that would effect this change, any thoughts?
Kenneth von Wolf Lewis

A spark is a spark. Timing will change lots of things.
Barry
Barry Parkinson

I agree with Barry - I have a feelig your timing was changed during the various alterations you have made.

Always nice when they stay cool - make sure you are not too cool however.

JD
J Delk

I am inclined to think that the Pertronix system did change the timing and thus caused her to run hotter. Am very happy to have her run a bit cooler on most days, thus she will handle the very hot days and standing traffic better. At her current temp she seems to run very smooth and strong.
Kenneth von Wolf Lewis

Ken
to clarify: The pertronix did not change the timing - the removal and replacement with points resulted in the timing being changed. It would be very dificult to keep the timing unchanged upon converting either way-- to or from points.
Once you make the change, the ignition should be retimed. It sounds like a serendipidous change that changed your ignition timing for the better.
Barry
Barry Parkinson

Barry,

I think that serendipidous is exactly correct as I did nothng else to effect the timing. There must be some unavoidable differences in the location within the dizzy of the respective units. do wonder if this is another example of the quality control problems which plague the reproduction industry. A friend reports similar quality contol issues with parts for his classic Porsche as does another with parts for his Alfa.
Kenneth von Wolf Lewis

Maybe I am misundestanding this but I would think if you change your points, either from mechanical to electrical or even mechanical to mechanical you reset the timing (as Barry said)?
Simon Jansen

Kenneth may have a valid point, his observations are worthy of investigation. I too have noted a noticeable change in the timings when using inductive triggered systems such as the Pertronix Unit. These inductive triggered units have no moving parts (apart from the distributor shaft) and rely on a moving magnet (on the dizzy shaft) triggering a semiconductor ‘hall effect’ switch that in turn interrupts the current flow in the coil, causing the collapse of the coil’s magnetic field and the rise of the HT voltage to give you a spark. Plus sometimes addition circuitry to provide variable dwell based on coil current saturation.

Any way, in the standard, points/dizzy, the position that the points ‘open’ is fixed ( ok - slightly different between engine accelerating and decelerating due to backlash in the camshaft to dizzy gears and chain tension) in relation to crankshaft position.

Now the inductive type devices do have some inherent design ‘characteristics’! Notable the relative switching position is NOT fixed. This is due to the fact that the semiconductor ‘hall effect’ device responds better to a fast moving magnet than a slow one. In my experiments I have noted up to 3deg (advance) of skew gradually added to the advance curve.

So, the setting at idle can be achieved to give the correct advance on fitting of the unit, but when the engine gets spun up to 3600rpm the actual timing point is 3deg further advanced. This on an already ‘lean’ set-up B-Series engine, could indeed increase the running temperature as Kenneth has noted.

The B-series, also runs cylinders 1 & 4 lean and 2 & 3 rich, relative to each other, but that’s another story!

When these type of inductive devices where used on production vehicles, the distributor curve was modified to take account of this ‘characteristics’, I don’t believe that the manufactures of the after market Pertronix Unit advise their customers of this fact.

Reverting back to points (or an optical device) will then have the effect of removing the additional advance and a ‘normal’ advance curve.

Answer to the problem, if you want the increased reliability of electronic points, you need to get your distributor advance curve ‘matched’ to your particular engine.
MG Mike

Absolutely as Simon says - even if you change one set of points for another, or even the gap of an existing set, you must recheck the timing afterwards, any of these changes will almost certainly change it, points gap definitely so. I've heard in the past that some of these after-market triggers can change the trigger point (and hence the timing) so much that that the spark moves out of the range of the rotor )i.e. points phasing) and you can get missfiring at one centrifugal extreme or the other.
Paul Hunt 2

As various people keep saying, changing anything in the distributor requires reset of timing. Early electronic systems tended to have a built in progressive retard to the curve, much less so with later versions; I have no experience with the built in advance Mike mentions, but it could be. All electronic conversions I've seen have instructions regarding phasing of trigger point to rotor, or specific units for certain distributors; if not followed, the thing will start firing the wrong cylinder as Paul says, and it may also aggravate the known rotor breakdown issues when the spark finds no convenient cap terminal to jump to.
FRM
FR Millmore

I second MG Mike's notes, almost. The distributors actually tend to LOSE an average of 2 degrees from their curve when adding a Pertronix, so you need to advance the timing 2 degrees at idle to get them to work as close as possible to original, unless you want to have your distributor recurved. The igniton curve however is affected by your dwell which can be adjusted with points, not with a Pertronix.

Pertronix units also tend to "hold" 2 degrees of advance during deceleration. This has a tendency to keep the idle speed slightly higher when you drop off the throttle to idle, preventing stalls, as well as speeding the acceleration process when you get back on the throttle.
Jeff Schlemmer

This thread was discussed between 10/09/2006 and 11/09/2006

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