Valve spring selection

[Joump5]

Anyone know of a rule of thumb for
calculating valve spring size/spring
rate for a small gas engine? Any
advice on selecting or sourcing
springs?

 

[Brian Rupnow]

If it is a model engine with cam operated exhaust valve and atmospheric intake, use a spring of 0.022" wire diameter for the exhaust and use a spring of .012" wire diameter for the intake. as a generalization the outside diameter of the spring should be about 1/4".

 

[WOB]

The important thing is to get the proper spring force. For the size of engines usually made by hobbyists( valve head under 1/2"), 2 lbs compression when installed with a max of 3 lbs. will do the job 99% of the time. A good source of springs is mcmaster.com.

WOB

 

[stevehuckss396]

Grainger.com has a HUGE selection of compression springs. I just ordered springs for a project. You can have them sent to a store if there is one near you and save the shipping. I have one about 6 miles from me.

 

[Joump5]

It will actually be a relatively large engine. 2” bore.
Both valves operated by cam, pushrod,rocker.