Jensen heritage for the next generation

Ignition System

Dear Diary discusses the iginition system fitted to Jensen FF chassis number 119/191

From the Jensen FF Mk1 sales literature relating to the iginition system: “Ignition: Automatic and vacuum advance. Ballast resistor for initial spark boost.”

Photo of the replacement silicon sparkplug leads from Customville. Fitted OK. I also ended up using some plastic ties to help hold No 1, 6 and 8 leads away from the exhaust manifold. The lead set was £38.93 + vat from Customville (2005).

Firing order: On the left side of the engine (left side of car) from the front, the cylinders are numbered 1-3-5-7, and on the right side the cylinders are numbered from the front 2-4-6-8. The firing order is 1-8-4-3-6-5-7-2. The rotation of the rotor in the distributor is counter clockwise.

I purchased a high output coil from Customville £33.04 +vat. After buying I noticed, however that it says it cant be used with electronic ignition? the Chrysler version of which I intended to buy in the near future ( £199 from Cropredy Bridge Garage)(prices 2005)

I was advised that Autolite 85 Spark plugs are very good, as are Blue Streak contact breaker points.

May 2005 Photo of all 8 sparkplugs after removal and in their correct locations The Left hand side of the photo being the front of the engine They look a little lean to me even though there is a new Edlebrock carb with richer needles fitted. (see Carb section) I thought that there might have been some difference between the cylinders that would have indicated that I needed to put in spark plugs with different heat ranges in different cylinders. there was a rather good article in the White lady by Mike Lotwis, had the following to say on the subject:

“Hotter Plugs
Due to the age, mileage, and oil burning of most Interceptor engines, I find it advisable to use at least one heat range hotter plug in both the 383 and 440 engines. A Champion J-11Y is standard, but I recommend using at least a J-12Y plug to help prevent/reduce carbon/oil fouling of the plugs. Actually back when I used to service some 20 Interceptors in the New York area, I used to custom tune each engine by using as many as 3 different heat range plugs, J-12Y, J-14Y, J-18Y – hottest heat range. Most Interceptors burn more oil in one or two cylinders, necessitating the use of the J-18Y plug in just those 2 cylinders to keep the plugs from carbon fouling up in 3 to 4,000 miles. Don’t use the J-18Y plugs in all cylinders, because too hot a plug in a good cylinder will cause the plug to wear out prematurely.”



I wrongly believed that the retard and advance mechanism in the distributor wasn’t working properly because of pinking under acceleration. If I adjusted the timing by rotating the distributor when the engine was at idle to achieve a nice “fast” idle then the car would start better but I would get pinking on acceleration. If I adjust the timing with a strobe and then backed off the timing by trial and error to stop pinking at anything other than full open throttle acceleration then the engine is not so happy at starting and the idling is a little lumpy.

The reason I haven’t invested in an electronic ignition system is that the ordinary one has proved very reliable for me and because of John Wild comments on his FF blog as follows:

“The FF has a different distributor advance curve compared to the 2WD Interceptor. The photo below shows how different strength centrifugal weight springs are used in the distributor to modify the advance curve. An interesting exercise would be to determine an ideal advance curve for the FF running on modern fuels, and to make available springs and weights to produce this mechanically.”

His observations suggest that with modern fuels the centrifugal weights may not be producing the best results anymore..
I asked the List for their views:

I removed the distributor and did a minor strip down as follows:
1. Removed the capacitor and contact breaker set
2. Removed the vacuum advance unit by undoing the two screws that attach it to the distributor body and then unhooked the operating rod from the base plate. Just checked it by sucking on the vaccum pipe that connects it to the carburettor.
3. Removed the base plate by undoing the two screw that attach it to the distributor body. This exposed the centrifugal weights that operate to advance the timeing as you go faster.
4. Everything appeared to be OK. So I just oiled everything and put it back together.

The vacuum advance mechanism is removed by undoing two screws (the other one is on the other side). The baseplate is similarly removed by undoing two screws ( again the other one is on the opoisite side)

Photo showing part number on distributor body “2875 731 37 8”

Photo showing anumber on the operating arm of the vacuum advance mechanism “10.5L ” But no idea what this indicates?

View of inside of distributor after removal of distributor cap

View of base plate after removal of capacitor, points and rotor arm.

Photo of another number on the distributor body

Photo showing the part number for the vacuum advance mechanism.

Close up of one of the of the counter weights springs

Close up of the other counter weight spring. Note the difference.

View of baseplate before removal.

View of baseplate after removal.

View of the underside of the base plate after removal and showing the three legged metal spring that holds the two halves of the baseplate together. It is the relative movement of the two baseplate parts that gives the advance and retard effect.