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MG MGB Technical - Lucas 40897 and 40897 E

Does anyone know the difference between the Lucas 40897 and 40897 E ? Any difference in timing?

Tore
Tore

Forgot to say they are distributors. Variants of the Lucas 25D. But I guess you already knew that... :-)

Tore
Tore

Indeed. The usual sources only show one variant - A - but for others with multiple letters all the curve data is the same. I suspect it is just internal differences when ordering replacement parts, like for starters and alternators.

But if you have both they are unlikely to show the same curve on test, but that will just be passage of time and miles :o)
PaulH Solihull

Thanks Paul. You are probably right. I thought perhaps it might be high and low compression versions, but it would of course be much more logical to change the number on the distributor when the timing is changed.

Tore
Tore

Tore,
The only way to be sure is to remove the top plate to see what degree advance is stamped on the weights. You also need to check the advance numbers on the vacuum unit. The springs on the mechanical advance weights could be streched or replaced with incorrect ones, so I think a advance curve machine is the only way to determine its actual operation.

Joe G
J. E. Guthrie

The advance isn't stamped on the weights, it may well be stamped on the stop-plate, which is what governs the *maximum* advance. The *rate* of advance is governed by a combination of the weights and springs, so there is no possibility of marking either with advance info. Vacuum advance operates completely independently of centrifugal advance, adding more or less according largely to throttle opening.
PaulH Solihull

Paul. I have seen one set of weights, out of over twenty examples of the Lucas 25D4 distributor, which had a number stamped on them. In that instance, each weight was stamped with a 5 and the distributor in question was designed to give a total of ten degrees of distributor advance (20 degrees at the crankshaft) and the distributor cam stop was not marked as all the others in my collection are. I have always wondered about that particular example.

Les
Les Bengtson

Some useful information on Lucas distributors...

http://www.teglerizer.com/mgstuff/advance_curves.htm
Dave O'Neill 2

Paul,
You are correct. The stamped number in degrees is stamped on the plate. The 40897 distributors I have show 10 degrees on the plate and 5-13-10 on the Vacuum advance. The springs are an unknown quanity of course.
Joe G
J. E. Guthrie

That's 10 distributor degrees of course, 20 crankshaft degrees. Same with the vacuum capsule, the first number is where vacuum advance starts in in.Hg, the second where is finishes, and the third the maximum advance.
PaulH Solihull

This thread was discussed between 09/02/2011 and 17/02/2011

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