The BSA A7-A10 Forum

Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: Zander on 10.02. 2017 08:59

Title: PRV
Post by: Zander on 10.02. 2017 08:59

I've looked at other posts about the PRV so sorry if I've missed the answer to my question / query, which is:
Among other things I ordered and received a new ball and spring for the PRV.  The existing spring is comparable in size to the new one, but the ball I removed is about twice the diameter of the new one, which I would think affects the operational efficiency of the valve.  I'm inclined to fit the new, smaller ball, but before I do, any comment or advice would be much appreciated.

Title: Re: PRV
Post by: dave55 on 10.02. 2017 09:19

Just a thought but is the one you took out the correct one ?

Title: Re: PRV
Post by: Zander on 10.02. 2017 10:09

Have to confess to getting it a bit wrong here *sad2*  The removed ball is 5/16 diameter, and the new one 9/32 diameter, so only 0.032" difference in diameter.  Not been able to establish ball size (!) from the prominent suppliers' web sites, apart from Classic Motorcycle Spares who give the size they supply as 5/16" dia. 

Title: Re: PRV
Post by: bikerjohndavies on 10.02. 2017 12:54

Draganfly also list the ball as 5/16 so I would go with that.

Title: Re: PRV
Post by: Zander on 10.02. 2017 16:32

It was Draganfly that supplied the 9/32" dia ball!

Title: Re: PRV
Post by: WozzA on 11.02. 2017 00:22

I've got my 51 A10 motor in bitz & pieces, this pic is of the what I believe to be the standard ball in inches...
 4 U 2 work out  size..  *smile*

Title: Re: PRV
Post by: trevinoz on 11.02. 2017 02:15

I'd reset the vernier and try again Woz.

Title: Re: PRV
Post by: WozzA on 11.02. 2017 02:32

 *eek*   Thanx Trev...  Buggered if I know how that happened?   *conf2*
anyway correct measurement below..

Title: Re: PRV
Post by: coater87 on 11.02. 2017 03:42

 Wozz,

 Either your digital "guess-o-meter" is a little off, or that precision ground .3125 ball bearing is off. ;)

 Lee

Title: Re: PRV
Post by: KiwiGF on 11.02. 2017 08:09

Quote from: coater87 on 11.02. 2017 03:42

Wozz,

 Either your digital "guess-o-meter" is a little off, or that precision ground .3125 ball bearing is off. ;)

 Lee

It's a bit tricky measuring the diameter of a sphere using the knife edges of a vernier  *doubt*

Title: Re: PRV
Post by: Zander on 11.02. 2017 08:36

That's the trouble, these days - you kids totally reliant on technology.  I measured mine by running a piece of string round the ball, cutting it to size, measuring the length and working it out from there. *smiley4*

Title: Re: PRV
Post by: bsa-bill on 11.02. 2017 09:57

Oh I once could work out the diameter of a sphere from it's circumference off the top of my head, I  would need Googles help these days.

Thing to remember about digital gauges is they all have a certain tolerance, often a thou, which means your measurement of any object twice could be two thou out.(stretching a point),
I was fortunate to get a Staratt/Bsa micrometer off Ebay for very little, no test piece so accuracy is in doubt but good for comparison purpose.
Even with a micrometer I suspect a feel factor that would come from regular use would help accuracy.

Title: Re: PRV
Post by: dave55 on 11.02. 2017 10:49

Seems like a case of ....Who ate all the Pi  *grins*

Title: Re: PRV
Post by: Triton Thrasher on 11.02. 2017 10:51

Quote from: KiwiGF on 11.02. 2017 08:09

It's a bit tricky measuring the diameter of a sphere using the knife edges of a vernier  *doubt*

There's a flat jaw section. Use that.

Title: Re: PRV
Post by: WozzA on 11.02. 2017 21:39

 *rant*  Thats it...  last time I'm going to show you lot my BALLS...    *eek*  *shh* *whistle*