# If/how to re-temper a coil spring end



## Joel_BC (Nov 10, 2009)

I'm doing some work on the mower portion of a John Deere lawn tractor. A coil spring snapped at one end, where the end of it had a hook formed in it to a slightly acute angle.

To give a sense of what it is, this spring is made from 10mm spring-steel wire, the coil is about 3/4-inch outside diameter, and the coiled portion is a bit over 3.5-inch long. Not "a really big spring" but not a tiny one either.

Using acetylene I extended a bit of wire out from the coil and then re-hooked the end. What I did _not_ do was quench the hot end in water or oil. I don't know enough about spring steel to know if I need to quench it in order to restore enough temper that the hook end will hold some shape.

I thought if it didn't really need to be quenched, then maybe I shouldn't attempt that - because I don't want the wire to become too brittle. If it's necessary to quench the hooked end, I can of course re-heat it. I don't have any fancy oils here (such as the "quenching oil" knife makers sometimes use), but do have motor oil on hand.

So I'm looking for advice about this.


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## nosqrls (Jun 9, 2012)

I would of just gotten a new spring. Because what you have done is turned spring steel into mild steel and it will bend real easy now and you changed the spring rate of that spring. In my book that is asking for trouble every time I have seen this done it ends badly or in a new spring.


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## Joel_BC (Nov 10, 2009)

nosqrls said:


> I would of just gotten a new spring. Because what you have done is turned spring steel into mild steel and it will bend real easy now and you changed the spring rate of that spring. In my book that is asking for trouble every time I have seen this done it ends badly or in a new spring.


Thanks for the reply. I get your point... almost didn't write the post here, asking for info. 

The John Deere dealership is over 200 miles away. There were numerous variants on the lawn-tractor model #170, so the dealer's parts dept sometimes has trouble supplying just the correct small part via a telephone or email order. And then it takes three or four days to get to me -_ unless they have to special-order it from the distributor_ (in which case it takes more).

Yeah, I would have just gone in and bought another spring, if I lived near a dealership and that was an easy thing to do!


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## ace admirer (Oct 5, 2005)

reheat it to maybe an dark orange color, quench in what ever oil you have around,burnt motor oil is fine. last i did was three days ago, broken mower recoil spring


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## wannabechef (Nov 20, 2012)

You have also made the spring rate stronger because you removed a coil, and depending on how well you kept the heat from the rest of the coils you likely weakened the coils closest to the hook you made. Your fix should be fine until you order a new spring but it will end up snapping.

I did similar on a mower and it lasted long enough to get a new spring.


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## Joel_BC (Nov 10, 2009)

ace admirer said:


> reheat it to maybe an dark orange color, quench in what ever oil you have around,burnt motor oil is fine. last i did was three days ago, broken mower recoil spring


Thanks. Yeah, I can do that.

Ace, have you found that working with coil springs in the way you describe can provide you with a long-lasting solution? Just wondering if the rehabilitated springs wind up breaking sooner than later ??


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## ace admirer (Oct 5, 2005)

as others have pointed out, the localized tempering , forming and rehardening is rough on carbon and steel structure. a truly neutral flame is needed on the torch, over heating could have burnt carbon in the spring steel, (did it spark?) the spring already has work fatigue. your rework doesn't make it a new spring, just workable, for how long? who knows but yes i have experienced many reworked springs last 4 decades so far.


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## Bret4207 (May 31, 2008)

I've done the same thing in "need to get by for today" scenarios. Sometimes they last great, other times....not so much. Consider going online to the JD site and figuring out exactly what spring you need. Then punch that number into your search engine. You'll probably get 35K hits, the first 100 of so will be Ebay items and lawn and garden suppliers- both likely less expensive then Mother Deere and often with free shipping. Running to the dealer is sooooo 1990's!


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## Bearfootfarm (Jul 13, 2006)

I'd consider just using a piece of stiff wire to attach to the end as an extension, since it will be impossible to retemper the spring.

The more you heat it, the more damage you'll do


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## ace admirer (Oct 5, 2005)

i think a good read of a artisan tool making/blacksmithing, 
book will alleviate some of the misconception here. 
www.anvilfire.com might be a good place to start.


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## Wis Bang 2 (Jan 12, 2010)

Growing up when trucks and autos used more leaf springs, the local spring shop would insert a new leaf into the spring pack w/ a new center bolt and would heat, re-arch and re-temper the whole spring pack. the pack came back looking like a new spring.

Someone mentioned that the spring already was work worn before OP annealed the end to bend a new hook. Work/time fatigue is a real consideration. Mack had huge 'camel back' leaf springs and when one broke they used to rebuild them in the 70's. By the 90's they would install a new spring and quickly learned that the weaker sister would break soon. Then we would replace both w/ new and save the old one and would put that one back in the next truck that broke a spring and the two old springs would last a long time.


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## davel745 (Feb 2, 2009)

When my belt tensioner spring broke I just took a pair of pliers and re bent a hook on the broken end. It has a little more pull but it works ok.


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## Joel_BC (Nov 10, 2009)

davel745 said:


> When my belt tensioner spring broke I just took a pair of pliers and re bent a hook on the broken end. It has a little more pull but it works ok.


The wire wouldn't have permitted it, in the case I originally posted about. It's about 1/10-inch dia wire, and _very stiff_ spring steel.

Update report: To everyone who took the time and thought to write, thanks.

I ended up "going by feel" on this one. I reshaped the spring so it would fit in-place again. Using a fairly small brazing-type O/A tip, I pulled a little wire out from the coil, straightened it, and hooked a new end. Getting the length and shape exactly right took a couple trials. I let the metal just air cool, as I thought I'd see how it behaved if I did _not_ try to temper it.

I was surprised to find that the remaining coiled portion acted like spring steel, even in the area that got very hot by proximity. Meaning, the whole spring acted like a tension-style ("_pull_ type") spring and there was no obvious loss of temper. The _composition_ of the steel wire seems to be where most of the sping-like quality resides. I put the spring back in place. So far, nearly three days later, it's still functioning. I have no idea how long it would work without breaking, though.

This has given me the time to zero-in on the part needed from the John Deere supplier. It was a complicated over-the-phone procedure, let me tell you! That's because the only manual I have for my machine did not give a part number for this spring, and did not even provide a verbal description of it. But the replacement is on its way. I should have it in less than a week.


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## ace admirer (Oct 5, 2005)

a big part of being a craftsman, besides true knowledge and developed skill is just doing it
i would have to see the repaired spring through to the ends, just for kicks


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