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Hit & Miss Gas Engine Discussion

Replacing Cast Iron Pistons with Aluminum


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  #1  
Old 08-14-2019, 07:34:25 AM
Joe Aletto Joe Aletto is offline
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Default Replacing Cast Iron Pistons with Aluminum

I have some of my engines running on newly machined 6000 series aluminum pistons. These pistons run the engines extremely well and can be operated at lower speeds.... Are there any disadvantages using aluminum pistons in these older engines?

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Joe Aletto
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Old 08-14-2019, 09:12:31 AM
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Brian Lynch Brian Lynch is offline
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Default Re: Replacing Cast Iron Pistons with Aluminum

I had a Cushman model X once with a aluminum Wisconsin VF4 piston in it. Worked perfectly, ran great. I see no problem with running aluminum pistons.
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Old 08-14-2019, 10:13:15 AM
J.B. Castagnos J.B. Castagnos is offline
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Default Re: Replacing Cast Iron Pistons with Aluminum

We use aluminum pistons in our marine engines, a four pound cast piston is under 2 pounds in aluminum, makes for a much smoother engine and is easier on bearings. The only disadvantage is cosmetics if it's visible.
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Old 08-14-2019, 11:04:19 AM
Tracy T Tracy T is offline
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Default Re: Replacing Cast Iron Pistons with Aluminum

unless you are lugging the crap out of it, i see no down side.
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Old 08-14-2019, 12:51:07 PM
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PistonRing PistonRing is offline
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Default Re: Replacing Cast Iron Pistons with Aluminum

Hi Joe-
If you are referring to the 6061 aluminum that is a bad alloy to use if you are going to do any real work with the engine and it gets hot. It expands like a rubber band with heat and will seize in the cylinder if you get it too hot. Do not use 6061 in a throttle governed engine that may work or get hot. Hit and miss may work if you don't run under any load if you fit the piston with sloppy clearances. I know of tractor pullers that have to have 15 to 18 thou cold clearance on a 6 inch 6061 piston and they get almost tight at the end of a run.
The only way to tell what you will get is to measure the piston cold, put it in an oven to operating temperature and measure hot. Better yet use scrap car or truck pistons or buy the right alloy. You need 12.5 to 13.5 % silicon content for temperature stability. Do your homework and research the alloy if you are planning on running the engine long enough to get it hot. If you see steam coming out of the water hopper your piston may be 250 to 300 degrees F and the piston may be growing. With the right aluminum alloy you can rest easy. Some modern car engines are fitted with 0.001" clearance on a 3 1/2" bore using the correct alloys. 6061 may do fine if you only run for 5-10 minutes and shut down. If you belt it up to a load it may get tight. When choosing aluminum for pistons look up the thermal stability of the alloy before hogging out chips. And figure out the correct cylinder wall clearance for final fitting so it doesn't have problems. It can be done as long as everything comes together and fits right.
Thanks,
Dave Reed
Otto Gas Engine Works
2167 Blue Ball Road
Elkton MD 21921-3330 USA
phone 410-398-7340
http://www.ringspacers.com
http://www.pistonrings.net
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Old 08-14-2019, 03:56:15 PM
Joe Aletto Joe Aletto is offline
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Default Re: Replacing Cast Iron Pistons with Aluminum

Thanks Dave ... I have been using 6061 because they are scrap ends from a machine shop I acquired for free. Which is the best aluminum alloy that you would suggest?
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Old 08-14-2019, 10:40:22 PM
uglyblue66 uglyblue66 is offline
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Default Re: Replacing Cast Iron Pistons with Aluminum

There is or was a company call EGGE that made aluminum pistons for the model T ford.I have them in 1 of my engines. I bought it freshly overhauled and had no idea what I was going to run into.
Turns out folks that bore the cylinders for these pistons were not being given the right bore size.this lets the piston get hot,gauld to the cylinder and makes for a mess.
What ever you use for aluminum to make them or buy them,make sure your cylinder is bored enough to allow for the rapid swelling.
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Old 08-16-2019, 11:47:04 PM
tdmidget tdmidget is offline
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Default Re: Replacing Cast Iron Pistons with Aluminum

Quote:
Originally Posted by Joe Aletto View Post
Thanks Dave ... I have been using 6061 because they are scrap ends from a machine shop I acquired for free. Which is the best aluminum alloy that you would suggest?

360 would be a good alloy for cast engine parts. It would be found in pistons, cylinder blocks, heads, and gearboxes. It flows well, resist corrosion and has the expansion characteristics that Dave mentioned.
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