Timing Light puzzle

[bobashton]

Dear All,

Having recently completed a full rebuild on my standard sprint spec twincam engine, I have experienced the frustration of trying to start it for the last three weeks and am now beginning so get a little frazzled!

I have read every previous posting on this subject and am confident that the cams and distributor are properly timed in relation to the crank and each other, there is healthy compression on all four cylinders, I have stripped, cleaned and refitted the Webers (again) without evidence any major air leaks, lots of petrol is being squirted in via the pump jets. The motor was running perfectly in April when I stripped it after the head gasket failed and inspection revealed the bottom end was worn and new water pump required, the head was done by QED. The rebuild has assiduously followed the Wilkins text without cutting any corners.

The area where I am least confident is the ignition timing, I have a 'Bestek' ignition system fitted last year which included a new distributor (similar to Aldon's system) feeding Magnecor Electrosport blue cables. After setting up the disributor by eye, my inductive timing light did not pickup any spark when cranking over on the starter, however, when taking the plugs out and grounding them all four show a big spark at the plug. I tested the timing light on my VW Golf to find it working OK, subsequent contact with technicians at Magnecor suggested the cables did sometimes shield out the spark signal. I therefore repaced the no. 1 cylinder cable with a cheap version and still got no spark, when I run the Magnecor cables on the Golf the light operates perfectly. Therefore, I must conclude the plugs are sparking but not showing up on the light - although I must have used it successfully to fit the system last year (probably with the engine running). My engine runs a generator, could this be a factor in that the signal is weakened until the engine is up and running under its own steam?

The best I have achieved up until now is a brief firing on a couple of occassions but without any real prospect of running. When fitting the distibutor I ensure the rotor arm is pointing at No. 1 with crank at 10 degrees BTDC and then adjust until the sensor and the rotor are in visual alignment, this was enough to get it running when I fitted it last year but I would feel better if I was able to confirm this with the timing light. Unfortunately I do no have option of converting to a conventional points system at present as the old distributor was a complete wreck.

Any observations or views would be greatly appreciated, apologies if this reads like a disjointed rant but my sanity is feeling particularly strained at present!

Bob
[quote][/quote]

[tonycharente]

Couldn't just be that you set the ignition timing 180? out (i.e. on the wrong stroke)? Sorry if this too obvious. Tony

[bobashton]

Tony,

Thanks for the post, yours is a fair point and one which I have checked ad-nauseum over the past few days, rotor arm on No 1 while cam lobes on cyl 4 and sprocket marks face each other. I timed the camshafts during the re-build so they are spot on with the crank.It may well be that I have become fixated in the wrong area but I am concerned that somehow the plugs are not sparking when back in the cylinder head - hence no timing light flash. Doesn't seem logical to me but then I am struggling with that particular concept at the moment!

Many thanks

Bob

[ppnelan]

Bob,

Have you checked that the engine has a good earth connection to the chassis ? There should be a big braided earth strap across an engine mounting to do this.

After dropping & breaking my cheap timing light, I now use 4 of the 'in-line' spark plug testers (only a few pounds on eBay) to show me if there IS a spark, and a 'proper' inductive pick-up timing light with engine speed facility to set the timing.

Matthew

[Elanman99]

Bob

From your description you seem to have done all the right things. I am not conversant with the 'Bestek' ignition system but still dont see how if there is enough energy to create sparks why the timing light is not being triggered.

What I would try is to see if you can put the timing light sensing clamp on the HT lead coming out of the coil and see if that triggers the light. Another thing you could do to save flattening the battery is pull the distributor out of the engine and rotate it by hand whilst it is still all wired up (you would probably need to fix a temporary ground lead)

Lastly, I once had a problem with my Aldon ignition when the tiny magnets in the rotor became displaced so it may be worth checking that nothing is adrift.

Ian Phillips

[bobashton]

Thanks for the replies, the ground strap is in place but I have ordered an in-line plag tester off ebay now. The distributer appears intact and the system ran perfectly just a few weeks ago. The HT lead is equally dead to the timing light and yet each plag is producing a big fat spark when grounded against a cam cover stud. I just have a nasty feeling that in looking too deeply I am missing the obvious, but the timing light is the only fault I can find.

Bob

[Rob_LaMoreaux]

If you take the plug out and ground it good does the timeing light work?

If you have wet plugs the current will flow at a lower voltage and the light may not trigger.

Rob

[M100]

(granny sucking eggs mode)

Forget viewing the cams

Take out all the spark plugs, put a finger over the spark plug hole on the front most cylinder and get a willing helper to turn the engine clockwise on the crank pulley bolt until it is near top dead centre. Get to the point where there is compression pressure under your finger. Stop turning.

Remove the distributor cap and see which way the rotor arm is pointing.

Now check that the distributor cap HT contact that the rotor arm is pointing to goes to the front most cylinder.

In order from this contact going anti-clockwise make the firing order 1342. Don't get confused by the distributor cap layout if it's the direct wire in screw piercing type rather than the ones with push on connectors in the top.

Use jump leads to another vehicle or put a second battery in parallel so that the volts always remain high during starting.

Burn off any deposits/wetness on the spark plugs with a hot air gun/blowtorch.

Pump the throttle pedal slowly a couple of times, forget the choke!!!

Leave the distributor clamp bolt slack and while the engine is being cranked with the throttle depressed slightly swing the timing a few degrees each way until the engine fires. There should be no backfiring.

(I'd dump the ignition system too and revert to standard, they are a LOT easier to fault find)

[Galwaylotus]

Just a thought. If you get no spark at all when the plugs are installed but a good spark when grounding a plug to a head stud, it shows you have a good earth from the head stud. Is there any possibility that the head itself isn't grounded? I mean, did you install any insulating washers for instance which would prevent good electrical contact between spark plug/head/block/chassis?

[bobashton]

Gents,

Thanks for the replies, I have completely run out of ideas so any fresh viewpoint is welcome. Rob, I have put the inductive pick-up on the lead when the plug was out and sparking and still got no flash. Martin, I followed your procedure to the letter tonight, despite having done something similar countless times, still no joy there. As for the grounding issue, I was fairly sure but I'll go away and check that through again. Part of the problem is that I don't know whether or nor the plugs are firing when in the combustion chamber - I simply cann't see why they wouldn't be. I guess my next move, other than suicide, will be to convert back to points for the sake of simplicity.

I'll let you all know how I get on, if I ever get to the bottom of it.

Regards,

Bob

[dmreeceuk]

I have had exactly the same problem with an inductive timing light. It worked for about 3 flashes then died. Tried it on another car - no problem was still working. Coundnt work out why? Tried it again a few weeks later it worked. I think there is something wiered about the inductive pickup on older cars. Perhaps it suffers from interference like the rev counter seems to do

Dave
Elan S4 DHC (For sale)

[denicholls2]

While M100's procedure should have got you there, swapping the plug leads 180 degrees should be a quick and effective method of accomplishing the same thing, to rule out other possibilities. Or doesn't your cap allow removal?

If you've not seen a spark, how do you know you are close enough to proper timing? That's the problem with inductive pickups. With points, you just hook up a dwell tach or ohm meter (or lamp) and time the opening somewhere near the right timing mark.

If you're confident you aren't 180 degrees out, mark where you are and move the timing about 5 degrees each way from the mark until you get a better result. If 5 doesn't work, try 10. Dry plugs are a necessity.

[alaric]

Sounds like the inductive timing light is causing confusion at the moment. When I started my engine for the first time a couple of months back I'd managed to get the leads all mixed up - it fired a couple of times and made some wonderfully loud backfires. I ended up lifting off the distributor cap and rotating the engine to work out what the correct lead positions were. It then started first time.

If you're getting a nice big fat spark from the plugs then I can't see why you wouldn't be when the plugs are in the head as long as it's earthed, which you've checked. You should get a spark if you rest the plug on the thread of the spark plug hole.

I had hassles getting oil pressure too - that was quite stressful. At least you're not doing any harm at the moment.

Good luck.

Sean.

[M100]

While M100's procedure should have got you there, swapping the plug leads 180 degrees should be a quick and effective method of accomplishing the same thing, to rule out other possibilities. Or doesn't your cap allow removal?

Swapping round spark plug leads won't resolve the problem of incorrectly thinking the firing order is 1342 clockwise or having the plug leads 90 degrees out of position.

Going back to basics and making sure there is compression in the cylinder, then getting the spark to that cylinder followed by the others in sequence is the only sure fire way to be absolutely certain there is not a screw up. Believe me I'm speaking from experience having inadvertently swapped the plug leads to cylinders 2 and 3 on my fathers car many years ago during a spark plug change. The car started and ran in a fashion but despite the static timing being right and all the marks aligning it won't make the slightest bit of difference if the plug leads are in the wrong order and you swap them all by 180 degrees

It took 2 days going though every possibility to finally find the cause of my screw up. Spark plugs and leads were changed, as were the coil and points. I had incorrectly assumed the firing order was 1342 clockwise, not anticlockwise so swapping 2 and 3 and then counting round from 1 clockwise made my sequence look correct. Funny thing was the plugs didn't foul. I wasn't aware of cylinder rpm drop testing then which would have revealed the fault quickly and I didn't have the equipment to test this accurately anyway.

It's not a mistake you make again!

[M100]

Bob, just had a thought.


What spark plugs are you using?


Are the HT leads the plain type or resistor type?