Advice needed - how best to shift a seized hex bolt

[BC'er]

Is it in an area you can apply a torch to? If it is and losing any heat treatment of the screw or the surrounding metal is not a problem, then I'd suggest heating it up as much as you dare then letting it cool and repeating the process a few times if you are not using a red heat for whatever reasons.

The thermal expansion of the heated parts will crush the rust or deposits which are binding the threads and removal should be easy after everything cools down. Some oil will help and best applied while the parts are still warm after the last heating and cooling cycle.

If you can get a suitably sized rifle bore brush or other dense round wire brush of the right size, chuck it in a drill and use that and compressed air to clean out the threads above the recessed screw.

Excessive force is probably going to damage the socket and in the process possibly expand it against the female threads making the screw harder to remove.

 

[Bingy man]

Several good ideas above but no one has mentioned the fact it’s a mower that maybe gets used once or twice a week for a few months then mm its in a shed for the rest of the year. It’s subjected to rain, condensation and possibly the forces of centrifugal forces so it’s not going to give up especially if rust is a factor . There is not much meat on a 6 mm Allen key , cheap ones will simply round off , better quality can snap against the resistance of the bolt you are trying to remove. So assuming it’s a r h thread I would also recommend plus gas , and heat if possible. Failing that a short sharp shock applied with a blunted centre punch or similar if that still fails then I would be looking at the socket type bolt/ nut remover tools if there is enough clearance to grip the head in the recess ..be prepared to replace the bolt once it’s removed ( if it’s removed)

 

[BC'er]

Yes, so once removed put anti-seize compound on the threads before retightening and pack the top of the bore hole with grease. If it's in an area where centrifugal force would throw the grease out another option would be to replace the recessed allen screw with a hex head bold with fully threaded shank, and again plenty of anti-seize.

 

[Dave Moore]

From your description I take it you have one of 2 kinds of plug. Either a pipe plug or a flanged internal hex plug. Examples below if the links work.

https://www.amazon.ca/Metalwork-Sta...886e1c3d172c3160ab8aba56c65804f6&gad_source=1

https://www.amazon.ca/Assortment-M8-M22-Values-Internal-Reusable/dp/B0DBZZ4HMH

If it is a pipe plug be very careful about tightening before loosening. Some graunch artist may have overdriven it in and that's why it is so far below the surface. If there are threads in the hole above the plug that is the sign you have a plug. On either case forget the Allen wrench and get a quality proper hex socket and use a breaker bar or an impact driver to back it out. Use lots of pressure to ensure the wrench doesn't cam out and mess up the socket in the plug.

Pete

Which ever of these it is and I suspect the first example you show, they are both parallel thread so it’s been in a long time or it’s got thread lock in it, or cross threaded. When he gets it out I suggest using ptfe tape when refitting. This will guarantee removal in the future.

 

[Stevekane]

I have to say Im not totally convinced I understand what it is our friend is up against,,6mm Allen screw doesnt sound like much of a hole to check gear oil??,,,,would this be some sort of tapered plug,,or somthing,,,,a picture is worth a thousand words an all that…
Steve.

 

[Phil Pascoe]

a hex head bolt with fully threaded shank

A set screw, on this side of the pond.

 

[Sailormantom]

Thanks for all your response. I will have another go next week and report back on my progress

Cheers, tom

 

[Sideways]

What @Inspector said above.
6mm allen key in a 10mm theaded capscrew or whatever. Scratch the socket as clean as possible with something pointed and whatever keys you use, only use ones that are a really tight fit.
You can break allen keys as long as you like, those are cheap, you don't want to round out the socket in the bolt head or you will be drilling it and trying to repeat the whole process using a stud extractor.
Keep a lot of pressure straight inwards to stop the allen key from camming out and damaging the socket.
I would buy a special bit with a 1/2" square drive socket to go on a breaker bar (18" 2' long) and a hex end to fit the bolt. You can get these in impact rated. V tough. You don't want either the key or the bolt head to round.
Heat and penetrating oil are the main options really.
Going to an impact driver is a roll of the dice. It can help break a rusted connection but is risks rounding out the socket in the bolt head.
Hammer blows square on the end of the bolt may do a little to crush any rust in the threads and at least won't round the socket.

Worst case scenario, you are going to strip the socket, you'll drill the bolt and try a stud extractor, that won't work either, you'll drill again to totally remove the bolt and the mating thread, then you will have to re tap the hole with something like an M12.
If there is no room to retap the hole, maybe it won't matter and a metal or plastic dowel with o rings will do to plug the hole, maybe you'll write off the mower....

 

[Sailormantom]

To answer some of your questions:
Yes the mower is used 2 to 3 times a week in summer but only once a month or so over winter.

The plug or whatever it turns out to be is about 10 or 12mm in diameter in a hole of similar size so only way to remove it is by the hex socket. The hole fills up with grass and dirt in use so is an ideal candidate for rusting

The allen key snapped rather than rounded off - in fact the remains are still in the hole which is anther little problem for me to sort out!

I have better quality tools in my own workshop than those at the club so will load up the car and have another bash at it once I have cut the green on Monday

Thanks again, Tom

 

[Amplidyne]

More likely to be metric if the mower is only 10 years old.

Likely yes, but my old American Cub Cadet, which was admittedly 25 years old was all Imperial, and UNC / UNF. Don't know about more modern ones.