Early LAnchester 10 (and probably Daimler 15) spark plug access

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Simon Hyslop
Posts: 190
Joined: Wed May 04, 2016 3:30 pm

Early LAnchester 10 (and probably Daimler 15) spark plug access

Post by Simon Hyslop » Sat May 27, 2017 3:39 pm

This subject has come to my mind a few times and came back today as I was looking at the plugs on my LA10. It may seem very obvious but here goes. The tubes in the head through which the plugs (3/8" reach, Champion J8, NGK B6 etc) are inserted are very narrow. So narrow in fact that many spark plug sockets will not grip the plug hexagon to the point where the plug is actually tight enough in the head. Of spark plug sockets I tried, 5 out of 6 wouldn't tighten a plug enough and the more modern plugs are more difficult because the hex on them is usually shallower than on a Lodge or KLG plug.

3/8" drive or 1/2" really made no difference and the one that fitted was a Britool 14mm plug socket from some time ago - EBH814. Kamasa, Sealey, Elora, King Dick, Gedore and other nameless ones, all too wide. I do have a cheap one where I had ground down the outer nose to get it in far enough to grip. Probably a box spanner would do provided it was older rather than newer as the newer stuff all seems to be made on the basis that more cheap steel is as good as less quality stuff.

Anyway, it struck me as something worth thinking about because a) the plugs need to be decently tight rather than just so-so, b) if you needed to change a plug on the road chances are unless you had a proper fitting tool with you it's unlikely you'd find one in the average toolkit.

The later heads are, IIRC, a different design and so it doesn't affect them.

Geoff Douglas
Posts: 328
Joined: Sat Feb 13, 2016 5:08 pm
Location: Helensburgh, Argyll

Re: Early LAnchester 10 (and probably Daimler 15) spark plug access

Post by Geoff Douglas » Sun Nov 19, 2017 12:41 pm

I've just read this post and it brought to mind one of the easiest to solve SP250 mis-fires I've ever dealt with, many many moons ago. Circumstance - sudden onset of significant mis-firing. Pull over to investigate. Open bonnet, start usual visual check of carburettors and ignition components. Cause fairly obvious, one plug blown right out of plug tube and lying on rocker cover still attached to plug extension and lead. Plug carefully re-inserted in case cylinder head thread damaged, but no problem there. End of misfire; I wish they were all so simple to cure.

Cause of loosened plug unknown since I've always tightened them in the recommended way to avoid over-tightening. Perhaps I failed to tighten it fully having put it back after cleaning, but I recall thinking that this was unlikely at the time. Back when it was my everyday car doing many more miles I cleaned and checked the plug gaps regularly and having done one side would recheck the tightness of all four before replacing the extensions and leads. Now I do not do it very often, less than once a year since the car has done less than 1000 miles pa for some years. But it has never happened again with either the SP or the Century. And thankfully there is no difficulty finding a socket suitable for the plugs in either the SP or the Century of course.

Perhaps a section for "unusual breakdowns I have experienced in a very old car" might be of use, interest or amusement? I could probably muster a few more.

Cheers

Geoff

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