Hi there,

That second jump is the valve bouncing/floating all over the place out of control, and you can see all the vibrations from this reverberating through the whole valve train assembly.

Cheers

the cranks we had tested for hardening depth years ago (my dad did this when i was a kid) & worked with "Heat-treatment" up here in Brisbane --> the hardening would go about 15-18thou deep, & also found it to be very uneven through the crank,,, but if we left the crank in the center of the tank, for the whole weekend, the depth increased to 25-30thou & was more even thickness right through the crank

can i tell you a story???

when i was a young fella, i`d rip down to Byron Bay surfing (nothing`s changed there) & a mate of mine (Troy Story) had an old ex-army EJ holden Ute & we`d hop in that thing & fang it everywhere, but,,, we`d pin it hard as we could all the way to Lennox Head (when the surf was good at Lennox obviously) & it would crunch gears in every gear, it would leak oil everywhere, fume like a smelter, it was just crap, the whole car was just stuffed , but it just kept running

However,,, what surprised me the most was---> (now read this the right way if you may) that it would struggle (like any engine does) at valve float point,,, then struggle & complain at valve bounce (like they all do) & while i was waiting for a valve head to pop off & smash the entire engine to bits (The noise was deafening & giving me goose bumps,,, i was always waiting for that inevitable long walk home),,,, i was cringing the whole time , but Troy would always say "Trust me" & kept his foot in,,,, well,,,, the thing would suddenly smooth up, quiet-en right up, & then "SING" & continue to rev to the moon, smooth as silk, quiet as a mouse,,, it was like Magic

it went past/through that valve bounce harmonic & proceed to accelerate up to the next harmonic zone (which happened to be about 8500-9000rpms

now this was an old 138 side-plate grey motor & i`m not kidding you, it went fast!!!!!!

now i would never suggest to anyone to fit softer springs than needed, because it`s simply asking for a catastrophic failure with regards to valves &/or springs breaking,,, but this car & it`s ability to rev past valve bounce (SSOOOOOOooooo Many times over a 10 year period) & it`s sweet smoothness after said harmonic,,, really woke me up & made me look harder at valves , valve springs & engine harmonics

Moral of the story,,,, you`ll never know if you never go

Matt, a couple of quick (if there is such a thing) questions;-

What type of 'hardening' did these cranks have?
What type of 'hardening' did you dad do (or did he have it done)?

when I was working at rev-master we used a combination of sodium cyinide and potassium nitrate for the case hardening and sodium chloride for the tempering .
When we made the billet cranks the base metal was either Q10 or L7 ,[a spring steel compound] these metals had a high resistance to twisting, but if they were hardened over the complete surface then they would become brittle and suffered from surface cracking.
The wearing surfaces were only hardened. The cranks were coated with a asbestos refractory compound with the wear surfaces exposed then immersed in the salt bath.
Very hard overall is not good ,imagine a crank made of tool steel

PK, if you read up on nitriding it puts the surface layers of the metal in compression, thus increasing fatigue resistance. That is why they nitrided the whole crank.
see http://7faq.com/owbase/ow.asp?SurfaceHardeningOfSteel
scroll down to `nitriding'.

The depth of case produced by nitriding is relatively limited but as the core material is of high strength this does not cause any practical problems.

Care is needed when selecting materials. EN41B may be considered better as the surface will be harder than EN40B treated in the same manner BUT the surface of EN41B becomes so hard that it will not tolerate any point loads or bending without cracking.

There is an expansion of the surface caused by the development of the nitride layer and this creates large compressive stresses. These compressive stresses create a very significant increase in surface hardness (potentially 1000Hv) and also cause a significant improvement in fatigue strength. (It is obvious to develop a crack tensile forces must be present and if residual surface compressive stresses are generated then the superimposed stress caused by operation must first overcome the compressive stress before a tensile component can cause damage)

I think piston speed done this.

holy mother of god, that's not piston speed just piston shambles