Tapping a new thread

[andy-xr]

The part of the inlet where the ISCV bolts to has stty threads and I cant get a good seal. The threads were for fine M4 bolts.

I fancy redrilling and tapping to M5 as I have a load of course bolts that'd fit fine. But I've never done it before. Is it just a question of redrilling out the holes and keeping it straight then using a tap set to set the pitch, or should I cover and redrill the ISCV and manifold it bolts to?

[Krikkit]

Have you tried running an M4 tap into the hole? Often works wonders in my experience, and is especially good for bolts which don't hold much of a joint (i.e. not really bearing much load)

[andy-xr]

Its a bit loose and the bolt isn't really gripping after a medium tap so that's why I was thinking of going up to m5 really

[hidetheelephants]

Go for your life; standard M5 tapping drill is 4.2mm, you might get away with 4.5mm with care but I wouldn't advise it. Use lube when tapping it and take care to keep the tap inline with the hole, backing it off every half turn to break off the cuttings.

[andy-xr]

Goodo, thanks v much