The threads are gone on my cylinder head. I was going to helicoil it but someone suggested I just tap it to the next size and fit bigger plugs. It currently has M12 x 1.25 plugs. M14 x 1.25 is a common size so very doable. Which would you do?
If you drill and tap it larger, will the flat area for the copper sealing area (or tapered area if it is conical seal type) be big enough for the larger plug to seal? Do you have the facilities to recut a seat for it if needed?
quote:No, I don't have those sort of tools. Beyond tapping a hole, I'd leave the job to a specialist.
Originally posted by SteveWalker
If you drill and tap it larger, will the flat area for the copper sealing area (or tapered area if it is conical seal type) be big enough for the larger plug to seal? Do you have the facilities to recut a seat for it if needed?
If entrusting the work to an engine specialist, I'd be inclined to seek their advice on the best course of action.
Making sure the larger diameter opening doesn't intefere with oil or coolant passages for example.
Are M14x1.25 plugs readily available with the same spec as the M12x1.25 plugs?
i would deffo be taking it to a specialist
I am guessing, is it an ali head?
personally I would use helicoils, but as others have said it is best done by a specialist, unless you take the head off.
Well here's something. I found my digital callipers and have measured the helicoil kit. The tap is 16mm OD and 1.25 pitch, which is correct. The pilot drill is 14.3mm which I believe is correct for the tap. The coil is 16mm OD so will fit in the hole made by the drill and the tap, but the inside of the helicoil is 14.3mm diameter. My spark plug is 13.7mm OD, which is good enough, but clearly nowhere near the coil. It must be that the coil wire they used is wrong. Like all wrong. I'm glad I checked it before drilling the head.
quote:
Originally posted by smart51
Well here's something. I found my digital callipers and have measured the helicoil kit. The tap is 16mm OD and 1.25 pitch, which is correct. The pilot drill is 14.3mm which I believe is correct for the tap. The coil is 16mm OD so will fit in the hole made by the drill and the tap, but the inside of the helicoil is 14.3mm diameter. My spark plug is 13.7mm OD, which is good enough, but clearly nowhere near the coil. It must be that the coil wire they used is wrong. Like all wrong. I'm glad I checked it before drilling the head.