123 distributors for MK 4 engine

It looks as if there is a 123 electronic distributor available for the 3.5 litre Mk 4. Be interested to hear from anyone who has had experience of it in their own car/s.

Without having used a 123 on my own car, here is my anecdotal experience which includes over two decades on my own 3 1/2 litre engines and also aiding several friends with theirs (none of which have had non-standard distributors). Ten to 15 years ago there were problems with badly-designed reproduction rotors and caps for the Lucas distributors. There also were problems with corrosion on new, very old, stock caps. The aftermarket then produced some good caps and rotors amid the poor choices.

I last changed the points 5-10 years ago, over 5,000 miles ago. At my present rate of driving the old Jag, those points should never need replacing.

On the other hand, a 1930 Ford Model A which I keep outside and had not started since September did need some 2000 grit on the points to get the car on the road yesterday after our over-normal winter rains. As a side note, the 10% ethanol fuel in the Ford was from last June, so obviously there are no ethanol concerns in my circumstances. All of my friends and I run only the California pump gas in our 3 1/2 cars, this gas runs about 10% ethanol year round in Southern California; factory distributor settings work fine on our cars.

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For what it’s worth my experiences also correspond with Roger’s


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I agree with Peter and Roger. I have a restored original distributor in my MK IV, (3.5) and used an original distributor in my MK V (3.5). I only put a few hundred miles a year, but never had problems using 93 octane with 10% ethanol mix.

I once had points failure with my '38 SS, and it took me a half hour to diagnose the problem, clean the points with a nail file, and get going again. I found that modern motorists are very unsympathetic towards a guy with an old car if it is broken down and blocking traffic.

If your engine is after serial number S2643 and you have the vacuum advance, your distributor is likely the same general model type DVXH6A GC47 as was used on Mark V, Mark VII, XK120 and XK140.

Some XK120 and XK140 owners on the XK Forum have reported using either the Pertronix or the 123 electronic conversion in their DVXH6A distributors. Some are happy with it, and some have had sudden failure and are distrustful of it. They mention carrying a spare set of parts to convert it back to points operation if they find themselves stranded out on the road somewhere.

So the takeaway is this, to be aware of possible problems and know how to diagnose and deal with them.

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Thank you. Do you know the difference between DVXH6A, DXH6A and DHA6A? I ask because I’ve seen reference to all three being allegedly the correct distributor for the 3.5 MK 4.

The earlier ones were manual advance by a lever on the steering wheel.
These screen captures are from the Spare Parts Catalogue.


This last screen capture is from the Amendment Supplement.
The V indicates Vacuum advance.

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