Tore My Rix SA-6B Apart

[rob.mwpropane]

Well I finally go around to finishing the rebuild. Fired it up a little bit ago. It starts great, builds pressure great, but when I shut it off I get a good bit of blowby from the 3rd stage piston? A good steady hissing until I bleed it down.

The only thing I can figure is maybe it takes some time to "seal" the new rings / teflon to the walls?

I cleaned each cylinder with soap and water during rebuild, nothing else. The 3rd stage piston is brand new from the factory loaded directly into the cylinder with the correct tool. Just pushed it in very lightly.

As far as the pressure goes it seems to be building pressure just as it did before, so I don't think I'm getting any blowby while it's running. Any thoughts?

 

[Golan68]

Well I finally go around to finishing the rebuild. Fired it up a little bit ago. It starts great, builds pressure great, but when I shut it off I get a good bit of blowby from the 3rd stage piston? A good steady hissing until I bleed it down.

The only thing I can figure is maybe it takes some time to "seal" the new rings / teflon to the walls?

I cleaned each cylinder with soap and water during rebuild, nothing else. The 3rd stage piston is brand new from the factory loaded directly into the cylinder with the correct tool. Just pushed it in very lightly.

As far as the pressure goes it seems to be building pressure just as it did before, so I don't think I'm getting any blowby while it's running. Any thoughts?

I would look into the head valve not piston.

 

[rob.mwpropane]

I would look into the head valve not piston.

Why / how would that cause blowby from the bottom of the piston? I was hoping you would chime in, so thanks!!

I took things back apart. Cylinder walls look immaculate, 3rd stage head looks dirty. I don't know about the 3rd stage piston. When I put it into the cylinder I didn't get as much resistance as I though I would. I've never done it before, so not really sure what to expect. It just kind of slipped right in.

Obviously need to replace the 3rd stage o ring, @iain/hsm said I would probably damage that, he was right. The 3rd stage head was pristine when I rebuilt / installed it.

Brand new piston on the left (might have 20 min on it), old on the right.

 

[-JD-]

I wouldn't be surprised if the "dirty" aspect is the new rings wearing in a bit. There seems to be some schmutz on the new piston towards the bottom too.

I can't remember at the moment - Did you do a full rebuild of the valves?

Out of curiosity, is mine exhibiting the same 3rd-stage leak-down when you run it?

Pulling it out of a place without sunshine speculation ....

You have a full output pressure reservoir in the seperator pushing back through. The 3rd-stage discharge valve is a leaf valve and it is likely NOT expected to be 100% sealing. Same for the rings in the bore. Under operation the rings and valve seal well enough to obtain a practical amount of functional efficiency, that is balanced against the needs of durability/rebuild-interval. i.e. I'm thinking limited leakdown and blow-by are there all the time and baked in - you just don't notice it in operation.​

Waiting for my smack-down by he who really knows how these things work.

 

[rob.mwpropane]

I wouldn't be surprised if the "dirty" aspect is the new rings wearing in a bit. There seems to be some schmutz on the new piston towards the bottom too.

Dirty could be wearing in. Also maybe a chance I let it sit for a while and dust got into the lines? I pulled the 1st and 2nd stage pistons and they look good. I guess I need to pull the heads and see what they look like.

I can't remember at the moment - Did you do a full rebuild of the valves?

I replaced all the o rings but kept the reed valves as all looked great.

Out of curiosity, is mine exhibiting the same 3rd-stage leak-down when you run it?

I haven't ran your in a while, but I don't remember that. On mine before I rebuilt I would get 2nd stage blow by, but never 3rd. @1bubbleoff said his doesn't have any blowby from 3rd either.

Pulling it out of a place without sunshine speculation ....

You have a full output pressure reservoir in the seperator pushing back through. The 3rd-stage discharge valve is a leaf valve and it is likely NOT expected to be 100% sealing. Same for the rings in the bore. Under operation the rings and valve seal well enough to obtain a practical amount of functional efficiency, that is balanced against the needs of durability/rebuild-interval. i.e. I'm thinking limited leakdown and blow-by are there all the time and baked in - you just don't notice it in operation.​

I am ok with "some" blowby, but what I hear seems larger than what I think I should have.

Waiting for my smack-down by he who really knows how these things work.

One can only hope, lol. If we do enough stuff wrong I think we can conjure him up!

 

[rhwestfall]

Beetlejuice Beetlejuice Beet.....

 

[-JD-]

Beetlejuice Beetlejuice Beet.....

If only it was that easy!

 

[-JD-]

Dirty could be wearing in. Also maybe a chance I let it sit for a while and dust got into the lines? I pulled the 1st and 2nd stage pistons and they look good. I guess I need to pull the heads and see what they look like.

I replaced all the o rings but kept the reed valves as all looked great.

I haven't ran your in a while, but I don't remember that. On mine before I rebuilt I would get 2nd stage blow by, but never 3rd. @1bubbleoff said his doesn't have any blowby from 3rd either.

I am ok with "some" blowby, but what I hear seems larger than what I think I should have.

One can only hope, lol. If we do enough stuff wrong I think we can conjure him up!

Give it a spin as a comparison. I seem to remeber it hissing a good bit when shutoff ...

 

[rob.mwpropane]

Give it a spin as a comparison. I seem to remeber it hissing a good bit when shutoff ...

Mine always hissed a little, but this is more than that. And I was thinking (because everyone says the 3rd stage is supposed to blow by a little after shutdown as the expander rings relax), I think I have debris in the 3rd stage head. If my head is leaking back through then I'm getting a lot of blow by as the colescer blows down. Maybe some debris made it's way to the reed valves.

I think I have a game plan... sure do wish the almighty would chime in and tell me I'm wrong

@-JD- do you ever remember anyone saying the holes in the 3rd stage piston had to be facing up when inserted? I don't, but someone said they should... I can't see how that would matter?

 

[-JD-]

Mine always hissed a little, but this is more than that. And I was thinking (because everyone says the 3rd stage is supposed to blow by a little after shutdown as the expander rings relax), I think I have debris in the 3rd stage head. If my head is leaking back through then I'm getting a lot of blow by as the colescer blows down. Maybe some debris made it's way to the reed valves.

I think I have a game plan... sure do wish the almighty would chime in and tell me I'm wrong

@-JD- do you ever remember anyone saying the holes in the 3rd stage piston had to be facing up when inserted? I don't, but someone said they should... I can't see how that would matter?

Sorry, no info on piston holes that I remember.