front iso elastic bottom bolts

Lower front bolt passes thru a dowel in the crankcase. That you can turn the bolt after heating the crankcase suggests that the steel bolt is rusted to the steel dowel. I've never seen this on a Commando but, from similar constructions, I'd say this is nasty.

Don't heat the crankcases, this will only allow the dowel to rotate, possibly loosen it in the crankcases and won't help get the bolt out. And don't hit anything with a hammer, the risk of damage is quite high.

I'd suggest laying the engine (whole bike in your case) on its side so the nut end of the bolt is uppermost (should be right side up). Then you could try pouring penetrating oil down the bolt & hole to try to free it up. But I suspect oil will not be enough in this instance and I think I'd go straight to acid. Choices range from relatively mild - Coke (dilute phosphoric acid), vinegar/acetic acid - to agressive - strong phosphoric acid or hydrochloric acid (sold as brick cleaner in builders merchants). Apply pressure to the end of the bolt with a G-clamp (put a tube over the bolt head so it's free to move) and leave to soak. Remove the clamp from time to time and try rotating the bolt with a wrench.

In similar situations the parts have been rusted solid and I've ended up cutting the assembly apart to get the bolt/shaft out - not an attractive proposition. I don't envy you...

..that before you try acid (real risk of destroying crankcases!) that you cut the nut off the bolt.

Probably doable with a dremel or similar. Sawing is not so easy as stainless work hardens.

There is a good chance that it will release ok once you have done so as a stainless bolt shouldn't 'gall' into the dowel as there is no motion/pressure for it to do so, unlike when a nut has been fitted without lubricant.

Regards, 

George 

I jumped to the conclusion that this must be one of those "barn finds" that you see advertised; a non-runner that's been stored under a plastic sheet for years with corrosion just about everywhere. But it sounds like that's not the case. As said, I've never seen Commando engine bolts rusted in - there's usually too much oil around a running bike. And replacing bolts with stainless sounds like it's had some recent attention.

I'm kinda stumped as to what is going on but I can't imagine the crankcase dowel would be replaced with stainless and, while a stainless bolt will rust, it shouldn't be so bad or have had the time for it to seize in. Are the bolts oversize, e.g. 10mm; that might bind on the dowel.

So I wouldn't go down the acid route and instead try pressing the bolt thru with the head end of the engine mount/crankcase fully supported and a good soak in oil ahead of time.

Ok, you say the bolt is stainless steel. Is it a 3/8 UNF or 10mm bolt? Did the head of the bolt look like it had been hammered in? What kind of hammer and punch did you try with? A toffee hammer and a tiddly 4mm punch is no good here. A decent 2lb hammer (or larger) and a big punch, say an inch diameter steel or brass (better) and a foot long is needed to get the bolt moving. (i know this sounds like overkill but you need to control the punch while you hit it and it is far easier to hold and control a big punch than a small one) Especially if you are working on the ground and don't have the bike up in the air on a bench. Undo the nut to the end of the threads before hitting, this will help prevent mushrooming.  If you have mushroomed the thread already you will have to grind/file the mushrooming off.

Use penetrating oil and heat accordingly