Mysterious Engine Failure - Ideas, please

[Graham Barker]

My measurement is definitely in thousands of inch. Points gap is now about the same as the plug gap.
There is no looseness in the top bearing of the distributor. I don't know if there is play in the bottom bearing. Distributor spindle is not bent because I checked the points gap against all four lobes and found it to be the same.
Yes, I had to adjust the timing after opening the points gap. 
Please don't consider that I have definitely cured the engine failure until I have done a long run.
Graham O has kindly offered to follow in a towing car when I do the run on Thursday. 
Regards 
Graham.

[Reckless Rat]

Graham, if it's any help my RP used to suffer from occasional and persistent misfires and the problem was sorted by changing the Lucas DK distributor for a Bosch one from Willie McKenzie. I have looked at the old dizzy, which I keep on the shelf just in case and there's nothing really tangible about why it causes the misfire, but the change certainly put the car right. Might be worth trying a known good dizzy to see if it solves the problem.

The Bosch was fitted over 15 years ago and has worked perfectly, having since covered many thousands of trouble free miles.

[John H]

FWIW, our chummy (fitted with a DJ distributor) requires a points gap of about 20 thou to get the required 50 to 60 degrees of dwell (measured with a proper automotive dwell meter). The engine runs very badly with the recommended gap of 12 thou. The cam lobes are not obviously worn out, but I've found that using a dwell meter is the only way to set the points up properly, at least on this particular distributor.

[Steve kay]

To add to the above, I would only get a reliable Bosch dizzy from Willie McKenzie, other items in a box labelled "Bosch" could be very dubious. Similarly with NGK plugs, unless from a wholly trustworthy source, to be avoided. Perhaps these manufacturers just can't keep up with forgeries and the distribution thereof, but it certainly damages their reputations.

[Steve Jones]

Bosch haven't made their 009 distributors for some years. Anybody telling you they're selling you a new Bosch 009 distributor isn't doing so unless they're new old stock and that hardly exists. The 009 type distributors available today are copies. They've been made in various places and the quality varies enormously. However, good copies are about. Those from the VW parts supplier Machine 7 are good as are those from the VW parts arm of GSF. I've converted a lot of copy 009 type distributors and these are the only places I'll buy from. Even then, I throw away the distributor caps, points, condensers and rotor arms and replace them with Beru brand items.

The conversion needs doing properly using the correct drive gear and the correct roll pin. In addition, although many don't agree, I also extend the spindle so the gear is fully supported/located rather than having it simply hanging off the end. Done properly, there's no reason why a converted copy 009 type distributor shouldn't work well and give good service for many years.

Steve

[A G Wood]

FWIW, our chummy (fitted with a DJ distributor) requires a points gap of about 20 thou to get the required 50 to 60 degrees of dwell (measured with a proper automotive dwell meter). The engine runs very badly with the recommended gap of 12 thou. The cam lobes are not obviously worn out, but I've found that using a dwell meter is the only way to set the points up properly, at least on this particular distributor.

This is the correct and proper method imho for any distributor regardless of number of cylinders or its mechanical condition. It is a good simulation of actual operating conditions. To speed the process,  what we used to do is adjust to the low end of the nominal dwell setting while motoring the engine on the starter motor (obv. you crank handle aficionados cant do this) with the main HT lead from the coil shorted to earth (or a gap type spark tester attached) and the spark plugs out. Then reconnect everything, start the engine and after a short idling period  (5 minutes or so) readjust to suit, remembering always that dwell angle has an inverse relationship to points gap.

[John H]

I've always checked the dwell with the engine actually running, and iteratively adjusted the points to get it right. Measuring it with the engine running has the added diagnostic that you can check the dwell doesn't significantly alter with revs. Some modern systems have "variable dwell", but certainly not the DJ !!

[A G Wood]

I've always checked the dwell with the engine actually running, and iteratively adjusted the points to get it right. Measuring it with the engine running has the added diagnostic that you can check the dwell doesn't significantly alter with revs. Some modern systems have "variable dwell", but certainly not the DJ !!

Try the starter motor method for the initial setting,  it can save a bit of time. Although if you know your own vehicle's quirks perhaps not. One thing I forgot to say is, remove the rotor before you try this... I used to envy the GM guys with the DELCO 'window' distributor:  fit points, eyeball the gap, fit the cap, grab your hex (Allen) key and tweak it to spec with the engine running. Some of whom we call bush mechanics (shade-tree mechanics in the US) eschewed the dwell meter and just adjusted for best results.

[Graham Barker]

I am pleased to report that my Ruby ran well for about 12 miles up and down dale.  I was followed by Graham O incase a tow was needed, but all went well.
The contact points gap has reduced to about 21 thou -  I guess from the new cam follower bedding in.
Uphill was better than ever before.  Graham O had a drive too and thought the uphill performance was good.
I don't plan to worry about insufficient points dwell time, because the performance is good enough for my needs and am happy to have a car that goes. I might consider going to an electronic distributor.  That may be a subject of a future post.
Thanks for all the contributions towards resolving my problem.
Regards
Graham

[Bob Culver]

Over the decades we have had some electronic whizzes in the Jowett Club. With the cyls near the wheels, poor plug covers, exposed coil etc, like early Minis, prone to trouble. Most reverted to standard eventually. The high available voltages could not be exploited and generally more troublesome and unfixable. My RP ran fine on the original components. In Wellington head winds, with horizontal rain and sea spray it never missed, despite exposed plug tops etc. Economy is no longer prime objective and weak mixtures seem to erode valve seats. With normal mixtures ign demands are not great.
As above I suspect the nature of the spark influences effective advance so differences are apparent but can be gained by tinkering the original.