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Chilled cast iron piston casting

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bricky03/02/2016 21:46:51
567 forum posts
68 photos

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.


mark mc03/02/2016 22:14:13
92 forum posts
16 photos

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.

bricky03/02/2016 22:21:48
567 forum posts
68 photos

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?


JasonB04/02/2016 07:22:52
22555 forum posts
2634 photos
1 articles

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.

bricky04/02/2016 16:59:49
567 forum posts
68 photos

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.

bricky05/02/2016 07:43:58
567 forum posts
68 photos

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.


MichaelR05/02/2016 08:21:41
465 forum posts
73 photos

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


old Al05/02/2016 09:46:20
186 forum posts

Send it back

Ian S C05/02/2016 11:33:24
7468 forum posts
230 photos

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 Ctest 044 (640x480).jpg

KWIL05/02/2016 14:29:04
3546 forum posts
70 photos

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.

MalcB05/02/2016 17:55:49
257 forum posts
31 photos

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 105/02/2016 19:46:23
9 forum posts
3 photos

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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