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Broken valve spring

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Riley View Drop Down
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    Posted: November-02-2014 at 11:33am
Last summer while cruising along in our Barracuda, the engine tone suddenly changed. The engine still ran well, although idled a little rough. We knew there was a problem and finally did a compression test which suggested #2 had a sticking valve. Eventually someone suggested checking the valve springs and sure enough one was broken. It appears that the dampner kept it from dropping down too far into the cylinder and the valve appears not to be damaged. We've replaced the spring and hopefully, we'll be good to go in the Spring. Not sure why it broke, possibly age or prior damage?

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MrMcD View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MrMcD Quote  Post ReplyReply Direct Link To This Post Posted: November-02-2014 at 4:01pm
Valve springs are made from Steel, the steel is a special blend and the wire is rolled out into lengths, they study it for defects as it is rolled out and most times they catch the defects before it is made into springs. If a defect gets in an engine it will eventually fail.
The length of steel rolled out is determined by a detected defect. The steel is monitored electronically as it rolls out and most times defects are caught. You just had bad luck.
If this is an old engine I would change the one spring, if it was recently rebuilt with all new springs I would change all 16 springs. I say this because if one is bad the whole batch may be bad.
The only other time I see broken springs is from over revving an engine.
When over revved the springs may coil bind, open till the coils are collapsed this can fracture a spring.
On a HD Truck engine over rev might be 6,000 RPM, on a Race engine over rev might be 10,000 RPM springs are purpose built and have limits.
Over Revving in a boat is not common since the prop limits RPM with constant load. Were you jumping wakes in this boat at full throttle with the prop coming out of water? Not likely.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GottaSki Quote  Post ReplyReply Direct Link To This Post Posted: November-02-2014 at 6:58pm
Like Mark sez, it happens

Had a rebuilt 68 302 in my 81 stang, broke a spring just going down the highway easy. Spring steel is funny like that.
Seems the oddity is the double-break, less that it happened at all.
"There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing."

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8122pbrainard View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: November-03-2014 at 8:49am
With my being in the metal stamping business for 20 years, I've seem plenty of broken springs. Failures were always due to exceeding the life of the spring or more common was exceeding the compressed length limit. A material defect will show up in relatively a short period of time which I feel is not the case with Bruce's engine. Spring wire whether round or square is made under very tight quality controls. Defects typically show up during the wire drawing process.


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Riley View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Riley Quote  Post ReplyReply Direct Link To This Post Posted: November-03-2014 at 9:48am
The engine has been rebuilt, but the springs were not replaced. I'm guessing they are the originals. They were tested for height and spring pressure before they were installed. It's possible we've floated them as we've run the engine up to 4700 and the redline is 4000-4400, depending on which manual you read. We get popping at 4700, and we haven't determined the reason, but valve float is one possibility that has been suggested. We haven't run it much at 4700, just full throttle bursts occasionally and it's been backed right off when the popping starts. When it broke, I had been cruising along in the 2000s for about a half hour. We've replaced it with an old spring that had the proper pressure and height. We will start it in the Spring and make sure it runs well and then replace all the springs. Right now I'm glad compression is normal in that cylinder. This is one more thing I'm learning about, and am surprised to learn that a valve job does not include all new springs. The springs do not bind, so hopefully as Pete suggests, it broke due to its age.
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