Valve Spring Free Length Limit

A

athomas

New Member
I'm currently undergoing a tear down of my GN250 to figure out why a pair of valve collets removed themselves (Engine shutdown while out riding due to no compression, it seems one of the ex valves removed its own collets but luckily didn't drop and destroy the piston!). As part of trying to understand what caused this so I can make sure it won't happen again I'm looking at the valve springs and the free length and spring tension limits.

Suzuki have this down in the service manual as the following:

"If the limit indicated below is exceeded by the free length reading [...], replace with a Suzuki spring" Service limit is 39.8mm

I'm assuming this means anything ABOVE the limit is out of spec? Can anyone confirm this? (I'd have thought that a spring is likely to shorten as it wears so the manual goes against my own logic!)
 
The 39.8 is likely to be "installed height" not a bench measurement (I did not look up specs)... measure one installed, then check seat pressure at that height, should be 50lbs < 3-4 lbs (again check specs) is okay but if they are way low on seat pressure you need to look at new valves and possibly seats. Take some pics and if you don't have a way to measure seat pressure, you can take the numbers and springs to a machine shop and ask them... call ahead if you plan to wait.

Not the first valve to spit the keepers bro :o have a look at the retainers for wear also... cheap after market "Ti" retainers suuuuck.
 
Actually it very specifically says 'Free Length' (I've included the section) which is what has me confused!

Stripped everything down today and it looks like there is no other damage except a slightly bent valve and a couple of minor marks on the piston, so my current theory is a weak spring letting the cotters slip out or the cotters themselves failing.

As soon as I rig up a way to check the spring tension I should be able to decide one way or the other!
 

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Tune-A-Fish said:
The 39.8 is likely to be "installed height" not a bench measurement (I did not look up specs)... measure one installed, then check seat pressure at that height, should be 50lbs < 3-4 lbs (again check specs) is okay but if they are way low on seat pressure you need to look at new valves and possibly seats. Take some pics and if you don't have a way to measure seat pressure, you can take the numbers and springs to a machine shop and ask them... call ahead if you plan to wait.

Not the first valve to spit the keepers bro :o have a look at the retainers for wear also...
Tune-A-Fish said:
The 39.8 is likely to be "installed height" not a bench measurement (I did not look up specs)... measure one installed, then check seat pressure at that height, should be 50lbs < 3-4 lbs (again check specs) is okay but if they are way low on seat pressure you need to look at new valves and possibly seats. Take some pics and if you don't have a way to measure seat pressure, you can take the numbers and springs to a machine shop and ask them... call ahead if you plan to wait.

Not the first valve to spit the keepers bro :o have a look at the retainers for wear also... cheap after market "Ti" retainers suuuuck.
Click to expand...
Click to expand...
They all do???
 
Of course not, but there is some cheap stuff that you should steer clear of. I won't mention names, but I have pulled valves that sucked up in the seat with very low hours and retainers that sucked down through the springs. good parts are never cheap.
 
xb33bsa said:
if the springs are spent/no good they will be shorter than 39.8 when as shown free legnth
Click to expand...

That was my logic and why the service manual confused me, I'm going to put it down as a translation issue and assume when they say exceed the limit they actually mean smaller than the limit.

Pulled the rest of the valves and the keepers look fine, hard to tell if the damage to the failed valves' keepers was due to wear or them bouncing around for a while after the failure, either way I've ordered a full new OEM set of springs/keepers to be on the safe side as these are almost certainly the original factory ones.

Seems like a good excuse to check everything else and give it a good clean while I'm at it!
 
Tune-A-Fish said:
Of course not, but there is some cheap stuff that you should steer clear of. I won't mention names, but I have pulled valves that sucked up in the seat with very low hours and retainers that sucked down through the springs. good parts are never cheap.
Click to expand...
I have an idea who you are referring too. Biggest problem I've encountered with the Ti is with SOB retainers using 13mm shims. They egg out and the shim gets loose. I have had better luck after DLC treatment.
Funny thing is I have seen OEM hard anodized aluminum retainers under the same conditions come out mint....the Japanese have their shit together. Here is proof....these are steel

http://shop.yoshimura-jp.com/en/product/syousai.php?id=1604
 
Yes, Yosh knows rotating mass as well as any and that is skeletonized "tool" steel at it's finest.

These guys do a bang up job also:
http://www.ferrea.com/product_images/catalog-file-3.pdf
 
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