I was thinking, could the plug-hole not be opened out (drilled and re-tapped) to take a 10mm plug?
Is there enough 'meat' in the head (between the valves I'm thinking) to do it?
Would the larger hex (or rather the socket for it) fit in the tunnel?

Like I said, just thinking . . .

DocV400 wrote:I was thinking, could the plug-hole not be opened out (drilled and re-tapped) to take a 10mm plug?
Is there enough 'meat' in the head (between the valves I'm thinking) to do it?
Would the larger hex (or rather the socket for it) fit in the tunnel?

Like I said, just thinking . . .

dont think so, heres a close up of lukemillars build pic



full thread here

viewtopic.php?f=62&t=30587&start=50

It's been claimed to have been done,
But the heads would have to be removed,
And with head gaskets at £100 is it worth it.

hunter wrote: . . . the heads would have to be removed . . .

Not necessarily.
A Plastic drill guide could be machined to fit the Plug Tunnel, and the hole opened up with a long-series drill.
With the piston about half-way up on the exhaust stroke, exhaust valves open, Vacuum cleaner hose in the exhaust port to suck out the swarf.
Then re-tap, using another machined guide for the tap, Vacuuming as you tap . . .

I reckon it could be done.

I dont think you can do it.. the NC24 had 10mm plugs but smaller valves.. they made the smaller plugs becuase 10mm plugs dont fit...

Perhaps it will phsyically fit just about but i reckon the metal will be too weak.

no other reason Honda would have used smaller plugs

No, I guess not, shame though.