Valve spring free length - when to replace?

[SammoHung]

Long time no MSC! hope you are all doing ace

When should valve springs be replaced (due to a reduction over time in their free-length )?.

...1mm short, 2mm short, 4mm short, 8mm short,16mm short....

or maybe

0.1% short, 0.2 %, 0.4%, 0.8%, 1.6%

What say you all valvetrain gurus ?

Cheers

 

[frank]

change if you are getting valvebounce sammo, otherwise dont bother

 

[SammoHung]

Oh god..how do I know if ive got bounce?
pitty my uselessness....
...but between me, you and other readers my springs are all around...6mm down on the book 47.odd

 

[SammoHung]

Hia Frank and All,

In the end, I decided to buy a new set of valve springs, (since the whole block needs attention too). To my supprise when i measured the genuine nissan new springs, they all measured 40.8mm (not 46.7mm as per the Haynes manual)!!.

The 25 year old springs that I removed from my head measure around 39.9mm.

So; what I though was originally a 6.8mm reduction in length (aprox 15% squashed)...was in fact only a 0.9mm reduction in length (2% 'squashed')....[and infact I suspect worn rather than squashed]...and that is on an engine that has had at least three major overheating events and lots of regular high RPM action

Any way, the point of this post is to hilight an apparent error in the haynes (one of many others no doubt)...so hopefully if somone else does this measurement check and has the same concers that I had...they will be able to know that the new free length of the MA valve speings is 40.8mm (not 46.7mm in the haynes)

Happy springing