ORIGINAL: downunder
The only engines where you have to be really careful about plug reach is on some of the older (non Schneurle) baffled piston engines. A lot of them had the plug off set to the transfer port side and the plug was located directly above the baffle. Too long a plug would then extend down into the baffle slot in the head and physical contact would be made. Not good
. An idle bar plug would only make things even worse. With modern Schneurle port engines this can't happen unless you have a very small engine. My smallest is an OS .10 and I could only get slight contact by using a long reach idle bar plug without the washer fitted.
An idle bar plug will cause piston contact in 90% of car engines, oddly enough. You do have to watch yourself there.
I must admit I'm surprised that the turbo plugs (as used by a lot of car engines) haven't started to appear on plane engines because they avoid problems with plug length, give a better combustion chamber shape and are now available in a quite a few heat ranges.
They haven't even taken cars over. I, personally, don't see a point to them, the combustion chambers are so small that I doubt the 'ideal' contours make much of a difference. a couple hundred RPM and 0.05HP is not worthy of requiring significantly more expensive plugs IMO.
ORIGINAL: Gray Beard
I'm stuck in a rut, these days I pretty much only use the OS 8 and type F plugs in my engines. I think the smallest engine I have on hand are a few .25s but I haven't used them in years.
Nothing wrong with that. I use OS 8s in all of my engines.
Admittedly at this point it's just two, an OS 18 CV-RX and an OS 46AX, but still. I've never met an engine that didn't like OS 8s.