The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: brettsyoung on 25.06. 2016 01:59

Title: Valve springs - dual or not?
Post by: brettsyoung on 25.06. 2016 01:59
Hi all.  This is probably a stupid question, but do all A10s have dual valve springs?  Pulled my engine down to find singles, but my manuals and other pictures I've seen all have duals.  I'm kind of assuming the duals are for RGS etc and not the standard bikes.  is this right?  cheers Brett
Title: Re: Valve springs - dual or not?
Post by: TimK on 25.06. 2016 03:23
Brett,

my 59 Gold Flash has dual springs, but whether all A10s have dual springs I'll leave to wiser heads than mine.
cheers

Tim
Title: Re: Valve springs - dual or not?
Post by: duTch on 25.06. 2016 03:27

 I think singles are an anomaly,  and added by a PO.
 There's been discussion here not too long ago if you do a search
Title: Re: Valve springs - dual or not?
Post by: muskrat on 25.06. 2016 21:48
All A7/A10's both iron and alloy heads used duel springs.
I'm not 100% sure but I think there was a mob making single beehive springs a while back.
Cheers
Title: Re: Valve springs - dual or not?
Post by: Klaus on 25.06. 2016 22:14
I had never seen a single spring at A10 heads.
But I have converted to one spring most of my bikes and they run without problems at road or racetrack.

cheers Klaus
Title: Re: Valve springs - dual or not?
Post by: RichardL on 25.06. 2016 22:22
http://www.rdvalvespring.com/spring-kits.html
Quote from: muskrat link=topic=10809

msg80937#msg80937 date=1466887703
All A7/A10's both iron and alloy heads used duel springs.
I'm not 100% sure but I think there was a mob making single beehive springs a while back.
Cheers

...and I believe the above  must be the mob.

Title: Re: Valve springs - dual or not?
Post by: Klaus on 26.06. 2016 13:51
Here a picture from my conversion.
These are Gene Berg Valve springs from the VW Beetle.

cheers Klaus
Title: Re: Valve springs - dual or not?
Post by: terryg on 26.06. 2016 14:52
Klaus - Beetle pushrods and now Beetle valve springs.  What other Beetle bits have you found A10 uses for?

Mods - accepted this may need another thread if Klaus has been particularly inventive.
Title: Re: Valve springs - dual or not?
Post by: worntorn on 26.06. 2016 16:01
The RD stuff is as good as it gets. About 20 years ago the local club here had RD make up a batch of Valve springs for Vincents. This was after it was determined that the replacement springs sold by the UK vendors were going soft after a couple of thousand miles.
Those fitted with the RD springs got back the fabled Vincent top speed, which really had become a bit of a fable with the poor springs fitted.

I wonder if the RD springs might help an A10 in the same way?

Glen
Title: Re: Valve springs - dual or not?
Post by: TT John on 28.06. 2016 10:41
Here a picture from my conversion.
These are Gene Berg Valve springs from the VW Beetle.

cheers Klaus
Klaus. I can see the point in using these springs, as they look stronger than the normal A10 springs, the idea of double springs was to eliminate valve bounce, just wondering whether these springs would help in the old WD M20s, which only have a single spring, worth trying I guess.
TTJ
Title: Re: Valve springs - dual or not?
Post by: brettsyoung on 29.06. 2016 23:17
Thanks for the reples all. I've gone and purchased a new set of SRM double springs as a result. The bloke at RD said he had springs for the A10, if anyone is interested,  but at $265 a set they were a bit rich for me! Cheers Brett
Title: Re: Valve springs - dual or not?
Post by: Rocket Racer on 30.06. 2016 02:13
old school classic mk1 850cc mini's ran/run single springs only pull to around 5500, while the sportier coopers ran dual springs. 
I'm no engineer but I recall the duals having differing tension reduce spring bounce at higher revs. I believe modern springs with variable tension can get around this.
Title: Re: Valve springs - dual or not?
Post by: jjbsa on 01.07. 2016 12:42
Hi, it's Jon here, but I'm replying with my Ebor Bikes hat on.

Single valve springs have their place, but there are 2 widely appreciated reasons for fitting dual springs
1 There is one spring left if a spring breaks.  This is important!
2 Dual springs that are designed to rub against each other essentially eliminates spring surge, which happens at specific rpms with a single spring and which is a cause of spring failure.

BSA knew this when they designed the dual coils for the DBD34 Gold Star engine.  These springs rubbed together and the outer spring was variable rate, which also acts against spring surge.  The Eddie Dow valve spring conversion for the alloy head A10 used DBD34 springs for that reason.  In comparison with the standard Super Rocket springs, this conversion has a lower valve seat force when the valve is shut and a higher force at full lift, in common with modern practice.  The Dow conversion also used alloy collars, which in combination with the smaller Goldie springs, reduced valve train inertia very substantially.

In the distant past, using this conversion with Terry's Goldie springs, I had an outer coil break but the bike ran as normal below 6,200 rpm, i.e. the inner coil alone kept the valve under control till then.

I have come across customers who have been running the Dow conversion ever since the 1960s.

The spring wire we use is one of the best modern specialist valve spring alloys and is to a considerably higher standard than was available years ago.

My preference is for double springs.
Title: Re: Valve springs - dual or not?
Post by: Greybeard on 01.07. 2016 15:40
Now there's another great piece of information!
Title: Re: Valve springs - dual or not?
Post by: duTch on 01.07. 2016 17:00

 Yep I knew I'd read somewhere the logic behind double springs...
Title: Re: Valve springs - dual or not?
Post by: RichardL on 01.07. 2016 17:40
Just checked the Ebor Bikes site. Verrry interesting.  https://eborbikes.com/index.php?route=product/product&product_id=56

Richard L.
Title: Re: Valve springs - dual or not?
Post by: East_Coast_BSA on 02.07. 2016 07:09
Double springs deal with spring Resonance and Harmonics.  Every spring has a natural frequency and by using two different springs with two different rates, the resonance will only affect one spring at any given RPM.