Valve float

[toofast2race]

 

This and related videos are pretty interesting... now I know why Triumph ohv engines that see a lot of revs are so mullered in the topend area  ;D ;D . Random shitty components (soft alloy valve caps for example) or just random component weakness due to old age will cause destruction in a moment if you are using big revs and get unlucky with the harmonics....  remember you're old head Dave.

Thing is 'we' modify the engines with camshaft X and roller rocker Y and valves Z etc and does ANYONE actually record what all these bits are doing as a package when say a race 1300 spit or 2 litre six is buzzing along at 7000-8000 rpm???... I would say the line between mechanical survival and blow up is pretty thin and not that well understood...

[spitNL]

Pretty cool clip. 8)

They do this on a device called a spintron, basically an engine with the crank, rods and pistons taken out, and the valve gear driven by an electric motor.

I am pretty sure none has done this kind of test on their Triumph, I know Nascar teams test extensively with this, OHV they still have pushrods. :

 

I know engine analyser has an option to input the valve springs pressure, weights of the different parts and can the give an indication weither valve bounce is likely.

Haven't used it though, because if you want a good predicition you'll need to measure the entire cam/valve lift curve.

[DaveNotSoSideways]

Yes missed this, quite amazing an engine actually stays together at all at these rpm.

 

Imagine if the crank came out at 9000rpm, that's insane rotational speed for an object of that weight, so much energy.

 

 

 

[willcolumbine]

It's 9000rpm flywheels coming out that worries me!  ;D

[PeteClan]

My flywheel became detached at Colmar Burg earlier this year at 9000+ rpm.  Fortunately it stayed on the splines of the transaxle input shaft with no damage apart to the ciontered clutch plate that was jammed by the sheared bolts.

 

Pete Richards

[flatter4]

 

Great clip.

Don't take all that is written as gospel though - for example "valve bounce is the direct result of insufficient spring pressure".  If you hit something hard enough it will bounce, in some cases it is valve closing speed too fast; or even too stiff an assembly that causes a problem.  If the valve spring is too stiff - the valve will bounce!

As Andy Thompson says at the top - most of what we do is by feel, and learning from prior knowledge.

 

A few rpm of valve rotation is good too - to even out wear.