Timing

[Steve Clare]

I thought I would time my engine this afternoon- it's got a finned Cambridge head. When I took out no.1 plug, of course there's only a view of the valves!
How do I assess TDC when I can't see the pistons, or use a gauge to get accurate TDC? Is it a case of looking at the valves, and when they're both closed it's about TDC?

Thanks

[David Stepney]

Assuming your car is manual ignition, I would time it this way:

1. Set the distributor points gap to 12 thou fully open.
2. Remove No 4 sparkplug and the cover over the flywheel.
3. Turn the engine over until No 4 exhaust valve is fully open.
4. Turn the engine until the 1/4 mark is about 1 and 1/2 inches away from the rear stud holding the block to the crankcase (i.e 1 and 1/2 ins before TDC)
5. The engine will then be firing on No 1 cylinder. Set the advance lever to fully advance and adjust the distributor so that the points are just opening.

[Bob Culver]

If a stock camshaft, the vaves "rock" at about 7 deg ATDC. Assumig you cannot access flywheel. With manual advance can sort out running, so 25 crank degrees prior this would be a start. Half as many deg on the cam pulley which you may be avble to calibrate.

[Chris KC]

The best way would be either to expose the timing marks on the flywheel or whip the head off to view the pistons - though I must say I'm never keen to remove a head if it's sealing nicely.

Keep in mind flywheels are sometimes found to have been reversed, so always check you are on compression stroke (thumb over spark plug hole).

Failing the above, as long as you are close the car should start, then a certain amount of fine tuning 'by ear' is necessary anyway. If in doubt err on the side of caution - too much ignition advance is a dangerous thing.

[Steve Clare]

Thanks very much for the suggestions. I can access the flywheel easily, so will give it a go.
Cheers.

[Dave Wortley]

You could use the soap bubble method to find tdc. Create a bubble on the spark plug hole and it will be at its largest at tdc.

[Tony Press]

I have just had a brilliant idea !

An old plug body and a baloon !! 

I wonder if I can patent it omline 

[Bob Culver]

Hi Tony
Recenly I was loaned a Javelin car. It seemed to go too well for its apparent spark timing so I did not trust the flywheel mark. I forced wood into a plug shell, a thin tube thru that and a piece of glove finger laced ove rthe end. Adequate for purpose.

[Chris KC]

...or you could just stick your thumb over the plug hole...

[John Mason]

I don’t know if I have an insensitive thumb or that I find it difficult to hold my thumb over the plug hole making a seal whilst cranking the engine but this never works for me. I have an old plug with the ceramic and electrode removed then a rubber glove thumb fixed over the top and held tight with a couple of rubber bands.

John Mason.