Measuring valve spring installed length

[PaulB]

Hi guys,
I am presently trying to get my head around the issues presented by building a competition Sprint cylinder head.

It appears that the valve springs should be shimmed so that they all have the same and recommended installed length. The is quite a good youtube clip which explains how to measure the valve length using a valve spring micrometer.

https://www.youtube.com/watch?v=igDKPVxPtcc

and also a good technical article on the burtonpower website

http://www.burtonpower.com/tuning-guide ... iming.html

All this seems reasonably straight forward until you look at the Sprint cylinder head. The exhaust valve springs are easy to get at, but the inlet valve springs are buried down inside the casting.

Does anyone have any clues on how this is done on a Sprint head?

[soe8m]

The installed lenght is not that importand. You have to check the force what is needed for opening the valves the same discance. Valve springs can vary slightly in lenght and force and shimming to the the same lenght does say as much as installing with no shims. You still do not know if they are equal.......

Jeroen

[PaulB]

Thanks Jeroen,

I thought you might know the answer. So how do you measure and adjust the installed valve pressure?

Could you describe the process to set it up?

[soe8m]

Adjusting you can do with shims. You do test it with a valve spring tester what is suitable for testing the springs in situ. That is a device what you can hook behind the rockershaft and then open the spring/vale combi. You can read the force what is needed to open and then have all the same. I never used it on a sprint head but it would work. I think when you fit a tube instead of a camshaft with another tube welded on it where you can hook behind you can use it for the inlets. You can make one yourself from some iron strip and spring loaded strip if you do not mind how much force is needed but only want all to be the same.

Mine does look about this:

Scan_20150125.jpg (33.03 KiB) Viewed 3966 times

You hook it behind the rockershaft. The spring strip with the knob has the scale attached. The other is a solid strip. You can read when you pull the knob howmuch force is needed to open the valve and what is needed to keep it open at a desired distance.

Jeroen

[tony g]

Paul when I checked installed heights on modern 16v engines with the same type of clearance as the sprint inlets what I do is:
Get a piece of tube turned in lathe so nice and even on the ends and measure the length. Aim for around 1" or 25mm whatever is easier.
Put the valve in and the "tube over the top and fit the retainer and collets.
You can now measure the installed height by pushing the valve down til it stops on the retainer (tube must fit retainer like the spring does) Record this distance then ADD the length of your "tube" to give the installed height.
I have found small changes in installed height affect pressures quite a bit and if it were me I would try to correct as much as possible.

BTW is the installed height in the workshop manual? Ive not seen it for the sprint
Tony

[PaulB]

Thank Jeroen and Tony very impressed with your ingenuity and cunning!!

I am looking at using Cosworth YB valves which I think have a recommended installed length of 34mm. I quickly measured the standard installed valve spring with a steel rule, not very accurate I know, but does look pretty similar.

Thanks for your help.....

[tony g]

When you say YB valves, do you mean YB valve springs? Where are you in the country? I have a very nice valve spring tester at hand that will tell you pressure v's length that I will gladly use on your springs if you want to get the real results

Tony

[soe8m]

A sprint has a small lift, even with a hot cam, about 11mm max. Compared to some 2 valve heads which have a lift of 15mm with a hot cam.
The valves are very light and small compared to the bigger 2 valve head valves.

There is no need for stronger valve springs. It only causes wear and more strain on the timing. If you are planing to rev it above 10.000rpm you maybe have to look for some stronger ones.

Jeroen

[PaulB]

Sorry, yes I meant YB valve springs. I'm thinking just to use the single valve YB spring not double.

What I don't know is how the YB valve strength compares with the standard Sprint one.

I live near Chester, I might ask for help measuring the springs if I decide to go down that route.

[tony g]

Youre welcome to come down for a spring test.
as Jeroen says standard springs are adequate even for performance cams. If using "new" pattern springs i would definately get them checked-have heard some bad things about them.

Tony

[PaulB]

Thanks Tony,

What tester do you have?

[tony g]

Buxton

Tony

[tony g]

This one:
http://www.buxtonengineering.com/valve_ ... tester.php

Tony

[soe8m]

These do the job. But, the best is to have a little bush in the centre to centrate the valvespring. These devices can read a totally different rate when the springs are not centrated. When you have one spring about 3mm of centre when testing and then 1mm of centre the opposite direction you will read a noticable difference with the same spring.

Jeroen