Tech Q&A: Fall 2006

By Kelvin Dodd

Sorting Out Distributors

Q. There seems to be a lot of different options on the market for electronic ignition conversions and distributors, and it gets pretty confusing. Can you break it down to basics?

A. The Lucas 25D type distributor was made obsolete by Lucas in 1974; from then on the new 45D type unit was supplied that had greater resistance to arcing due
to a redesigned cap and rotor. This new distributor was supplied in points form for 1975 only in the U.S., and then it was replaced with a 45DM4 integral amplifier electronic ignition distributor. The 45DM4 proved to be problematic and a distributor with external amplifier unit, the 45DE4, was often installed under warranty. This latest version, referred to as the Constant Energy Ignition or C.E.I., remained in use for many years and was quite dependable.

The high failure rate of the 45DM4 internal amplifier distributor prompted an American company, Pertronix, to design a replacement hall-effect type pickup and module that would fit under the distributor cap of the Lucas unit. These proved extremely popular with service shops, as there was now an easy and relatively inexpensive fix for their customers. During the 1980s, service shops and parts suppliers could diagnose a defective amplifier immediately from the comment, “The car died, rolled to a stop, but then started just fine after a few minutes.”

Attempts to fit the Pertronix unit to the earlier 25D points type distributors proved difficult at first, as the smaller diameter of the body posed problems with the size of the original amplifier package. These problems were solved with a redesign of the amplifier, and now there are Pertronix conversions for most popular early British applications.

Electronic ignition failures and worn out 25D points distributors in US vehicles produced a demand for replacement points type distributors, which was filled by importing a variety of new Lucas 45D4 units designed for the British and European markets. The most popular units were the Lucas 41427 (Moss 143-110), which was a replacement for the 1962-67 MGB, and the 41610 which was original on the European twin HIF equipped later MGB. Both of these 45D4 distributors used the DSB108 (Moss 153-915) point sets, and DCB104 (Moss 154-020) condensers as used in the 1975 federal models, so tune up parts are readily available.

Some later 45D units using the DSB191 self-wiping point sets have been imported by Mini and Land Rover parts suppliers, so it is important to identify which point set you have before ordering replacements or electronic conversion kits. Moss Motors does carry Pertronix Electronic Ignition Retrofit kits for both of these types of distributors. Part number 222-435 fits the 1975 original 45D4 distributors and other Lucas four-cylinder distributors using the DSB108 style points. Part number 222-495 fits Lucas four-cylinder distributors using the DSB191 self-wiping point sets.

The DSB708 as fitted to the Lucas 41427 and 1975 Federal applications is on the left. The DSB191 self-wiping point set is on the right; the points are wiped across each other as the white lever to the bottom of the point set is moved.

Lucas is no longer manufacturing new distributors, so supplies are becoming hard to find, although there is now a good quality reproduction distributor available that replaces the Lucas 41427 unit. This new distributor (Moss 143-115) adds another wrinkle: it does use the DSB108 type points set, but the cam is larger in diameter so Pertronix and other brands of Electronic Ignition Retrofit kits will not work. The Moss Technical staff has been working with Pertronix to develop a retrofit kit for this distributor and it is now available. The new distributor can be easily identified, as it has no part numbers on either the body or vacuum advance unit.

When replacing points or installing a Pertronix unit if is often difficult to get the small hold down screws started without dropping them. A magnetic drywall electric screwdriver adapter makes an easy job of offering up the screws.

New from Pertronix is the Flamethrower distributor. Designed to directly replace worn out points or electronic distributors with a dependable modern amplifier design built into a new distributor body with an advance curve suitable for early cars and performance use. For more information check out our website at www.mossmotors.com.