Hello all, I have a strange thing going on with the regulator ring on my Oval and would appreciate your thoughts.

The thermostat and operating mechanism is all set up as it should be and appears to be working properly. When the engine is cold the regulator ring nudges up nicely against the rubber stop and when the engine has reached operating temperature the ring has moved out the normal 2cm (approx).

The problem comes when the engine revs are increased as the regulator ring gets drawn back into the fan by the suction, thus reducing the air flow. I’ve checked all the usual stuff, the fail safe spring is in place and apparently properly set up – when the adjuster bracket is loosened it pushes the ring out which indicates that it is preloaded.

Has anyone else suffered this strange phenomenon and if so, how did you remedy it?

Your thoughts, as ever, would be greatly appreciated.

Mike 😎

---

Logically, the link mechanism is bending or distorting when the air flow pushes it back into the housing.

It sounds as if it is corretly adjusted.

Is the push rod between the cylinders straight? Might it be weak or bending under the load?

Is the thermostad bracket tightened correctly?

Is the thermostat strong enough to resist this force?

I'll be looking out for this when I first fire mine up..

Cheers,

Andy

---

Not trying to teach you to suck eggs, is it definitely hooked up correctly? This is a 34 horse engine, but it's all the same.

---

Actually, might you bracket just be bending?

---

Hello Fellas'

Many thanks for the replies. I'm confident it is hooked up ok, I've built up a lot of 30 horse engines over the last 30 years but definitely still have a lot to learn about sucking eggs :wink: . It's an interesting thought that the bracket might be bending, what I haven't done is look form underneath whilst revving the engine to see if there's anything going on down there that might explain what's happening. I guess it's possible that the bellows are fatigued and there's maybe a bit more flex in them than there should be, or as you chaps have suggested, there might be a loose bracket or bending operating rod.

I'll have another check over the weekend, which will be my next opportunity to get into the garage, and then report back.

Thanks again for your input!

Mike 😎

---

Mike - just for the record - mine did exactly the same as you reported.

Not sure if there is actually a fault or if this is a design charactaristic.... here's my thinking.

When I installed the mechanism, I held a hair dryer in the heater box until the thermostat was fully open agains the braket and set the top ring gap at the correct 20mm.

I then tested it a few times and got the same readings of 20mm - this is because the mechanism is locked solid against the thermostat bracket end stop and cannot physically open further, hence accurate and repetitive readings.

This tells me that the theromstat and the linkage mechanism is working correctly.

I don't know about you, but when I ran my engine for the first time, it was 4 degrees outside and very chilly, and although the car had been idling for some time and had been driven up and down the road a few times, I wouldn't have called it 'stinking hot' by any stretch.

Following your initial post above, I thought I'd check mine which was when I discovered that mine was sucking closed too...!

However..... despite running and idling for a good while, my air horn ring gap at the top was not 20mm away from the housing - probably barely half that.... which means that the thermostat is not fully expanded within it's mount and is therefore not providing the same force as it would when it was fully hot, as with the hair dryer which had it on the end stop.

This means that there is insufficient force from the stat (at this temp) to overcome the return spring force and it is therefore closing shut under vacuum - which will hinder cooling and make the engine run hotter..... which will apply more force to the thermosstat until it eventually gets hot enough to overcome the force of the return spring and stay open the prescribed 20mm.


That's my theory anyway.

The only alternative would be to set the ring further round the shaft so there was less initial spring retuirn tension on it for the stat to overcome, but this means that if it got any hotter, it might open further than the 20mm and then foul the fan with that horrible screeching noise - hence you set it at 20mm with the bellows fully expanded.

To test this theory, next time I run it, I'll hit the stat with the hair dryer as well to make sure it gets properly hot and opens fully leaving no doubr over whether the engine temp is relevant or not. If it no longer closes under vaccum, my theory is correct - if it still closes undere vacuum, I need to rethink the process.

Have you come to any conclusions or had any successful investigations?

Cheers,

Andy

---

Hello Andy

Interesting to know that you are experiencing the same thing with your regulator ring. I haven't done anything more with mine yet as I am aiming to have a replacement '57 engine rebuilt and installed by Bad Camberg time and I have been concentrating my efforts on that.

If it's any comfort though, I drove the oval to Stanford Hall from Worthing in reasonably hot weather last year, mostly on the motor way, and the engine didn't appear to run hot at all. Despite the odd behaviour of the regulator ring.

The only detrimental effect it seems to have is on the performance of the heater! The heater on the oval is very effective, but interestingly using the highly scientific fingers over the demister vent technique, it's possible to detect that the air flow increases as the engine warms up, but then, when the engine is at operating temperature, the air flow doesn't incresae proportionaly with the engine revs. Presumably because the regulator ring is being drawn back into the fan.

I wonder if this same thing is happening to other peoples cars?

Gentlemen (and Mrs Herbie), if I could ask you to fire up your ovals, get the engines nice and warm and then observe the behaviour of the regulator ring as you increase the engine revs...

Mike

---

Nice to speak with you Mike, look forward to meeting you at Stanford.... :thumbup:

Here is how I set mine up - see if you can spot any issues with my method, in case I'm, missing something.

I set it up as per the Bentley manual - opened the stat fully with a hair dryer so it was hard up against the top of the mounting bracket, then tightened the pinch bolt so the top centre of the control ring was 20mm away from the housing.

I then let it cool which firmly closed the ring against the housing, then just to check, I applied the hair dryer to the stat to make it fully open, which then opened the control ring exactly 20mm again - as per the manual.

















As I know that it will open the full 20mm when the stat is fully open as I've tested and demonstrated it to myself, and that with the engine running on the drive the other day, the ring was only opening about half way, maybe 10mm or so, I suspect that it wasn;t getting hot enough to go past the equilibrium state in the middle to firmly hold it open beyond what the suction force might overcome?

Maybe a way to test it would be to run it up again, but this time put a hair dryer on the stat for a minute or two to raise the stat temp further to get it to fully open hard against the bracket, then, if the ring opens the full 20mm and the suction doesn't affect it, I know it's just a case of the engine not being at full opperating temp.

On the right lines?

---

Change the thermostat .If you need to check them heat them slowly in water .From experience i can tell you that heat guns seem to destroy them.

Serves you right for polishing it 😛

Stat is perfect Mike - I tested it in water and it is fine.

Also, the heat gun was only wafted in front of it for a few seconds to get it moving, I didn't cook it.

I since tested it when installed with a hair dryer from a distance, gently over 5 mins and it opperated perfectly.

I unerstand where you are coming from, but I can assure youm the stat is fine - it pulss and pushed vey firmly and smoothly.

---