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oldtuckunder

measuring valve spring rates insitue?

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ok wise sideways engineers  i have been pondering a little problem, have an idea, but would value any further input ideas.

i would like to test/measure the effective rates of some valve springs whilst head and rocker assy still on engine. my prime requirement is to see if they are all the same, and/or if one or more are softer either over all or at a specific point. anything beyond that i.e approx what poundage they are is just a bonus. bearing in mind my current lack of two handed dexterity it has to be something i can easily construct or get an apprentice to construct.

my idea was to make an arm that hooks on the rear of the rocker arm(push rod side, has a pivot point that sits approx over the rocker shaft with a bracket to support it, and then the arm projects outwards a measured distance say 2 or 3 ft (thinking maybe there is some ft/lb calculation i can do later) on the outward end of the arm have a rod or something hanging that i could slip weights onto to pull the arm down. theory being that i ought to be able to now run along the valves and measure compressed length for given hanging weight and compare, and perhaps even measure inter coil gaps to see if at a given weight some may have gone soft in a given section. 

what do you think, any suggestions.

of course what i really need is an arm with a with a ft/lb dial gauge in it that i could hook on, apply a given pressure and the just measure spring height, but havent found anything yet.

alan 

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Apparently they actually exist...…. though necessarily fairly application specific

http://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=254079146476&category=42605&pm=1&ds=0&t=1557317578094

Looks like it hooks straight onto a rocker for zero dismantling.  Ingenious. Something similar used with a spring balance (or electronic dangly scale thingy) should do it. I guess you'd also need some king of stop or marker so you know when you've compressed a certain amount?

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Hello Alan

                  It maybe easier to remove the rocker shaft and just push down in the valve tip with a scale and a stop built in?

Roger

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Nick's 'Moroso' spring tester was the type that came into my mind, but with Alan's long lever for weights.   No need for a separate pivot, use the rocker shaft. Problem would be to firmly attach the lever.   The Moroson has a special casting.

Dial gauge indicator to, er, indicate valve depression.     You're not going to get an inch of depression without binding the spring.   If, say, you get 100 thou with Z kgs can you say that the spring is 10Zkgs per inch?

John

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In the "on car" context a comparative measurement could be almost as useful as absolute as a finder of "soft" springs damaged by long periods stood compressed

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Of course..... the problem with the Moroso style tool is that it seems to use the rocker as part of it's lever system, so you need to know the true rocker ratio...… and how it varies through its arc.....:blink:

Alan is well placed to comment on this of course :smile:

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3 hours ago, JohnD said:

Nick's 'Moroso' spring tester was the type that came into my mind, but with Alan's long lever for weights.   No need for a separate pivot, use the rocker shaft. Problem would be to firmly attach the lever

actually you are right, if the lever will hook over the back of rocker, the lever can lay on the rocker and extend outwards,  a heavy weight slid around or hung from it with marker points on the lever would allow  comparison by measuring compressed spring length with a vernier probe at given marker points. would give a simple direct comparison between the springs, which is really what i'm after.  of course with the results, knowing rocker ratio (and as nick says definitely may not be not linear) weight applied, and movement out on lever, you could get close enough to calculating spring rate, or at least close enough for me not to want to spend £200 on a tool.

alan

looks like next time someone turns up here with two working arms, we are going to be bending a strip of bar :biggrin:

 

2 hours ago, Nick Jones said:

In the "on car" context a comparative measurement could be almost as useful as absolute as a finder of "soft" springs damaged by long periods stood compressed

 

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This involves springs off the head, but I've compared them by just compressing two in series in a vice.     Same compressive force for both, their compressed lengths provide the ratio of their stiffnesses.

John

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there are several inexpensive tools for removing valve springs on installed heads (plus compressed air to keep the valve seated). Once the valve spring is removed tape on the stem will keep it in place. Once all are remove the seat pressure at installed height and pressure at max lift can be measured.

spring tester.JPG

tool.jpg

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First pic above is Rimac spring tester, just the job, but at £730 + import duty and VAT, not a cheap one.

The second is a Bergen "Overhead Universal Valve Spring Compressor" at only £12!  

But, if you're seriously worried about valve springs, off with its head!   The cost of a new head gasket is trivial.

John

Edited by JohnD

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8 hours ago, 122344 said:

there are several inexpensive tools for removing valve springs on installed heads

a 20p piece of rope in the cylinder works quite well :thumbsup:

45 minutes ago, JohnD said:

if you're seriously worried about valve springs, off with its head!   The cost of a new head gasket is trivial.

 

if seriously worried then yes, but a fair amount of work, draining, manifolds off,followed by disassembly, checking, re-assembly, torquing, re-torguing head etc. and whilst i have a few spares if this was the vitesse and i didn't (as i usually manage to do) save and re-use the copper gasket, then these are now £50 a pop when i can get them.

how much simpler like the Moroso tool to just pop the rocker cover off and be able to check them all quickly for continuity/sensibility, either at the track (Moroso suggestion) if you suspect the onset of a problem, or after a winter or longer layup (which i'm being told can be more common than suspected if a spring is left in compressed state.

of course if you find an obvious problem then you have to do the work, but far better to know you have to, rather than do the strip and then find on checking it was unnecessary.

alan 

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"off with its head!  " exactly. otherwise it's like trying to sew a button on you shirt while you are wearing

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Those valve spring compression testers are very similar to 'Hardness testing' rigs.

You apply a force 1Kg to 150Kg  and see how far the tip has depressed into the test specimen. The harder the test specimen the less depression.

 

Roger

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10 hours ago, 122344 said:

"off with its head!  " exactly.

if you wanted to know how much oil was in the sump, would you use a tool like a dip stick as a sufficient indication, or would you unbolt the sump for a precise measurement? after all sump gaskets are dirt cheap. :dry:

alan

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Valve spring compressors measure rate of pressure. You measure the pressure at the spring's  installed height to determine the pressure on the seat with the valve closed and the pressure at full cam lift/max. spring compression to determine force on the cam lobe. if you wish to determine the volume of oil in the sump drain it and fill until the dip stick read full.

 

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