Jump to content

Valve springs


Recommended Posts

It has been mentioned before & in John's "Engine post mortem" thread that TT yellow valve springs (which I think are Kent?) are too strong. So what do people use with fast road cams?

I remember GT mentioning Jag springs but there must be something more easily available, can you get away with standard springs?

I'm interested in the 1500 but the same applies to other Triumph engines.

Link to comment
Share on other sites

  • Replies 84
  • Created
  • Last Reply

Top Posters In This Topic

Witor Springs seemed a sensible tension.

 

Those Kent springs are WAY to hard.

 

I was using some "terry" springs from the 60's, came off a Ford Crossflow :)

 

1500?

 

Just use normal ones, check they don't go bound? I doubt revving to 6000rpm will stress them out, yes maybe 7000-7500.

 

I have purchased a set of Chris Witor's Valve Springs (red) to replace my TT1207

toilet tune springs (yellow) = 206 lbs & 35 lbs.

 

I agree that these yellow springs are way too hard and cause undue wear on cam followers and valve seats.

 

I had considered using the Jaguar Springs, but have been quite unable to source any original Jaguar Springs. (Jaguar AJ6 (1990-92, 4.0 Litre) Valve Springs: Part # EBC4871).

 

 

The specification of valve springs is critical to the correct functioning of any engine. The spring rate is the amount of load the spring applies                                                  

to close the valve. It has to cope with the weight of the valve and cap, and significantly, in a very brief space of time. At 6,000 rpm, each valve                                                   

opens and closes 50 times per second. It also has to do so for the correct period of time as per camshaft requirements. Lastly, sufficient                                                     

clamping pressure must be available to seal the combustion chamber while combustion takes place between 8 and 11: 1 compression ratios.          

 

The rates have to be kept as low as possible to reduce camshaft and follower (tappet) wear. The spring height and wire thickness enables a                                                   

variety of camshaft profiles to be coped with. As you may notice from the figures above an uprated spring doesn't necessarily mean increased                                                    

rate. A modern method in use to control valve closing is 'interference' valve springs, i.e. where there is friction between the inner and outer spring.                                                  

This damps the valve movement without resorting to heavier springs.

 

The springs and ratios listed are based on original specifications (including uprated springs) in use during production, (1967 to 1976),

The critical areas are installed height to give 'closed' load and full lift load with adequate clearance to allow 'working clearance'.

Coil binding is to be avoided at all costs, so allow a working clearance between coils, fully compressed of at least 0.030".

Check when installed. Failure to check this at each valve could result in smashed springs, damaged rocker gear, damage to camshaft/followers,

damage to rocker studs and locating studs - but more likely bent push rods.

 

Don't recall exactly where those notes came from but they seem pertinent in this thread.

 

L

 

 

 

 

 

                                        

 

 

 

 

 

Link to comment
Share on other sites

Using spring interference may be a desperate measure.

The need for two springs is related to harmonics.

 

A spring will have a base frequency, the one you hear if you strike it.

Push that spring at that frequency and it will resonate, like a child on a swing, the response getting greater and greater as energy is added to the system in precise phase with the base frequency.

Such base frequencies will be higher than the 50 cycles per second (Hertz) that leon quotes (50H is a low note, not the 'ting' of a struck spring) but as long as the base  frequency is an exact multiple of the input frequency, this resonance will still occur.  Push the child on the swing every two or three swings - it'll still go higher.

If the spring's ocillation is being amplified by resonance, then it will not seat the valve correctly, as it will press it down then let it off as the sping contracts in it's own oscillation.

 

A system of two springs of different base frequencies will have a base frequency that is the multiple of the two springs' frequencies.  Thus the input frequency must be different and much higher to achieve resonance.

   I realise that this is different from damping - ideally, there should be damping in such an oscillating system to prevent the natural frequency being imposed on the output frequency.    Interference springs can achieve this, but such springs are usually made from steel ribbon, rather than wire, so that the inner spring present s flat surface to the inner surface of the outer coil of wire.

 

I've never seen a Triumph with springs like that.

John

Link to comment
Share on other sites

Measured some used standard 1500 & TT yellow springs at my local machine shop today.

Rate:

Std: 330 lb/in

TT: 219 lb/in   TT quote 206+35=241 lb/in so mine may have weekened a little, unless TT are quoting load at compressed height not rate (they weren't clear) in which case its closer to the mark. edit: that last bit is crap!

Pressure at install height of 34mm:

Std: 37 lb

TT: 70 lb

Pressure at max lift 9.1mm (std cam 1.5:1 rockers) spring height 24.9mm:

Std: 155 lb

TT: 149 lb

Pressure at max lift 11.0mm (R83 cam 1.5:1 rockers) spring height 23.0mm:

Std: 180 lb

TT: 165 lb

 

So the std springs are stiffer than the TT springs but the TT springs are installed with a much greater preload.

I presume the TT springs are weaker so as not to overload higher lift cams at max lift.

This was not what I expected but I've never given any thought to valve springs before  :)

Link to comment
Share on other sites

Science?  No.  Lots of bs though.

 

On my original 1200 engine (and the SAH head that followed), I had those funny push on valve caps and soft springs.  That engine used rev to god-knows-what (no tacho, ignorance is bliss  ;D) without valve bounce.  Then, recently I saw someone working on the cylinder head of a modern sports bike with a redline somewhere in the low teens and that had single valve springs that looked like they'd come from a ballpoint pen - could compress them between finger and thumb.  Ok, so the valves are pretty small and light but even so.....

 

Presumably if you use lightweight tubular push rods, less spring pressure is needed.

 

Trouble with installing springs with greater preload is that they will go soft quicker.  I believe the TT ones are known for this?

 

NIck

Link to comment
Share on other sites

Originally fitted the Wittor / County red strpie springs with Wittor alloy seat for the inner spring.

This worked fine but the engine wouldn't rev above 6750 rpm, checked the rate of various springs (yellow's / standard / red stripes) in different combinations, after several calculations I ended up with the red stripe springs and the original pressed steel spring seat, which in theory should have let me rev to 7300 rpm without losing control, actually now revs to 7400 so wasn't too far out.

If using a high lift cam you will need to check that the springs are not going coil bound at max lift, I think this is the reason CW sells the inner alloy spring seats, increases the fitted / compressed length of each spring by approximatley 1mm.

 

I have a chart somewhere of the various spring combinations measuring the spring force at fitted length (think I used 35mm) and max valve lift which I think from memory was 11mm, I'll try and sort it out.

Link to comment
Share on other sites

Spring Info

Thanks Mike that's great, I take it the ones you settled for are the green text, 46.5 lbs fitted, 138 lbs at 11mm lift? How did you decide how much force is enough?

 

I ended up with the red stripe springs and the original pressed steel spring seat, which in theory should have let me rev to 7300 rpm without losing control

How did you work that out?

 

I wonder why the standard 1500 springs seem to be so much harder than your red springs which I understand are standard 6 cylinder jobs?

Link to comment
Share on other sites

Ok I think I have a plan. What I need is a slight increase in seat pressure from the 37 lbs of the std springs but not as much as the TTs 70lbs.

I also don't want the large increase in full lift (nose) pressure that the std springs would give if I shimmed them with my higher lift cam.

So I can use the std outer springs with the TT inners:

 

Springs    Instal 34   Full lift std cam 9.1   Full lift R83 cam 11.0

Std            37 lb            155 lb                    180 lb

TT             70 lb            149 lb                    165 lb

Std/TT       50 lb            149 lb                    170 lb

 

Any flaws in my logic?

Link to comment
Share on other sites

Originally fitted the Witor / County red stripe springs with Witor alloy seat for the inner spring.

This worked fine but the engine wouldn't rev above 6750 rpm, checked the rate of various springs (yellow's / standard / red stripes) in different combinations, after several calculations I ended up with the red stripe springs and the original pressed steel spring seat, which in theory should have let me rev to 7300 rpm without losing control, actually now revs to 7400 so wasn't too far out.

If using a high lift cam you will need to check that the springs are not going coil bound at max lift, I think this is the reason CW sells the inner alloy spring seats, increases the fitted / compressed length of each spring by approximately 1mm.

 

I have a chart somewhere of the various spring combinations measuring the spring force at fitted length (think I used 35mm) and max valve lift which I think from memory was 11mm, I'll try and sort it out.

 

Please do, I will have to recheck my parts on hand, not sure if I have any of these mentioned inner alloy spring seats?

 

L

 

 

 

 

Link to comment
Share on other sites

Charlieb

 

Measuring the springs and coming up with the various scenario's was fairly easy, I cant take credit for the predicted RPM limit for the setup I used. I work with some pretty talented engine development engineers who make it sound very easy when they do the calculations, I'll see if I can dig out the paperwok.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...