[Mg-mmm] MG PA spark plugs

[Lawrie Alexander]

Hi, Sven,

Thanks for your reply to my question. Peter Green in England confirmed that 
the plugs were originally 1/2", so that question is settled.

The position of the "plug hole" in the combustion chamber is sufficiently 
high that there's no way it could interfere with the piston, even if the 
plug were twice as long, so that's not a concern (but thank you for 
mentioning it). Your point about carbon on the threads is a good one but, 
again, the threads in the head are so long that the threads of a 3/4" plug 
would still be fully contained and not exposed to the combustion process.

I still think a 3/4' plug might well give more efficient burning of the 
mixture but one has to wonder why the factory specified 1/2". Perhaps it had 
something to do with the less volatile petrol available in the thirties 
having a slower flame front? If no-one else has tried longer plugs, maybe I 
should try both sizes and see if there's a noticeable difference.........

Cheers,

Lawrie
----- Original Message ----- 
From: "bispmotala" <bispmotala at hotmail.com>
To: "'Lawrie Alexander'" <lawrie at britcars.com>; "'MMM Group'" 
<mg-mmm at autox.team.net>
Sent: Tuesday, October 27, 2009 1:39 PM
Subject: SV: [Mg-mmm] MG PA spark plugs


Hi Lawrie

Original plug reach was 3/8" but most people run 1/2 " reach nowadays. I
think that 3/4" reach plugs would need careful monitoring to ascertain that
there is sufficient clearance to pistons. Also the thread will probably be
exposed in the combustion chamber which might give problems with removal at
a later date due to carbon build up.

Good luck

Sven
Sweden  L types.

-----Ursprungligt meddelande-----
Fren: mg-mmm-bounces at autox.team.net [mailto:mg-mmm-bounces at autox.team.net]
Fvr Lawrie Alexander
Skickat: den 27 oktober 2009 18:08
Till: MMM Group
Dmne: [Mg-mmm] MG PA spark plugs

Hi, Folks,

My rebuild of PA engine # 1038A/135P continues, following the disappointing
failure after 118 miles when the core plug on the top of the head decided to

pop out. I'm glad I decided to tear the engine completely apart rather than
just draining the oil several times as numerous problems were revealed,
largely due to, shall we say, less-than-exemplary work by the English
specialist rebuilder.

While I had the head on the bench this morning, I noticed that the spark
plug hole threads are quite long. The engine had been fitted with 1/2" reach

plugs which, I noted, put the spark gap barely inside the combustion
chamber. I tried a 3/4" plug and it appears to put the gap closer to where
the incoming mixture leaves the intake valve. My Blower's manual references
a KLG LK1 plug as being the one the factory fitted but I have no reference
books which tell whether this was a 1/2" or 3/4" plug. While the car ran
reasonably well with the 1/2" plugs, I am wondering if there is anything to
be gained by fitting 3/4" plugs.

Any comments from our P-type owners who may have tried both?

TIA,

Lawrie
Mg-mmm at autox.team.net
http://autox.team.net/mailman/listinfo/mg-mmm

You are subscribed as bispmotala at hotmail.com

http://www.team.net/archive