Commando Fork Oil Drain Plug Stripped Threads

[rockitdoc]

Hi all,

Just discovered my drain plug is stripped. Ugh. Helicoil 1/4-20? Or drill and tap to next larger size? 5/16" is too big. 7mm is about right, but finding a coarse 7mm thread will be an issue. What do you think?
S

 

[Danno]

I'm not sure what the original size is, but I think I'd use something fine-threaded rather than 1/4-20.

 

[gortnipper]

I'm not sure what the original size is, but I think I'd use something fine-threaded rather than 1/4-20.

1/4-20 is the stock size.

Helicoil it I would think.

you would need an M7 tap/bolt if you went metric. M6 is too small and M8 bigger than 5/16.

 

[rockitdoc]

I'm not sure what the original size is, but I think I'd use something fine-threaded rather than 1/4-20.

1/4-20 is the stock size.

Helicoil it I would think.

you would need an M7 tap/bolt if you went metric. M6 is too small and M8 bigger than 5/16.

Helicoil is what I'm gonna try. I only thought M7 because it is the next larger size to the 1/4-20, but a coarse thread would be difficult to find, and it needs to be coarse to avoid stripping it again.

 

[rockitdoc]

Helicoiled it with a 1/4-20. Did the trick.

 

[bill]

you NEVER want to use a fine thread in aluminum.

I'm not sure what the original size is, but I think I'd use something fine-threaded rather than 1/4-20.

 

[swooshdave]

TIMESERT, screw that Helicoil crap. It will pull out sooner or later and then you're really fooked.

oil-drain-timesert-repair-t16154.html

 

[JimNH]

TIMESERT, screw that Helicoil crap. It will pull out sooner or later and then you're really fooked.

oil-drain-timesert-repair-t16154.html

While I'll agree that timeserts have their place and in some places they're superior, there's no reason a 1/4-20 helicoil, properly installed, should ever pull out. Light aircraft engines have many installed right from the factory in places subject to frequent use such as rocker covers and spark plugs. Yes, most light aircraft have helicoils from the factory in the spark plug hole, none have simply threaded parent metal. Older radial engines typically have an insert that is something like a timeset although shrunk-fit in a heated head. Various accessories, pumps, etc in heavy jets also employ helicoils in aluminum castings as they greatly increase holding power with little chance of stripping or wearing out from use.