Fitting Powerspark distributor and Omex rev limiter

Since I recommissioned this car its always had a problem in that the spark would drop out and it would die. Frequently this would happen after a short run of 10 min or so and the car wouldn't restart for say another 10 min when the problem would vanish and the car run as if there had been no problem at all! Running was then fine for many miles.

The waiting time suggested to me a fuel excess, but I could find no evidence of flooding (prior to my attempts to restart the car that is), and there was always pressurised fuel at the carb. Consequently I could exclude both fuel starvation and excess is the cause. Spark was absent (although it often returned during my testing which made the fault very difficult to identify) so I've been concentrating on ignition. The usual tests did turn up a few problems which I have fixed- many of which such as the distributor wiring and AB14 lead and amplifier are covered in this blog. I also found an internal wire break in the black/white coil wire and a separate loose spade contact. Although things have improved, none of this has stopped the spark dropout. This has made me doubt the quality of my repairs so I decided on a radical alternative- I can replace most of the ignition system with new components by fitting a Powerspark distributor.

Picture from powerspark (simonbbc.com)

Although Powerspark do offer a pickup system to fit inside the distributor, they also offer a complete new unit. In my case their complete D23 distributor. This model lacks a vacuum advance system as this wasn't fitted to my year of car. The powerspark model replaces my Lucas 43D distributor, the AB14 amplifier and of course the troublesome lead between the two. It costs about the same as the lead and pickup combined but provides greater certainty because it replaces more components than just these two. Of course its not original and I don't like that, but I will put up with it if it helps remove my problem.

Unit arrived promptly- good service from Powerspark. It didn't come with installation instructions, but my confirmation message from the company simply said connect red and black leads directly to coil + and -! That seems to be all there is to do.

First step- was to make sure that I knew what timing my car was actually set too. I had set it myself and got the motor running very nicely, but it was later reset by Miles at Fibreglass Services who told me it had been  "well out". I have an adjustable strobe and by turning the advance dial until the marks coincided at 0 deg I was able to determine that it was set to 10 deg btdc at idle (750 rpm) and 30 deg btdc at full advance (over 3.3k rpm). That's actually where I had set it anyway so maybe I wasn't so far out after all....?

Anyway to start the swap I removed the aircleaner and box to provide better access.

Aircleaner removed and set aside.

Box to be removed with internal trumpets- bit of a pain!

Disconnect the two breathers entering the box at the left/rear

Remove the  nuts holding the trumpets and the box will slip off... still a bit of a pain. It did seem that there is an excess of fuel from no 2 cylinder although I cant explain that

Removing the box gives good access to the existing distributor.

Before removing the distributor I set the motor to tdc with compression on no 1 cylinder.

Timing marks aligned at tdc.

Disconnect the AB14 lead and remove the distributor cap

Note the position of the distributor cap clamps and note the position of the cap orientation lug (there is only one of these). Take pics as appropriate. Finally remove the cap and check the position of the rotor arm which should be pointing at the cap terminal for number 1 plug. In my case the  rotor was pointing downwards and slightly in towards the block... equivalent to about 7 O'clock if (it could be) viewed from the drivers seat.

Distributor top cap removed. Rotor arm surrounded by flash shield, arm pointing down and in towards block. Cap orientation lug just visible at top of the distributor rim, clamps are oriented vertically

In removing the distributor I wanted to preserve any timing setting in case I needed to refit it. Sadly this didn't work out (see on) but to achieve this I removed the distributor by releasing the bolt between clamp and block (upper nut below with stubby spanner attached). This leaves the clamp itself tight on the distributor body and so doesn't disturb its setting.

The new distributor comes with a new clamp- so no problems in doing this you would think... not so! The new clamp turned out to be the mirror image of the existing. If fitted as it comes, the clamping mechanism would be positioned between the block and distributor which means it will be the devil of a job to tighten/loosen if the timing ever needs to be readjusted when the air box is back in place. Sadly you can't just flip the plate over as its canted with an offset around the block mount.This offsets the block mounting position towards the base of the distributor. Both distributors are shown below with the offset pointing upwards in each case, note that in this position the clamp bolts are on opposite sides.

Clamps as fitted to the distributors, mounitng hole is offset upwards (towards camera) in each case but the clamping bolts are on the opposite side.

This means that I needed to swap the mounting plates obviously loosing the old timing setting but "needs must..."!

Distributor with reused clamp

For some reason the black wire on the new distributor was much shorter (ie too short) than the red and didn't reach the coil. I crimped an extension using silicon wire terminating in a spade male connection. I decided to leave all the original components and wiring in place for the sake of easy reconversion to standard. I will tidy them away as best I can once I've got everything working.

Fitting the distributor was reasonably straightforward. Use the cap orientation lug  on the rim of the distributor to hold the new distributor in app roximately the same position as the old before removal. In my case this meant that the lug was positioned on the top of the distributor facing almost straight up with the two cap clamps almost vertical. Then turn the shaft so that the rotor approximates to the position in which it was found when removed (ie pointing at the terminal for no 1 cylinder downwards and slightly in towards the block). Finally loosen the clamp and swivel it round so that it will slip over the mounting stud when the distributor is set up like this. Holding the distributor in this position it should slip into the oil pump drive with some fine adjustment of the rotor arm until the dogs at the base engage with the drive inside the oil pump. It did slip in quite nicely with the dogs engaged, but I did feel that it should slip further into the oil pump drive shaft because the collar around which the clamp fits doesn't quite slip into the end of the oil pump. I suspect that the clamp should be sandwiched snugly between oil pump body on the right and the distributor on the left and nothing of the collar should be visible. Its possible that the shaft below the drive dog is a little longer in the new distributor but the drive engages fully.

Old distributor- seemed to slip farther into the oil pump in that the clamp collar is largely obscured.

I swapped the HT leads to the cap that came with the new distributor because my existing cap seemed loose on the new distributor (must use silicone/carbon leads not copper). Having done that, and with the distributor hopefully in approximately the right position I could attempt to start the motor before refining the timing with the strobe. 

It was decidedly difficult to start and I could find no spark. However suddenly it burst into life and I was able to time it. BUT and to my shock it seemed that the spark was still coming and going-possibly even worse than before and running wasn't reliable! This suggests that I do indeed have another fault. I discovered that when the spark vanished I still had 12V at the coil. To eliminate a distribution failure I tested for sparks on the king lead using an inductive detector  and found these were also absent. 

There's not much left of my original ign system now, but one constant has been the rev limiter. I have tried disconnecting this in the past in case it was the cause of any misfiring I'd experienced, but frankly I didn't understand this component and I hadn't expected it to have any role at all at low speed... Well I've never had a car fitted with one of these before so it was new to me! Anyway, I'm not sure if I had ever tested it in connection with my ignition failure. To my surprise, disconnecting the rev limiter led to reappearance of the spark and immediate restarting! I now know that the rev limiter works by shorting the ignition trigger pulse to earth, and its prone to failure- by that I mean "sticking". Seems that this may have been shorting out my ignition system erratically and it could account for my symptoms- lesson learned I think! It could have been a contributor  (perhaps the main or the only contributior) to my problems. If so then all my previous repairs may well have been fine! Still, at least I have a shiny new distributor...  Perhaps if I had known more about what rev limiters do I would have suspected this component earlier.

Sadly there seems no way to test the rev limiter except by replacement.... and Lucas versions are now very expensive.  Some Powerspark systems have an inbuilt rev limiter - but sadly when I checked, this doesn't apply to the D23. A word to anyone going down this route; Powerspark can make a custom distributor incorporating a limiter if asked and this is by far the cheapest solution replacing distributor, AB14, its lead and the limiter all in one fell swoop. Sadly though I didn't know this when I ordered my parts! I therefore now need a separate but compatible limiter and many have fitted the more modern adjustable Omex item to replace the Lucas. I may well have to explore that route. 

I bought the Omex clubman limiter: Its compatible with most electronic ignitions but not those using CDI. The Powerspark system uses the Hall effect so its compatible and luckily for me, it's default settings mean that it works straight out of the box. These settings are: 4 cylinder motor, 6k limit and soft interrupt. Its fitted using 3 wires which connect exactly as the existing limiter: live coil (red), negative coil (violet) and earth (black).

Limiter comes with loads of flex, a couple of terminals and some cable ties.

 I will fit male spade terminals to each and then I can reuse the existing  Lucas 3-spade (female) plug. I don't want to remove that as it looks like a difficult item to replace if anyone ever wants to return to the Lucas setup. However for the time being I don't have male spades, so I used piggyback connectors to install the wiring directly to the coil and a ring terminal for the earth so I can test it. 

Bit of a lash up, but temporary connections to coil

In fact the hardest part of the installation is deciding where to fit it. I decided to fit close to the original limiter beside the VIN plate although others have fitted it inside the car next to the fuse box. Fitting internally may be a good idea since if you do ever want to adjust the presets then its a multistage process involving turning the ignition on and off- obviously easier if everything is inside the car! Personally I can't think of any circumstances under which I would need to alter this (unless I swap it into a different car maybe) so I'm happy with the present position. 

Installation. The box is self-adhesive so I cleaned up the bulkhead with meths and stuck it next to the VIN plate. Note ring terminal using the old AB14 earth

Installation was straight-forward and the car started immediately. I haven't checked the rev limiting function as I'm still running in, but frankly its the lower end of the rpm spectrum that concerns me at present. I will tidy up the wiring when I get some spades and hopefully this will solve my problems. I will report later.

Ok so it is now sometime later and Im delighted to report that Ive had no recurrence of the spark drop out!!! Success i think!