My cousin was the fastest guy on 760's I ever saw. He could do the 760/761XL in under 10 minutes each. We had pistons and valves already made up ready to put in so it was really fast.
Loosen the barrel support, drive the front pivot and remove the pump group.
Make sure the barrel is clear of projectals and close the bolt tight and remove the valve screw. Apply shop air to the tip of the barrel and blow the valve out the front of the tube. Be careful it is putting out some fpe. Best to have a punch in the crosshole.
Tap the front end of the tube on the work surface and the cap will slide out the guide. Toss a rebuilt valve, cap and piston in the gun and reinstall all the Hardware removed.
If the breech seal is blown the valve will not blow out the front. It helps to put the web of your hand in the cutout of the breech when you blowe the valve out.
If the back of the gun is all correct you do not have to take it apart to do a valve on a early 760, 1400 or 130 as long as the brech seal is tight. 1400 & 140 are a little trikier to do but they can also be done from the front.
If you are really carefull you can take the brass bolt of the 760 and peen down the tip to enlarge it so it seals better on the leade of the barrel.
Tightening the breech screw really good and tapping a little barrel material into the slot of the screw is how every Mac1 /McMurray and Son rebuild was done on all 760's so if you see that you know who did it. That is the signture for a Lloyd Treadwell/Timmie Max 760 or 761. In the 70's we did 1000's of 760 rebuilds.
There was a recall of the plastic forearm and we took all the inventory K-Mart had and installed wood in place of the deteriorating Plastic Gen I forearms. We did 1000 of those lever swap outs alone. Pellgunoil was making the open cell foam forearms crack at the mounting pins. Nightmare in plastic. R&D done wrong!
Crosman had a west coast Service Center Training course in Fresno one year and my cousin and I went. We raced side by side to see who could tear down and reassemble the 760 back end faster and Lloyd beat me by about 45 seconds. We were both under 3 minutes and everyone got a good laugh.
The Business model my Dad had was $15 rebuilds to $30 guns. It worked but you had to do a lot of $15 rebuilds.
"NO GUNS WOULD BE A RIOT"