very stuck left crank nut

I have put a lot of pressure on the left side crank nut and it will not budge. I am using the correct puller, grade 8 bolts, and the usual method of tightening the center bolt and smacking it with a hammer. Done this many times. I used heat with MAPP gas. Nothing. I have a piece of aluminum on the end of the crankshaft to protect it. Used a steel drift to tap on the side of the sprocket. Right now there is a lot of pressure on the nut and puller. Any good ideas?

I assume you mean stuck crank sprocket,.... Go buy a big bag of ice. Pack the whole sprocket area in ice overnight. In the morning take the ice off, tension the hell out of the puller, and fire up the map gas torch and go at the sprocket only and try not to heat the crankshaft with the torch. Hopefully the sprocket will heat up and expand fast enough to pop off the cold crankshaft. A few raps on the puller nut sends a shock down the crank and it should help it pop off. Usually if they are that hard to remove, then they come off with a "bang", so stay out of the line of fire when it pops. That's all I got....

I've had mine stick only once and when it popped loose, I thought someone fired a gun. It was that loud.

the electronics world has a spray that cools down parts for testing...REALLY cools them down. perhaps I could speed up the process by trying to freeze the crank with spray stuff then quickly heat up the sprocket.

fought with it for another hour using the electronics freezing spray. Nothing whatsoever. When I began this project I noticed that the end of the crank was mauled by a puller in days gone by. Perhaps the previous owner was unsuccessful, too. I have never had a taper fit grab a sprocket this hard. How hard can I smack the pusher bolt without causing any damage? I've hit it pretty hard and tapped all around with a steel drift. I have a steel plate covering the end of the crank. Open to any ideas.

We just had to deal with the same problem with the neglected and corroded '74 Commando 850 Roadster I recently bought.
I fortunately had the help of a 77 year old "retired" bike dealer and mechanic who sold Commandos (and Triumph, BSA and Velocette) back when they were new.
I thought we'd never get the thing off. Despite several attempts at heating the sprocket, tapping/hammering the dammed thing just wouldn't budge. It even stripped the thread on the "multi-bike" universal puller my old friend had made himself and used successfully for over 50 years on hundreds of (mostly British) bikes.
In the end, based on the advice of a Technical College teacher, we soaked the sprocket in VINEGAR overnight!! (Build up a rim with plasticine or similar to make a "bath" and tip the bike over to keep the vinegar in place). Between this, and fitting a finer pitch high tensile nut and bolt to the puller, and some more heat and hammering the wretched thing finally came off. But boy it was hard. Next step was an angle grinder!

YIPE! What if I put the outer case back on and filled the primary side with vinagar. The clutch basket and chain would also get the vinagar bath. Iwonder what vinager does to loosen the taper fit?

Grinder. Slice & dice.

Oxygen Acetylene torch. Tim the Tool Man Taylor approach.

Seriously, my Norton sprocket never seized but I've pulled many a tight gear or hub. The Oxy/Acetylene heats the subject gear faster and hotter than any propane or MAP gas torch. And yes, it probably will finally release like a gun going off.

Funny story: I was pulling a gear off a tractor transmission. Puller up way tight, lots of heat, was at it for hours and finally gave up and closed the shop for the night. The next morning I found the gear off - way across the room and the puller parts scattered around everywhere. I'm glad I missed it!

I use a puller very similar to this:
http://www.spxflow.com/en/power-team/pd ... uller-set/

Use all grade 8 or better bolts to grab the sprocket. Try and get the tool as close to the snout of the crank so there is less chance for it to twist and go off center. I found that by using air tools I get the best results. Get everything pulled as tight as you can and then hit the sprocket with an oxy or brazing torch. When the sprocket is good and hot hit the head of the puller hard and sharp. If it doesn't release try the impact hammer again, not necessarily on full power. If still stuck let it cool. Sometimes they release as they cool down. Liberal use of penetrating fluids is also good, but beware they will sometimes ignite under the torch.
I had the same thing happen as the previous poster. I was trying to pull a flywheel off of a beat up outboard motor. I put a puller on it, heated it up, hit it with a hammer with no results. Went back into the garage to get something (probably a bigger hammer) and the flywheel popped off with a loud bang.
How much heat and how tight you pull with the impact is something you will have to figure out as you go along.
Good luck, I'm sure you will get it off

Pretty much the same results with a very beefy puller. VERY high preload. acetylene torch with cutting tip or rose bud. I protect the end of the crank with one of my clutch rod seal holders since the gearbox is the same thread as the engine (alternator only). or a chunk of aluminum.
For the atlas I had to make a custom set of jaws for my 3 jaw puller due to the very limited access around the stator housing which only comes off AFTER the sprocket.

Instead of tapping the centre screw of the puller, tap the end of the puller bar, alternate ends, tighten more, repeat. stand clear.

I've done that.

Have you tried a hydraulic puller? They exert significantly more pulling pressure (some tons) and may help. I'd certainly second the use of an oxy to heat the sprocket and would do it all while standing on the timing side of the bike in case it all comes off with a bang. I have in the past had to resort to using an angle grinder to cut off the sprocket on a P11 I was working on many years ago. I made the cut in line with the taper but about 3/16" out. That did the trick when all else failed.

SUCCESS! I heated the sprocket with a turbo torch and used an electric impact wrench. I just left my finger on the trigger and it finally broke free.

Hurrah! Can you still thread the nut onto the end of the crank?