Valve train mods

[JEM]

Just noticed this on the Jabiru technical site - concentric inner and outer springs for 2200 engine.

 

Apparently kits will become available

 

See http://jabiru.net.au/forum/engines/36-valve-train-mods#139

 

 

[jetjr]

is this a step forward?

 

 

[bexrbetter]

IMO, nonsense:

 

The low rpms, low lift and short duration of the Jab do not call for resonance control in the slightest.

 

The extra 20% seat pressure merely puts extra strain on the whole valve train.

 

In this day and age if they are having broken valve springs, that is virtually unheard of in the modern engine industry, then it's the supplier's fault.

 

My simple advice if you want to do something in this area then simply buy quality direct replacement springs from a number of proven brands starting with Crow Cams for example.

 

Give them the required info such as; free length, wire diameter, number of coils, inside or outside diameters, installed height and valve lift along with max rpm and they will spec a spring for you, most of them offer this service.

 

FWIW, the recognised 'best' aftermarket valve springs in the world are made by PAC in the US.

 

 

[facthunter]

When any particular engine went to hydraulic lifters the spring pressure was increased usually, at the same time. The Continental 0-200 runs 3 springs and a high seat pressure, but that's also to do with the lead in the fuel. Many modern valve springs are barrel or conical shape, and one only fitted and you never hear of failures being a problem.

 

I doubt it gives reliable redundancy in a real sense, by having multiple springs. Might get you home but if you keep running it then it will not be adequate for the job with one only. Nev

 

 

[Jaba-who]

Has broken springs been much of an issue?

 

 

[facthunter]

If they have any rust pits on them they break. Nev

 

 

[bexrbetter]

The Continental 0-200 runs 3 springs and a high seat pressure, but that's also to do with the lead in the fuel.

Likely because it was certified in the 1950's when valve springs did actually break.

 

 

[frank marriott]

And Rotax (at least the one I saw pulled apart anyway)

 

 

[bexrbetter]

And Rotax (at least the one I saw pulled apart anyway)

Rotax run at 5800 rpm, 2 valves (i.e. heavy) and obviously enough valve lift and duration to generate over 80hp per liter so wouldn't surprise me if they ran multiple valve springs.

 

Jabiru is not the same scenario.

 

 

[jetjr]

There has been problems with lifters pumping up and coil bind, complicated by head recession. Recent changes to oil pressure too are maybe related

 

More than a few dropped valves. The flycut pistons and thes spring setup are ways to acoid catastrophic damage if things go wrong. Not convinced this is a way to adapt to problems.

 

I heard..... Could easily be wrong, that a dual sping engine had issues recently