lower valve cover drilling

[philip j]

Hello all; Can someone comment on this? I have read that some guys use a 12mm plug instead of the 21mm plug. I cannot get the spark plug out from the lower #3 cylinder, unless I remove the scavenge pump, and rear tin. My 12mm spark plug wrench does not even fit through the valve cover opening. Is there enough strength on the cover or any reason why I could not redrill the cover to get my 21mm plug wrench in? thanks Philip

[Walt Fricke]

Philip

12mm plugs are 12mm at the threads. They do use a smaller wrench, though. The stock plugs (single plug) are 14mm at the threads, with a correspondingly larger socket size.

The most common reason to drill heads for twin plugging at 12mm is that the narrower socket allows you to deal with clearance issues from the head stud nuts. But it sounds like you have 14mm plugs - same as you use up top? Would be a bit complicated to reduce the threaded hole to 12mm, I suspect. Or are there 14mm plugs out there with a smaller wrench (not 12mm, though) size?

Guys with head stud nut clearance issues sometimes resort to making a thinner wrench. The factory plug wrench, which is fairly slim, can be ground down some more.

I suspect that hogging out the hole in the valve cover would not cause problems when it comes to sealing the oil in. It would mean a rather less efficient air seal around the plug connector, though.

[philip j]

using a die grinder to open up the hole. Now I can get my factory wrench in, and get the plug out. Philip