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MG MGB Technical - 25D4 distributor cap

Are the 25D4 caps that have the wires coming out of the side and the cap that has the wires out the top interchangeable please. Assuming they are, Is there any reason for me NOT to convert to the to pop off top connections?
jjralston

They are interchangeable and there is no reason not to change. Cheers - Dave
David DuBois

The version with the cables coming out of the side is the older design. The newer one with the connetions to the top is interchargeble, as long as it is made for a 24D4.

Ralph
Ralph

thanks guys
jjralston

The old style cap was needed on the right hand drive cars to allow the steering shaft to not interfere with the spark plug wires, possibly causing a short as the shaft rubbed against the wire's insulation. Back in those days, the stranded, copper spark plug wires were the norm and the side entry cap, with its pointed screw making contact with the copper wire worked well.

Modern spark plug wires are no longer made with copper wire. The pointed set screw, forced into the softer core of the modern leads tends to damage the lead. But, it works most of the time.

The top entry, with push on connectors, is a far better system unless one needs the other style of cap--as on a show car where points may be lost for originality if the more modern cap and leads are used.

Les
Les Bengtson

Funnily enough the connections coming straight off the top are the more modern as has been said which *does* cause problems on RHD cars, with one at least of the plug leads getting abraded by the UJ.
Paul Hunt

Is it possible to get side entry caps with a push fit connection? I would like to go back to the side entry cap which seems a neater solution. Plus I have the original rubber cover for a side entry!

John
John U

John,

there are no versions with push fit connectors for a D25, but it is easy to use cupper core cables on the side entry version. These cables are offered by many speed shops and they also have the right spark boots for this (DIY) assambly and installation.
This setup has proofed to be more relyable than modern graphit core cables, althoug radio interference is worse on some frequencys.

Ralph
Ralph

Thanks Ralph,

Interference not an issue for me (no radio). Just a shame that I haven't had the modern HT leads for long.
Probably buy the side entry and leads and keep top entry as a spare.

John
John U

The original carbon string HT leads do degrade significantly over time, but what I call modern leads are silicone cored and they are absolutely stable. I've never had one of those fail or go HR in over 20 years.

If you fit copper-cored cables you must fit interference suppressors either in-line or as plug caps. Radiating interference *to others* is an offence, it is much less to do with any interference it might cause to your own radio.
Paul Hunt

This thread was discussed between 13/11/2008 and 18/11/2008

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