How to / DIY > Engines

valve stem end and cap hardening

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mobile_bob:
 have an old book outlining how valve stem ends are hardened, not sure about the caps, as i have not held one in my hand.

the valves are stood up in the bottom of a pan, fill with water up to just over the stem top, about 1/8" above
using an oxy/acet torch the end is heated dull red, the torch flame will displace the water, when the flame is removed the water will rush back over and quench the end of the valve.

this method will provide approx 1/16 of hard face without hardening the rest of the stem or distorting it.

my bet is the caps can be done the same way, then reground and polished smooth.

anyway that is how i would do it

one caveat,,, the metallurgy of the cap will have to be of sufficient carbon content to harden using this method. if it is too low it will not harden in this manner, and will either have to be case hardened or made of a steel with sufficient carbon,

bob g

Doug:
I once saw a video of a shop in Pakistan making guns. They case harden parts by wraping the steel in leather, sealing that in clay and roasting the Clay in a forge. I don't know how much carbon migrated to the steel or how well this works....

Doug

hotater:
Doug and all---

Heat-treating is a distinct art.   FIRST you have to know what steel you're dealing with.

Pushrods made in India seems to be a generic 80-100 points carbon steel, for the purposes of heat-treating.  MUCH different than the commercially used 'blow the water away' process descibed above.  It works too good on the steel we're dealing with.
 Harden ONLY THE ENDS!!!

Here's a simple to do, home process for that steel. 

Polish the part to it's final finish before hardening. 

Use an oxy-act torch with a NEUTRAL flame...this is important.

It's best to be out of direct light...a corner of the shop is ok.   Have an open topped quart of ATF or hydraulic fluid within a foot of the part.  SPEED is as important as HEAT.

Stick a small magnet to the part being heated...wave the torch and turn the part so that it's evenly heated.  When it reaches the 'temperature of transformation' (about 1750 F) the magnet will fall off.  Go a *little* hotter than that, but not much.  Make sure it's the same, even color all over and QUICKLY, without cooling, plunge the part into the oil so that the part is at the center of the can, swish it around a little.

The part is now *hardened* to it's near maximum hardness.  (hardness, to a certain extent, depends on the quenching medium.).  Rockwell 60C is what you'll have and nothing but a new file will 'grab'.  A file should 'skate' over it.

If it ISN'T hard it means,  1) it wasn't hot enough, 2) the part has insuffiecient carbon to harden it.

This hardness is ALL the way through the part and it's very BRITTLE.  It needs to be 'drawn' or 'tempered' back a bit.

Re-polish the part,  GENTLY and carefully wave the torch along the shaft of the pushrod and out to the end, but back WAY off... all we're looking for is about 450 degrees which will show up on a *polished* part as a 'straw' color.  This temperature needs to be constant all the way through the part, not just the surface, so take your time and slowly build it up and watch for the color.  The first will be a very slight yellow, then straw, then turning to a near purple before fading into bright, then pale blue at about 850 F. Blue is 'spring temper'.   We want a medium straw color.  The resulting hardness is about 55 RC which is the same as a saw blade or knife blade.
   When it turns straw, Quench it in the oil again.

IF the part does not have enough carbon it's time to "Case Harden".  That involves holding the part above the transformation point in a high carbon environment.  Leather, charcoal, cyanide, and ammonia atmosphere all work, but there CAN'T be oxygen.  The easiest for the home mechanic is a grainy powder called  "Casenite", I just saw some at the local Norco welding shop.  Follow directions.  HAVE GLASSES USED FOR GLASSBLOWING HANDY.  Others will NOT work.  I do this for a living and I'm still using a can of Casenite that's now 40 years old!

Point of reference--  Water quenching makes steel harder---and much more brittle.    Hence the instructions above.   Water is used on steels having less than 60 points carbon.

To "anneal"  (to make dead SOFT) a hardened carbon steel, heat it to and just above the temperature of transformation and plunge the part into dry lime.  Pack the lime around the part and wait an hour.  It'll still be HOT, but it'll also be as soft as it'll get.

Doug:
I wish I could drop in on you and watch you work. Infact, it would be great to an entire group together and make a work shop of it all doing what we do best and build a genset....

This of course would be more than just a little difficult and expensive, but I suspect we could solve a lot of issues in a matter of days.

Doug

mobile_bob:
Hotater and all:

i hope i didnt lead anyone to believe this is a particularly easy thing to do,, from just reading the post... only that it can be done.

not knowing the metallurgy of the part, and the small nature of a valve cap make for a little bit of a hassle to get right.

having spent some considerable time, behind a coal fired forge, and anvil, i learned how the processes are done,, but as Hotater has posted there are numerous and better ways of doing it.

i am left to consider though the following

the book i have has the directions and illustrations of a manufacture hardening the ends of a valve stem as described above, with the stems in water they cannot get up to critical temp and therefore are neither hardened or annealed,, just the very end is effected.

my thinking was perhaps doing the caps in a similar fashion would work,, that way the rest of the cap is not overly hard and in need to tempering and allow the face to be as hard as it will get.

the use of water was because of the acet torch being used,, one could not use oil
in this described procedure for obvious reasons, but a brine mix could be used to keep from
getting too brittle perhaps.

bottom line is one would probably be better off, making up new caps out of a known steel of known carbon content
and then harden, polish and temper as Hotater has described.

it is a very interesting process, i have done knife blades, custom cutters, and drill bits, chisels and punches etc.
it is a great art to learn.

i think i would like to try both methods, to see how effective the torch over water method might be,,, it seemed to work on valve stem ends,, perhaps sitting the caps ontop of a valve and trying it would prove out the concept,
failing that i would go the full route as described by Hotater.

good stuff,

bob g

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