The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: A10Boy on 19.10. 2009 15:10
-
Anyone found this with their PRVs ?
I bought one at the Stafford Show on saturday and it wont screw into the cases, it starts but binds up. I measured the thread diameter of the old and new and the SRM one is about 0.025 wider which is a significant difference.
The geezer at SRM said it cant be wrong mate, its CNC, he blamed my cases !! Anyway, I sent it back and wait their verdict.
-
HI Andy,
Yes I had the same problem,
They told me to expect that it would be tight going in as apparently original ones varied quite a bit
and also the threads may be distorted in the casing as well
I used some antiseize on the threads and worked it back and forth a bit until it fitted
Cleaned it all off fitted the PRV and hav'nt looked at it since *smile* *smile*
Cheers
John
-
I tried that a bit but mine seems too far from the correct size to fit. There's no way I'm going to force it and risk cracking the cases. I will stay with the old ball type unless they can ease the thread on their widget.
I don't know too much about thread British Standards or tolerances but their CNC must be at the top of the size range.
-
hi i got one and had no problems took old one out put new one in
maybe your threads are a bit worn
-
A10Boy,
I have just installed a new SRM unit also, the thread was tight, it was my cases.
Borrowed the correct tap from a friend , and ran it through the thread, fit the new unit into the case nicely.
The one thing I am quickly learning is that all threads need cleaning with a tap/die before fitting new nuts and bolts.
-
I'll try that. Did you do it on a complete engine or with the cases stripped ?
Cheers
Andy
-
Stripped, I would not do it to a complete engine, unless you can be completely sure where the mess will go.
-
What actually is the thread spec.?
-
7/8" x 16TPI.
Tracey Tools have the tap.
Regards,
Richard
-
Is that a definate ?
-
A10boy, it was Richards tap that fixed my cases, so yes.
-
yep, me too-bought one this week, goes in 1/4 turn and stops dead. Out with the mike, O/D is, as mentioned above o.025"larger than the old one.The old relief valve is admittedly quite slack in the cases, perhaps in an effort to address this SRM have backed off the die a bit , but methinks a tad too much!!! Bob `C`
-
I bought one from SRM a couple of months ago, went in fine but the release was far too high to my mind, it opened at 70 to 80 psi, my old one opened at 50, which I consider perfectly adequate. As per all the earlier discussions, if the valve is not opening, ie when the engine gets hot and oil thins, then the cam gets less oil. From my perspective let it stay open a little longer while the oil warms up and keep to the original valve.
Regards
Nigel
-
Nigel, in your 25 Sep 09 different thread on this subject, Manorman said that he was able to remove some washers under the spring to get the SRM valve pressure back down to normal, if this is possible to carry out, the question then remains as to whether SRM's plunger instead of BSA's ball is better.
My PRV hexagons are chewed up and I was going to replace it with an SRM unit to tidy up that area and upgrade to the plunger type at the same time. Any thoughts anyone on why the plunger is used by SRM over the old ball, since it must be more expensive to produce?
-
HI Alanp - go here for more info http://www.a7a10.net/BSA/oilrelief.htm
All the best - Bill
-
I see the link to my old valve comments page, the "round'top" came from SRM, no thread problems, and has been in use for 6 or 7 years. But I seem to remember swapping the provided fibre washer into a slightly thinner one.
-
I had a response from the nice man at SRM.
They sent me a different PRV with a letter explaining that they had tried several PRVs in various cases they have in the workshop.
They said that their PRV was made by CNC to the correct spec, and that they had discovered that theirs would screw into all the plunger cases OK, but was tight in all SA cases that they tried. They said that in their opinion, the tooling used by BSA had worn over the years so that the thread in the later BSA cases was slightly undersize.
Obviously the thing to do,- which I didnt, not knowing about this, is to run a Plug tap down the thread as Richard and others have done during a re-build.
The PRV they sent me is a few thou smaller, and I will try it when I can be arsed. They have offered to re-fund me if it doesnt fit which is good of them.
Also, new Stainless Steel PRVs to the std ball design are available at the moment.
End of Message
-
Andy, where are the SS ball PRVs available from? I can't imagine it being SRM since that would kind of clash with their plunger PRV sales pitch.
Alan
-
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=140350807833&ssPageName=STRK:MEWAX:IT (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=140350807833&ssPageName=STRK:MEWAX:IT)
-
SRM sell both types, I believe the plunger type is for A50/65 but fits A7/A10, could be wrong on this but I think that was the case when I bought mine from them. I bought the plunger type and have it in my A10 - which is still to be fired up, - one of these days *whistle*
All the best - Bill
-
I see on the British Cycle Supply website an SRM PRV that has a popup to indicate pressure release point has been reached.
Part number 70-2795/SS (my price sheet shows $89.00 seems a bit high).
Anybody have any experience with that one?
-
ill tell you what thou i had a bit of trouble getting the old one out couldn't find a socket to fit the
bolt head that went into the crankcase i tried grinding the edges of the socket to make it fit
i ended up taking the bike to a local engineering shop the guy got a big hammer and punch and with
one blow the bolt came out he was a biker and i offered him a go on her he came back with a big grin
on his face i can understand why there a great bike and what a lovely sound they make *smile*