Tore My Rix SA-6B Apart

[-JD-]

These are the "pressure breaker rings". Each is a set of 2 pieces, they go around the piston like a 1/2 moon on each side. Part # 18-C1603-4.5P (my picture is backwards from this diagram, but you get it)

View attachment 830648

OK, I thought you were mixing the compression rings into the post too since you listed 4.

 

[rob.mwpropane]

OK, I thought you were mixing the compression rings into the post too since you listed 4.

Ah, understood.

When I 1st took things apart I thought they were broken but that's how they come.

I emailed Rix getting ready to call them. I was hoping Iain would chime in but he's mia, hasn't been on here since Feb I was hoping he would say they can be lightly sanded down to spec or something...

 

[rob.mwpropane]

Wanted to also add about the heads. I have not ever been able to find anything specific on the heads, how hard they are to take apart or what was entailed. Rix Industries was nice enough to send me their latest bulletin which made it much easier (I posted it somewhere in this thread). The heads are dead simple. Because of how amazingly small the guide pins are I wouldn't recommend a rebuild "in the field" but it's not hard. The 1st stage gave me the most trouble. The bulletin doesn't discuss the 1st stage at all, but it only has a few parts. I had to smack it down on some wood to get it to come out, that was easy. The hard part was scraping the old gasket off. It was really on there pretty solid. I soaked it in the US cleaner for hours coming back every so often to scrape some more (with a plastic scraper).

Also, one of my guide pins is busted. So on top of the other above noted problems I have to order another pin. I don't know how it broke, it was just shorter than the others when I pulled everything apart, so maybe it was broke before I took things apart.... So more waiting Anyone following this be super careful with those pins. They look like they're SS but they're so tiny! I put them all in a glass jar and I still have a hard time seeing them at the bottom, and my up close sight is perfect.

The o rings for the heads states in the bulletin that they should have a light coat of lubricant. None of the o rings I got had any. I have put the 3rd stage head together without any but I think it would be wise to have a light coat. The 1st guide pin is easy to put in and then the discharge vale, an o ring, and then the valve seat. The reason I mention this is because you can't see the pin when you drop it in there. You have to line it up and push down lightly to get both the pin aligned and the o ring to set on the valve seat at the same time. It's not "hard" but it's not as easy as the rest of it. If I can do it, anybody can!

I soaked everything in the US cleaner and ran it for probably 30 minutes for each piece.

Here are some pictures!

 

[rob.mwpropane]

Woops.. wrong thread.

 

[iain/hsm]

Also, one of my guide pins is busted. So on top of the other above noted problems I have to order another pin. I don't know how it broke, it was just shorter than the others when I pulled everything apart, so maybe it was broke before I took things apart.... So more waiting Anyone following this be super careful with those pins. They look like they're SS but they're so tiny! I put them all in a glass jar and I still have a hard time seeing them at the bottom, and my up close sight is perfect.

The "guide pins" as you call them are the plastic 1/4'Diameter that fit into the outer bearing retaining ring
and stop the rod end bearings clattering onto the swash plate housing six (6) in total 2 per rod end bearing. This is not the part your want stop calling it a guide pin you will confuse the natives.

The "tiny" stainless pins your describing are part number 17-757 Pin, Valve

Granted its known to the rest of the world and most engineers as a dowel pin
but Pin, Valve describes the application better as far as the product is concerned.

Dowel Pin. Heat treated stainless steel hardened 1/32" diameter x 1/4" long
per ANSI ASME B18.82 standard series base diameter if you want the full description.

Granted they are small I wouldn't say tiny its not a watch part just don't drop them on a rolling deck in the dark I guess LOL Iain

 

[iain/hsm]

The hard part was scraping the old gasket off. It was really on there pretty solid. I soaked it in the US cleaner for hours coming back every so often to scrape some more (with a plastic scraper).

Heck? That what a steel razor blade or Stanley knife blade is for. If the gasket is suck on the stainless valve plate scrap the old gasket off with the razor blade getting it under the hardened gasket and only if required lap the valve plate with a fine 600 -1200 grit wet and dry or if in doubt use Brasso a brass polish on a flat glass plate (just clean the paste off well after) Don't scratch the valve plate or dig chunks out of it.
I use an old Buck rosewood handled knife for the purpose but that's classed as a luxury tool now a days

If the gasket is stuck inside the aluminium head again I use an old Parker brass flat blade end of a O Ring pick tool (sharpened) Its also used for lifting rings and removing piston o rings

Pardon Our Interruption

 

[iain/hsm]

The reason I mention this is because you can't see the pin when you drop it in there. You have to line it up and push down lightly to get both the pin aligned and the o ring to set on the valve seat at the same time. It's not "hard" but it's not as easy as the rest of it. If I can do it, anybody can!

To line up the valve onto the dowel pin discharge side I use a pair of Waldes Truarc straight circlip pliers (old school) if I was buying new today I would use a pair of Knipex Straight circlip pliers 3-10mm
The essential part you need to be aware is only poke them into the holes that are on the recessed half of the valve that way you don't "form" the holes on the ground flat side half and cause the reed valve to leak over your created raised edge.

This also ensures you don't fit the valve upside down or you will blow yourself up.

Use this principle for both the 3rd and 2nd stage you should also note that the hole you're grouping for is in line with the valve head body mounting holes.

Snapping the dowel pin by janking the valve around "looking" for the hole to fit the valve body into the dowel pin will make it shorter yes just try not doing that in future. Iain

 

[iain/hsm]

Gosh you have a good memory! These were the last thing I needed, they were on backorder for 3 months

These are the "pressure breaker rings". Each is a set of 2 pieces, they go around the piston like a 1/2 moon on each side. Part # 18-C1603-4.5P (my picture is backwards from this diagram, but you get it)

In regards to the 1st stage, I looked at pictures when I took it apart. That gap had nothing, but I'd like clarification on what it does before I put it back together. If you handed me the parts I would have thought the o ring should go in the gap. It even feels weird with the compression ring pushed out and the rider ring more in the groove below the compression ring. You can kind of see what I'm talking about in the picture I posted.

View attachment 830648

The pressure breaker rings are a matching pair and should be in a small plastic bag. Don't swap the halves over with another matched pair or you end up with two mis matched pairs.

You also should have asked this question before ordering these rings, We stopped using them some time back at the Skunk works and use for our current builds just two additional pairs of compression rings instead.
Talk about the right hand nor knowing what the left is doing.
All you need to remember is Rule 1. Engineers rule.
On the bright side after your 3 month wait you saved yourself $2 I guess. Iain

 

[iain/hsm]

That gap had nothing, but I'd like clarification on what it does before I put it back together. If you handed me the parts I would have thought the o ring should go in the gap. It even feels weird with the compression ring pushed out and the rider ring more in the groove below the compression ring. You can kind of see what I'm talking about in the picture I posted.

View attachment 830648

It did have an o-ring but years ago I will pull up the part number for the old rider ring 0-ring when back at the works It was a carry over from the SA-6A

The reason the groove is still machined is because changing the cad drawing and dfx file for the CNC is much too complicated for highly paid engineers.................Nah just kidding

The other reason is keeping the piston groove is consideration to the "weights" in balance on the swash plate running at 1500 RPM on a 32mm stroke. Consideration to the mass weight acceleration and deceleration at TDC and the need to match the weight transfer over the other two pistons over the piston stroke over the travel length.

If by way of example you were to change the gas molecular weight or say you want to change to nitrox
engineering considerations would require changing from a fully aluminium piston to say a bronze lip design and that additional weight flying about would have effect. Now for ease you could consider say more grooves or deeper grooves in the piston or a scooped out back to lighten the weight to match the original weight etc etc hence why if you have no change in gas or pressure or rod loading and no real need for the o-ring itself it was removed but the groove remained for the purpose of weight reduction.
Clear as mud I know but one day I may learn to give better explanations. Iain

 

[-JD-]

You also should have asked this question before ordering these rings, We stopped using them some time back at the Skunk works and use for our current builds just two additional pairs of compression rings instead.

For those of us doing future service. Should those 2 additional compression rings (in lieu of pressure breakers) be backed by o-rings like the original 4?

Thanks for your insights!