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Spark plug cover - Barker LD10

mikemillen
Posts: 307
Joined: Mon May 03, 2021 8:34 am
Location: Bognor Regis

Spark plug cover - Barker LD10

Post by mikemillen »

Does anyone have the bakelite spark plug cover for a Barker LD10?
I'm interested to know what it says on it regarding the plug gap... 20 thou or 30 thou.

The manual for my 2nd series Briggs car says 30 thou and so does the bakelite cover, so I'm fairly confident that it's correct.
The manual for the Barker-bodied cars, 1950-1951, states that the gap is 20 thou. What does the bakelite cover say?

Simon Hyslop

Re: Spark plug cover - Barker LD10

Post by Simon Hyslop »

Dear Mike,

This thread :

http://forum.dloc.co.uk/viewtopic.php?f ... =ld10+plug

may give you an idea of the sort of price that you might have to pay for one if a single cover comes up for sale on the open market. I never did get my 3D printer and the "word on the street" was that there was a possibility of some copies being made.

By way of some sort of comparison, P1 and P2 Rovers have a not dissimilar idea and I'd say there was a similar amount of material in the 6 cylinder version for one of them. They cost £49.65 +VAT from Meteor Spares and they are still having new batches made so it's not a case of it being an old stock price. Of course, the money is in the tooling but that's where clubbing together comes in to make projects happen.

mikemillen
Posts: 307
Joined: Mon May 03, 2021 8:34 am
Location: Bognor Regis

Re: Spark plug cover - Barker LD10

Post by mikemillen »

Simon Hyslop wrote: Tue Jul 20, 2021 8:09 pm Dear Mike,
This thread :
http://forum.dloc.co.uk/viewtopic.php?f ... =ld10+plug
may give you an idea of the sort of price that you might have to pay for one if a single cover comes up for sale on the open market. I never did get my 3D printer and the "word in the street" was that there was a possibility of some copies being made.
I'm not looking to get a cover... I have one for my car, although it's currently in 3 pieces. I plan on repairing it by fibreglassing the underside.

I'm interested in what spark plug gap setting is embossed on the cover for the Barker cars.
My cover (Briggs) stipulates 30 thou... I'm interested to know what it says on a Barker-bodied cover.
Does it match the Barker manual at 20 thou?

Simon Hyslop

Re: Spark plug cover - Barker LD10

Post by Simon Hyslop »

Yes, I was just about to edit my post and add that I hoped that one of the people who had a cover would be able to reply to your actual question ! I have searched the really good LD10 website and elsewhere and can I find a photo of a cover ? As some sort of consolation, it might be of interest to know that the in period Champion Plug Guide lists a gap of 20 thou.

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migray
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Re: Spark plug cover - Barker LD10

Post by migray »

This thread http://forum.dloc.co.uk/viewtopic.php?p=33400#p33400 may be more help. It shows a photo with 20 thou highlighted. Elsewhere the owner says he has a Briggs bodied car.

mikemillen
Posts: 307
Joined: Mon May 03, 2021 8:34 am
Location: Bognor Regis

Re: Spark plug cover - Barker LD10

Post by mikemillen »

migray wrote: Tue Jul 20, 2021 9:48 pm This thread http://forum.dloc.co.uk/viewtopic.php?p=33400#p33400 may be more help. It shows a photo with 20 thou highlighted. Elsewhere the owner says he has a Briggs bodied car.
Odd that it's the only piece of text that is highlighted... I wonder why?
He says he was given that cover by a friend, so it may not be from a Briggs car.

Anyway... my suspicions are confirmed... Lanchester changed the plug gap from 30 thou to 20 thou at some time.
The next questions are why and when?
Would it have anything to do with lowering the compression ratio?
I wouldn't have thought so, as a lower ratio allows a spark at a lower voltage... the 30 thou gap would work fine at either CR.
Was it during the Briggs-bodied run or only for the Barker cars?

Does anyone have any further knowledge of this?

Brian-H
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Re: Spark plug cover - Barker LD10

Post by Brian-H »

If you have a sufficiently high and consistently reliable HT voltage, then a wider gap gives a cleaner burn, so it might be that they used a different coil (or different HT leads) originally on the Barker-bodied cars, 1950-1951, and didn't think it consistently gave a high enough HT voltage.

Simon Hyslop

Re: Spark plug cover - Barker LD10

Post by Simon Hyslop »

I dug out the copious amount of paperwork that came with my LD10 but the only thing I found was a "Trader Service Data No 138 for the 46-47 LD10 showing a plug gap of 30 thou. It got me thinking about what might have influenced a change in this value and I'm going to suggest it was the petrol.

Pool petrol was in the region of 68 octane and remained so until about 1950. The LD10's engine, with a compression ratio of 7 to 1, was rather higher than some other makes at the time : Riley 6.8, Rover 6.25-6.5. It might not seem much but having settled (pre war) on a "modern" engine design (in particular the cylinder head) which would have been intended for petrol of about 80 octane (80 being the top grade compared with 75 as standard) presumably it was a case of finding the cheapest solution for what would be hoped to be a short term problem. *

A read of what is here :

https://www.icengine.net/spark-plug-gap

explains better than me wittering that a large plug gap will probably ignite low octane petrol more efficiently compared with a higher octane. By the time of the Barker bodied models, although petrol was still rationed and pooled, there was probably enough hope that the octane of even the pool petrol would be rising and that a more normal plug gap would be adequate. Although the actual rationing ended in 1950, the rise in octane seemed to take a while to return to pre war levels but if I had to guess on available information, that would be it. As an aside, the octane details above show how the octane of our current petrols still exceeds the actual requirements of the cars' designers.

* It's maybe worth considering that as Lanchester's only immediate post war offering, given that the smallest Lanchester available immediately before the war was the 1444cc 11, anyone who was already a Lanchester owner buying a new car was probably going to be unimpressed by any obvious lack of power.

mikemillen
Posts: 307
Joined: Mon May 03, 2021 8:34 am
Location: Bognor Regis

Re: Spark plug cover - Barker LD10

Post by mikemillen »

Simon Hyslop wrote: Wed Jul 21, 2021 4:39 pm I dug out the copious amount of paperwork that came with my LD10 but the only thing I found was a "Trader Service Data No 138 for the 46-47 LD10 showing a plug gap of 30 thou. It got me thinking about what might have influenced a change in this value and I'm going to suggest it was the petrol.

Pool petrol was in the region of 68 octane and remained so until about 1950. The LD10's engine, with a compression ratio of 7 to 1, was rather higher than some other makes at the time : Riley 6.8, Rover 6.25-6.5. It might not seem much but having settled (pre war) on a "modern" engine design (in particular the cylinder head) which would have been intended for petrol of about 80 octane (80 being the top grade compared with 75 as standard) presumably it was a case of finding the cheapest solution for what would be hoped to be a short term problem. *
There's a wealth of data on the steady change in CR and octane rating here: https://www.energy.gov/eere/vehicles/fa ... ine-octane
A read of what is here :
https://www.icengine.net/spark-plug-gap
explains better than me wittering that a large plug gap will probably ignite low octane petrol more efficiently compared with a higher octane.
I'm not sure that article actually implied that... the energy needed to ignite a certain fuel mixture of, say, 80 RON, is no different, all other things remaining constant, than igniting a 100 RON mixture.
By the time of the Barker bodied models, although petrol was still rationed and pooled, there was probably enough hope that the octane of even the pool petrol would be rising and that a more normal plug gap would be adequate. Although the actual rationing ended in 1950, the rise in octane seemed to take a while to return to pre war levels but if I had to guess on available information, that would be it.
It makes a plausible theory, but as I say... the spark energy requirement doesn't change with octane rating.

My guess is that either Lucas changed the coil specifications or Lanchester discovered that the smaller gap gave a slightly improved tickover.
They certainly thought the change was worth implementing, to change the mould for the bakelite ignition cover.

Do we know precisely when the compression ratio was dropped from 7.4:1 (Briggs) to 7.0:1 (Barker)?
Was it during the Briggs run or only for the last few hundred cars?
Maybe it was after the first series of Briggs cars when the exhaust manifold was changed to give better gas flow?

It would be tempting to say that the change in CR was the reason for the change in plug gap, but the spark energy requirement drops with a drop in CR, so the 30 thou gap would still be OK when the CR was lowered.

I'd certainly like to discover the true reason.

Simon Hyslop

Re: Spark plug cover - Barker LD10

Post by Simon Hyslop »

Dear Mike,
I'm sorry to say that I don't believe I can help you any further with this but hopefully others can.

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