Ford NH 1920 injector O-rings

[AlbionWood]

I had the injectors rebuilt and when I got them back, it seemed like the new O-rings were the wrong size. They were too large diameter, fit very loose in the groove and were extremely difficult to install. But I got them in and it seemed like it was running well, although the sound did seem just a little off; not quite the smooth purr it used to have. Couple days ago after working it pretty good for a few hours, it suddenly began making a loud tapping noise... I thought maybe a valve lifter needed adjusting, so did that but everything seemed pretty good; put it back together and it still made the noise. Made myself a stethoscope from a piece of plastic tubing and found the noise was coming from one cylinder - sounded more like it was from the injector than from the valves. Pulled the injectors and lo - that one is carboned up and the O-ring is shot. So I think I was hearing the detonation because the injector wasn't sealed into the head and was blowing back a little.
Now I need new O-rings and have to try to figure out what size. Any tips?

 

[Harry in Ky]

Injection Pump & Lines - 1920 | New Holland Agriculture | MyCNH US Store

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The injectors aren't sealed to cylinder compression with an O ring. The O rings are only there to keep dirt and such out of the bore. Your compression leak is a copper washer. Were those properly installed? (item 7)

 

[AlbionWood]

Injection Pump & Lines - 1920 | New Holland Agriculture | MyCNH US Store

Find schematics, manuals, specifications and diagrams for INJECTION PUMP & LINES - 1920. Find genuine OEM parts for your needs.

www.mycnhstore.com

The injectors aren't sealed to cylinder compression with an O ring. The O rings are only there to keep dirt and such out of the bore. Your compression leak is a copper washer. Were those properly installed? (item 7)

Hmm. Yes, the copper washer was in place and seated in the bottom of the bore. Is there a trick to installing them that I don't know about?

 

[Harry in Ky]

The only "trick" I'm aware of is make sure the old washers are removed, the surface on the bottom of the hole is clean and smooth. Install new washer, the injector, (with a liberal coating of never seize) and tighten the hold down bolts evenly. Usually works for me.

If that washer was properly seated then compression wouldn't blow out the O ring above.

 

[AlbionWood]

It looks like I installed the O-rings incorrectly - they don't seat in the groove in the injector body (what is that even for then?), they go in at the top and are held in place by the "Sealing ring collar" (part 34 on the diagram). Those collars are aluminum and got deformed when I pulled the injectors this time, so I now need new collars, O-rings, and washers. Once those arrive I will try again.

I think what happened when I installed the injectors is the O-rings got messed up and caught under the sealing collars, deforming those, and one injector was somehow prevented from fully seating on the copper washer.