Valve spring preload

[camelotr]

Hi,

Is there a formula to count valve spring seat pressure? I am building a Land Rover 2.25 petrol engine, and cant find info on the subject.

Edited by camelotr on Tuesday 7th April 19:54

[Pumaracing]

Do you mean how to measure what spring pressure you already have so as to compare against a specification or how to calculate the ideal pressure for a given valve train mass and engine rpm?

[Snake the Sniper]

As it's for a landy 2.25, I'm curious as to how/why it matters? Or is it just for curiosity?

[Pumaracing]

You've gone very quiet after asking this.

[camelotr]

Hi,

Thanks for the answers. I was soo bussy for a few days that no time I had for the net. Sorry.

So, my question was how to count how much seat pressure does an engine need of a given size valve/valve seat area - if there is a way to count.

The Landy I am rebuilding has very-very low seat pressure, I am pretty sure its springs are gone.

[Snake the Sniper]

With something like the 2.25, I wouldn't even bother checking them if in doubt, as they're £3 or so each.

[Pumaracing]

The calculation is very complex and depends on the mass of the valve train components, the peak engine rpm and the camshaft lobe acceleration. I wrote a computer program to do it many years ago but I really wouldn't bother unless you want to get into race engine design principles at the highest level.

It's easy enough to make a valve spring tester from a set of bathroom scales and something to compress the spring a given amount. I used to do it on my milling machine with a dial gauge. Any sort of press would do just as well or a long lever bolted to the wall.

[camelotr]

Hi David,

I think we are misunderstanding each other.
I would like to get only the seat pressure, and not peak pressure. Seat pressure is something that is important on all engines even with stock springs.

Is there a way to count minimum seat pressure for a given valve seat area?

[camelotr]

Snake the Sniper said:

With something like the 2.25, I wouldn't even bother checking them if in doubt, as they're £3 or so each.

I ordered the springs, they are on their way, but I would like to check them as they are REALY inexpensive right down to a level, where I have doubts...

Btw an engine is an engine. No matter what kind, I try to give the same amount of precision to each. On one bench I do this Landy, on the other a 930 Turbo.

[Pumaracing]

camelotr said:

Is there a way to count minimum seat pressure for a given valve seat area?

By "count" do you mean "calculate"? I'm not really sure what you're asking.

[Pumaracing]

Hmmmm.. I see Hungarian uses the same word "szamol" for both "count" and "calculate" so not surprising we are having trouble understanding what you mean.

[camelotr]

Exactly. That was a bad hungarism.

Me sorry :-).

So, "calculate" is the right expression.

[Pumaracing]

The contact pressure over the area of the valve seat is not an issue in engine design. What matters is the spring force when the valve is closed. For normal sized up to 2 litre automotive engines this varies from about 50 lbs for low speed engines to 90 lbs or more for high speed race engines, obviously both highly dependent on valve train mass and peak rpm. On a single cylinder lawn mower engine I worked on for use in racing karts it was less than 20 lbs due to the low rpm and light components.

The calculations are far too complex to go into here. For a standard engine I wouldn't worry about it. The engine designer will have done the sums.

[camelotr]

I have found an old book in my schools library, and it had some information, quite similar to what You sad. I will take it a a guideline. Although the seat pressure of this landy is definitely too low. I can fit the valve caps by bare hand :-).

Kart? What type? I just decided to build a cyclekart with my kids for fun.

[Pumaracing]

Not sure what type of kart. I only worked on the engine.