Spark plug life.

In the old days, I seem to remember spark plug life was about 12,000 miles with regapping usually required at 6,000.

Now, it seems, some cars come with spark plugs which are supposed to last for 100,000 miles!

Comments, anyone?

But not much...

I'd have to disagree. When I started, I didn't just carry spare plugs but points, a condenser, fan-belt, and radiator hoses. And two or three times a year I'd expect to change something on the road.

& uf 6k to 100k isn't much one wonders what would be?

No offence intended, but if it was done as part of your servicing schedule you wouldn't be doing it on the road ? ... although that said who knows when something is going to bugger up... pah ignore me :)

None taken. I wouldn't usually carry new spares, but ones which had been taken out on scheduled servicing. Hoses or fanbelt look a bit tired, pop in new ones but stick the old ones in the toolbag. From time to time, that came in handy.

Admittedly I was running old cars in those days, but you'd not get more than

12k out of a set of points, and that with cleaning once or twice. Rotor arms and plug caps were other items which failed randomly.

But with modern fuel and ignition systems hardly anything ever goes wrong.

Also, in the old days, engines were made from various grades of cheese (Okay, not real cheese, but material science has come a long way since I started motoring)

I still run a 1968 petrol Land Rover, and I carry the fan belt, points, condenser and a coil with me. The new silicone hoses mean I don't worry about those, and the same for the modern ignition leads. Distributor caps and rotor arms seem to be worse than the older ones.....

Worryingly, the (Pre-1980, possibly much older) engine has at least

50,000 miles of mainly short runs under its belt.

12K miles? Pah!! You was lucky. 1974 Honda CB125S.

Plug (singular), points. 3000miles.

It took all of 1L of oil but had oil changes every 1000 miles. Along with tappets and timing check. Failing to do the tappets and timing would result in it's top speed dropping off by 5mph to 60mph by 1500 miles.

The good thing was that if it wasn't up to scratch there was only the one cylinder that could be the cause.

Precious metal, fine wire electrode. They cost 4-6 times as much and last 5-8 times longer. Back in the 70's they would have been called "racing plugs", aka Champion Gold Palladium. Only people willing to pay the 20x price back then were racers.

Went to a Champion spark plugs promo night in the late 80's. They were introducing a new range of plugs. The Copper Core range, I was flabbergasted. I'd been using NGK copper core plugs for the last 10 years and hadn't realised that market leading brands still made cheap tat plugs without a copper core. Though in '82 I had worked a summer on Green Goddesses and on commenting on the plug tester they had in the workshop, I was told they had sometimes to open a 2nd box of 10 to get a set of 6 that tested OK. I just put it down to the Home Office having bought a bulk supply of plugs that were now vintage, along with the SPs (had quaint leather axle grease seals).

In the 70's NGK plugs made many British 2 strokes into something that resembled usefully working bikes. Before that it was clean the plug before every trip and sometimes part way to work.

[...]

Although I agree wholeheartedly about NGK plugs, there were other factors at work at that time. Primarily, fuel/oil ratios changed from 16 or 20:1 of normal 4-stroke oil to 50 or even 100:1 of oil specifically designed for the purpose.

The same sort of reasons have also helped to some extent with the plug life of modern cars. It's very rare nowadays to see even an older car leaving an oil haze behind it, and electronically controlled fuel injection ensures optimum mixture. Add to that the fact that the spark voltage is around 50% higher than when Joe Lucas was making crap, and it becomes clearer.

In the late sixties I was racing a single-cylinder 4-stroke British motorcycle that was a purpose built racer. It was necessary to start and warm it up on a soft road plug, then swap to a racing plug. If you tried to start it from cold on the racing plug, the plug would probably foul, and couldn't be re-used.

Whilst waiting to go to the start line, it was important to keep it warmed up, but not overheat. If the start was delayed due to an incident in the previous race, it was a real dilemma. Keep it running and risk cooking the plug, or stop it and risk not being able to restart.

Whilst attending classic race meetings where the same, or at least direct replicas, are being raced has prompted laughter when I've discussed this in the paddock. They just stick a suitable road plug in, and forget it.

There are two major reasons; the carburettor they use is not just like an on/off tap! It actually meters the fuel as it should. Secondly, the old Lucas magneto has been replaced with electronically controlled coil ignition.

Chris

and what a brilliant little machine they were too, compared to a BSA Bantam or a Tiger Cub they were like something from another planet.

[...]

Indeed, but to be fair the Bantam was designed in the 40's, and the Cub in the 50's.

The Bantam power unit (although I'm not sure 5bhp counts as power!) used

*five* different thread forms in its construction...

Chris

Chris Whelan gurgled happily, sounding much like they were saying:

Nearly 7 times as much power as my VeloSlowlexes...

The later ones had 13bhp, perhaps not a good idea as the original DKW design from the 1930s started life with just 4bhp. But they did make the bigend 1/16inch bigger for the last model in 1970.

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The later ones also had the main bearings fed with oil from the gearbox via drillings, rather than (not) being lubricated by the petroil mix.

Main bearing failure, causing the seals to leak and hence making starting impossible was a common fault, as was the contact breaker pivot pin coming loose in the alloy housing it was moulded into.

Chris

My CB125S did 80mph at 12,000rpm, not once but twice. Red zone was from 9,500 to 11,000 rpm. Much later I learnt that the red zone on the CB125S tacho was the yellow, amber or hatched bit on everyone else's. OK for brief excursions. 1,000 rpm back into the green above the red zone was a bit OTT.

For some bizarre reason I'm now doing stress analysis to certify that Jet engine turbine and compressor discs stay in one piece at 125% of redline speed.

And it was a mirror image of the DWK, story goes some photos were taken of the drawings that the USA commission (polite name for war reparation raiding party) had acquired and printed backwards. BSA left them mirrored as it put the chain and gear change on the "right" side. They converted all the bolt and thread sizes to imperial but left the bearings metric. Didn't want to re-calc the bearing fits but didn't have metric taps and dies and didn't want to buy new ones.

Harley Davidson also made a version - the Hummer. Harley got the drawings as war reparations. It seems the Yanks also gave a copy to Yamaha. The Russians took a bit more than plans, bits of the factory and some people. DKW became MZ.

Everyone had equal opportunities. The results were somewhat different.

I had one of the DKW wankel engined machines, the first one that sold in the country in about 1978 I got the one that had separate oil injection, I lent it to someone to go the Isle of Man for TT week, he crashed it very lightly and it was written off.

The Saab turbo engines were designed around a standard NGK plug, the plug performs several function as the ECU accurately measures the current to determine knock conditions and also fires a current for a short while after switching engine off the clean debris off the plug. Since parameters are adjusted to this plug at the engine design stage, it is common knowledge by saabists never to use any other kind of fancy plugs as it only causes grief. I change plugs at 24k miles as a matter of course, but the old ones always looks fine.

DKW had a joint project with BSA before the war.

Post war DKW became MZ and the TS 125/150 engine was made until about

1986.