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Set in valve springs?

04/25/2009 9:41 AM

Do valve springs, or other cold loaded parts take a set? The question was raised on another forum because of a concern about valve springs taking a set in an engine that had sat for a few years- possible to the extent that the valve would float or the spring would break under use. Will the springs that have been loaded for a few years perform the same as the unloaded ones?

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#1

Re: Set in valve springs?

04/25/2009 1:37 PM

They will probably take a small set, but less than the manufacturing tolerance in the first place. Bear in mind these things have been manufactured pretty reliably for many years now.
If you were blueprinting an engine you'd possibly want to go into the parts store and select all the longest valve springs, other than that, it's hardly a consideration.

Del

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#2

Re: Set in valve springs?

04/25/2009 11:52 PM

I agree with Del; but it's worth noting that some racing engine springs will take a bit of a set from use in a lot fewer hours than would be acceptable for production road vehicles. This is especially true in older modified US rocker arm engines with a propensity to float their valves in competition. This valve spring checking was standard procedure in the old days of drag racing even with the best competition valve springs.

Rather than worry about whether or not valve springs take a set just go measure them. It's relatively easy to set up and do the measurement. You'll need a drill press and an old spring type bathroom scale or something similar. (New digital scales my be a pain to use with the way they want to reset themselves).

Chuck a 3/8 cap screw, a nut and a fender washer in the drill press to push the spring against the scale. If the surface of the scale is a rubber mat or something soft put a metal plate between the spring and the scale surface. Set the stop on the drill press to the exact height that is given in the spring spec. This may take a bit of creative thinking since it's not easy to get a dial caliper in there to measure and a simple machinist scale won't be accurate enough unless your eyes are pretty good.

Then just go ahead and check all the springs and if you have the patience mark the pounds on each spring with a fine sharpie pen.

Ed Weldon

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#3

Re: Set in valve springs?

04/26/2009 12:29 AM

Valve springs are compressed (loaded) even when the related valve is on its seat. That's why you need to use a valve spring compressor to remove and install valve springs. So any engine that is a few years old (whether or not is has been run) has valve springs that have been under load for those few years. The running engine has the disadvantage that the valve springs have also been flexed millions of times, subjecting them to fatigue.

I've worked on engines with valve springs that have been installed for 20 years which still meet their specs for installed length load.

The car will also be sitting on suspension springs that are a few years old, yet will still have essentially its original ride height.

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#4
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Re: Set in valve springs?

04/26/2009 2:38 AM

As a kid, my mechanic father had us do valve jobs for spare cash. As a result, I've removed and installed a s#*t-load of valve springs from some very old motors. Never once saw a bad spring.

If you want to test 'em, I suggest gluing them on the bottom of your tennis shoes, and then checking how high you can jump.

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#5
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Re: Set in valve springs?

04/26/2009 3:17 AM

I now understand why your Avatar is always jumping, its testing valve springs on its shoes for your Dad!!!

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#6
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Re: Set in valve springs?

04/26/2009 8:44 PM

No. That's just normal for him.

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#12
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Re: Set in valve springs?

04/27/2009 3:24 PM

Yeah, Andy! What he said!

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#7

Re: Set in valve springs?

04/27/2009 12:55 AM

I asked this question once to the people at Engle Cams and they said they were curious about that sometime back, so they clamped up a spring in a C clamp and put in a drawer for 20 years, when they checked it, it was still at original spec.......Always worrys me tho, I have a new motor in a boat that i have lost interest in always wonder what will happen when i start it. On the engine spring checkers are avalible tho, so check them that way......if you are still worried. By the way i would worry more about pre lubing the cam and lifters more that the springs loosing pressure.......

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#8
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Re: Set in valve springs?

04/27/2009 4:10 AM

Ya think this is a job creation effort?

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#15
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Re: Set in valve springs?

04/28/2009 10:28 AM

GA. I have always wondered if the springs on a stored engine that were on lobe would loose tension also. Thanks.

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#9

Re: Set in valve springs?

04/27/2009 10:47 AM

I gotta go with Ed on this one, when I helped with competition engines (never more than a wrench chaser) we would *match* them, but the concern wasn't with set over time, but rather matching what was within tolerance more closely.

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#10
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Re: Set in valve springs?

04/27/2009 12:05 PM

Hmmm, you agree with Ed, and Ed agrees with me, but narry a GA... serves me right for mentioning your pantyhose fetish.
Del

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#11
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Re: Set in valve springs?

04/27/2009 12:46 PM

Behave or I'll "Off topic" ya!

Wife has been trying to butter up a stray cat in the neighborhood - little dry foods, bowls of water, escalating to canned food, little pad on the bench she sleeps on - can't touch her. Lots of appreciation - no pets.

Yesterday she has to be gone late in the evening, way past normal snack time, well into dark.

Comes out at dawn with some canned food and gets a cat in the lap, lots of petting, purring.

Lessons:

1. Beware what you reward with anyone.

2. Especially with cats.

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#13
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Re: Set in valve springs?

04/27/2009 8:33 PM

I would compress them, both inners and outers separately, to installed height and zero the readout, then increase compression to the expected lift, Then line up the outers in descending order and next to them, the inners in ascending order and mate them. Then retest with a retainer to introduce the inner spring installed offset. I rarely found a difference of as much as 1%. If I did, it was a lot greater, indicating impending failure in my mind. After all that, I would burnish every surface of each spring with crocus cloth in an effort to diminish stress risers.

This was for street and race performance engines. For stock engines, I didn't worry about any of that unless it was high mileage, then I'd buy a new set.

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#14
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Re: Set in valve springs?

04/28/2009 6:07 AM

You should then finish them by painting Angels dancing around each helix using gold paint and the finest squirrel hair brush....

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#16
In reply to #13

Re: Set in valve springs?

04/28/2009 10:31 AM

Stock engines need to have springs tested as a precaution when done at a shop, because the shop has no way of knowing if the engine has overheated. Overheated springs will loose tension. One of the reasons for valve spring shims.

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#17

Re: Set in valve springs?

04/28/2009 3:19 PM

The valves springs are bathed in 80 to 125C oil. They mostly live in a 100C to 150C place. If they are worked hard, with no oil, will they get much warmer? I cannot see them running for long at 500C, which would be needed for a loss of temper. Steel does not soften at the temps that engine parts live in. Very old springs do get a bit shorter, but I had associated this with too many cycles, and very deep ones. If the heat harmed the spring's temper, think what the 500C would do to the gaskets, the important aluminum bits and so on.... Miles shorten springs, not years, IMHO.

David

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Andy Germany (1); Blink (1); bob c (2); bwire (1); Del the cat (3); dhgrant (1); Ed Weldon (1); edignan (2); Jaguar (2); the wrench (1); vermin (2)

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