Inner/outer valve spring contact, is there a special orientation when installing?

ahh911 · 12:31 PM

Hi,

A perhaps naive question. I installed some valve springs on the 911sc today, noticed afterwards that the inner and outer coils make contact with each other maybe two coils down from the retainer. I took it apart, flipped the inner spring and now there is a gap where they would have contacted. Besides having the more tightly coiled section of the outer spring nearest the head, is there a trick that is used to align/position the inner and outer springs relative to each other so they don't bind? I've searched online for 1/2 hour, I can't be the only one who's wondered about this, and they were seated right, I believe. (new german oem brand springs)

Phil

Walt Fricke · 10:13 PM

Never heard or seen mention of this - Anderson, Dempsey, Factory Manuals, posts, etc. What I do know (or think I do) is that the inner and outer are supposed to rub, and this acts as a damper, sort of maybe like the really old shocks which were friction disks with one rotating against a fixed one. Avoids harmful harmonics. So I'd say don't worry.

However, I believe that the distance between coils (maybe only on the outer) is not even - there is a tighter end and a not so tight end. And a convention for which goes where - I think tight goes against the spring seat? - because you save a bit of energy that way by not moving the heavier part as far. But maybe both are wound this way?

In my ignorance I have just plopped them in any which way the two times I have worked on my own valves to include removing and installing springs instead of sending the heads to a shop, concentrating on getting installed height right. Engine ran fine, didn't blow up, etc. But maybe I left a little bit on the table. Maybe search for which way is up for valve springs or some suitable search term.

brighton911 · 08-08-2020, 03:42 AM

No worries, the upper retainer & lower spring seat take care of the alignment for you. And yes, there can be contact between the two. In some engines (non air cooled), the inner spring is more of an interference fit to prevent harmonics. And in the case of some triple valve springs, there is a flat spiral wound "spring" that increases the friction fit, again to prevent harmonics. You are good to go!

ahh911 · 08-08-2020, 12:49 PM

Thanks Guys,

I put them in the retainer and swirled the outer one around till there was no contact and marked them. Then I installed them and ran a .3mm wire around the outer coil and had all of them contact free. I don't know, the contact might or might not be made otherwise, so this way at least it's consistent. As mentioned, the first time I rotate the engine the springs would probably make a twang sound and move into alignment anyway, but what the heck, you can really spend a lot of time doing very little on this engine. I have yet another post about new "Verbus" T marked rod bolts coming up, yet another time soak over slightest of details.

Phil

ahh911 · 06:02 AM

Another note, the new springs seemed to have an oval shape to them making for interference if not aligned, I had checked on installation with the original springs to see if they were oval, the one I looked at seemed so, but now that I checked a few more I'm not sure if the old springs aren't more circular, in which case there would be no contact between inner and outer I assume.

**** (EDIT: Removed a spring pair again to check for squareness and measured the circumference, new and old springs are not oval, at least for the purpose of contact between the inner and outer springs. Oval was a visual or optical illusion and contact between outer and inner springs most likely was just the way the springs were sitting, but don't know for sure. They were around 1/16 " out of square and I may have aligned the inner and outer springs to have their deviation from square characteristics in the same locations, may not be the right thing to do.)***

I've also heard of harmonics, how does one explain this? Do the eigenvalues of the two springs in our engines appear so close that the need for damping is required? I don't know how that would happen exactly, but I'd think it would require more precise spring tolerances then I saw so that a known contact point/points are guaranteed between inner and outer springs.

Phil