Advice needed - how best to shift a seized hex bolt

[Sailormantom]

Hi All. I have recently taken over as Greenkeeper at my local bowls club and one of my duties is servicing our machinery (some of which is nearly as old as our members!) I have a problem with our ten year old mower which has some gear oil in the centre of the roller which needs checking and or refilling. Access to this is by a 6mm hex bolt sunken in a hole about 5mm below the surface. I cannot shift this bolt (I suspect it has been in there since the machine was built even though it should be checked every few months). I have poured in WD40 and broken one allen key already without success in shifting it at all.
Any advice on the best way to tackle this would be appreciated
Thanks, Tom

 

[Amplidyne]

So it's a 10mm socket head screw? A "hex bolt" is normally one with the usual hex head for a spanner to fit.
Proper penetrating oil. Not WD40 unless it's their penetrating oil they make, and a good quality allen key.
10mm allen keys shouldn't just break.

 

[Jake]

As a first step, get some proper penetrating oil rather than WD40. Ideally soak it rather than just spraying, if the mower can be put on its side you have a ready-made reservoir (tape over the top to stop evaporation, leave it for a few days or a week). That sounds easier said than done though, in which case add something to act as a reservoir for the soaking - hot glue a bit of pipe over the hole, with the end of the pipe cut at an angle so it points upwards or something like that.

If not just spray it a lot very often for days, but a constant soaking is better.

 

[Stigmorgan]

Are you able to heat it up? The expansion/contraction might help break the rust seal that's been created.

 

[Phill05]

Soak it with WD40 then if you can use the broken key put it in the screw and give it a hit with the hammer a few time to try to shock the screw then try a good fitting key it should work okay.

 

[JSW]

Or try giving it a righty-tighty turn first before trying to undo, barring that, impact driver

 

[Phil Pascoe]

Don't use WD40. Use PlusGas and leave it for a day or two. As above, try tightening it first and use an impact driver. Use Copaslip or similar when you replace it.
I watched an excellent mechanic some thirty years ago, he had been apprenticed to a chap who retired the day he qualified (that used to be the way it was done). He said he'd been taught to wire brush anything threaded before replacing it and always to use either Locktite or Copaslip depending on the circumstances, because if you take short cuts the jobs have a habit of coming back to bite you. It's always seemed sound to me.

 

[Jake]

Have to adjust torque settings if you grease a thread though (assuming it's important enough to have a set torque)

 

[Sailormantom]

Thanks to all for the replies. Nice to know the proper name for the set screw. It was 6mm not 10mm but even so the allen key shouldn't have sheered.
I will have another go at it and try your suggestions

Thanks again, Tom