seized front engine mounting bolt

If heat, plus gas and large hammer are not enough to shift it, whats the next step, cut it?

Mines seems to be seized on the left hand side only, I don't want to hit it any harder, have been using 2 heat guns, plusgas, crash cooling with water, working up to a sledge hammer with a drift. I don't know if its worth purchasing a blow torch and persevering or just try dremel it out. 

Any tips welcome!

update: bolt seems to be fused to the engine on the left side, both spacers are now running reasonably free. have ordered a blow torch to up the heat as it would be a sad day if I cracked the aluminium mount while hammering the bolt through

anyone gone through this before?

I think a more likely question is who hasn't been in that situation
I have done so many now that it's a well practiced manoeuvre. 
I cut out the middle section with my trusty dremel cutting disc, this means you're only going to be dealing with one end at a time. I have found in some but unfortunately not all cases that viakal the limescale  remover actually dissolves the crap that causes this issue. Most time the bolt head needs to be drilled off as the ends need to be removed by drifting through to the now empty centre space. Still not an easy task but doable.

Interesting, thanks for sharing your method Andy, good to know it's not always easy. 

I'll look out some limescale remover. Would you go at it with blow torch Andy? I'm aware its going to be near impossible not to directly heat the aluminium at the same time, I appreciate ali is great for dissipating heat but the torch is going to be pretty focussed to get enough heat into the steel.

Try to heat the aluminium rather than the steel. Getting the aluminium to expand without the steel is the key.
This is what prompted me to make stainless replacements in the first place.

I suggest better a hot air gun ...... and WD40 on the thread.
Put two nuts and with an impact screwdriver try to loosen the assembly
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Has anyone tried drilling these out?

Got mine out today after many hours, blow torch seemed to convince it, still had to cut the bolt head off and drive it through enough to get the other side in a cordless screw driver chuck and spin it out. A pig of job

Well done! I think I'm lucky, they don't chuck salt on the roads here in Normandie so my engine bolts actually came loose and I had to tighten them!
I have thought what if you slackened the nuts and put a locknut on the bolt so as not to lose the first nut and then just ride the bike and see if the engine vibrations would shake the bolt free?
I always think that if a screw or bolt won't come out and you have to get tough and destroy it it's easier to cut it flush, centre punch it and using successively large drills drill it out. No heat, bashing, worry about breakage and excessive swearing!
 The other day I drilled out a 4mm brass grub screw in a fifty year old Honda 125 throttle slide. For screws I use left hand drills, when they grip most of the time they unscrew the piece of screw that's left! I did go slightly off centre with it but it just left a small c shaped remnant that fell out and left the threads in the slide intact. For a piece like an engine bolt if you wander half a millimetre it doesn't matter, you will still have enough metal to bolt up after.
I am sure that a lot of the electrical earth problems I have seen reported on this forum are due to corroded engine bolts insulating the motor. Just like when people repaint the frame then find nothing works!
Carry on the good work, keep riding, keep safe.
Dave.

I drilled mine out in the end. Absolute pig of a job!