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MG MGB Technical - 25 D Distributor Question

I am trying to figure out what vintage distributor I have in my 74 1/2 "B" Roadster. It is definitely a 25D, and the number stamped on it is 41401 A . All the books say it should have a 41491. I've re-examined the number and it is definitely 41401. I saw on one list that a 41400 is used in a midget. My Engine is 18V837Z-H1496. The car has dual HIF-4 SU's, and based on the "H" is High Compression. This engine was NA Export model. Would appreciate any clues as to whether this is the correct dizzy, and/or any specs for it. Thanks, Doug Keene
Douglas Keene

Yep, the books are correct...that number doesn't show up. BTW, if your engine has ever been rebuilt, the engine number may no longer indicate the compression intended by the currently installed pistons. I have an "L" block, with HC pistons. Also, the 18V 837 engine # doesn't look familiar...is this an MGB engine or an 18V from something else? Regardless, it wouldn't be from a Midget, although I couldn't say one way or the other regarding the distributor's origin.
Barry Kindig

Barry..The engine # is correct..it's listed as a North American Export in A.Clausager's "Original MGB". I just had it rebuilt, but am not certain what pistons were put in it.
Douglas Keene

Douglas. One source states the 41400 was used on "73 MG", but does not state which model. It shows the advance curve of 7.5 deg @ 950, 12 deg @ 1350 and 18 deg at 2100 rpms. The reference is not the best and does not say if the degrees are distributor degrees or crankshaft degrees. I suspect that it is listing distributor degrees and the crankshaft advance is twice what is listed. The basic, Lucas 25D4 distributor was used on most of the Brit cars, hence the large number of variations. You should be able to check out the actual advance curve, using a dial type timing light or making and additional, temporary timing mark on the pulley, then compare what you have to what you should have. Remember, these distributors may well have been rebuilt over the years and the markings on the distributor body may not reflect what is actually inside it. Les
Les Bengtson

Douglas,

I haven't seen the Clausager book since I've moved...but if he says it's correct, then I'm sure it's true (that particular book is one of many items I know are still in boxes somewhere...hopefully).

Les's numbers make sense.

Have fun,

Barry
Barry Kindig

The distributor on my 74.5 Roadster was made up of half 74 and half 75 parts as it came from the factory. I have since rebuilt it using an electronic ignition and that particular distributor is in my 74 GT along with a Gold Seal Austin Marina engine, so I don't have any numbers handy.
Michael Wish

This thread was discussed on 06/04/2002

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