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Thread repair
joneh - 28/3/19 at 10:06 AM

Morning all,

I have a stripped engine mount thread on a crossflow block. Only noticed it after finishing the rebuild - rookie mistake.

Whats the best method of fixing this, being cast iron? I'm thinking an m8 tap as its slightly bigger than 5/16 UNC? The bolt spins freely so I assume I can't use an original size tap. If that doesn't work can I helicoil it by hand?

Jon

rusty nuts - 28/3/19 at 10:47 AM

Personally I would get a Helicoil repair kit and do a proper job. You never know , you may need it again . Failing that find someone with one? I’ve lost count of the times incorrect fittings have caused me problems.

joneh - 28/3/19 at 11:10 AM

quote:
Originally posted by rusty nuts
Personally I would get a Helicoil repair kit and do a proper job. You never know , you may need it again . Failing that find someone with one? I’ve lost count of the times incorrect fittings have caused me problems.


Sounds the right approach. Is that easy to do by hand into cast iron?

MikeRJ - 28/3/19 at 12:22 PM

quote:
Originally posted by joneh
quote:
Originally posted by rusty nuts
Personally I would get a Helicoil repair kit and do a proper job. You never know , you may need it again . Failing that find someone with one? I’ve lost count of the times incorrect fittings have caused me problems.


Sounds the right approach. Is that easy to do by hand into cast iron?


If you can drill a hole straight and start a tap straight then it's a piece of cake.

rusty nuts - 28/3/19 at 01:08 PM

As Mike says really, only thing I would add is use plenty of lube when drilling and tapping. Drilling and tapping fluid from Toolstation is cheap

steve m - 28/3/19 at 04:26 PM

I helicoiled all my crossflow mounts to 8mm, as the old 5/16th threads were manky

helicoil kits are easy to use, and once bought, used them loads of times

steve

907 - 28/3/19 at 07:54 PM

I would drill it out to 8.5 mm and tap M10. Drill the mount 10.5 mm

joneh - 28/3/19 at 10:02 PM

Thanks all, the hole is pretty beat up, so might have to go to 3/8 unc or m10. Will take a look tomorrow.

Jon