JUPITER SPARK PLUGS

[aj4cks]

I HAVE FITTED NGKB6HS WHICH MY REBUILT VIG30 CARBS TEND TO RUN RICH KNACKERING THE PLUGS. WHAT ARE THE BEST PLUGS TO FIT? MY DIZZY IS A DM2
ALSO I WANT TO CHANGE THE CARBS TO EITHER DELLORTO OR SU. DOES ANYONE KNOW WHERE I CAN GET SOME. OLD FIESTA CARBS I THINK.
REGARDS,
TONY JACKSON NWS.

[Alf Heseltine]

Hi Tony I use these plugs in my Jav. with no problems. The plugs do show a rich mixture on idle but no running problems.
I have the carbs. set up this way to give optimum performance.
Best wishes

Alf.

[aj4cks]

Hi Tony I use these plugs in my Jav. with no problems. The plugs do show a rich mixture on idle but no running problems.
I have the carbs. set up this way to give optimum performance.
Best wishes

Alf.

Hi Alf, the Javelin use to have L10 and the Jup L10s. When I once used the Jav plug my engine on shutdown would send the fan in the opposite direction like an aeroplane prop. The NGKs we both use may be ok for both. Just wanted to know what other Jup owners use.
Thanks for your response.
Tony

[Mike Allfrey]

G'dday From The Super Sunny South,

My experience after quite a bit of trial and error, resulted in using Champion L87-YC sparking plugs. These have been very successful here in Australia. These are an extended core nose type of sparking plug, that places the spark about 3 mm further into the combustion chamber. When first installing these sparking plugs, it is a good idea to screw each plug with a blob of plasticene over the earthing electrode, turning the crankshaft through two complete revolutions, unscrewing the plugs and inspecting them for valve head clearance. It's called peace of mind.

I should also mention that, with the lousy petrol that our engines have to contend with, it is a very good idea to convert to electronic ignition. The reason for that is to have a spark of higher intensity and longer duration to thoroughly burn the petrol/air charge. I believe that this is more important than fiddling with different types of sparking plugs.

By the way, we are enjoying a superb Indian summer down here. The river Murray is in full flow and paddle steamer cruises from Echuca are sensational. The skies are clear blue and at night the stars are crystal clear!

All the best with the plugs search, but please consider the other part of the ignition system. I never touch plugs made in Asia - but that is me!

Mike Allfrey.

[aj4cks]

Hiya from the cloudy north.
Glad you are enjoying a good indian summer. In regards to the Champion plugs, I will give them a try. As for electronic ignition I have thought about it and even adding an alternator but I am reluctant to change to a negative earth due to perhaps irrational commitment to the original Jowett set up.
Our summer is close and the weather here is a mix, as usual, of sun and showers.
Thanks for your reply,
Tony J

[Leo Bolter]

Interestingly Mike, I gave up on Champions back in the 80s (or was it the 90s) when I found that I (almost!) consistently needed to buy 6 plugs to replace the 4 plugs in a 4 cylinder engine . . . they were that unreliable (well, the ones that were available in NZ were that bad). I haven't been back to that brand since, so I may be quite unaware that they may now be completely reliable!

I have successfully used NGK 4111 BP5HS (extended nose) spark plugs for ages.

Of additional interest may be that the Jupiter engine's compression ratio is 8.9 : 1. The carbs are Zenith 30 V.M.5s jetted as standard for Jupiter. I use 96 octane fuel and put a shot of Valve Master in with it about the equivalent to every tankful. The camshaft is a "slightly warm" grind (reputed to be a Padman grind). The distributor is a D.M.2. The ignition timing is set up at TDC. This was the result determined after running on a rolling road dynamometer and the distributer adjusted to give the best power at 3,500 rpm . . . sorry I can't remember off the top of my head what the power was, but I could look it up in my records, if pushed!

Cheers.

Leo.

[aj4cks]

Hi Leo,
I take it you have not modified the head to take unleaded fuel as you add an additive. Like Mike do you have to check that there is no risk of a valve hitting the NGK plug?
Regards,
Tony

[Leo Bolter]

Hello Tony.

No the seats in my Jupiter have not been modified with hardened inserts or welded. The only thing that was done way back when the heads were "built" was to utilise slightly oversize exhaust valves so as to make new seats outside the originals, as those seats had become very recessed. I used modified Ford Zephyr valves, I seem to recollect. I must admit I don't recollect doing the check as advocated by Mike . . . but I reckon it's a good idea for peace of mind when the engine is in a assembled state.

I have included some images of "what the piston sees" to show the two types of plugs in place in regard to the comparative placement of the spark gap and another to try to show the clearance of the valve to the extended nose spark plug.


Showing the difference between the two spark plug insulation and electrode positions (NOTE: the heat range remains the same for both).



This image is blended from two images so as to show the different ends of the two types of plug when screwed in place. (NOTE: the spark area is slightly shrouded in the case of the standard plug. This is because the plug ends don't reach the end of the hole).



When the extended nose plug is in place, in his case there appears to be ample clearance at all times when the exhaust valve is opening (NOTE: Oversize exhaust valves could mean fouling trouble . . . check with Plasticine or BluTac with assembled engines!)

[Mike Allfrey]

G'dday From A Slightly Cooler South!

To me it is very strange that there seems to be a world-wide supportive recommendation for NGK sparking plugs. Did that develop because they were once cheaper than established brands like Champion, AC, KLG, Lodge and Bosch? Or, was the profit margin greater?

Back in the late 1950s, my favourite was KLG, simply because they could be easily dismantled for thorough cleaning -- not because they performed any better. In those days, I was involved with two-stroke motorcycles, which did require that the sparking plugs were kept clean.

Over the years, I have experienced excellent service life from Champion and Bosch sparking plugs, and the Champion L87-YCs currently in my Jupiter have been in use since 2000, purchased in Bristol the day before leaving for Le Mans with the other Jupiters. The old new stock water-proof KLGs, equivalent of our old favourite the Champion L10, gave up on their diet of Lousy Rotten Petrol that was dished out to us down here for a spell. Also, conveniently, the same L87-YC plug type suits my V8 Rover P6B and, after being installed in 2005, they showed excellent performance on a dyno tune test just yesterday. Having the two cars fitted with L87-YC sparking plugs, means that I have bought two packets of six to cover my eventual needs, whenever that may be.

Leo is correct about the risks associated with oversize exhaust valves, and his illustrations are excellent. In the 1950s we could not have dreamed about such information being circulated in this manner! Thanks Leo.

I remember very well, during the Suez crisis and its petrol rationing, removing a set of KLG sparking plugs from a Standard Vanguard engine, and finding them absolutely choked with carbon deposits. It was soon established that the poor engine had been running on paint thinners (some of it had been used for spray gun cleaning!). The combustion chambers and piston crowns were also badly clogged with deposits from strange combustion. However, those KLGs were dismantled, cleaned, reassembled and refitted into the engine to continue performing well on a healthy Cleveland Discol petrol diet!

At 2/6d each, sparking plugs were considered to be expensive and, therefore, well worth cleaning. I remember reading in a trade magazine that the price had been kept at 2/6d for many years due to continuing improvements to sparking plug manufacture, i.e. savings in production costs passed on to the buyer. Would that happen today? I doubt it!

On a slightly different topic, and after looking at Leo's photos, a recommendation is to grind flush the lingering sparking plug threads in the cylinder head to help reduce pre-ignition resulting from glowing portions of the thread form.

I often wonder if the cause of perceived sparking plug failure is actually a plug performance problem, or is it a simple case of combustion deposit fouling? During my apprenticeship I cleaned and tested hundreds of well-used sparking plugs, of all brands, in one of those compressed air driven Champion plug cleaning and testing stations. It was extremely rare to find a failed plug under the station's spark test. So, I wonder why Champion have such a poor reputation in current times?

To get back to the original question, my recommendation is to install Champion L87-YC sparking plugs in your Jupiter.

All the best,

Mike A.

[Forumadmin]

It is very difficult to draw conclusions from even 40 years of Jowett driving and be definitive on the relative merits of any component. You are subject to competitive marketing, peer recomendations and your own, usually misleading, experience. I, like most, started on Champions and had, up until the garage clearout, some of the 'second hand' ones. It seems that they were changed often, perhaps due to the recomendations in the manual or as, I recall, because of problems. Yes, misfiring was common until the whole engine was made new for rallying. Igniton leads, distributor, bad pistons or valves , and coil all contributed to failing spark plugs.

Once competitive driving started most of the Jowett Sport team used NGK and I cannot remember ever having to change a plug, usually it was an ignition lead.

[aj4cks]

Really pleased with the response to my question about spark plugs for the Jupiter. In the end I fitted some Bosch WR7 BC+. So far so good..
Need to change my carbs so advice on Dellortos etc would be welcome.