Spark plug caps

[Tman]

Right then, next question from the new boy. My ’47 Flying Squirrel appears to had had 18mm-14mm plug adaptors fitted. A good idea given the poor range of 18mm plugs, but my usual choice Lucas/Champion all-rubber plug caps don’t fit as they’re too tall to ease onto the spark plugs under the rad.
Do I really have to use the old open brass terminal-type plug connectors, or are there better (hopefully insulated!) types to be had?
Thanks.

[chris wastell]

The screw down terminals are great (IMHO). I’ve never had any trouble from them and they are far enough away from the rad to suffer shorting out onto it, which I reckon could happen with caps in the rain. I am, by no means, any kind of expert though 😀

[BRIAN MARSHALL]

If you have magneto ignition on your ’47 you really should not have ‘radio supressed’ plug caps. Much better to use a plain brass connector or the QD Scott ones. If you buy a pair of those note that ‘modern’ spark plug tops are threaded 4mm, while older plugs are threaded 3BA, so the bronze balls will have to be threaded accordingly. On my vintage TT Scotts I have a pair of ‘period’ Lodge H1 (18mm) plugs in for display purposes only, and for actual running I use the new ‘repro’ KLG ML50 plugs sold by the Green Spark Plug Company, and I have to swap from 3BA to 4mm threaded ball connectors. If you go onto Tim Green’s website you will find lots of different plug caps and fittings.
Brian

[TedParkin]

😀 😀 😀 😀 On my MPG Scott I did 2 Mods. 1. Cut 3 threads (in The Lathe) off the bottom of the plugs, cleaned them up, then fitted them. Perfect Mod!! 😀 😀 Or! (and as a belt and braces mod) 2. I stuck a couple of rubber patches underneath the rad! Worked for me on the race track and on the road!! 😀 😀 Just my 2 pence worth BTW!!!!Caveat Emptor! Regards Ted

[BRIAN MARSHALL]

Ted, I don’t understand your mod to plugs ! Machining off some of the threads won’t make the plug screw any further in towards the combustion chamber. The only way to achieve that is to machine metal off the main body of the plug. Not necessary with the new repro KLG ML50 plugs from the Green Spark Plug Company as they are a lot longer reach than NGK A6 or A7 18mm plugs.
Brian

[Peter Scott]

Too easy this one…just head on down to your local lawn mower shop. You need a couple of the rubber plug caps as used on Briggs And Stratton motors. They are a “squat” version of normal plug caps, they fit on under the radiator without resorting to foul language , and are direct connection to the HT cable (copper core of course ) no suppressor , no electrickery !!!
Been using them for years
Peter Scott

[BRIAN MARSHALL]

The machining of spark plug bodies to increase the reach of the plug was nothing to do with plug/radiator clearance problems, and was to reduce the shrouding of the electrodes caused by using short-reach 18mm plugs in the Scott cylinder head. There has been a dearth of suitable longer-reach 18mm plugs for many years, until the recent manufacture of the KLG ML50 by Tim Green. Not only is combustion improved, there is a useful increase in compression too! There was a good article by Glyn Chambers in Yowl about machining NGK plug bodies to achieve these ends, but it was a good few years ago.
Brian

[TedParkin]

😀 😀 😀 😀 😀 I think that the problem is twofold Guys!(and some are missing the point) You cant fit the plugs coz of the distance between the plug and the Rad. Hence the Mod 1.(fitting the plugs is a doddle) 😀 😀 Mod 2 resolves the 2nd point. This keeps the *look* of originality. Re the rubber plug caps. Nice one Peter!!! I’m off to the lawnmower shop as we speak! 😀 😀 A good solution!! 😀 😀 Regards Ted

[Tman]

Good tip re the Briggs plug caps, but if you’re not careful and buy (such as on Ebay) part number 66538S “plug cap” what you’ll receive is merely a rubber boot, so you’ll need to ensure that part number 493880S (the internal connector) comes with it. Some mower parts suppliers seem to be supplying both parts together, which would probably be the best way to go.

[Steve Bowles]

Got my Briggs and Stratten caps this morning.

Very neat indeed – so a top tip.

Steve

[Mike Fennell]

Here’s another simple option – the KLG spring clip replaces the original screw-down item and holds a standard spade HT lead terminal loosely
( but surprisingly securely ) in place. The pair I bought in the late 50s for about sixpence have never once fallen off in use. The only real risk is losing one at a road-side plug change by pinging it into the long grass from the finger-tips. The Green Plug Man sells them at £1.02 each. Catalogue number is HT23 – GS

[James]

heres something interesting

https://www.ebay.co.uk/itm/NOS-KLG-WML60-WATERPROOF-SPARK-PLUG-BSA-AJS-JAP-TRIUMPH-VINTAGE-TRIALS-18mm-/311262438463?pt=LH_DefaultDomain_0&hash=item4878afe43f

[Tman]

Problem solved. The Green Spark Plug Co sell four rubber plug caps + four internal connectors (a set for old cars, obviously) at just over seven quid delivered. They fit, look the part, are waterproof and I’ve got two spares. Happy days.. 🙂

[Author]

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