super rocket valve spring installed height problems

[mikeb]

I’m having trouble getting sufficient installed spring height on new valves, springs, caps, keepers on a ’61 super rocket (alloy head, 67-1547). All the new stuff is from SRM. They cite a minimum installed height on 1.375” for a 356 cam (which I’ll use) or 1.400” for a 357. SRM say that BSA never published a figure for this but that’s their recommendation. On the Eddie Dow ‘twin tips’ sheet with a 357 cam he suggests 1.312”: http://bsa-a10.hailwood.com/tt11.html

When I measure the new srm setup I get an installed height (from the underside of the top cap to the top of the bottom cap) of 1.26”. When I measure with the old valves, caps, keepers I get about 1.30”-1.32” – so that would match the Eddie Dow figure but way short of srm figure. The valve seats are actually a bit recessed (see pic) so I don’t think they are shortening the spring height. If anything I may need new valve seats which would further shorten it.

The srm stuff is pretty much exactly the same dimensions as the old stuff. I’ve noticed some of the new srm keepers don’t sit well on the valves/caps and hence the top cap sits a bit low, which could account for some difference from my old valve gear. srm suggested I send them back for checking (that’s a 24,000 mile round trip and more delays) or maybe I could take to the back of them with some emery paper. But even if I fix this I’ll still be far from 1.375”. I could get maybe another .025” by grinding down the underside of the bottom cap.

I’ve searched a lot and not found any good info on this. A couple of britbike threads suggested others have had this problem and ended up just installing them and testing for coil bind. But that doesn’t explain what the problem is (if there is one).

I’ve also attempted to calculate the valve lift but I clearly don’t know how to do this. The cam lobe is about 0.3” lift (from the atlanticgreen pic and my measurements), the rockers approx 1.31” from shaft centre to tappet, and 0.85 from shaft centre to pushrod cup, so 0.3 * 1.31/.85 = 0.45”valve lift… But that makes no sense as the outer springs compress to 0.95” + 0.45” lift = 1.4” min spring height on the 356. So I’m wrong.

All this means I’m confused. So questions:
Anyone else had this problem?
What height to aim for / figures to trust?
Would shaving a bit of the keepers be achievable/wise?

Thanks

Mike

[RichardL]

I'm no expert here, but aren't keepers usually flush with the top of the cap? It looks like there is about 0.050" there. Then, in the top picture, I think I'm seeing a shadow under the bottom cap. Is it all the down over the valve guide? I'm almost sure I must be wrong, but can't understand the shadow.

Richard L.

[bsa-bill]

but aren't keepers usually flush with the top of the cap?

You could have a point there Richard, I cant recall if mine protruded over the top cap or not, springs would put pressure there of course so might be a bit of space to come.

I think I'm seeing a shadow under the bottom cap.

You would, that's correct, they are similar shape top and bottom, if I recall correctly the flange is of different widths, I do recall wondering which way they went

[chaterlea25]

Hi mike and All,
Attached photos of an SR thats on my workbench for far too long
As Richard says the collets should be about flush with the cap
When I went to build this engine  found that one collet (new) was not profiled properly where it fits into the groove on the valve, the bump was more "square" than semicircular if  you can follow my meaning??

have you fitted the bottom washers the correct way up? another possibility??

When you fit the cap and collets can the cap be "rocked" from side to side?
If it can then thats a problem  that needs sorting or you will wind up in tears

HTH
John

[RichardL]

Bill,

Yes, I forgot the collars were shouldered on both sides.

Richard L.

[mikeb]

helpful pics John. yes i think my keepers are not sitting in well and thereby holding the cap lower, hence my idea of taking some emery paper to their tapered side.... is this wise? did you get your misfitting keepers from the same place as me?
the bottom cap is the correct way up - quite a bit of shadow partly coz the camera/light and also it has a foot on the underside that i could make a bit lower - maybe save .025". a pic below showing the srm stuff and while only one side of the bottom cap shown i think it is the underside (both sides are similar in having the stepped areas, tho the radius is less of that on the underside).

but even then I might get back to 1.315" installed height which remains a long way from the 1.375" srm are recommending.

???

[chaterlea25]

Hi Mile,
Check each collet in turn, degrease them and a light coat of engineers blue or a felt pen
then fit each in turn to a valve, rotate the valve/collet relative to each other 
See where the collet rubs along the valve stem, it should contact the stem evenly along the collet length
and not be held away by a too thick part that fits the groove
I would not use emery on the tapers
I checked some SR valve springs and they have 6 1/4 turns 0.145in diamater wire
Yes,  the bottom collars go bigger step upwards, (other way up when using the goldie spring conversion)

It was only one dud collet out of the set that gave me problems,
Do you have any of the original BSA components to compare with ?

HTH
John

[mikeb]

I’ve measured up the keepers and found variance of upto .006” at the top wall thickness – these measures not the most accurate but are repeatable. They are all a little longer that the old (worn) keepers. When matching biggest with biggest new keepers etc and selecting the most fitting valve stem they now can fit almost flush into the caps with no movement – see pic. John I haven’t check the fit to the valve stems yet with blue – will do. I still get an installed height of 1.275” – way less that the old 1.315” or the srm figure of 1.375

The new springs are mca brand - 6 ¼ turn x 0.144” wire thickness. The old springs – no idea what they really are – were 6 turn x .158” wire. With that extra ¼ turn the new springs compress to 0.95” approx. whereas the old to 0.91”. so I lose another 040”. everything else new vs old measures up about the same.

One thing I just can’t find is data on the actual SR valve lift or the rocker ratio. I crudely measured the rocker ratio as about 1.5 (making 356 cam valve lift as 0.45 – that’s not right) and on the bench tried measuring the rocker movement directly by depressing the pushrod cup 0.30 -> 0.38” tappet movement – but these measures are too rough to calculate what spring height I need.

Does anyone have this data?

  John – if that SR engine on your bench is complete with a known cam, would you be willing to turn it over and measure the spring/tappet movement????

Cheers

Mike

[duTch]

 

See where the collet rubs along the valve stem, it should contact the stem evenly along the collet length
and not be held away by a too thick part that fits the groove

 This made me remember I had a similar issue, and made the groove in the stem a tad bigger to suit, while trying to maintain same length from valve head....was a bit of a minor shiffight if I recall; had to compromise some , and ulimately just threw it together to find out

If it's any consolation, I dug out my notes on spring compressed lengths; collars from SRM and collets same (I think); Inlet valves SR I think  from a BSA packet circa 1980, Ex-Valves modified stainless Gemini items, seats are cut but not deep, but a few thou here and there adds up .
Valve Spring compressed lengths;     
     Left Ex; 1.363           Right Ex; 1.348
     Left In;  1.351           Right In; 1.364..... , so in my case could explain a slight difference in plug colour L/R..?

 I can't find any subsequent notes, so may be as is... runs ok though

 Mike posted while I was doing that

 

[duTch]

 hey Mike, You only mention one spring? I guess it's not relevant here,but how about the inner..?

 Just though I'd add as comparison;
My SR Valve spring specs (as far as I can decipher my notes ), maybe not sourced from SRM
                   outer                     inner
 OD              1.386"                   1.064"
Wire size       0.144"                  0.114"
Coils             5,1/4 turns           6,1/2 turns
Length          2.157"-2.174"         1.990"

[mikeb]

thanks Dutch. i overlooked the inner as it compresses shorter, so the outer is the limit.
you've still got 090" more installed height than me...    .. where has mine gone!
are you running a 357 or 356 with those figures?
you didn't happen to write down in that notebook the actual SR valve lift did you?

mike

[duTch]

 

you've still got 090" more installed height than me...    .. where has mine gone!

  ...only thing I can think of at the mo is either my stems are a bit longer (I have measurements/drawings for that somewhere), or the seats are cut deeper....or..

 I'm running a 357 that's been ground,

you didn't happen to write down in that notebook the actual SR valve lift did you?

 Like you, I think I was trying to work it out and gave up for a while

 I'll have a dig later and see what else I can churn out

[Klaus]

Hello Mike,

another way to get a solution is to know the presure of the springs.
I do racing with A10 an converted to one spring. IHMO i belive in knowing the valvespring pessrue when the valve is closed and in hight lift opened. I use megacycle cams with 1 mm more lift as the 357 at my racer. The road bikes are also converted by using the 357.
The original valvlespring pressure is low and causes in shifting wrong gear to valvle masher.
So I prefer  a closingpressure of 35 kg and at hight lift 85 kg.
The easy way to find out, is to press the springs with all components on a scale.
Messure the hight in fit condition and with the real valvle lift by full opening.
If you get a result nearly the the named kg, every think is ok.

cheers Klaus

[duTch]

 Hiya Mike- I dug ou the other notes I made, and am now understanding why I'm not an academic ....I measured just about everything I could think of, and the best I can decipher is;
 
  357 Cam- calculated lift (measured with digital sliding caliper)=
    Cam Lift; average             0.337 " give or take 2 or 3 thou

O/A Length of Valves        3.933 +/- a few

Head of Valve to                   
Tip side of                        ~3.787 to 3.798 <----- I figured this is fairly relevant
 Collet groove ?

 I can't quite figure out the measurements of the rocker arms, it seems both arms of the inlet rocker (p/r>shaft< 'tappet' ), are different to both arms of the exhaust rockers (p/r>shaft< 'tappet' extra*rant*)... ...I think about that point I just threw it all together  ....but that was 3+ years ago*smile*

 The figures I have are maybe these, read at own risk ;
 Inlet     (p/r>shaft) = ~0.750"                &     shaft> 'tappet' extra*rant* = ~ 1.245-1.273"                   *  1.517"  (unsure what this is)

Exhaust (p/r>shaft) = ~ 0.993-1.008 ?    &     shaft> 'tappet' extra*rant* = ~  1..487                            *   1.790"      ditto

  I've added a pic of one of my valves closed as a indicator of where the collets/keepers are sitting after I had the grooves made bigger to fit,
 and I also found some other "installed spring height" figures, but am not sure what was the reference point (0.0, maybe from head, not the spring seat); range of  1.456" - 1.506"

 And don't forget that more winds in a spring makes it softer...

     - you'll need it 

 Klaus, I had a notion the reason double springs are used is something to do with reducing valve bounce, because the two springs have different load rates, so they counteract each other...or something along those lines  ???

 

[Klaus]

 Klaus, I had a notion the reason double springs are used is something to do with reducing valve bounce, because the two springs have different load rates, so they counteract each other...or something along those lines  ???

Hi duTch,


a lot of work to messure 

most old engines use double valvle spring, I gues this is caused by fear of spring breaking.
Modern steels are much better, so my intension is to low wight by moving parts.
The original spring set with all parts is 101 gramms. The one spring conversion is 61 gramms.
This will reduce the oszillating masses huge and give the engine a longer life, an dbeing sure the tappets will not bouce on the cam.

cheers
 Klaus