[Kaleb]

I'm constructing a diesel engine (not the HCCI type used in model aircraft), but I'm not sure about the specific metals to use for the piston, cylinder and rings
I've been told that an aluminium piston is the way to go, but does it need to be a particular alloy? Will 6061 do the job?
The cylinder liner should apparently be cast iron, but should I go with grey or nodular cast iron
What metal is best for the piston rings? I'd assume some sort of heat treatable carbon steel.

[johan jorez]

hi,
could you not use piston and sleeve from a " real " engine like the Citroen xud
engine

[Kaleb]

I'm not sure if I could. The engine I'm building will have a 60mm bore. The only diesels I can find with that bore are some Chinese built engines, but I haven't seen those particular ones being imported by anyone here.



This is one of them. It's very different to the usual Yanmar copies. Haven't seen these in Australia (perhaps surprisingly).

[Till]

Originally Posted by Kaleb

I've been told that an aluminium piston is the way to go, but does it need to be a particular alloy? Will 6061 do the job?

You need material with low thermal expansion, because diesel pistons will become extremly hot. In therms of aluminum alloy, this means lots of silicon (plus it eases casting).
Second: With direct injection and acceptable power output, the piston will become f*cking hot. If you go with aluminum alloy, you'll likely need a shaker for cooling. Without the cooling, it'll become so hot it will become very unreliable under load condition. I'd choose an high silicon aluminum alloy piston with a steel insert for the combustion chamber. This is easy to manufacture, as the piston can be cast from scrap automotive pistons and the shaker could be easily turned on the lathe from the piston roof side. It will be closed afterwards by pressing in the steel insert, so it forms the desired donut shape

Originally Posted by Kaleb

What metal is best for the piston rings? I'd assume some sort of heat treatable carbon steel.

Cast iron is fine and you'll take great profits from the superior heat conduction.

[dieselpilot]

It's very unlikely that any model injected diesel, let alone a hit n' miss, will ever see temperatures high enough to worry about. Quite different than a marine or stationary engine running at full output for long durations. I do agree with high silicon alloy, but unless you use scrap to cast your own stock or piston, high silicon aluminum bar will cost more than an OEM Yanmar piston and far more than a Chinese copy. http://www.ebay.com.au/itm/Yanmar-L4...item4842a51ee0

[Till]

I didn't know the question was for a hit n miss engine. Diesel + hit n miss is a rather "strange" combination by the way...

[wings_of_fire]

The question is tough to answer if you need to make a reliable engine. 60mm diameter piston means a pretty big engine. I think you should get hold of a good IC engine book that has all the calculations explained. You need to solve this problem from a mathematical point of view before you do actual machining. This way you will get closer to your answer or else trial and error is the method.
In your calculations you might also come to know that its fine to use an aluminum piston based on the thermal calculations....and then comes the question of piston, rings and cylinder liner tolerances.

No matter what material you use, you should know its coefficient of thermal expansion. It changes with the material composition.To be sure of its co-eff of thermal expansion, you need to buy the material with the specific material composition, or you need to melt/forge it with the right composition. I doubt about getting the composition right at home in a personal foundry without being versed with using ferro-alloys.

Engine designing is an art because it has so many interwoven factors that need to be synchronized in balance. Not easy unless the process is organized.

[Mechanicboy]

There is plan of 20 ccm Lister diesel engine available and here is the model dieselengine.

http://www.youtube.com/watch?v=zXzqGHn0CDY

The cylinder can be made of cast iron or hich tensile steel with piston ring of cast iron and piston cast of old piston from scrapped diesel engine.

[Kaleb]

Would those be Listeroids by any chance? The design is very good, but they have a bit of a reputation for poor quality control. Most of them have to be dismantled to check for problems like casting sand in the crankcase and poorly aligned valve tappets, among other things. So I am a bit wary here. Also, I'm only looking to build one engine.

[Mechanicboy]

Originally Posted by cynthiamyra

Don’t have much experience. But all I can suggest is use wear resistant metal for making piston rings. Because as they move up and down the cylinder bore due to their own load and due to the gas load acting on the rings. You can use Cast iron is also a low thermal expansion material which can bear high temperatures when diesel pistons work. On the other hand steel is also a good choice.

However, if you want an accurately designed engine parts with accurate specifications you can go for professional manufacturers. There are many vendors available in market which can help you in this matter. For example - http://top-seiko.com/guide/low-therm...ion-materials/

Use cast iron as piston ring material. Where get cast iron: old brake disc or cam shaft (no cam lobe who is hardened, between cam lobes only).

How to make piston rings follow here-- > http://modelenginenews.org/techniques/piston_rings.html