Ferret thermostats adjustable?

[LRDG]

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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[Robin Craig]

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

[Lynn Eades]

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.

[LRDG]

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

[Lynn Eades]

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.

[LRDG]

That's a good idea, Lynn. I'll try that.

[Robin Craig]

Great information and suggestions all with great reasoning.

Thanks

R