Mixing up valve springs???

[Sam 78 GS750]

How bad is it to mix and match inner and outer valve springs? I kept them together with the valves since I took the engine apart. But when I took the head to get decked and valve seats cut, the machine shop gave me my parts back all mixed up in a bag.

Manual says they're a matched set, and they're sold in pairs. I really don't wanna spend 80 bucks on all new springs, and have to wait a week to get them b4 I can put my head back together... At the same time, if it's really that crucial and can mess up my engine, I don't wanna be stupid...

So what's the worst that can happen if the inner and outer springs are mismatched?

[Sam 78 GS750]

This is on a new head by the way... Not sure if that makes any difference.

[chuck hahn]

Ive never mixed them up so I dont have any sage advice. What i will offer is that you get a 12 spot muffin tin and mark one row "I" for intake and one row "E" for exhaust. then add numbers 1 through 4 above corresponding wells. When you remove intake 1 guts you put them in row I..number 1 and so on. The remaining 4 wells can be used for keepers or whatever.

[Steve]

Sounds like he might have done that, Chuck, but the machine shop did not keep them separated.

I kept them together with the valves since I took the engine apart. But when I took the head to get decked and valve seats cut, the machine shop gave me my parts back all mixed up in a bag.

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[sharpy]

What about spring tension on the old springs? are they within spec.

[bobgroger]

It's not going to matter. As Sharpy said, they should be checked to see if they are in spec by someone with the proper spring pressure tester. They ARE 35+ years old and many of them have been open for years of that time. If they are, put them back in. If not, or you don't test them, don't count on that last 1000 RPM before redline.

[Nessism]

I wouldn't worry one bit. Doesn't matter. Measure the height and tilt and as long as everything checks out, assemble and go.

[sharpy]

If not, or you don't test them, don't count on that last 1000 RPM before redline.

Oh its BEFORE the redline. opps

[GregT]

Measure them - free length. You don't say if it's a 16V or 8V engine.
If it's an 8V, the 4 longest outers and 4 longest inners go on the exhaust side.
If it's a 16V, the 8 longest outers and 8 longest inners go on the exhaust side.

You're in more danger of tagging an exhaust valve than an inlet so if you must use secondhand springs, best ones go to the exhaust side.

[Sam 78 GS750]

OK, so general consensus seems to be that a matched set doesn't really matter. The only thing I can think of that they would match for is combined tension between the inner and outer spring to come up with a number for overall tension pulling the valve closed...

I don't have a tool to measure spring tension, but free length for the couple I measured is about halfway between the "Standard" and the service limit. I'll measure the rest after work... I'm wondering now if I should just replace them anyway, to know that they'll be good for another 40 years.

If I understand this correctly, the concern is that the right amount of tension is needed to pull the valve closed completely for max compression, and also to pull the valve closed quickly enough at high RPMs so that it doesn't come into contact with the piston. Do I have that right?

[Steve]

Yes, that is the basic concept. You also have to keep in mind that, if the head was sitting for many years without the engine running, there was at least one or two valves that were being held open by the cam(s). Those springs have been held in a compressed position for YEARS, which might have reduced some of the tension on them. That is why you should really check tension, not just static height. Yeah, the height might be a bit less, too, but they will certainly have a bit less tension.

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[Nessism]

The risk is extremely low. Since joining this forum more than 11 years ago I can't remember even one case of someone experiencing valve spring failure on a stock build/restore. The GS1000 uses the same valve springs and those valves are heavier because they are larger and those bikes never have issues either.

[hannibal]

Yes, that is the basic concept. You also have to keep in mind that, if the head was sitting for many years without the engine running, there was at least one or two valves that were being held open by the cam(s). Those springs have been held in a compressed position for YEARS, which might have reduced some of the tension on them. That is why you should really check tension, not just static height. Yeah, the height might be a bit less, too, but they will certainly have a bit less tension.

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Never considered this.