12G940 unleaded head

[Captain flint]

Hi all,
How can I tell if the 12g940 head I have is unleaded or not?
Many thanks for any help.
Marin.

[bmcecosse]

It doesn't matter - the 'unleaded' is not necessary - just set 15 thou valve gaps. If it has the larger inlet valves it is certainly NOT unleaded. But seriously - don't worry about it - and don't waste money on daft 'additives' ! What engine is it going on ??

[amgrave]

As above, you do not need unleaded seats. I ran a Ford Escort MK1 for nineteen years with a standard leaded head and had no problems. They say valve recessing will happen if you don't change the seats and more so if you run the engine at high speed, well I used to run my Escort at 80MPH on the motorways and in that time the head suffered no recession. Just change the valve gaps to 15 thou from 12 thou.

[Captain flint]

Hi,
I agree,it's not worth worrying about,it's going on a Midget 1275cc engine about to be fitted to my Morris
Minor.
Hell,I'm 71,I am never going to wear it out!.
Once again many thanks,
Martin.

[bmcecosse]

You really do want the large valve head for that engine then to get the best from it.

[Nickol]

Inlet and outlet to 15 thou " ????

[philthehill]

The 'A' series will always runs better with 15 thou valve rocker gaps even when not modified.
The 'B' Series engines are run with 15 thou gaps as standard and no problems there.
The valve gaps on my modified 'A' Series are 19 thou.

[bmcecosse]

You can hold the inlets to 12 thou if you wish, the reason for 15 thou is the increased temperature of the valves with unleaded fuels leading to expansion and the gap closing up. I'm with Phil though - and ran my engine at 18 thou all round. The tiny difference in valve lift is negligible - and the idea is to eliminate any chance of the gaps closing up when the engine is running hard. I have also heard a theory that the larger gap is better because it 'snaps' the valve open - but frankly can't put any faith in it .. or any sense to it either.