Preferred method for measuring valve spring pressure (2020)

It's about valve spring pressure. The tester gives you the spring pressure at the specified spring compression.

All interesting info/ideas.

Nothing much to add except measuring free length is not the answer.

I had a customer insisting he needed new springs because they were old. So, I installed a new set from AN. Out of curiosity, I measured the old and new. I've lost the measurements but remember that the new outers were a little shorter than the old, the new inners were a little longer than the old, and none matched the free length in the workshop manual. I couldn't tell any "seat of the pants" difference in the running of the engine but, he was happy and that's what matters for a casual street rider IMHO.

Please read the following understanding that I am guessing: I guess the pressure at fitted height and at valve fully open height are important, but it seems to me that the fitted height ought to be the shortest possible without coil bind at high RPM and the pressure at rest should be as small as possible (within reason). I guess that's why progressive valve springs exist for many engines - do they for Norton?

All I do is measure the spring rate on a spring tester up to coil bind.

Then instal on the bike and when the cam is at full lift put a dial guage on top of the valve retainer and with a lever compress the valve spring down to coil bind.

Then compare the distance to coil bind to the distance and spring pressure I measured on the spring tester.

I use a minimum of 50 thou clearance to coil bind and then add or remove shims to get the pressure I want.

marshg246 said:

All interesting info/ideas.

Nothing much to add except measuring free length is not the answer.

Click to expand...

Spring free length as per the manual is about all the home mechanic with basic tools has to determine if the springs are within the service limit.

RatedSpeed said:

It's about valve spring pressure. The tester gives you the spring pressure at the specified spring compression.

Click to expand...

That is correct but what is the specified seated spring pressure at factory installed or fit height ?
The manual does not give that as it is of no real importance with a stock camshaft.

acadian said:

I've previously set them up in the head using only the installed height figures, but I've got some beehive springs on the way, and I'll be using a press with a scale this time before installing them in the head, my plan is to try and achieve the poundage at specified height in the press using shims, but once installed in the head I can't think of a way to verify the setting. I've looked at some fancy in-head spring load gauges, but they're far too pricey and I doubt they'd even work on a brit cylinder head. Anyone have a tip they could share?

Click to expand...

This was the query and relates to installed height to attain seated and open spring pressure, the rate of the spring should meet that requirement from the seated height.

My previous post and picture was more related to the recent post and video.
You can not set an installed height if you do not know the present distance from the under side of the retainer to the base of the lower spring cup (in a Commando or any other engine) without measuring it.
Instead of telescoping gauges as per the video all I use is a set distance piece that is shorter than the present gap, the valve collets are seated in the retainer and the dial gauge measures the valve movement when cycled.
That reading is added to the that of the distance piece for a total, that measurement is then compared to the manual installed height, if it was over measurement shimming would be an option to meet the recommended height.
That's all.
In the pic, lifting the valve will get the needed add on measurement.



The factory manual only gives a height assuming they set that to meet the spring (rate used) the poundage is worth what as information over the more relevant installed height measurement.
With the original post from 2020 if it was a cam kit with springs then an installed height would be included, the installed height would set the seated pressure, the spring rate would match that needed at full lift.
That comes back to finding the present height then meet as necessary the height recommended, workshop manual or performance spec sheet on aftermarket parts.

The stock AN springs are less than US$10 a pair so hardly going to break the bank as a replacement item at a general rebuild or restoration.

I would assume something like a JSMotorsport beehive spring set for example would have a recommended installed height (to meet specified seated and open spring pressure needed) and work within the available space (measurement) in the Norton cylinder head, perhaps with some shimming at most.
There would be little need to check that in a valve spring tester unless you did not trust the supplier and that test would be easy at any decent performance engine shop with their spring height/pressure tester.

I see now it is a Triumph post in the Commando forum.
Nothing would change and would come back to present height measurement and needed measurement not pressure.

You just manually measure your installed height from spring seat to under retainer , if dual springs are installed you need the retainer on your spring to test , good practice to calibrate the tester I have a crane test spring with its calibration chart , then it's easy to check your installed and over the nose pressures , and you can visually see how close your coils are .cheers.

It is good to know your spring pressures are correct, the same as piston to valve clearance, exhaust clearance generally being + .020" more , because the piston is chasing the ex valve up the bore so it's reliant on spring pressure to keep it in contact with the cam lobe , but on the inlet it is mechanically following the piston down the bore .