Author Topic: iron vs Aluminum piston weight  (Read 225 times)

38ac

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iron vs Aluminum piston weight
« on: October 30, 2020, 12:19:07 AM »
The discussion below about piston weight made me curious enough to weigh some. A std bore cast iron R.A. Lister piston with pin and ring package weighed 9 lbs, 9.2 oz , an India aluminum piston with same components came in at 4 lbs 7.6 oz and an India iron piston weighed 9 lbs, 5.8 oz. You KG types will have to do your own conversion but by any system the iron piston weighs in over double it's aluminum counter part. Somebody a lot smarter than me could do the math for the inertia loads but your engine is starting and stopping that piston 20 times per second @600 RPM. The extra inertia involved at 850 RPM concerned R.A. Lister enough to lighten the pistons for the 8/1 and at the same time upgrade the big end bearing materials. In its favor the CS has a very long rod vs the stroke and the resulting rod ratio reduces the forces at each end of the stroke.
I certainly cannot argue with the success reported previously with higher speeds and iron pistons but I also have to think that Lister didn't change the piston material on a whim? Thus when iron piston engines leave my little enterprise the owners are cautioned to keep them under 650 RPM.

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veggie

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Re: iron vs Aluminum piston weight
« Reply #1 on: October 31, 2020, 03:03:50 PM »
38ac,
That's good info.
Thanks for taking the time to weigh and report it.
I would agree that doubling the piston weight must lower the limits on the reciprocating frequency.

One way to compensate for heavier pistons at higher rpm is to increase the weight of the crankshaft counterweights to offset the increased inertia loads at each end of the stroke. Has anyone notice larger counterweights on the higher rpm cast piston engines.?
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38ac

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Re: iron vs Aluminum piston weight
« Reply #2 on: November 01, 2020, 02:49:42 AM »
I don't have the figures but back when I was learning how to balance one of these engines I checked the off set weight in a Lister 6/1 spoked flywheel vs an 8/1 disk type and there was definately less offset weight in the 8/1 flywheel.  That being said a 6/1 with spoked flywheels will run very smoothly with an aluminum piston at 650 RPM but dereriates quickly above that.
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dkmc

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Re: iron vs Aluminum piston weight
« Reply #3 on: November 05, 2020, 01:00:27 PM »
Once again Butch, thank You for your generous contributions on this forum