Best way to remove rounded bolt please.

[fidzer]

Hi folks. Decided today would be a good day to drop the oil from my gear box. The car I have has 10mm allen key fill and drain bolts.
Decided to be sensible and check to see if I could remove the fill bolt first before emptying all the oil out. After a bit of a struggle, it eventually loosened off, so I unscrewed it all the way out to check the length and popped it back in as some oil was starting to come out. Nipped it up reasonably tight.
Moved onto the drain bolt. This one was tight as well. In the process of trying to remove it though the inside out the bolt rounded off a bit. Now I cant get enough grip on it without the allen key slipping out. I've tried to hammer the allen key in tight, but after applying a bit of pressure, it eventually slips back out again.
Any tips on what to do? Don't fancy drilling it seeing as it's the gearbox .
Cheers.

[japzap]

Penetrating fluid (no not that kind)
Allen head on a ratchet might be easier to apply pressure to
Apply heat...maybe...depends where abouts the bolt is

[ADEuk]

If it's rounded to the point the allen key slips try hammering a torx in.

[HustleRussell]

Sometimes the pointed edges of a 'TORX' bit will bite in where regular Allen keys won't. Impact/shock might help. Failing that it depends on whether the plug is flush or protruding at all, if it is then plumber's stilsons will probably work. Either way, order up a new drain plug before you attempt to get it out again.

[fidzer]

Thanks guys. will give this a go tomorrow and let you know how I get on. Was thinking of going down the torx route. Its been given a soaking of penetrating oil tonight so will have hopefully slackened off a bit by tomorrow.


Gives you an idea on access. Not bad but a bit tight to swing a hammer.

[Petrolhead_Rich]

ADEuk said:

If it's rounded to the point the allen key slips try hammering a torx in.

This!

In our job we are constantly dealing with corroded bolts or damaged heads, a slightly bigger torx is the answer, or if you can get a good quality fine thread stud extractor into the head, that will do it!

[lescombes]

Did a Corsa last week, the previous service apparently changed the sump plug washer...but there you go as it uses a rubber seal anyway. The Corsa and I believe a lot of Vauxhall's use the same plug, had been rounded out...so a quick tap in of a screw extractor (after a new sump plug has been obtained) and I managed to undo it, apparently the torque setting is 7 Nm.. so just a nip up....I wonder how many are out there like it.... But the same process should apply to all with allen head/torx sump plugs...
Don't have one on my vehicle as it was a 19mm hex one yet I still changed it for a Fumoto one from Quick valve. Being an old skool diesel the oil changes are more frequent. The Corsa owner is going for a Fumoto next oil change...

[rambo19]

ADEuk said:

If it's rounded to the point the allen key slips try hammering a torx in.

+1
But try doing it up just a nip before you try undoing it.

[yodel]

last resort get a nut welded onto the rounded plug. not an easy job but usually does the trick.

[R26Chris]

Can you cut a slot into the head and use a big screwdriver?

[Mr2Mike]

Cold chisel + hammer and order a new plug before you start.

[fidzer]

Thanks for all the advice guys. Just to bring this one to a close, ended up putting the car into a garage as it turned out the gearbox needed a rebuild. I was hoping it was the release bearing that was causing my issues, hence trying to drop the gearbox oil prior to taking it out to fit the new bearing, but sadly was a bit more serious than that.