It seems the bolthead is loose from the bolt body. When the bolthead is snugged up it does not align with the bolt body and will not go into the action at all. When the bolthead is allowed to align with the bolt body it slides into the action but the bolt will not close. 

A)what would cause this? 

B) how to repair?  

Thanks, Matt. 

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The photo looks pretty small, looks to be a sportered No. 1 SMLE, is that right?  Looks like the bolt is not turning very far either. 

Try pulling back the trigger while you insert and lock the bolt. 

The bolt was cycling fine right before this happened. 

It really is very strange it seems like bolt head can't go into the chamber enough to allow the bolt body to clear the back of the receiver. I've tried pulling the trigger, moving the safety, pulling back on the cocking handle etc and it just won't go. I also triple checked no obstruction in the chamber. 

Nothing lodged up into the breech? Nothing in the barrel? Extractor or extractor spring broken/bent? 

Running out of ideas…

Never seen a cocking piece break like that. Can’t imagine how that would happen. 

Yes, if you can remove the bolt, look for an obstruction, from a foreign object or broken part. See if the bolt locks with the bolt head removed.  Check the extractor and extractor spring to be sure they are not bent or broken. 

No obstruction of any kind.   

Bolt was cycling perfectly 5 min before this happened. 

Did you look closely at the extractor and spring? Does the extractor engage with the slot in the barrel and get crammed over to the right as you rotate the bolt? 

Having a hard time seeing that. If the safety is engaged, the bolt will not insert into the action body at all. Lever must be forward. Once the bolt is inserted, rotating the lever a small amount doesn’t prevent the bolt from locking, but rotating it a fair bit will prevent the bolt from moving at all as the Safety Catch drags on the bolt body.

  I’ve been trying this on my No. 1 skeleton action, can’t get the bolt to not lock fully as long as it can be inserted into the action. 

You could try removing the safety entirely, perhaps something there is bent/distorted? 

Correct, safety lever must be forward and cocking piece lug in the rear of the cam slot. Once it’s inserted, I can’t see how the safety can prevent the bolt from locking. 

Check the sear isn't hung up or jammed. Pull the bolt then while looking down into the rear of the bolt raceway pull & release the trigger several times. You should see the top of the sear rise up into & drop back down below the bolt raceway.

Did you remove the trigger guard from the stock?

If you did maybe the trigger & sear are swapped for position.

With the bolt out of the action, can you turn the cocking piece such that the small lug on the bottom of the cocking piece rides in the cam slot? Perhaps it’s broken or jammed here? 

A mystery so far. 

When you insert the bolt line the head up with the little spring, looks like a button, push down on the the bolt head then push the bolt in.

If it's not riding in it track it won't close properly.

Just a thought based on what I see in your pic.

Look at the removed bolt from the front.

Is the extractor spring sticking out?

Is there tension on the extractor claw?

If the "U" spring broke (a common problem) it could be causing the problem you describe?

I didn’t think of this.  The only No. 1 action I have is a skeletonized action and you cannot insert the bolt without first engaging the bolt head into the track.  

On this rifle that has had the charger bridge machined away, you can probably get the bolt in without engaging the bolt head into the track first, and then the extractor does not line up with he slot cut into the back of the barrel. 

Good news- the bolt now goes back in all the way!

Last night I thoroughly cleaned the rifle, broke the bolt down and cleaned/soaked everything really well. Looks as though the rifle hadn't been deep cleaned in a long time. Flushed out a fair amount of crud and can only guess that something had accumulated/stuck somewhere to cause the bind. Maybe if I had really bashed in the bolt it would have closed anyway but glad I didn't force it and everything works again now. 

Thanks again, Matt.