Stuck like chuck -Stuck Piston

[Swaggin_Waggon]

Looking for some advice.
I have been rebuilding my ‘71 cb750 engine. First timer and everything was going well until I had to fish out the chain. I put it back together after getting it out and now the 4th cylinder is stuck. I don’t know if I rolled a ring putting the pistons in the cylinders faster this time or ????
All new rings and checked to make sure they were the right size.
The motor turned over with the crank until this part of reassembly. It has to be something with the 4th cylinder. I went ahead and took out 2nd and 3rd pistons. I can’t get #4 out. I’ve used a rubber mallet etc. trying to be as aggressive as I can without damaging cylinder wall or piston.
Pics attached.
Thanks for advice!

 

[grewth]

Never had this problem myself, but logic would seem to suggest that you've got a ring issue there.
So now it would seem to come down to a sort of damage limitation exercise.
Worst case scenario, the liner splits as you force the piston out, then you'll have to either replace the barrels complete, or remove the liner, heat up the barrel and drop in another liner.
I did this on a CB400F many years ago, not as simple as it sounds.
But hopefully, you'll be able to tap out the piston with little or no damage.
Might need just a set of rings, maybe a new piston too.
Looks like any damage to the bore is going to be right at the bottom, so a clean up followed by a light hone will remove any high spots, and any gouges or score marks are going to be below the lowest point of piston ring travel, so probably won't affect compression or performance.

 

[Swaggin_Waggon]

Never had this problem myself, but logic would seem to suggest that you've got a ring issue there. So now it would seem to come down to a sort of damage limitation exercise. Worst case scenario, the liner splits as you force the piston out, then you'll have to either replace the barrels complete, or remove the liner, heat up the barrel and drop in another liner. I did this on a CB400F many years ago, not as simple as it sounds. But hopefully, you'll be able to tap out the piston with little or no damage. Might need just a set of rings, maybe a new piston too. Looks like any damage to the bore is going to be right at the bottom, so a clean up followed by a light hone will remove any high spots, and any gouges or score marks are going to be below the lowest point of piston ring travel, so probably won't affect compression or performance.