Ariel Owners Motorcycle Club

Yes Simes. But it also lets air through almost as soon as I do the first pump. I suppose I could try to put it in oil instead of water and see. Perhaps water is not dense enough to test it?

I did have 0 psi on the gauge when the engine was warm, so my conclusion was it was due to the valve not sealing. Cold the gauge would hit the top limit on the dial.

Gui,

What is between the retaining split pin and the spring ??

I had this problem a long, long time ago and found that I needed to put a washer between the spring and split pin in order to hold the spring 'square' to the bore and thus to the ball.

The oil can still escape via the hole in the washer but the spring didn't bind and fail to seal the ball.

It might be worth trying that in your test rig.

Bob.

Gui,

Are you pumping this up by hand or using a compressor?

My method (using the same test tool which Dad kindly made for me) is to put the regulator on your compressor to 5psi, and pump in to the tool, check for leaks.

Gradually increase the pressure and check for leaks in 5psi increments.

From memory, mine blows out at somewhere between 25-30psi, which felt sensible to me

Rob

I just started to question what the official running pressure of a KH should be (which uses the same PRV as a MK1), and found it should be 25psi.

I don’t have the information for a MK1, but my 4G manual states 45psi. So if that is the case on a 4, how do they regulate a different pressure with the same valve?

Bob,
At the moment the spring is just held by the split pin. I shall try with a washer and report

Rob,
I’m just pumping by hand using a bicycle pump. If I do it slowly, I can sort of regulate the pressure, but the result was the same.

Good question on the pressures. If the spring is the same I don’t see how the same valve could open at different pressures on different bikes.

If I remember correctly, I believe your dad mentioned 35psi for the MkI, but I would have to search for his post on it.

robjameson wrote: ↑Fri Feb 24, 2023 11:29 am So if that is the case on a 4, how do they regulate a different pressure with the same valve?

I've read somewhere that stretching the spring (yes, really!) will increase the amount of preload and thus the force acting on the ball when it is fitted into the OPRV.*

On Norton twins, the (much larger) spring can be shimmed.

*If this is bo*****s, please don't shoot the messenger.

Allan.

simon.holyfield wrote: ↑Fri Feb 24, 2023 9:06 am Can you introduce some oil to lubricate it and try again?

I do wonder if using just pressurised air is a reliable test. Air is not exactly viscous and may behave differently to hot or cold oil. Also, there will be friction inside the OPRV where the spring can kink and contact the body. Perhaps if oil were used, this friction could be overcome and the valve would operate properly.

All musings, really....

I do like the sound of Bob's idea with the washer, though. That sounds like it would provide additional support to the spring to prevent/reduce the kinking.

Gui, after fitting the split pin, do you open up its legs inside the bore of the hole in the OPRV? (apologies if I've missed this detail in your earlier posts.)

Allan.

Hi Allan,
No I haven’t opened the legs of the split pin. Are you supposed to?

I've seen a picture somewhere on this forum. I'll try to find it later, if I get a chance.

Viewing the OPRV from the 'open end,' imagine fitting the ball and spring and split pit. Whilst the split pin legs are still straight, insert a small screwdriver or whatever between the legs inside the hole in the OPRV.. When the screwdriver is between the legs, rotate it through 90 degrees to spread the legs into a sort of diamond shape.
Then you can bend the spare remaining legs on the outside of the body.

I think that the reasoning behind it is to provide more support to the spring (along the lines of Bob's washer idea, I suppose.) Also, to prevent the spring unscrewing itself outwards on the split pin (which is not split unless opened-out as described.)

I'm not suggesting that this is 'the answer' to your problem, but who knows?

I hope I can throw some light onto this but I don't have definitive answers. Firstly though, I am impressed with the thoroughness of you all. I have never tried testing the valve under water - I simply judge whether it is open or not by the noise it makes. I use the compressor to test, adjusting the pressure as described by Rob to find out when each particular valve "blows". I have found that stretching the spring or even changing springs seems to make little difference to the blowing off point. All the valves I have tested have been Ariel originals. Performance has varied, as I say, but one valve simply refused to seat whatever I did. I tried different springs, new balls, thumping the ball onto the seat and then another new ball - all to no avail. So eventually I did the sensible thing and threw it in the bin. So I have no experience of valves made either by Draganfly or ACME, although I do have an ACME valve on my 1936 4G which is of a different design. This prompts me to think how I would go about making a replacement valve and in particular how I would cut the seat. I would do this using a centre drill but withdrawing it at the end of the cut would be critical to avoid a ridge in the seat where there would inevitably be a constant leak. The only way would be to withdraw the drill slowly having held it stationary in the tailstock for some little time before withdrawal. Then it would be bash a ball into the seat thus created, scrap the ball and fit a new one. It occurs to me that there is one potentially significant difference between original Ariel valves and reproduction ones. This is that the Ariel originals are cadmium plated which is no longer an available process. But cadmium is fairly soft, which might well be just the thing for achieving a good seat for the ball.

On oil pressures, why would you have a different pressure for the Square Four and the KH when they both use the same timing side main bearing and big end shells? The only difference is 4 big ends as opposed to 2 but surely you would account for this by having a bigger flow rate through the Square Four pump? That said, I do prefer to see 35psi rather than 25psi but my KH varies drastically depending on how hot it is and what rpm is current, with a normal figure when riding along in the 25psi region. The 1936 4G never varies from about 25psi, once warmed up. The Healey, lacking an oil pressure gauge, lights up the oil pressure warning light at tickover since I changed from SAE 40 to 20/50 oil.

For the record, I have never run a 4F, 4G, Mk I, KH or Single on anything other than an original Ariel pump but I have never run a Mk II (or Healey) on anything other than a Morgo pump.

When I threw a rod on my KH, the first thing of concern when I stripped the engine was this:
I eventually concluded though, that the cause of the blow up was air leaking into the suction side of the feed pump due to a fibre washer which had "settled down", preventing the suction from opening the anti wet-sumping valve I had fitted. Nonetheless, I made a tiny stepped cylinder to hang on the split pin to hold the end of the spring in place.
Clearly, I have reverted to standard since, or this valve would not be in the spares box.

So what would I advise?

Use a compressor to check the valve operation. If, with it, you can discern a distinct difference in sound at a particular pressure, this is when the valve "blows off". If the sound is constant, at all pressures, my experience suggests that the valve is scrap. But I would strongly advise reporting back on the Forum to see what others think once you have done this.