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Discussion Starter #1
I found the cause of a hydro leak coming from the top of my transmission - a leaking seal on a check valve. I had the two valves repaird a couple of years back (with new seals), but I think user error caused the leak by torqing them up too much.

So I have got new seals, and installed. When installing I have some questions so that I don't mess this up again:

1. Manual states to dip in hydro oil. I can do that, but should the oil go onto the threads also, or does that mess up the install because they could loosen to easy? The shield that goes on top of the tranny seems to sit against the sides of the valves, so and so I presume will lock them in place in case of any vibration (they won't loosen by themselves).

Anyway, the question is here: oil on threads, or not? Maybe it doesn't matter either way?

2. How much to tighten? It is almost impossible to figure out torque (since clamping against a rubber seal, I guess it is # turns, not torque wrench job). There's zero detail in manual or anywhere about how much to tighten. From a video I watched here (same valve type as mine), it looks like the check valve is screwed in until the top seal seats by finger, then the valve is turned approx 1/2 turn. There appears to be 3/4 turn from seated to 'won't move', so I guess 1/2 turn is just about right?

Thoughts appreciated. Thanks!
 

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Rob, Unless specified not to apply oil, it's good practice to oil ALL threads. You can't put to much on either, other than maybe a little messy!

How tight is tight is a good question! Your "tight", my "tight" and Joe's mechanic down the street that works out regular, will have a different "tight". With a standard wrench or socket on a ratchet...NOT a 2 foot breaker bar with 4 feet of pipe on the end... pull tight and maybe a LITTLE extra jerk at the end. Start tractor and move hydro lever while walking along with tractor. Inspect for oil after going 20-50 feet. If no leaks show up, button it up! If leaks, tighten about one flat on valve hex and move tractor again.

More questions, come on back! Bob

It's been 2 years since I put valves in my 322 and my memory is shot! Some backup rings have a radius in them. This goes against the o-ring. If flat on both sides, no difference. The backup ring helps to retain the o-ring and prevent it from damage when installing/tightening mating parts.
 
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Discussion Starter #3
Thanks Bob!

I installed with 1/2 turn from the seal seating and still had leak, but again just on the one that was leaking before the seal swap. That's a little suspicious. The other one is bone dry.

So this time I tightened both until they stopped turning. Interestingly they didn't need hardly any force to turn to fully closed. I used a very short stubby wrench, could have just used my pinkie. Then they both stop, it is in exactly the same spot, so I guess the top of the head of the check valve just sits on the tranny case and just won't move any more. I have the type of check valve that is a self relieving type (from a cub cadet I think). Maybe I just need to just make them bottom out, then tighten at end.

I haven't managed to test again because now I have a fuel supply issue! Will post that in another thread. Grrr.
 

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I found the cause of a hydro leak coming from the top of my transmission - a leaking seal on a check valve. I had the two valves repaird a couple of years back (with new seals), but I think user error caused the leak by torqing them up too much.
That'd have to be AWFUL tight. These things are tough. They really only need to be a little more than snug.

So I have got new seals, and installed. When installing I have some questions so that I don't mess this up again:

1. Manual states to dip in hydro oil. I can do that, but should the oil go onto the threads also, or does that mess up the install because they could loosen to easy? The shield that goes on top of the tranny seems to sit against the sides of the valves, so and so I presume will lock them in place in case of any vibration (they won't loosen by themselves).
Dip "em right in. The seals should have been oiled prior to installation. If not, be sure to wiggle them around good to get oil underneath as well.

Oil can certainly go on the threads. It's not going to promote "self loosening" in any way. That's a common misunderstanding, but no worries. It won't bother a bit. There's also not enough length to allow adequate elongation for engaging the aluminum housing.... That's getting sciency, but what it means is that no matter how tight you make it, it's not going to act like a "normal" bolt. They kind of hit, and there is very, very little advancement for HUGE amounts of increase of torque...

These want to be snug. I say that, because of course they should be "just right", (which is of course "tight"), but given the size of the socket and ratchet that you need to install them, well, you won't be working all that hard to make it just right. It's not even in the same ballpark as a bolt of a similar size. DO NOT make any comparison to how hard they are to remove from an old transmission. That's a whole different and unrelated phenomenon.

Anyway, the question is here: oil on threads, or not? Maybe it doesn't matter either way?
Yes, oil them.

2. How much to tighten? It is almost impossible to figure out torque (since clamping against a rubber seal, I guess it is # turns, not torque wrench job). There's zero detail in manual or anywhere about how much to tighten. From a video I watched here (same valve type as mine), it looks like the check valve is screwed in until the top seal seats by finger, then the valve is turned approx 1/2 turn. There appears to be 3/4 turn from seated to 'won't move', so I guess 1/2 turn is just about right?
No.... Well, yes, if hot tight you make it was critical, torque would be the way it would be called out. This is WAY too short, and made of WAY too hard of a steel to even think about measuring stretch. (Torque/angle method). Its just not there in any tangible amount outside of a laboratory.

If torque were of importance here, it'd be in EVERY manual. It's not, because it's not that critical. You could go to a standard torque table (they have these for types of fittings, just like they do for standard bolts, with different metalurgy, different plating, different head design).... This is one of about three times in my life I'll ever say this, but here, it really is not a big deal. Presuming you're using a normal half inch ratchet, just make it "snug". If you're doing it with a normal 3/8 inch drive ratchet, go ahead and make it tight. (If you've got stubbys, or extended length ratchet handles, adjust accordingly).

Thoughts appreciated. Thanks!
The seal, and the seal protection, and the seal function is 100 percent independent of torque on the fitting. The o-rings are not "squished" like you'd think to make a hard seal. They are squished a little, but so long as the "nut" at the top of the valve is touching the aluminum housing, the fluid pressure will actually move and flex the o-rings within their confined area, pushing against the non-pressured faces of their confined area. More pressure equals more squish, equals more "sealing power".

When there's a premature problem with them, leaving out the obvious answers such as dirt in the bore, rust, pitting, corrosion, damage from installation, wrong size, all the easy stuff.... it's almost always because they aren't confined, they aren't the correct size, or they weren't lubricated adequately.

Not confined would be their space not being correct. The plastic backer ring missing from the lower o-ring. The fitting half a turn loose from fully seated. That sort of thing. Anything that changes the dimension of the area where the seal lives.

Not the correct size is pretty straight up, except that it can be hard to know right off. I've gotten a couple of seal kits that had multiples. That leads me to believe that there were options "somewhere". I don't have any standard o-ring numbers for that, but what that means in my world, is I go by the serial numbers and get dealer parts. Or OE parts if I can identify the component manufacturer. Or another application specific source. If I have a lot to do, I'll measure bevels and grooves and do some math, and get a number for an industrial lego replacement part, but for one or two... Just make sure it's for the right application. And I stay out of the "universal" o-ring kits that are (usually) low quality of whatever material you get, and are (usually) made "close enough" to save a buck by selling the same o-rings as SAE and metric. Fine for some things, but not for others. Not fine for hydraulics.

And lubrication. If the o-ring is not thoroughly oiled on it's entire inner and outer surface when you install the fitting, they have a propensity to deform on installation. (especially the ones in a "V" shaped groove, such as the top o-ring on that valve). They stick on the moving part, and the not moving part, and "drag" along, and get ripples in them (if not outright tears). It still seals right off, but leaves very high stress and very low stress areas in the material, and you heat cycle them, and pressure cycle them, and they're short lived.
 

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Discussion Starter #5
Thanks Jake! Well you seem to know a bunch about these.

- So I did lube the valves and threads. Check.
- I DIDN'T do the backs of the seals. So I will remove and do that again, will just get messy with lots of oil, dunk the valves, dunk the seals, install on the valves, dunk again!
- I will get the head of the valve seated against the tranny. Then give it a little snug, hand tight with a short wrench.

If that fails, maybe I've just got myself a bad check valve and I will get another.
 

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Discussion Starter #6
Got the valves back in, turned over the engine and turns out the real issue is a bad valve, not seals:


I ordered a new valve, will be here at the weekend.

I couldn't see where the oil was coming out before as the cover and gas tank were on. Just turning over the engine without the gas tank connected showed the problem.
 

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Discussion Starter #7
New valve did the trick. No more leaks.

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