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Old 01-25-2006, 05:37 AM
Garbonzo Bojangles's Avatar
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Compressed Valve Spring Fatigue

I have a 400 sbc is storage. It's a street motor and makes about 500 hp. It's got AFR 195s, solid lifters, Comp roller rockers, and Comp 986 valve springs (125 lbs seat, ~320 rate). Was assembled Jan 05. It's been sitting for about 3 months now, and I'm just wondering if the valve springs will be okay if I let it sit until spring. I know all of them are actually compressed a bit when installed, but there are also some on peak lift (.52") and could fatigue faster over time. I suspect they will be okay for 4 more months, but what do you think?

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Old 01-25-2006, 05:44 AM
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Should be ok but if you can get to it put a wrench on it and turn it over one time, it'll compress some different springs and also help the rings from getting minor rusting
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Old 01-25-2006, 05:53 AM
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springs

When i put my roll cage in my 66 it sat in my shop for over a year. I never backed the rockers off. I started it and it ran fine made a few passes no problems... i then checked the seat pressure on the springs and all of them were the same as when i assembled the engine....

So IMO i don't think there is any issues with it sitting...

Keith
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Old 01-25-2006, 06:22 AM
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I maybe wrong in my theory {& it is before noon so } but metal fatigue happens from multiple expansion & contraction{stress} of metal especially metals that are not designed to go back & forth as SPRING STEEL is made to move .
I couldn't Begin to explain the difference I just know that there is.

I understand your concern with the big cam but typically motors have sat for years & started up & run fine

well there is my $.02 & my MHO

Good luck


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Old 01-25-2006, 07:13 AM
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Dude it is best to back off the springs that are open.

It is easy to do and no one can argue that it will do more harm than good.

Unless you forget and start it up. LOL
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Old 01-25-2006, 03:37 PM
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Thanks for the advice guys. K-star, that is exactly what I wanted to hear. I'll leave it for a while. I would back the rockers off but it is very inconvenient to get there, especially since the lady who owned the place just died... I planned on starting it every few weeks, but that never happened.
Oh, I know "fatigue" is not the best word to use, but it got the idea across I guess.
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Old 01-25-2006, 05:41 PM
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I don't believe that your springs are suffering because of inactivity.

Think of a valve spring like a piece of wire. If you bend it enough, it will wear out and break. If you merely place a load on it and keep that load applied, it will not do any harm to the material, particularly for the amount of time you are talking about.

Now, over eons of time, that might be a different story.
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Old 01-25-2006, 06:36 PM
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I also believe those springs will be fine for now. If they were 325# seat and 800-900# over the nose, I'd go ahead and back em off some after each weekend.
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Old 01-25-2006, 06:44 PM
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If it were a new rebuild I would be more concerned with the rings marking the cylinder walls... Ring tension in a freshly honed cylinder can cause marks in them and cause some compression leakage... Also as for the springs if the lift of the cam is not to excessive (like .600+) it should not be a big issue... But a once in a while crank turn 180 degrees should help...

Dont quote me on this but more than one machinest has told me this (about the cylinder walls)...
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