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#578242 12/27/14 1:18 pm
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gunner Offline OP
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Does any one know the thread side for an A65 OPRV?

I want to test the oil pressure on my 1968 A65 but since this is the earlier version, it doesnt have the extra hole for the oil pressure switch.

The engine was built a a couple of years ago with all new components including TS journal, reground crank, big ends, pistons etc and I'm using a SRM type OPRV which I believe is working fine.

However as I am using the original 1968 alloy oil pump (which I meticulously rebuilt) I want to check the oil pressure.

My plan is to find a suitably sized bolt, drill and tap a hole in the center for an oil pressure gauge. With the engine warm I should be able to remove the the SRM OPRV and temporally add my test gauge for a minute or to, checking the pressure at idle and at 3k rpm or so.

All I need to know is the OPRV thread size to proceed with my experiment.

Thoughts and comments welcome.


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Hi
Reading this thread its 7/8" x 16TPI

http://www.a7a10.net/forum/index.php?topic=1861.0

HTH
John

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Beware the British pipe thread is not the same as NPT in US. It is not tapered and I believe the TPI (thread per inch) is different.

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Hi,

Originally Posted by gunner
My plan is to find a suitably sized bolt,

Measure both the diameter and tpi (threads per inch) very carefully. If, as said, it's 7/8" x 16 tpi, you have absolutely no chance of finding "a suitably sized bolt"; the thread is a Unified Constant Pitch Thread and BSA probably chose it precisely to stop shade-tree mechanics 'fixing' an oil pressure problem by replacing the oprv with "a suitably sized bolt" ... grin

That said, it's hardly difficult for a competent machinist to die or screw-cut what you want? smile

Hth.

Regards,

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Hi,

Originally Posted by Redd32
Beware the British pipe thread is not the same as NPT in US. It is not tapered and I believe the TPI (thread per inch) is different.

Uh-uh. I don't know what Nick's referring to by "1/8 bsp plugin the lower part of the case" but you're thinking of the oil pressure switch; as the o.p's posted, his engine is a '68 and doesn't have any provision for an o.p. switch.

Hth.

Regards,

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gunner Offline OP
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Thanks guys, looks like my idea wont work as sourcing a Unified Constant Pitch Thread bolt is impossible without having one specially made.

I dont think I have a 1/8 bsp plugin, but will double check.

I guess my best bet is to find an old A65 spring & ball OPRV and adapt it.


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Gunner:

seriously I would be careful , I did similar to what you are talking about on my A10 with a temporary oil pressure gauge off an opv. Started it up and it pressurised so much it actually busted the gauge (but it was only a old leaky cheap POS so I wasn't too fussed) . Thing is that it went way over 100psi just for a few seconds and I shut it down immediately.

It seems like an oxymoron saying watch out for excessive oil pressure on your BSA , I know, but real high oil pressure can do very bad things to a motor, and your meticulously rebuilt pump!.

that is why they had an opv.

but yeah I hear you with the wanting to see it ...maybe just see the gauge go up while you are kicking it over might be enough ?? just a thought .

edit to add:

I had made a "bush" to press into the body of the opv to blank off the 4 holes that the excess oil would normally return through so all in all it was a huge wasted effort , but at least I knew oil pressure was defo there !

Last edited by Ignoramus; 12/28/14 4:09 pm.

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gunner Offline OP
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Thanks Ignoramus, I'm now thinking you are right and its probably not worth the effort of building an adaptor to measure the oil pressure.

What does give me some confidence is that I have a new TS bush line bored with the drive side and the bush was reamed to fit the crank journal. Additionaly I'm using a SRM oprv and can see a good return flow of oil to the tank via the return line oil filter and magnetic sump plug.

Hopefully this all means I have good pressure at the big ends and so my confidence is restored, for now at least.


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After having my SRM OPRV stick through Id be keen to keep an eye on the oil pressure. I retrofitted the ball type unit from lyford classics. If you have the SRM unit I would reccomend splitting it and checking the piston


Now let’s all have a beer beerchug

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yep Gunner... you know the pump is doing its job with good return... I have fitted a permanent oil pressure gauge to my 70 a65 (which is really easy as it already has a tapping for the 'idiot light') . It behaves in a totally predictable manner ie pressure drop as it warms up etc . But it does make me feel a bit better so it stays.

I am convinced that the best thing about an oil gauge is psychological... trouble with that is if you are a worrier you will probably have the motor apart again first time it drops to sod all at hot idol ...if you are not a worrier it gives you the opportunity to engage in pedantic discussions with clowns who lecture you about originality .

sounds like you have done a thorough job and should be fine ... best of luck dude.



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Ironically a o.p. gauge nearly cost me a T150V engine. I ordered a tacho/speedo bracket from Triple Rules, for a few quid more I could get one with an optional o.p gauge so that's the one I got, for the coolness factor an all. The kit came with a nylon line that ran from the engine to the gauge. I have a Hooker 3 into 1 on the bike that runs fairly close to the frame tube. well it seems the nylon line flexes to and fro as the wheel is turned from side to side. The bike sat idling while I locked the garage door and finished putting on my gear. I turned to get on the bike and saw vast amounts of smoke rolling off the header, it seems as the bike sat at full left lock the hose contacted the header and melted through.
After that I replaced the nylon line from the engine to the headstock with a bit of steel brake line and a bit of nylon line from there to the gauge so it can still flex.
For me I don't care if the gauge is 100% accurate as long as it will tell me if there is a drastic change.


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gunner #579070 01/02/15 12:39 pm
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I have converted my 66 to a guage for my peace of mind. I also have an oil pressure control system of my own design. While it is not perfect (too small relief for cold oil)it works well and oil pressure is excellent with 30w oil. Protect your bush with a filter. I have had the 7/8ths x 16 tpi bushes made to fit a gauge. Have a sketch also. You can also take a early ball/spring cap and tap it for 1/8th npt to adapt a test gauge.

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Originally Posted by Mr Mike
You can also take a early ball/spring cap and tap it for 1/8th npt to adapt a test gauge.

I wonder what it would show me to put an old valve in place, the kind with the indicator. At the very least it might confirm my suspicion that the damn thing is stuck open when I see 20psi on the gauge and the piston is still poking out.


It's not a bug, it's 'character.'

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Originally Posted by Mr Mike
You can also take a early ball/spring cap and tap it for 1/8th npt to adapt a test gauge.

I wonder what it would show me to put an old valve in place, the kind with the indicator. At the very least it might confirm my suspicion that the damn thing is stuck open when I see 20psi on the gauge and the piston is still poking out.


It's not a bug, it's 'character.'

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David,
I had grave concerns about the OPRV system and that is why I modified my system so I would know what my oil pressure is.
When you convert an old OPRV to make a test pressure port you disable the relief system and must be careful that you do not overpressure the system. The first time I performed such a test I ruined my new oil filled gauge as it was immediately pegged at 110 psi when I revved the engine with cold oil. I think the design of the OPRV cavity is the problem and that they are prone to leaking and loosing valuable oil pressure that should be going to the bearings. A lot of guys say an oil pressure gauge is jut something else to worry about. I take a contrary view...it is most important on the BSA twins.
Mr Mike

Last edited by Mr Mike; 01/04/15 1:24 pm.

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