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Tractor Talk Discussion Forum

Valve Springs

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Jim

12-23-2003 16:00:03




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How can you tell whether a valve spring for the intake is worn out or not?




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buickanddeere

12-24-2003 07:22:07




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 Re: Valve Springs in reply to Jim, 12-23-2003 16:00:03  
Test it's free length then pressure at seat and full lift. Rebuilds without new valve springs or testing of old ones are false economy. Worn/reused cams,lifters,springs etc have doomed many overhauls.



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Wayne

12-23-2003 18:56:02




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 Re: Valve Springs in reply to Jim, 12-23-2003 16:00:03  
Jim, you don't say what kind of engine your working on here. For the sake of helping I'll assume it's a small engine of some type. Some brands have a compression release made in with the cam. It's designed to keep the intake open long enough to get the engine spinning over fast enough to start easy. At a certain speed centrifugal force takes over and kicks it out letting the valve close and the engine actually start. Like the other posts said you may be able to find a spec for the spring and test it (in some cases only if you have the right tools. It could also be the seat has worn enough to close up the clearance between the valve and lifter which will cause it to remain open. In this case you can usually grind the valve stem to regain the lost clearance. Hope this helps.

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Hal/WA

12-23-2003 18:03:17




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 Re: Valve Springs in reply to Jim, 12-23-2003 16:00:03  
If the valve is not closing all the way because the spring is too short for the valve it is on, the engine probably will not start. If the spring is too weak, the engine will "float the valve(s)" and have trouble gaining RPM's because of misfire.

But a more likely expanation is that the valve has been adjusted with insufficient clearance or the valve is stuck open. I have run into this problem and the engine just will not start.

A compression test should be an easy way to find out if there is a problem. If the cranking compression is way down from what it should be, maybe the clearance is a bit too tight. If you have adjusted the valves recently, check your work. An easy fix, if that is the problem. Good luck.

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Jim

12-23-2003 16:37:56




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 Re: Valve Springs in reply to Jim, 12-23-2003 16:00:03  
Would the intake valve spring being not to specs keep the valve from closing all the way, preventing the engine from starting?



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Ron

12-24-2003 21:38:16




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 Re: Re: Valve Springs in reply to Jim, 12-23-2003 16:37:56  
The valve will close with weak springs, but heat transfer is lessened--the valve runs hotter--and also, the valve may bounce on the seat, instead of closing tight on contact--causing accelerated wear, and lost power.. Since I usually build more power into my engines, I like the "seat pressure" to be at Least equal to the highest recommended for the application.



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CRUSADER

12-23-2003 16:28:41




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 Re: Valve Springs in reply to Jim, 12-23-2003 16:00:03  
If you look into the repair manual, you should be able to find the spec's for the springs. Take a measurment and you will know if they are within tolerances. You can also put them on a tester to check to see if they meet the required tension. Hope this helps you out a little.

Jim



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