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Old 11-01-16, 12:00 PM   #1
micro
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Default Spark Plugs

Hi
Can anyone tell me if I can fit a new long reach plug in a Lister D with a reducer to make it fit I see the reducers for sale so you can use a smaller thread plug the plug in mine does not go all the way into the combustion chamber

thanks mike
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Old 11-01-16, 12:13 PM   #2
martinpaff
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You probably could, but why? Just buy a plug to fit your engine - I believe the Champion D21 is considered suitable.

MP
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Old 11-01-16, 12:27 PM   #3
micro
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thanks for the reply
the problem I have my plug soots up after about half an hour looking into the plug hole the thread on the head only goes in about half way then the hole is recessed it looks strange that the plug electrode falls about a quarter of an inch away from the combustion chamber
mike
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Old 11-01-16, 12:37 PM   #4
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I have a champion 7 and a \denso m14 ill go on ebay and try to find the right plug

Last edited by micro; 11-01-16 at 12:39 PM. Reason: extra added
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Old 11-01-16, 01:54 PM   #5
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Sounds more like it's running rich and sooting the plug.
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Old 11-01-16, 02:52 PM   #6
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yes but if I turn the mixture screw in any more it just falters and cuts out
mike
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Old 11-01-16, 02:54 PM   #7
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Quote:
Originally Posted by micro View Post
thanks for the reply
the problem I have my plug soots up after about half an hour looking into the plug hole the thread on the head only goes in about half way then the hole is recessed it looks strange that the plug electrode falls about a quarter of an inch away from the combustion chamber
mike
Many engines are like that, Wolseley WD's and Petter W1's for example use a short reach plug in a deep threaded aperture. It helps to shield the plug from oiling up. As Appletop said, it is possibly running too rich?

Pete.
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Old 11-09-16, 11:23 AM   #8
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I have the same problem, either the engine is running too rich or it won't run very well at all (with a load of approx 1/2KW). This may be caused by a severely worn throttle shaft but since that is difficult to fix (how do you get the throttle valve screws out??) I have been trying various spark plugs to see if this makes any improvement.

The Lister D combustion chamber is a bit weird in that the plug sits in its own small chamber which in turn is connected to the main chamber by a port. Why it was done like this I have absolutely no idea, but it means that the 'ignitability' is not as good as if the plug were placed directly in the main chamber itself. The mixture is pushed through the port and impinges directly onto the bottom of the plug in line with the center electrode.

I have found that my engine definitely does not like the modern J-strap style plug which has the ground electrode mounted over the center electrode. The strap (particularly the 1/8" wide type on 18mm plugs) tends to shroud the spark from the incoming charge. The large amount of metal in the ground electrode also tends to cool the spark which is also supposed to be not good.

Older 8com type plugs have a side mounted ground electrode which means that the spark appears directly in the path of the incoming charge through the port and ignitability is therefore vastly improved. I have no doubt at all that the Lister D was designed for a side mounted ground electrode type plug. As it happens you can easily make these from J-strap style modern plugs by 'side gapping' which is described in detail on various websites on the internet. Its very simple, the end of the strap is cut off exposing the center electrode and spark to the bottom of the plug.

I have also tried a spark plug adapter insert (brass seems best) initially to try to prevent wear to the plug thread from the endless process of removing and reinstalling plugs to check the color. I have had good success so far with side gapped 14mm standard extended nose plugs such as NGK BP4ES to BP7ES. The heat range does not seem to matter as hot or cold they all get sooted up the same anyway.
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Old 01-12-16, 12:27 PM   #9
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Well after trying every plug I could get my hands on the answer is: D21.

This plug has the following advantages:
1. Its hot, hot, hot. The insulating cone is 1" long and very thin. I find that even with a rich mixture as shown by black on the inside of the steel threaded shell, the insulator and centre electrode always remain clean.
2. It has a thin ground electrode, 3/32" wide instead of 1/8" such as found on D16 or AB-6 type plugs. This electrode will not quench or shield the spark as much as the heavier type 1/8" wide ground electrode does.
Since installing a D21 plug I have had no problems with misfiring at all. My engine had a problem where it would misfire occasionly (once per minute) after several hours of running under load. The plug showed that the mixture was not too rich, but still misfires occurred, a mystery. Since installing D21 misfires have gone away completely! Highly recommended.
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Old 01-12-16, 12:31 PM   #10
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Exactly what I found with my 6AP, runs well with no fouling.

D21's are available new, don't buy secondhand ones.

Peter
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