Glow plug position

[creast]

Hi Guys,
This has also been posted on HMEM site.
I am currently building the David Parker Vega V twin aero engine (work in progress) and am at the point of machining the cylinder heads. I have trial fitted the glow plug after tapping the thread and hadn't realised just how far back the plug is from the combustion chamber, approx 3mm at a guess. The head is machined according to the plans so I am carrying on regardless but would like any input on just how close the plug end should be to the chamber?
Can anyone advise?
Thanks in advance.
Rich

[seacat]

If the engine is a 2 stroke, the end of the glow should be level with the end (combustion surface) of the cylinder head. 

If it is a 4 stroke, the the end of the glow plug - the bit from the end of the thread to the glow tip - should stand proud of the head; if this would mean the plug end fouling the piston at TDC then recess the end of the plug in the head.  This is because with a 4 stroke, the plug end needs to heat up and hold the heat twice as long as a 2 stroke plug does! Hope this helps,

Chris