Valve springs parked to death

[raz]

This is a silly little theoretical topic that has tumbled around among my few brain cells for a while, while commuting in a cage. I can't really figure it out myself. Not that I need to know I can't even figure out why I'm asking this.

 

Say you find an Ambo that sat 25 years in a barn. Say the cam just happened to have stopped in a position where some valve springs were at more or less max compression.

 

Compare that scenario to the Ambo in the neighbour barn that happen to have settled in a position where all springs are at max rest.

 

And now, the 10.000 rubel question: will the springs that were compressed be ruined? How ruined? How bad is it, doctor? Would it matter if it was three or fifty years?

 

And, for the non-metallurgists, a slightly different question: what are the odds of either of this happening?

 

[Guest ratchethack]

It's a reasonable Q, Raz. As far as the odds -- are you a betting man? Fancy games of pure chance? Craps? Roulette? Wot you've suggested has been the death of many a valve spring. The length of time it takes to root the spring is exactly as you've thought. It would depend on if a particular valve is left open, and how far. They usually have tolerance specs for free length and/or load. The Guzzi manual spec's the following for V11's:

 

OUTSIDE SPRING:

 

free length, 40.3 mm -- packed length, 21 mm

load of 20.33-22.47 Kg at 35 mm (valve closed)

load of 60.8-67.2 Kg at 24.4 mm (valve open)

 

INSIDE SPRING:

 

free length, 37.9 mm -- packed length, 19.6 mm

load of 9.215-10.185 Kg at 33.5 mm (valve closed)

load of 31.35-34.65 at 22.9 mm (valve open)

 

Most of the manuals I'm familiar with simply spec a free length tolerance, outside o' which you pitch 'em. I've pitched a fair number myself, including on a current moto, which suffered a blown head gasket at the hands of the PO, a likely symptom of overheating, which apparently took the temper out of an exhaust valve spring whilst in process of warping the head. (I resurfaced the head meself on the tried 'n true plate glass with series of wet 'n dry paper method, as I have done with several others.)

 

[BrianG]

Sorry Ratch.... ol' buddy but your clearly off in the toolies on this one. That is IF the springs are made out of high quality spring steel, which I'll assume good old Guzzi parts are.

 

Fact is that spring steel fatigues from motion. It is the repetitive stress of the load-unload cycle that does in the crystaline structure of the metal. A good quality spring compressed to any point short of deformation will not take a set.

[pete roper]

I've never actually given it much thought? I'd simply take the buggers off and measure 'em. If they were out of spec or if there was a significant difference in free length between any of 'em I'd throw 'em away

 

No need to take the heads off even, just do the indian rope trick and use a push compresor on the caps to get the poxy collets off.

 

Of course if it's been sitting for 25 years I'd take it to bits whollus-bollus anyway to clean the earwigs out of it!

 

Pete

[mike wilson]

Errr.... even when the valves are closed, the springs are compressed......

[Guest ratchethack]

Sorry Ratch.... ol' buddy but your clearly off in the toolies on this one. That is IF the springs are made out of high quality spring steel, which I'll assume good old Guzzi parts are.

 

Fact is that spring steel fatigues from motion. It is the repetitive stress of the load-unload cycle that does in the crystaline structure of the metal. A good quality spring compressed to any point short of deformation will not take a set.

Well Brian, I'm not sure your assumption is necessarily warranted here. It seems you're putting 40 year old Guzzi valve springs in the same category with today's springs. Since the days of the mighty Ambo, generally speaking, valve spring manufacturing and performance have improved a great deal. As far as motion being the only possible cause of spring fatigue, and a fully compressed spring (valve fully open) left for decades in a barn being immune from fatigue? Seems more'n a bit implausible. It'd be a new one on me, and contrary to wot many have observed upon restoring old motors (myself included -- a Norton and a BSA from the '60's come to mind, British spring steel of that era not being the best, not to mention US and European 4, 6 and and 8 cyl car motors of the same era), but then I learn somethin' new here every day. . .

[GuzziMoto]

The question is not whether the valve springs are still good but rather whether or not the valve being open will sitting for a long period of time would make a difference in whether or not the valve spring still being good or not.

And the answer is it should not matter.

[Skeeve]

I'm w/ Pete: if it's been sitting 25 years in a barn, you're going to want to do a partial tear down anyway just to get the accumulated munt out of it; just replace the dang springs as a preventative measure & be done with it!

[raz]

I was thinking a really anal winter preparation (you know, wheels off ground, new cheapo oil inside that you will replace after just a thorough warmup etc) could include that you find a home-brewn mark at the flywheel where all valves are closed. I'm not saying I would do it (I don't do much of the other stuff except drain the polluted oil immediately) but it would be pretty easy.

 

But now that I think of it, if I'm not mistaken there is no such spot in the 720 degree cycle on a Guzzi. If there was, it would be a nice place to set the engine at when setting the valve clearance.

 

 

I need a ride. Not far away now. Bike is almost done, temperatures are climbing.

[BrianG]

Well Brian, I'm not sure your assumption is necessarily warranted here. It seems you're putting 40 year old Guzzi valve springs in the same category with today's springs. Since the days of the mighty Ambo, generally speaking, valve spring manufacturing and performance have improved a great deal. As far as motion being the only possible cause of spring fatigue, and a fully compressed spring (valve fully open) left for decades in a barn being immune from fatigue? Seems more'n a bit implausible. It'd be a new one on me, and contrary to wot many have observed upon restoring old motors (myself included -- a Norton and a BSA from the '60's come to mind, British spring steel of that era not being the best, not to mention US and European 4, 6 and and 8 cyl car motors of the same era), but then I learn somethin' new here every day. . .

 

No assumption.

 

A spring compressed to any point short of deformation will not take a set.

 

 

Implausible to the non-engineer or not Ratch.... it's the fact.

[raz]

No assumption.

 

A spring compressed to any point short of deformation will not take a set.

 

 

Implausible to the non-engineer or not Ratch.... it's the fact.

I didn't know that. That is good to know and it makes my idea even more silly

[Greg Field]

On an Ambo that's sat for 20 years, it's the cylinders you need to be concerned about.

[Guest ratchethack]

. . .IF the springs are made out of high quality spring steel, which I'll assume good old Guzzi parts are.

No assumption.

 

A spring compressed to any point short of deformation will not take a set.

 

Implausible to the non-engineer or not Ratch.... it's the fact.

Brian, I think the assumption you made above is key here. Look. My object here is not to challenge you personally on this (after all, it was you who challenged me -- and I welcome it! ), but to learn the facts and conventional wisdom, and discover at overview level a little about the state of valve spring engineering as it relates to our Guzzi’s and that of a bygone era. I DO NOT wish this to become some sort of a “I’m right and you’re wrong” pissing contest. As far as I'm concerned, the question Raz posed is a good one. It presents another learning opportunity first and foremost, as does much of what I find here on the ol’ Tech Forum. Now this isn't directed at you, but I recognize that not everyone here comes here to learn, and I also recognize that very few care enough to do any research at all on technical stuff, and many more couldn't care less. I figure exploring and sharing qualified, credible knowledge is a primary puppose of this Tech Forum, but that’s just me. You can take this any way you want, but I'm hoping you won't be offended that I'm sharing wot I've learned here, thanks to Raz' question.

 

Again, I’m no Engineer, was never trained as such, and for the most part, I'm happy to defer to those with proper Engineering credentials on this kind of thing. But do I have the fundamental science behind engineering down pretty well by both academic training and by actual experience, admittedly shade-tree though it has been, and I find this often allows me at least a working-grade comprehension of stuff published by qualified Pro's (see below), which is always of interest WRT Guzzi's, at least as far as I'm concerned.

 

After reading a bit, it seems that for all practical purposes, relative to the question Raz posed in his opening post above, according to the source below, overall, we’re both generally correct to some extent. However, your blanket statement that you've presented as engineering fact, "A spring compressed to any point short of deformation will not take a set." appears to be incorrect, and "taking a set" would appear to be an entirely separate concept from what Raz asked about, and separate from "spring fatigue" as well -- the correct term being "relaxation" (see below).

 

According to the source below, coil spring technology (which -- again -- was not as “mature” in the days of the mighty Ambo as it is today), it's not all that simple to answer the question, and relative to current technology, you may be more correct here than myself. However, the question was posed relative to the technology of the 1960's.

 

There are numerous “dependencies” involved, 4 of which are identified below. Certainly, I think it’s fair to say unequivocally that what was generally considered “high quality” in a valve spring in the ‘60’s would be considered sub-par relative to what is generally considered “high quality” in a valve spring today. IMHO this is makes a critical difference, not only to the correct answer to Raz's question, but to all of us who're as sincerely interested in such things as Raz.

 

FWIW, here’s the gist of wot I’ve added to my understanding from sources indicated:

 

SPRING TERMINOLOGY

 

http://www.rockfordspring.com/springterminology.asp

 

SPRING FATIGUE (fundamental concepts)

 

http://www.rockfordspring.com/springfatigue.asp

 

RELAXATION OF SPRINGS

 

Most springs are subject to some amount of relaxation during their life span even at room temperature. The amount of spring relaxation is a function of

 

• the spring material

• the stress the spring is exposed to

• the temperature

• the amount of time the spring is exposed to the higher stresses and temperatures.

 

This relaxation is usually less than 1 or 2% at room temperature, but can be much more when the spring is exposed to higher stresses or higher temperatures.

 

Relaxation is different than ordinary set. A highly stressed spring will set the first several times it is pressed, but within 5 to 10 cycles it has set as much as it is going to set.

 

Relaxation of springs is a function of a fairly high stress (but usually lower that required to cause set) over a period of time. A spring held at a certain stress will actually relax more in a given time than a spring cycled between that stress and a lower stress. The reason is that it spends more time at the high stress.…

 

Rockford Spring Company has charts for several materials and temperatures. … For situations where the charts do not cover the specific case, we can do accelerated spring relaxation experiments for specific springs. This is done by measuring relaxation at short intervals such as 1 hour, 5 hours, 10 hours, 50 hours and 100 hours and then plotting % relaxation vs. log time. The resulting graph can be extrapolated to 5, 10, 20 years or longer to predict the % relaxation at the design life of the spring.

 

Relaxation in service can be virtually eliminated by 100% heat setting the springs. Heat setting involves holding the spring at a high stress at an elevated temperature and causing the spring to undergo all the relaxation it would be expected to see over it's lifetime. We would coil the springs longer, allowing for the heat setting operation. After heat set, the loads would be at the required specification, and would stay there for the life of the part.

 

SOURCE:

 

http://www.rockfordspring.com/relaxationofsprings.asp

 

Rockford Spring Company

3801 South Central Avenue • Rockford, IL 61102

[Steve G.]

Brian, I think the assumption you made above is key here. Look. My object here is not to challenge you personally on this, only to learn the facts and conventional wisdom on this, and to discover at overview level a little about the state of valve spring engineering as it relates to our Guzzi’s relative to that of a bygone era. I DO NOT wish this to become some sort of a “I’m right and you’re wrong” pissing contest. For me, the question Raz posed is another learning opportunity first and foremost, as is much of what I find here on the ol’ Tech Forum. Now I recognize that not everyone here comes here to learn, and I also recognize that very few care enough to do any research at all on technical stuff. I figure this is a primary puppose of this Tech Forum, but that’s just me. You can take this any way you want, but I'm hoping you won't be offended that I'm sharing wot I've learned here.

 

Again, I’m no Engineer, was never trained as such, and I'm happy to defer to those with proper Engineering credentials on this kind of thing. But do I have the fundamental science behind engineering down pretty well by both academic training and by actual experience, admittedly shade-tree though it has been, and I find this often allows me at least a working-grade communication capability with stuff published by qualified Pro's.

 

After reading a bit, it seems that for all practical purposes, relative to the question posed in the opening post above, according to the source below, we’re both correct. It would appear that from the perspective of the latest coil spring technology (which -- again -- was not as “mature” in the days of the mighty Ambo as it is today), you would be more correct here than myself. However, the question was posed relative to the technology of the 1060's.

 

There are numerous “dependencies” involved, all of which are identified below. Certainly, I think it’s fair to say unequivocally that what was generally considered “high quality” in a valve spring in the ‘60’s is considerably different than what is generally considered “high quality” in a valve spring today.

 

FWIW, here’s the gist of wot I’ve added to my understanding from sources indicated:

 

SPRING FATIGUE (fundamental concepts)

 

http://www.rockfordspring.com/springfatigue.asp

 

RELAXATION OF SPRINGS

 

Most springs are subject to some amount of relaxation during their life span even at room temperature. The amount of spring relaxation is a function of

 

• the spring material

• the stress the spring is exposed to

• the temperature

• the amount of time the spring is exposed to the higher stresses and temperatures.

 

This relaxation is usually less than 1 or 2% at room temperature, but can be much more when the spring is exposed to higher stresses or higher temperatures.

 

Relaxation is different than ordinary set. A highly stressed spring will set the first several times it is pressed, but within 5 to 10 cycles it has set as much as it is going to set.

 

Relaxation of springs is a function of a fairly high stress (but usually lower that required to cause set) over a period of time. A spring held at a certain stress will actually relax more in a given time than a spring cycled between that stress and a lower stress. The reason is that it spends more time at the high stress.…

 

Rockford Spring Company has charts for several materials and temperatures. … For situations where the charts do not cover the specific case, we can do accelerated spring relaxation experiments for specific springs. This is done by measuring relaxation at short intervals such as 1 hour, 5 hours, 10 hours, 50 hours and 100 hours and then plotting % relaxation vs. log time. The resulting graph can be extrapolated to 5, 10, 20 years or longer to predict the % relaxation at the design life of the spring.

 

Relaxation in service can be virtually eliminated by 100% heat setting the springs. Heat setting involves holding the spring at a high stress at an elevated temperature and causing the spring to undergo all the relaxation it would be expected to see over it's lifetime. We would coil the springs longer, allowing for the heat setting operation. After heat set, the loads would be at the required specification, and would stay there for the life of the part.

 

SOURCE:

 

http://www.rockfordspring.com/relaxationofsprings.asp

 

Rockford Spring Company

3801 South Central Avenue • Rockford, IL 61102

 

You must get alot of time to kill at work Ratchet.

Steve

[Guest ratchethack]

You must get alot of time to kill at work Ratchet.

Steve

Indeed I often do.. I kinda like it that way. . . You too, eh, Steve?