Some notes on Ignitition

Also on this page, click to viewV twin Ignition timing, by Mike Scott-Coomber
Pre-setting of the ignition timing of the V-twin trike engines is covered in theOwners Manual and in the Club Trike Manual, however this gives the initialsetting on number 1 cylinder only. What if the timing is not correctly phasedfor number 2?
The above instructions pre-supposed that the distributor cam is correctlyformed, and that the fibre cam follower is correctly positioned, together withthe points and the shaft. However, our distributors have in almost all casesgot worn parts, this can mean that the relative spark position between 1 and2 is no longer correct, and number 2 may be advanced or retarded relative tonumber 1. If this is the case the engine will never give its optimum perform-ance.
An indication of trouble can often be found by finding a level stretch of road,taking off one plug lead, and running the trike on one cylinder at about30mph. Adjust the manual timing on the lever to give the best performance,noting the required throttle pedal depression. Note also the ignition leversetting i.e. 10 past the hour or so – remember this! Then repeat the test on theother cylinder. If the optimum ignition setting is different to that of the firstcylinder, the timings cannot be synchronised.
A more accurate check can be made if you have, or can borrow, an ignitiontiming strobe light. Through the clutch oil filler hole set the flywheel to TDCwith the arrow aligning with the mark on the case. Clean off any oil with a rag and thinners or petrol, then paint a mark on the flywheel arrow with silver Hammerite or other oil resisting paint. The mark needs to be about 3mm wide by 10 mm up/down. Using the starting handle or a spanner on the starting dog, turn the engine until by means of a rod or pencil through the plug hole in number 2 cylinder (offside), the piston is at TDC. Take your timewith this and get it as accurate as you can. Now paint another line to coincidewith the mark on the case.
When the paint has dried, hook up the strobe light to number 1 plug. Start upthe engine on a slowish tickover and shine the light through the filler hole. Ifsurplus oil splashes out, either mop it up for a minute or so or drain theclutch. It won’t matter running the engine with a dry clutch for this test, aslong as you replace the oil (1/2 pint) before taking the car out. You should beable to see your paint line roughly stationary in the middle of the filler hole. Ifnot, adjust the timing lever until you can. Note the position of the lever.Now repeat the procedure with the strobe light connected to number 2; youshould see a mark in exactly the same position. If not, adjust the lever untilyou can. The difference between the two lever settings is the error in the sparktiming.
My experience is that I have yet to find an original used distributor that hasgiven good results on this test. This implies that, as I said at the beginning,the engine can never run with both cylinders firing correctly.
What can be done? New points and elimination of wear on the distributorbearing will help, but in my experience not eliminate the problem. I havemade new cams and tuned them to the distributor using a bench rig and thenin the car to correct any errors. This does improve things considerably, smootherrunning at low revs. and elimination of a flat spot I used to get, which Ithought was due to bad carbura+ion. However, the strobe light still showsweaknesses in the system in that the silver line never appeared still. It wouldhop about several degrees each side of centre.
The best solution I have found has been to change to the Lumenition OptronicIgnition system. This kit has been around for many years. However, you willneed a 12 volt negative earth electrical system. The points are replaced by alight beam and photo cell (optical switch) and the supply to the coil is switchedon and off by means of a chopper or rotating arm mounted on the distributorshaft.
As standard, Lumenition offer a range of mounting kits for their units to suitLucas distributors from many post-war cars, however none of these are suit-able for the smaller distributors used on the BSAs. Nor is a version availablefor V-twins. It is possible to fit the Lumenition units in our distributors however,although some precision engineering is required.
The photos show a distributor fitted with the optical switch and a specially produced chopper, mounted on a new shaft. This was timed to give the required on and off positions.
The old pointsand their mounts were removed, the plastic body of the distributor machined to takethe optical sensor and the required leads lead out through a hole in the rear of the unit. The rotor arm and cap remains standard. In addition to thesensor, a power module included in the Lumenition kit is required to amplifythe trigger signal to the coil. This can be mounted on the back of the scuttleunder the petrol tank, out of sight and potential damage.
If any members want to try this modification themselves I can supply drawingsof the necessary distributor shaft, plastic chopper and the required machiningof the distributor body. Alternatively I intend to offer an exchange servicewhere I will supply a rebuilt distributor ready to be fitted with the system. Asmentioned be-fore, your existingignition coil – 12volt – can be used,but this should bea post war type,the early good oldfashioned lookingones may nothandle the highervoltages or giveoptimum performance on this new system.
Now the bad news – cost.
Lumenition systems come at around £162 including vat ∓ post (you don’t need to buy the Lumenition fitting kit, this will beuseless to you anyway). There are several suppliers but Demon Tweeks (01978-664466) appear a reasonable starting point. In addition you will need mykit/exchange distributor body which will cost £64.50 plus £5.00 p and p.
All I can say is that my trike is running much smoother than it has ever done.Once set you should be able to forget the timing as there are no points towear, oxidise or move out of adjustment.

Mike Scott-Coomber

 

 

 

 


BSA Ignition Lesson!, by John Wise
We were on our way to a Ladies Day outing at Exbury Gardens on the Southern borders of the New Forest. Earlier that morning I had visited the localgarage, topped up with petrol and put a bit of wind in the spare tyre. Cameback home, ‘EJ’ (our Series 1 Scout) running beautifully. Loaded the picnichamper on the rear rack, encouraged Sandra into the co-pilot’s seat and offwe go to Wickham Square to meet the rest of the gang.
Just on 6.2 miles from home, coasting down the South side of Portsdown Hillat about 45mph on the Southwick Road when BANG! and other horriblenoises. Having declutched almost instantaneously, I idled to a halt and gin-gerly tried the throttle – engine does not want to know and died completely. Iraised the bonnet expecting the worst but, fortunately, no holes in the block.Head still in one piece with all the plugs in situ. Sump still attached. No oilgushing out on to the road. Perhaps at this stage I should have guessed itmight be an electrical problem, but why the mechanical BANG ……or was ita mis-fire?
Thanks to modern telecommunications a friend quickly arrived and took mehome where I shackled the trailer to the Scenic. Having returned to EJ, whichwas under Sandra’s watchful eye, it was loaded on to the trailer. We weregoing to return home, but decided to carry on to Exbury regardless, where wehad a most enjoyable visit, albeit having set a Ladies Day precedent by arriv-ing with our planned transport trailered!
At first I thought it might be the timing chain and if not that, then it might bea broken camshaft because the valves seemed to be out of touch with theignition cycle and not doing what was expected of them in mechanical timingterms. All very odd.
Yesterday, out came the bench seat and the fire bulkhead, then off came thetiming chain casing to reveal a perfectly normal duplex chain, all the teeth stillfirmly attached to their appropriate sprockets and no sign of any metal swarf.So, with the spark plugs removed, the engine was gingerly turned over by thestarter handle, only to find that it turned over very smoothly with no unwantedor extraneous noises.
No sense in attacking the valve assembly, because having set number one potat top dead centre by the clutch marking, the camshaft sprocket was in agree- ment and the valves all appeared to be functioning OK. So the camshaft was obviously not broken.
The plot deepens. Let’s face it, a side-valve engine is next to a two-stroke in terms of simplicity. What could have gone wrong? Better check the distributor, although I had significant doubts as to whether anything here could create such an apparent major catastrophe. (But how wrong can one be?).
Lift the distributor cap, all appears to be in order. Is it possible that the distributor drive shaft has lost some teeth, or that the cam has somehow moved in relation to its drive shaft? The points and condenser were removed, and then the head unit to find that one of the two auto advance mechanism bob-weights had jumped off of its guide peg. This should normally not bepossible but the cam locking screw (the one hidden down in the little black .hole in the top of the distributor drive shaft) had unscrewed itself a couple ofturns. (Well that’s my excuse). This created the potential for a gap betweenits base and the top of the advance mechanism. With one of the bob-weightsadrift, the distributor cap canbe manuallymoved throughan arc of almost90 degrees, (advanced – retarded? I can’tquite work thatone out in my tinybrain). Anyway,ignition even afew degrees outwill probablycause a backfire(the bang that occurred) and horrible kangaroo-likemovements as the engine tries to figure out what it should do whilst actuallydoing nothing useful prior to stopping completely.
And a salutary lesson, one that I shall not forget. When checking ignitionpoints – don’t forget to check the tightness of the cam locking screw under therotor arm. Fortunately there is no major mechanical injury – apart from themetal-to-metal impact marks caused by a bob-weight flying around in thedistributor housing. EJ is now nine-tenths back together, and I should be ableto give it a test run tomorrow, followed by an MOT in readiness for the nextClub event.

John Wise

 

 

 

 


The Old Spark still jumping, by Mike Scott-Coomber
Ray Waters, as usual, sets us a challenge to get our minds working on whichway to jump in the March issue of the mag. Ray who is well known for histendency to leap (that’s a big jump!) from being positive to negative andback, is worried about which way he should connect his ignition coil.I agree it can be confusing, with some cars negative earth and some positive,some coils marked SW and CB and some + and -.
I can’t always remember what I have read in the past, and am probably notalone, however some years ago I wrote an article in the mag. in this I pro-posed the use of more modern coils that gave higher voltages to overcomethe tendency for modern petrols to foul plugs. I guess Ricardo tried to avoidhigh voltages to minimise plug electrode erosion. This is not so likely with themodern plugs one buys. 18mm are readily available from NGK and Cham-pion (Club spares dept.) and are much better with higher voltages than couldbe obtained from pre-war coils.
Modern coils have the terminals marked + and – and I always connect asmarked, i.e. with a negative earthed car, Trikes, T9s and early Scouts; nega-tive connected to the CB; positive to the switch. Later Scouts, which are usu-ally positive earth, are connected the other way. I vaguely remember readingsomewhere that the coils do work better in one direction than the other. Duringresearch for the above mentioned article I checked the output voltage from anumber of coils connected either way and found no measurable difference.As to the direction the spark travels at the plug, irrespective of which way youwire the coil a negative earth system will always have a negative plug body sothe spark will jump from the body to the electrode and with a positive earth thereverse.
To avoid confusing Ray still further I should mention that the engine will stillrun in the normal direction just the same, and the car will go forward in firstgear as usual.
V-twin plug oiling has again been the subject of several technical notes in themag and in the Club Trike Manual. Due to their ‘advanced design’, trike V-twins suffer from a surfeit of oil on the nearside barrel and a shortage on theoffside one, for a technical explanation see the Club Manual. If the oilercontrol is fully opened, the nearside plug will oil; turn it down and the offsidecylinder will seize. The answer I proposed several years ago is to blank offthe oil feed to the nearside cylinder completely and use full flow on the off- side one. I have yet to seize an engine with this mod, or to oil a plug.
It is interesting to note that the works testers used to fully open the oiler for their initial runs on new engines to avoid seizures, then screw it down, both to give the customers some confidence that the oil pressure was OK when look- ing at the gauge and to avoid plug oiling. Fnally if you’ve read the article on Lumenition (Electronic Ignition Systems) I wrote again some time ago in the mag and repeated in the Issue 2 Trike Manual you will may remember my comments about synchronising ignition timing on V-twins to obtain peak performance. I have over the last year been experimenting with auto advance and retard distributors fitted with Lumenition systems on a few V-twins. The result is better smoother running and im- proved acceleration as the timing is always optimal which in modern traffic the manual control system is invariably not.
As always if you need any more information or advice, (it does sometimes help!), then don’t hesitate to contact me, address inside back cover. I must clean my glasses now so that I can see what I wrote.

Mike Scott-Coomber

 

 

 

 


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