boguing said:

To save myself scanning dusty textbooks, I grabbed this from Google.

It's partly to do with using the inlet gas to blow out burnt stuff, partly to do with keeping the gases moving as much as poss and partly because the valves aren't actually very far open at TDC.

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SpringDon said:

Yeah, that's what I said but with colouring in.

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SpringDon said:

Those are definitely the figures from the manual. And you may have to think about the engine a bit more. Even an low tuned engine will start to open valves before tdc, the plan being that the piston will have gone by the time the valve occupies the same space.
Also bare in mind that the cam rotates at half the speed of the crank.
Also it needs to have valve overlap so that gas is scavenged, ie the inlet opens as the exhaust is closing so that fresh charge helps to push spent gas out. This also help to fill the cylinder more efficiently.
As far as I know, no 4 stroke open valves after tdc.

This is a very safe engine and is reasonably conservative timing. If you want to see hairy timing, look at the figures from a zx10 or panigale.

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SpringDon said:

If you're keen, put a layer of plastacene (sp?) over the piston. Oil the valve head and turn the motor over. Then cut the stuff and measure the thickness at the indent point.
Never done this on a landrover but on bike engine the clearance could be 1.1-1.5mm without being scary.
You can also use soft solder in the same way to measure the squish but I'm not sure that's applicable on a flat head.

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SpringDon said:

One final thing to bare in mind then is that cam lift is not the same as valve lift due to the unequal rocker arm length. Don't know specifically on these but it tends to be about 1 to 1.2.

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