Chilled cast iron piston casting

[brickyParticipant @bricky]

I am building the Centaur gas engine and had problems with the cylinder liner being chilled along the mould joints.This caused an oval bore which took many hours to hone true.I have the same problem with the piston casting but it is 1/2" of the circumferance of the skirt.I am osing aTC tipped Knife tool but it is not cutting properly over the chilled area .Has anybody got an idea what to do,I am desperate for advice.

Frank

[brickyParticipant @bricky]

[mark mcParticipant @markmc72333]

Chuck it in there fire, no really. Have you a stove or fire at home, put it in and leave it in the fire till next moring to cool in the ashes.

[brickyParticipant @bricky]

I have had it in the fire and left it for hours then buried it in some kiln dried sand until cooled.The chilled area has migrated to the end of the casting or was at the end as well as the seams.Should I try again?

Frank

[JasonBModerator @jasonb]

The extremities and thinnest parts will be the most prone to chilling so it sounds like you have started to cure it but the end being the hardest still needs a bit more heating. Is it getting to a bright red as that is the sort of heat that you need.

[brickyParticipant @bricky]

I have had it in the fire overnight and then cooled it in a bucket of ash.Nearly there a third is still chilled so I am making progress.I have taken it to bright orange with my torches and buried it in the ashes,fingers crossed I might get a result.

[brickyParticipant @bricky]

The piston is now 1/4" chilled on the skirt I am thinking of changing tack and using a steel piston ,as it has piston rings I hope that differing expansion rates won't be a problem.

Frank

[MichaelRParticipant @michaelr]

I made a alloy piston for my Centaur, it works well in the cast iron liner.

Mike.

[old AlParticipant @oldal]

Send it back

[Ian S CParticipant @iansc]

Get an old window weight, I use them. I did have one of those that was chilled, I knew that when I dropped it, and it shattered, but try and get as fat as you can, it's the skinny ones that are a problem. Some weights are rubbish, but most seem ok, and if you don't have to buy them even better. This is the power section of my stove top fan motor, the piston is made from window weight cast iron, and is 30 mm diameter. Ian S C

[KWILParticipant @kwil]

The sure way is to heat it up in a temperature controlled furness, up to the correct temperature, hold it at that temperature for a prescribed period to ensure it is heated right through and then allow the temperature to drop, also in a controlled manner over a period much longer than you would think. Find somebody with such a furness or make a bar new piston from continuously cast iron bar.

Incidently if you have sufficient thickness available, a carbide insert tip is capable of taking a cut deep enough to get under the chill depth.

[MalcBParticipant @malcb52554]

Hi, just as KWIL has outlined really.

Dont know where you are located but if you can find your nearest profile cutting shop you could ask them if they would kindly drop it in with their next stress relieving batch.

It's not normalising as its only soaked at about 600 deg C but cooling will be controlled at 50 deg C per hour.

[John Gregson 1Participant @johngregson1]

Re grind a tungsten carbide tip to a sharp point . Run at low revs and get under the chill, or buy diamond tip.

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