SP 108 rebuild questions

[whaylonsmithers]

Hi everyone, I hope to get some tips about rebuilding an old SP 108. Thanks in advance for any comments.

The reg is the non-adjustable orifice type, has old (rubber? original?) mouthpiece and exhaust tee, not too sure about the other soft parts. It scrubbed up really well but I'd to replace some things before they fall apart.

1. The diaphragm is pale blue silicon, not the standard shape - more mushroom than dome. It fits perfectly and looks in good condition. If I need to replace it can a modern SP diaphragm be used? Or maybe a NOS 109 if I can find it?

2. I think the clamp screws are metric (not 5-40 anyway). Has anyone worked out the specs? My best guess is M3 x 0.50 mm based on counting about 18 grooves in 9mm of thread.

3. Does anyone know of an available exhaust tee that will fit? The ID of the old one is approx 26mm (.87"). The flange on the reg is 30mm, stepping down to 25mm. All circular. An OEM 109 exhaust tee fits with a lot of slop but might work. An aftermarket VDH one is even more sloppy.

4a. Exhaust diaphragm Q1.
Is the exhaust diaphragm 23mm? It looks tiny but I don't want to take it out and possibly break it unless I have a replacement.

4b. Exhaust diaphragm Q2.
Should I be doing anything with the bottom (metal) exhaust diaphragm cover? It doesn't look like it unscrews, does it just protect the diaphragm?

4c. Exhaust diaphragm Q3.
Is there an easy way to change the exhaust diaphragm? My first thought is to roll up the new one like a cigar, push it through the grill, then apply equal parts patience, alcohol and cursing until it comes good.

Regards, Michael.

 

[happy-diver]

Mate you've got it all worked out

Store | Vintage Double Hose

Get some vaseline on those rubber bits

Disengage the exhaust valve with a pen(s)

 

[Yawana-Dive]

That’s a very nice early model 108. It would have originally had 2 exhaust diaphragms like the Healthways models around the same time, but it only needs one. You can use a standard exhaust diaphragm from a $3 snorkel from your sporting goods store. Tie a bit of cotton thread around the tip, poke it through the gaps and pull it into place. You will need to shim it up with a tiny oring to make it snug.
To make the VDH exhaust tee fit, just pull off the mouthpiece from the $3 snorkel, cut it in half so you have a silicon ring to push over tee fitting giving it a wider diameter, then slide the new VDH tee over that and it’s a snug fit.
The main diaphragm looks fine. It’ll last forever.

 

[whaylonsmithers]

It had two exhaust diaphragms? Whatever possessed them to do that?

Yawana can you confirm the o-ring goes under the tip, inside the box? I'm guessing the tip is slender and pulls out easily. And I'm going to have to reacquaint myself with budget snorkels - have purge valves gotten a guernsey there? I thought they had fortunately dropped out of existence.

Also Yawana - I just googled you up. Western Province is on my bucket list but it's not happening any time soon I'm sorry to say. Had some wonderful dives in the Solomons a few years ago but didn't get further than Guadalcanal and Tulagi.

 

[James79]

I have a couple of the old style 108s.....

On the diaphragm, Yawana is right... taken care of silicone lasts forever. If you want to check for pin holes, hold it up to a light and very slightly stretch a small section at a time. If it's good, it will be roughly for eternity (in regards to degradation).

For the exhaust T, I 3d printed a bushing that makes the round exhaust port match the flared oval shape of a 109 so it can use the universal or 109 exhaust T's with a snug fit. If your in the US I can send you one, or if you know someone who can 3d print in TPU I can send you the file.

The double stacked exhaust valve was meant to eliminate any wet breathing (early exhaust designs sometimes let a bit of water in during the exhale due to not keeping the mushroom valve in an air pocket). It worked, but also raised the work of breathing. People soon found that just using the inner mushroom worked just fine. I use the valves out of a modern Aqualung ABS/LPO. It is 23 mm.
If you go with a snorkel mushroom, the reason for the o-ring Yawana mentions is to take up slack under the barb. The exhaust spider in a snorkel is thicker, so the barb is further down the stem of the mushrooms made for them. All that to say, yes... O-ring under the tip, inside the box.

Respectfully,

James

 

[Yawana-Dive]

Yes James just explained it better than I ever could. Once you get the exhaust diaphragm in place you’ll see what it needs to seal properly.
I think they put double exhausts in for a short while thinking it would improve the seal in currents, but it becomes difficult to exhale if you’re working hard underwater.
The first two digits of the serial number tell you what year it was made.
Those original mouthpieces are surprisingly comfortable. I got used to them and use them on all my vintage regs (after giving them a good clean).
The western province of the Solomons is a wonderful place for diving. Borders are closed but we look forward to seeing you here when things open up again.

cheers

Andrew

 

[whaylonsmithers]

Thanks James and Yawana for the great replies.

James - I found your exhaust tee bushing in the printing thread, no idea how to do 3D printing so I'll start with the improvised adapter and see how that goes. I'm in Australia so postage is pretty impractical.

Regards, Michael.

 

[James79]

Thanks James and Yawana for the great replies.

James - I found your exhaust tee bushing in the printing thread, no idea how to do 3D printing so I'll start with the improvised adapter and see how that goes. I'm in Australia so postage is pretty impractical.

Regards, Michael.

You can always ask in your local area if anyone has a 3d printer. Now, if you want to go truly improvised.... My proof of concept was done by building up the exhaust flange with electrical tape until it was shaped right!

 

[whaylonsmithers]

Hmmm - sounds like an excuse to heat shrink something new.

 

[halocline]

The diaphragms for the 108 and 109 are different and not interchangeable. It's a lever height issue. And, I think there were two different styles of 108s with different levers and diaphragms. I only have a couple of these regs and I rarely use them, but I have a memory of seeing two different lever/diaphragm configurations.

You should be able to carefully remove the exhaust valve by using a dull small blade to 'tuck' or push the edge of the stem into the hole and carefully pull it out. Just take your time, I've never torn one doing this.

I have found that the exhaust tees are different on the 108s as well, due to the different shape of the case. In mine the 109 tees have fit snugly on the flange but were the wrong size in terms of fitting comfortably around my chin. I really don't have a clear memory of exactly how they're different, but they are. If you can get a NOS 109 tee and it's ok against your chin, i.e. the only problem is that it's loose on the flange, you might try a short piece of bicycle inner tube, essentially a big rubber band, as a sleeve on the flange to improve the fit. I've never tried that, so I don't know if it will work. Just an idea.

Some of these old 108s can be surprisingly good breathers, but I have enough 109s so that my 108s basically live in a box.