GodISmE

Hi, I checked valve lash becasue compression was way too low, especially on cylinder 1. My intake cam lash went down to 0.05-0.15mm, so quite a lot! Exhaust side is fine, around 0.30mm on all of them. This is just after 1000 miles done on tracks (track car only). HR Heads were fully refurbished and lash was set at 0.25mm int., 0.30mm exh. Stock HR were used so I suspect this might be the problem. But I want to understand why - is it just the fact that they are two soft compared to upgraded Tomei springs or is it their compressed height? Or maybe somethings else contributed to it? Any experienced engine builders here?

Cams are 280/11,3 and 272/11. CP pistons 95.75, 11.6:1.

RobPhoboS

Well I can't give you an answer from an engineering point of view, only that when I did my cams JWT, I used their springs and shims. I didn't have an issue after several months and a few track days.
I'm just in the last stages of rebuilding my engine now with new pistons, rods, ported heads etc

I pulled my engine apart due to power loss, and I found I had a lot of damage to the valve seats, most likely from a bad/dirty intake filter as well as seriously scored main bearings !
So my valve seats we 5 angled cut, and of course this messed up a bunch of the cam/valve clearances and I need the valve tips to be ground down a tiny bit here and there.

Anyway, I can only assume (totally guess!) that by using the non-matched springs/shims you've caused some wearing to the valve seats on the heads (probably? the softest part in the valvetrain here). I'm not sure if the Tomei springs are harder or softer than OEM though but of course they aren't matched to your cams).
I doubt you wore down the valve buckets, and possibly the valve tips but they're tough too !

What are your valve bucket thicknesses on those most affected ?
Because you might be lucky to just replace the buckets, and carry on. Or if you really want to do your due diligence, then it's heads off and inspect for any wear.

Report back with what you find out as it's helpful and interesting to know what really happened

GodISmE

I'm looking for vq35hr valve spring measurements, installed. I can't find anything on the net, e.g. set length, compressed height, lift length and distance from retainers to stem seal.

Tomei springs are harder and taller and I have that data. But I canot compare them effectively to HR springs without these specs.

EDIT: found the specs except for compressed height, which is key in my case!

2007 350z HR
Standard: Intake and exhaust
Free height : 43.85 mm (1.7264 in)
Installation height : 37.0 mm (1.457 in)
Installation load : 166 – 188 N (16.9 – 19.2 kg, 37 – 42 lb)
Height during valve open : 26.8 mm (1.055 in)
Load with valve open : 502 – 566 N (51.2 – 57.7 kg, 113 – 127 lb)

Black Sabbath

Hi. It is quite common for a valve or two or more to take what I characterize as a "set". Meaning the decrease of your lash is due to the valve and the seat interface "settling in". Actually very, very common after a performance multi-angle seat grind where the valve was not fully lapped-into. This could also be due to a number of issues related to machining -or- it may be due to excessive erosion from the parts due to a slight mismatch of alloying or incorrect hardness profile. If it were my ride I would reset the lash and drive it. The valves will either stay where they are now -or- if there IS a pending issue the lash will tighten up again in which case I would suspect either improper seat grind or an incorrect seat manufacture at the liquid metal stage.