1967 4000 unloader valve question.

Headingfool82 · Nov 23, 2017

So I pulled the unloader valve. Everything looked good. Replaced the metal type ring on valve with the new o ring I got from local NH dealer. Went to reinstall and seemed as tho the o ring is to thick. It shaved some of the o ring off. My question is how freely is the valve supposed to move. The part number of o ring I installed was NCA 386B
<image src="http://forums.yesterdaystractors.com/photos/mvphoto6593.jpg"/>

Hobo,NC · Nov 23, 2017

Never worked on a 4000 are one that used a metal ring so what I have to say is my experience with 600/860/3000. The valve should float the o-ring should hold it just enoufh the valve will not fall out if you hold the cylinder vertical. I use a pocket magnet to test it will look for a link. Unlike most all o-ring applications a un-loader o-ring is unique it needs to be extremely sensitive to pressure differential on both sides. This were folks get in trouble you can use a standard sizing chart the o-ring to the grove/bore but that's not the way the engineer designed this application.

http://forums.yesterdaystractors.com/viewtopic.php?t=1204839&highlight=unloader

Bern · Nov 23, 2017

If it shaved that much off, then I'd say clearly you got the wrong o-ring. I've installed dozens of those very same o-rings, and have never shaved so much as a hair off of them. Once installed, the valve should move back and forth with very light finger pressure in a lubed bore.

Headingfool82 · Nov 23, 2017

I searched the web and that was the only part number I could find for the o ring. I was confused why it had the steel type spring o ring. Since you installed so many would you happen to have a different part number or info on what I need.

JMOR · Nov 23, 2017

Headingfool82 · Nov 23, 2017

The cast iron seal broke on me. I am wandering if I
can replace it with a different o ring.

BigDanT · Nov 23, 2017

Am I following you correctly, are you trying to put an o-ring on a unloader valve that originally had a metal split ring? I'm not a 100% but I think those are 2 different valves. It could be you cannot interchange the metal split rings with the o-rings. Part# for the valves are C5nn925A and C9nn925A.

Bern · Nov 23, 2017

I think you and JMOR nailed the problem. Without seeing how deep the o-ring groove was in the OP's picture, I simply assumed that the dealer gave him the wrong o-ring.

Headingfool82 · Nov 23, 2017

Ok I need a part number for the cast seal ring. Mine broke and rubber o ring want work.

BigDanT · Nov 24, 2017

Try this number...

Headingfool82 · Nov 24, 2017

I have found that number. I?m trying to find it on the net. Looks like I?m going to have to find a special tool to reinstall it tho. That may be hard to do.

1967 4000 unloader valve question.

Headingfool82

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Hobo,NC

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Bern

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Headingfool82

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JMOR

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Headingfool82

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BigDanT

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Bern

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Headingfool82

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BigDanT

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Headingfool82

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