Valve Spring Science.

[A10rocket]

Has any body got any info regarding valve spring tension.
I've stript the head (1549) down on my Super Rocket project and I've never known valve springs
as stiff these.  I've stript some heads down in my time both car and bike but these springs
have to be the stiffest ever.
 Surely this cant be good for the valve train. The cam is a 357.
The engine hasn't run for 40 years so I was toying with buying new but with
so much crap pattern stuff about these days it's a gamble if they would be right.

So,has anyone got any figures for testing the tension on valve springs for this engine ?

Regards Ken.

[bsa-bill]

don't think I've seen tension figures Ken but others here might well have, spring length I think differs.
But main point would be the cam there is a LOT more lift on a 357 which means a LOT more compression of the valve spring, I had a 357 in but went back to 356 until I get the bike starting and running good, I have had other issues that I think have made the motor difficult to kick over ( listed elsewhere later tonight)

[chaterlea25]

Hi Ken and All,
They are hard ba*&^%ds
On the ally head models the springs are different to all the other models, so the dimensions given in th Haynes manuals are incorrect
I would only buy new springs from someone like SRM who build engines using their own products
I have fitted several sets of their springs and have had no issues
Remember most car engines dont rev like bike engines so the springs are much softer
HTH
John O R

[andy2565]

the higher the rev range the harder the springs,or you may get valve to piston contact if they're to soft,progressive springs are good,we fit the porsche 911 early 2valve,to our grasstrack bikes and the bsa single scrambles bikes,bit of a secret that,have to check how they relate.

[NickSR]

Hi Ken
Not sure if this any help, but way back then (1966) when we built our Super Rocket Cafe Racers it was 10.5 pistons, spitfire cam and WS valve springs.

The springs were so strong they bent the valve compression tool, may be you have some of these ?.

The up side then - wow it was fast.

Down side -  wore out the cam followers also the cam and pinked, so within 6 months back to standard set up.

Regards
Nick

[A10rocket]

 
 Thanks chaps for your input.  I think I'll go with Johns tip on buying new from SRM.
They're not expensive. As he says, they use them in the engines they rebuild.

I was comparing spring strengh with that of a 2lt pinto I rebuilt a few years ago.
The valves were slightly bigger hence heavier, that engine will rev at 6500rpm all day
yet the springs were no where near as tough as the A10.

The double springs is to eliminate valve float as they have two different frequences.
I just think these hard springs are over kill and hence you hear of a lot of worn cams.

Regards Ken

[Mark Parker]

My A65 has a seat pressure of about 60lb with around 180lb at full lift of .410" its safe over 8,000 even with heavier valves and heavier C/molly rather than alloy pushrods. That sort of pressure seems ok to 9,000 with alloy pushrods and std spitfire cam. Though the alloy pushrods flex and loose performance. I think it depends a bit on the cam profile how hard it is for the valve springs to control it. No point putting massive pressure on stuff when its not necessary. The thing to really avoid is fitting a spring with rust.