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  #1  
Old 17-04-15, 01:18
LRDG LRDG is offline
Clifford Nyenhuis
 
Join Date: Jan 2005
Location: Milton, Ontario
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Default Ferret thermostats adjustable?

Hi, I working on a Ferret at the Ontario Regiment Museum in Oshawa.

It's running well, but too cool.

I pulled the bellows thermostat out of a spare engine (Smith's RE15943, 30065/25, 73C, 163F) and found the valve disk at room temperature sitting about 1/16" off the seat. About the only reason I can see for that is the bellows has stretched over the years, or perhaps someone had been prying on the disk in an attempt to get it out of the housing). I can close the disk onto the seat by lightly compressing the bellows with my fingers. The bellows does not appear to be leaking as the t/s still opens up wider quite linearly when heated in a pan of boiling water.

I suspect the t/s in the running engine has the same problem (or perhaps it's been removed).

I see the disk on the spare t/s is threaded onto the valve stem (the stem that's attached to the top of the bellows) and soldered to prevent it coming loose. I'm going to remove the solder and see if I can correct for the bellows stretch by screwing the disk further onto the stem until the t/s starts opening at 163F and continues to open until about 195F (right now, that's when the top of the bellows hits the brass bypass passage block.

Hopefully these pics will make this clearer.

Has anyone tried this? Anything I should watch out for? I want the old girl to run at spec temp to avoid plug fouling, etc.

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  #2  
Old 17-04-15, 02:44
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Robin Craig Robin Craig is offline
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I am not as far by a long way on my Ferret.

You are doing everything that I think I would do to overcome the problem. Sorting it out will pay you back big time as you say.

Please let the rest of us know what you find out.

The thermostats are available NOS as far as I recall, but respect it is a oney and time issue

Robin
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  #3  
Old 17-04-15, 04:18
Lynn Eades Lynn Eades is offline
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Just be aware that to much heat could result in damage. The path you are heading down is probably the way it was set up in the first place,(rather than being adjustable in service.
I am sceptical about why it has changed.
The bellows contains alcohol ? and I suspect the engine has been overheated (maybe no water around bellows) and each element has stretched beyond it's elastic limit??) to the point where it has stretched without failing (from leaking) If a bellows type thermostat fails, it fails in the closed position (bad) whereas a wax filled thermostat usually fails in the open position (better)
It will be interesting to know how it performs in the future.
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Old 17-04-15, 04:40
LRDG LRDG is offline
Clifford Nyenhuis
 
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Ive got the t/s opening at 155F based on a strip of 0.001" shim stock trapped under the valve coming free. The trouble is I had to screw the disk down about 1/8" which extends the bellows 1/8". This means there is now only 1/4" of free movement before the top of the bellows hits the brass housing, down from an original 3/8" so the maximum flow area is reduced by about 1/3rd. I am going to run this in the short term but a new t/s is in her future.

Malcolm

Last edited by LRDG; 17-04-15 at 05:00.
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  #5  
Old 17-04-15, 07:48
Lynn Eades Lynn Eades is offline
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Malcolm, have you the space underneath to undo the screws on the side and slot the bellows frame down further. this would in theory at least give you a new start point.
I do think a new one is the answer though.
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Carrier Armoured O.P. No1 Mk3 W. T84991
Carrier Bren No2.Mk.I. NewZealand Railways. NZR.6.
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So many questions....
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  #6  
Old 17-04-15, 16:28
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Clifford Nyenhuis
 
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That's a good idea, Lynn. I'll try that.
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  #7  
Old 18-04-15, 13:20
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Robin Craig Robin Craig is offline
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Great information and suggestions all with great reasoning.

Thanks

R
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  #8  
Old 18-04-15, 23:14
LRDG LRDG is offline
Clifford Nyenhuis
 
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I unscrewed the 4 screws securing the bellows to the t/s body and elongated the screw holes. (They were already slotted so are part of the original setup by the OEM, I guess.) That got me a bit more flow area.

I did a calc of the final fully-open curtain flow area at the valve opening and it is now equivalent to the flow area of the port under the valve, so my anal engineering mind is now satisfied. Of course, the real test will be what temp she runs at.

Last edited by LRDG; 19-04-15 at 02:31.
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  #9  
Old 19-04-15, 05:13
Lynn Eades Lynn Eades is offline
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Well done for having a go!.
The carriers have a radiator pressure cap that is adjusted then soldered, as is the oil cooler bypass valve.
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  #10  
Old 21-04-15, 05:45
LRDG LRDG is offline
Clifford Nyenhuis
 
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Since you raised the issue of rad pressure caps, I have some questions.

The pressure relief valve is a semi-permanent attachment to the top of the rad. Semi-permanent in the sense it is not just the standard screw-on cap. From the manuals, its setting is 10 psi.

The Ferret I am working on also has a "rad cap" on the filler opening in the line between the t/s outlet and the top of the rad, with a spring-loaded relief on it rated at 7 psi. I've tested this cap and it lifts at 6 psi.

So was the Ferret originally fitted with a non-relieving filler cap, leaving the rad-mounted relief valve to lift at 10 psi?

If I pressure test the whole system at 10 psi to check the system integrity and confirm the RV lifts, do I run the risk of finding it won't reseat, leaving me scrambling for a spare? It seems it has a soft rubber seat seal and who knows what condition it's in. (I think I know the answer to that question.)

I guess I run the risk of lifting the RV no matter what pressure I test at.

Is there a real risk of causing the pump shaft seal to leak in an unfixable way? It's a mechanical seal, and I know they can just let go if the rotor pops away from the stator and sticks open..
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  #11  
Old 21-04-15, 13:59
45jim 45jim is offline
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Default Replacement belows thermostat

I replaced the bellows thermostat in my Ferret with one from a VW aircooled van (type II) and it worked perfectly. The only challenge was the threads are metric, in hindsight one from a Chevrolet Corvair would be a better choice in that regard, I believe the Corvair one is rated at 165F. Both are widely available from many sources. My Ferret had a solid non-venting rad cap.

When bellows style thermostats wear out, the opening stroke becomes inconsistent while the opening temperature may be correct. One time it opens fully and the next it only opens 70% for no apparent reason resulting in elevated temperatures. They are designed to fail in the open position but that means fully open at 150F while at ambient temperature they will not close completely. I think the VW one costs $40.
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  #12  
Old 23-04-15, 04:09
LRDG LRDG is offline
Clifford Nyenhuis
 
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Thanks, 45jim. I found all kind of good info while searching on VW Bus and Corvair bellows. I even found a thread about how to top a bellows up with denatured alcohol. You actually have to boil the alcohol while soldering the plug back in so that it drives the air out out and when it cools down and condenses, the vacuum pulls the bellows tight together. Sounds tricky.

Anyway, today I found a brand new Ferret t/s while rummaging through some drawers at the museum. I assumed it was abandoned because it was bad but I checked it tonight and it opens at 163F and is fully open at 190F, so I'm good to go.
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