Cast Iron Alternative?

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OllyM

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Hi folks, hoping you can offer some advice. I recently bought the plans for a 17.5cc single cylinder four stroke from CAD+Modelltechnik Jung in Germany. (http://www.cad-jung-shop.de/epages/62479729.sf/en_GB/?ObjectPath=/Shops/62479729/Products/00-Z0001-0). This is to be my first engine project, thought I should get a proven design under my belt before trying to draw up my own. Although the plans have no instructions, the drawings are all very clear and detailed, very happy with them. I've had to translate the material specifications from the German standards listed to UK or US specs, but that wasn't too tricky with Google's magical help.

The problem I've got, is that I really don't like machining cast iron, and this engine specifies a cast iron liner and steel piston ring. I'm already planning on swapping them around and using mild steel for the liner with a cast iron ring, but is there any other material I could use for the rings that would eliminate the cast iron completely? I read somewhere that high carbon steel rings are compatible with mild steel liners - does that sound right?

(I've machined cast iron before and it made a terrible mess of my lathe, plus it isn't the cheapest material to buy)

Thanks very much for any help. Will be starting a build thread once I begin cutting metal.

Cheers,

Olly
 

velocette

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Hi Duct tape the vacuum cleaner nozzle as close to the cutting tool as possible to collect the chips . Good luck making cast iron rings you will need a good quality cast iron. Years ago we had lawn mower motor with a die cast alloy crank case and finned cylinder in one piece with a Chrome plated bore alloy piston and malleable cast iron rings.
Eric
 

SmithDoor

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I use cast iron weight
There are some places that sell cast iron bar stock with high price but very good stock

From McMaster Carr a bar 2" OD and 6" long for about $20.00

There are other places to bars

Dave


Hi folks, hoping you can offer some advice. I recently bought the plans for a 17.5cc single cylinder four stroke from CAD+Modelltechnik Jung in Germany. (http://www.cad-jung-shop.de/epages/62479729.sf/en_GB/?ObjectPath=/Shops/62479729/Products/00-Z0001-0). This is to be my first engine project, thought I should get a proven design under my belt before trying to draw up my own. Although the plans have no instructions, the drawings are all very clear and detailed, very happy with them. I've had to translate the material specifications from the German standards listed to UK or US specs, but that wasn't too tricky with Google's magical help.

The problem I've got, is that I really don't like machining cast iron, and this engine specifies a cast iron liner and steel piston ring. I'm already planning on swapping them around and using mild steel for the liner with a cast iron ring, but is there any other material I could use for the rings that would eliminate the cast iron completely? I read somewhere that high carbon steel rings are compatible with mild steel liners - does that sound right?

(I've machined cast iron before and it made a terrible mess of my lathe, plus it isn't the cheapest material to buy)

Thanks very much for any help. Will be starting a build thread once I begin cutting metal.

Cheers,

Olly
 

WOB

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The standard set-up in the USA is mild steel cylinder bore(12L14 alloy or similar) with cast iron ring(s) on an aluminum alloy piston. If you only need 1 or 2 rings, you would be better off buying the rings since the tooling and materials for ring making are not worth the trouble for such a small number of rings. You might have to modify the original bore dia. a bit to match commercially available ring sizes, but it should not be a problem. For example: https://www.pmmodelengines.com/shop/gas/piston-rings/
You could also shop this site: http://www.antiquengines.com/Davis_Model_Suppliers_List_.htm

RWO
 

Entropy455

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Second that idea - you could always purchase finished rings, and build everything else. . . .
 

Jasonb

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You need to decide if you want to polish your machines all day or get on and make some engines. CI is so commonly used that you will end up restricting your choice of subjects to just a few that either don't need it or where you can buy rings etc
 

Jasonb

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Just looked at the drawings and spec sheet and it says GGG (Globularer Grauguss) for the liner which I'm almost certain is SG Iron and that machines far more like steel than grey cast iron so you won't get the mess.
 

OllyM

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Thanks Jasonb, that might help. I bought the English copy of the plans, and that just states cast iron with no further spec. I should also have mentioned that I'm in the UK. I've seen small quantities of "meehanite" cast iron bar on ebay for around £2 per inch in the kind of size I'd need. I can tolerate that for a few piston rings, but liners would quickly add up!

Will see if I can find any of the SG grade. Is that "ductile" cast iron? Would that make decent rings rather than liners?

Eric - I've tried clamping the nozzle of the shop vac in a spare slot in the tool post, and covered all the ways with rags and I still got hot iron powder everywhere!

I've considered just buying commercial rings, and that's always a plan B option, but I'd really like to do as much as possible myself. I know they'll be one of the trickier parts of the build, but I'm already going to cheat and buy a carb off the shelf ;-)

Thanks very much for all your feedback!

Cheers,

Olly
 

Jasonb

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M-machine have the SG Iron and also list it as GGG40 would only cost a couple of quid more than EN1A

http://www.m-machine-metals.co.uk/mm_cat_2011.pdf

Rings are not too hard to make I do all my own, you should not be getting too much powder unless you are taking tiny cuts, most should come off as chips

 

OllyM

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Excellent, thank you! I'd not come across M-machine before. I'll order up a bit of the SG iron once I've finished my lathe upgrade, see how it machines.

Cheers,

Olly
 

Wizard69

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Your goal should be to run dissimilar metals against each other.

As far as cast iron liners I’d say go for it and realize that at times you need a more aggressive cleanup afterwards. Grin and bare it in other words.

As for cast iron liners if there was something better we would have seen a rapid change to something different in industry. Even model airplane engines with Anodized cylinder walls leave a lot to be desired over castiron in my mind.

However anodized aluminum cylinders might be a good choice for you. It is a technique that does work leaving an extremely hard but thin surface on the aluminum. I’m not sure how hard castiron rings would work on such a surface though.
 

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