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NGK BP5ES Spark plugs for Cambridge head

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NGK BP5ES Spark plugs for Cambridge head
seajayare Offline
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#1
10-08-2017, 07:36 PM
My new to me "special" ( Cambridge finned head, 2x SU H? carbs) came with NGK B6HS plugs. Looking at the old forum people were using NGK BP5ES plugs successfully. As I think a couple of my plugs were dodgy I bought 4 new BP5ES (less than £6 delivered for the 4) which arrived today. The reach is about 20mm compared to the current ones about. 13mm. Are these new plugs going to be ok do you think?
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Nick Lettington Offline
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Location: Essex
#2
10-08-2017, 11:26 PM
Dave Armstrong's old Speedex website would suggest not... but I have no personal experience...

http://myweb.tiscali.co.uk/speedex/index...ge1355.htm
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Ian Williams Offline
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Location: Auckland NZ
Car type: 36 Nippy, 31 RM, 38 Special, 24 Works Rep
#3
11-08-2017, 01:53 AM
(10-08-2017, 07:36 PM)seajayare Wrote: My new to me "special" ( Cambridge finned head, 2x SU H? carbs) came with NGK B6HS plugs. Looking at the old forum people were using NGK BP5ES plugs successfully. As I think a couple of my plugs were dodgy I bought 4 new BP5ES (less than £6 delivered for the 4) which arrived today. The reach is about 20mm compared to the current ones about. 13mm. Are these new plugs going to be ok do you think?

You probably need a BP5HS, the P is for projected nose, the 5 is the heat range and HS denotes short reach, the plugs you have purchased are ES which as you have discovered are long reach. There are two problems with these in a head with a 13mm thread length, firstly they will stick into the combustion chamber much to far and quite probably hit a valve. Secondly even if they do clear and the car will run, carbon will build up on the exposed thread which can lead to preignition, and worse when you try to remove the plugs later could jam and cause the soft aluminium thread to tear out.
Black Art Enthusiast
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seajayare Offline
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#4
11-08-2017, 09:04 AM
I have ordered some shorter reach plugs now just to be on the safe side. Be interested to here if the longer reach plugs are being used by anyone still

Cheers for the advice
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Speedex750 Offline
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Location: NE England
#5
11-08-2017, 09:25 AM
I agree with the others - you should fit BP5HS - that's what I've got in my finned head and they work well. With them having projecting electrodes watch out for touching the valves. I've got a high lift cam and the head must have been skimmed down in the past - I have to selectively fit the plugs with different thickness washers so the earth electrode runs across the engine between the valves. Put your new plugs in and slowly turn the engine over a few times, if the gaps close up you may have to do the same as me.

Dave
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