Timing changing on its own

[svenedin]

This is a weird one and I would be grateful to hear any thoughts on this.

Twice, the timing on my car has altered itself without me going anywhere near the distributor.

The first time, the car had been at a show all day with the bonnet open. I thought perhaps somebody had had a fiddle though this seems very unlikely.

The second time I had fitted a refurbished cylinder head and gasket. I thought I would check valve clearances, timing and mixture. I only checked the timing to be thorough and not because I thought it was wrong. When I checked with a strobe the timing had moved from 6 degrees BTDC to about 1 degree ATDC.

My car has a recently professionally rebuilt Lucas 25D with a Pertronix electronic Hall effect module inside. This inexplicable timing wander happened before when there were points fitted.

I am sure that the distributor clamp was tight both times......

Stephen

[kevin s]

assuming the distributor is ok I can only think it's either the distributor not being clamped tightly enough or if you have a damped pulley can the outer move relative to the hub?

if it's neither of those then I'd be taking a closer look at the distributor, you could also check the valve timing but I doubt that is the issue as you'd have a whole load of other problems as well.

a final thought, you could pull the distributor driveshaft out and check it isn't worn or missing the odd tooth but they don't usually wear.

[svenedin]

Thank you.

I have been mulling this over in my mind and I think I am being very stupid here. My timing light has a clever feature whereby the degrees of advance desired can be set in the light (say 6 degrees BTDC) and then when the strobe is activated the timing mark will appear at TDC when it is correct. This is much easier because there is no guessing at exactly where the mark is appearing in relation to the finger pointers. I think what has happened is the timing light has remembered what I set it at last time, which was almost certainly 6 degrees BTDC, and then when I used it today the timing mark appeared at TDC which made me thing the ignition had inexplicably retarded itself. This is my theory and I will check tomorrow. It is too late to be fiddling in the garage now. I really do not like equipment with minimal buttons that have to be pressed to display what settings are being used. I much prefer dials for the settings so it can be seen at a glance what the settings are. This also applies to the dishwasher, washing machine and tumble dryer!

Stephen

[svenedin]

I have confirmed that this issue was entirely caused by my inability to remember the instructions for my timing light from one use to the other.

My light, an Sp8000 has an advance feature. This enables the advance desired to be set in the unit and then when the timing is correct the mark on the pulley should appear at TDC. The trouble is, every time the machine is disconnected and re-connected this advance defaults back to the default setting of 10 degrees. If the light is to be used just like a normal strobe the advance has to be tediously set back to zero every time. Why the default is not zero (advance feature off) I cannot imagine. I had forgotten about this more than once and then assumed the timing had inexplicably changed.

Stephen

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[philthehill]

Remind me not to buy a Sp8000 timing light
My Gunson's Timstrobe Inductive is more than adequate for my needs
Complication I can do without.

[svenedin]

Yes I agree. I didn’t really want this “feature”. What I wanted was a tachometer function so that I knew the revs were low enough not to be activating the centrifugal advance.

Stephen

[oliver90owner]

Tacho? Timing light? On some of my engines (the multi cylinder ones) one uses one of the plug leads to illuminate the flywheel timing marks. Works OK in dim surroundings. Was the best they had, back in the 1920s.