Model Engine Maker

Help! => Specific Engine Help => Topic started by: Frank Boyle on February 05, 2016, 07:53:42 AM

Title: ic pistons
Post by: Frank Boyle on February 05, 2016, 07:53:42 AM

I have been having problems with chilled cast iron on the skirt of the ci piston provided for the Centaur gas engine.After the advice received I have heated the casting four times now and the chilled area has reduced each time but is 1/4" now.I want to know if I can use a steel piston as it will have cast iron piston rings running in a cast iron cylinder,or will differing expansion rates be a problem.
Frank

Title: Re: ic pistons
Post by: Jasonb on February 05, 2016, 07:58:04 AM

Should not be a problem, you can always make allowance for any expansion in the size of the piston.

Using cast iron bar or even aluminium would make for easier machining, Quite a few of the hit and miss engines I have made have aluminium pistons and don't have problems with expansion, just allow about 0.0025" per 1" dia of piston.

Title: Re: ic pistons
Post by: Ian S C on February 05, 2016, 12:35:54 PM

Frank, most of my hot air engines have pistons made from old window weights.  My pistons normally have a skirt about 1 mm to 1.5 mm thick, and a crown about 3 mm thick,  There is one on the work bench that was just too thin, it broke when I was putting the labrynth grooves around it .25 mm deep.  They wear well with little or no lubrication.
Ian S C

Title: Re: ic pistons
Post by: Brian Rupnow on February 05, 2016, 01:56:23 PM

I have 10 i.c. engines, and 9 of them are running cast iron cylinders and aluminum pistons with no problem.---Brian

Title: Re: ic pistons
Post by: Alyn Foundry on February 05, 2016, 03:52:36 PM

Hello Frank.

I have just been in the workshop to check if I had any stock left of the Gardner piston, I have several.

Having checked on Reeves site the casing would only require around 70 thou removal to suit an 1,1/2" bore.

If you're interested in a casting please let me know.

Kind regards, Graham.

Title: Re: ic pistons
Post by: Frank Boyle on February 07, 2016, 05:42:26 PM

Thanks for the offer Graham but I have decided that I will make the piston from steel.

Title: Re: ic pistons
Post by: Frank Boyle on February 09, 2016, 10:39:19 AM

The article on making the centaur piston says the little end should float between the gudgeon pin supports but does not give a measurement.Can I get advice on thie please.
Frank

Title: Re: ic pistons
Post by: Jasonb on February 09, 2016, 12:01:24 PM

Its a common thing on a lot of engines. The width of the slot inside the piston is wider than the width of the small end bearing so things can line themselfs up. So in the case of the Centaur you have a 3/4" gap and a 5/8" width of bearing, both these sizes are on the drawing