Morris Minor Owners Club

I have read in a couple of places that plug gaps on 803 and 948cc engines should be set to 22 thou, and 1098's to 25 thou. That is at odds with the more commonly read advice that the plug gap for all engines should be 25 thou.
Thoughts, comments?

The plug gaps should be set at 0.025" for all 'A' series engines except when you have a sports or high performance coil fitted when they can be set to 0.030".

Yes, that is what I would have said, but curious as to why someone should suggest 22 thou for an 803/948. Can't remember where I read it now........but I know I did somewhere!

Taken from the BMC wksp manual:

Series MM...........Champion L10...............0.025" gap

Series 2..............Champion N5................0.025" gap

Minor 1000.........Champion N5................0.025" gap

Minor 1098cc......Champion N5................0.025" gap.

Reducing the spark plug gas was sometimes done to overcome a weak ignition system/spark but in general not recommended.

Phil

Most plugs are likely fitted without even checking the gap; many would not really be able to measure the gap that accurately; the gap will almost certainly increase during service; there is likely no difference in the rest of the ignition HT generation system; 3 thous. is likely neither here nor there for most motoring (any data on it?).

When you say ‘ a couple of places’, is this the definitive workshop manual, some obscure publications or what?

Even magneto systems usually recommend a 25 thous. gap (but generally a reduced contact breaker gap) and tend to be lower energy systems than battery powered coils.

So if true, it must surely be something to do with the engines, but can’t see any logical reason, unless someone has got mixed up with side valve and OHV? Or dodgy HT insulation somewhere (distributor cap, rotor or rubber plug leads)?

Certainly higher energy systems would warrant a longer spark path and larger gaps should, if anything, reduce burning? Modern day electronic systems seem to burn plug electrodes much more slowly.

RAB

Plugs should not be fitted without checking the spark gap. They are not always as they should be even straight out of the manufactures packaging.
Checking the gap is easy to do and the only tool you need is a 0.025" feeler gauge which is not expensive.
The 0.025" feeler gauge blade should just be able & without difficulty slide between the centre electrode and the earth tag.

https://www.ebay.co.uk/itm/DRAPER-36174 ... xyzGlQ8zC4

Phil: "Reducing the spark plug gas was sometimes done to overcome a weak ignition system/spark but in general not recommended."
Similarly, Staton Abbey's Book of the Morris Minor 1000 (1960) suggests "If the plugs are prone to oil up, a smaller gap may be tried - say 0.020 or 0.022 in - but this must be regarded as a palliative rather than a cure."........

Oliver90 - I can't remember where I read this, but it is probably in my house......... somewhere!

Oh, I have found one source - in the Tech Tips section of the current Club magazine! In a couple of pages about servicing it says "Set the gap to 25thou (.02in) on 1098s and 22 thou (.22in) on the others."

OK guys, it gets more mysterious- in a review of the new SII Minor in The Motor magazine January 28th 1953, under "Maintenance" it gives spark plug gap as 0.017 - 0.018 in! Could this be something to do with old-style petrol??

Checked my Workshop Manual AKD 530D , naturally confirms Phils post !!!!

Pool Petrol was terrible stuff around 72 octane and would pink at the first opportunity and the ignition had to be retarded when using it.

Pool Petrol would still be around in January 1953 (and would linger on until 1954/55) so yes it could be relative to the use of Pool petrol.

I think you're on to something there, Phil. The article states:
"Our test was made on Pool petrol, and towards its conclusion pinking was beginning to be more prominent as carbon formation commenced inside a clean engine - over substantial mileages the performance figures published on the data page should be maintainable on premier grade petrols, but continued use of second-grade spirit might require slightly retarded ignition timing and a 5 per cent loss of power."

The trick for avoiding oiling (or possibly ‘spidering’) of the plugs on our Fordson Standard was to add a button (not a metal one!) in between the plug lead and plug. Presumably that increased the HT voltage, before it would arc across, but a larger effective spark gap. It worked, or would not have been used.

Back in the days of 72 octane fuel, regularly decarbonising the engine was all part of ownership. Intervals of 4000 miles, between ‘decokes’, was not an uncommon recommendation.

My favourite tractor still tends to ‘spider’ occasionally, if not worked to some degree. It runs on mostly kerosene, so a far lower octane rating than petrol (and likely lower than TVO in the 40/50s). I usually add some gas oil (about 10%) for extra lubrication - and some petrol, if run under light load.

When I worked for the Coal Board we used to set the land rover plugs using a piece of fag packet. Embassy was the preferred brand.

I always found that my BSA Bantam went better if the points were set using a piece of a Senior Service packet rather than a piece of a Woodbine packet. I suppose the bike just felt a little superior.
R.M.

My then BSA Bantam (D7) did not care what the cigarette brand packet was it just and always did smoke.

Did it ever try and give up? )
A credit card looks pretty close to 25 thou....

Human thumb nail is generally 25 thou thick, unless you are a mutant.

Just to note that in the sixth edition of the Morris Minor Series II Operation manual, page 19 states that spark plug gaps should be between 20 thou to 22 thou!