Aluminium type for making model diesel engine conrods?

[Andrew TinsleyParticipant @andrewtinsley63637]

Can anyone remind me what is the best aluminium for making model diesel conrods? The last time I made some, I think I used T6065, But it is so long ago, I cannot be sure.

Thanks,

Andrew.

[JasonBModerator @jasonb]

2014 is the usual choice which was the old HE15 or “Dural”. Better properties than 6082 T6 and as it also contains copper is a bit more self lubricating.

[Roderick JenkinsParticipant @roderickjenkins93242]

As Jason says.  Also known as L168. The copper content aids the precipitation (age) hardening which gives the alloy its strength. Metal Bar Ends on ebay usually has a stock of suitable offcuts:

Ebay Metal Bar Ends

Rod

[Andrew TinsleyParticipant @andrewtinsley63637]

Thanks guys,

Memory was playing me false!

Andrew.

[bernard towersParticipant @bernardtowers37738]

7075 every time

[JasonBModerator @jasonb]

Any particular reason for preferring that Bernard. Just about every IC engine drawing I have specifies H15 or if more recent 2014 with the Americans going for 2024 which seems to be more easily available over there. A Couple of the more recent German ones go with AlMgSi0.5. But I don’t recall any specifying a 7000series alloy.

Certainly all the engines I have built with Aluminium use it and I’ve not had a rod fail.

[bernard towersParticipant @bernardtowers37738]

Recommended by a friend who’s into designing and making ic engines and revisiting the specs would still recommend it.

[JasonBModerator @jasonb]

He must know something the likes of Westbury, Sparey, Whittle, Mason etc don’t. Even our own Ramon who makes and competes with Diesels used 2014 and again Nick Lickfold uses it in his competition engines as mentioned in this thread where the question was last asked, seems most there also suggest HE15 or 2014. Is he running with or without bearing shells?

I suppose at the end of the day do you want to risk a failed conrod in an engine you have spent many hours making from a less commonly used material or play safe and use what has done the job for100 years which is how far back some of my drawings go.

[Roderick JenkinsParticipant @roderickjenkins93242]

7075 has better strength, better corrosion resistance and better fatigue strength than 2014A.  Machinabilty and cost are worse. Experience tells us that 2014A is good enough for our purposes.  7075 is a more modern and expensive alloy so some our pioneer designers may not have had access to it.

Rod

[bernard towersParticipant @bernardtowers37738]

Oh dear

[Julie AnnParticipant @julieann]

What Rod says, although in my experience 7075 machines pretty well. It does tend to get hot though so coolant is essential. It can be a pain to hand tap as it gets hot and then contracts onto the tap.

Professional race engine manufacturers often use 7075 for conrods.

Julie

[JasonBModerator @jasonb]

Julie, do the pro engine makers run the aluminium straight on the crank pins as a lot of small model diesels do or use bearing shells? As I had always understood that the old Dural, HE15 and now 2014 and 2024 ran better straight on steel than the stronger 7075 T6 due to the copper content rather than 7075s zinc content.

2014 is also said to be more free machining which as a lot of hobby users don’t have flood cooling also makes it a better hobby option. Also stocked by several of the ME suppliers so easy to by an inch or two for a conrod

[Andrew TinsleyParticipant @andrewtinsley63637]

Hello,

I seem to have caused some controversy over my simple question! Not sure where this 2014 is readily available. I can get round bar in 15 mm diameter but nothing in the 6 to 8mm range that I need. Not to keen on making a large amount of swarf to make a small rod or two!

Andrew.

[JasonBModerator @jasonb]

As I said the ME suppliers do it. Both M-machine and College Engineering have 1/4″ and 3/8″ and Noggin have it from 1/2″. M-machine may be cheaper if you go down a page ortwo and buy rectangular section as that is sold by the inch. Some list it by old numvbers which is HE15

Oddly enough none list 7075, must be a reason why?

[Roderick JenkinsParticipant @roderickjenkins93242]

As I mentioned, 2014 is known as L168 in the aircraft industry. If you follow the link I gave above and search that site for L168 you will find plenty of off cuts suitable for model con rods at reasonable prices.  I have used them a few times and have been happy with the goods I received.

Rod

[Julie AnnParticipant @julieann]

Most race engines run with shell bearings. The rules in F1 have changed but when I was working in motor racing, mostly on Indy cars, the engines were completely rebuilt after every race. So wear was a moot point, as long as the engine kept going for the duration of the race. According to the datasheets 7075 does contain copper, albeit a bit less than 2014.

Forces are significantly higher in full size engines and many race conrods are forged and finish machined rather than fully machined from stock.

I would agree that 2014 is more readily available than 7075. Most commercial aluminium stockists list 7075 but it will be expensive.

Julie

[andy198712Participant @andy198712]

I use 7075 now and again at work, last time I used it was for a part for a chinook helicopter and one point to note, it’s very picky about heat treatments if your trying to SHT it you have to bang on with you timings and quench delay times….

boring fact I know.

2014 t3 or t6 is more common and probably a lot easier to get hole of, try searching other names for it, one are a BS name some are a US name ect but your getting into a bit of a rabbit warren than.

do you know the temper state you want? I would assume T6 for a rod

 

BS EN 2087

L165

L167

 

the L numbers are abit outdated and probably more likely to get hits on google with the BS number if it helps?!

[Graham MeekParticipant @grahammeek88282]

The Copper content in Aluminium or Duralumin causes “Age Hardening”. There was if my 70+ year old memory is correct a 5 day window for machining after heat treatment. Again if I remember correctly part of the pre-machining heat treatment involved keeping the parts in cold storage, but I may be wrong there.

After machining the parts start to get harder with an improvement in UTS.

Regards

Gray,

[old martParticipant @oldmart]

I looked up the modern equivalent of the classic Hiduminium RR56 developed by Rolls Royce for aero engines and used for con rods by Triumph, Norton and Royal Enfield and found 2618T61. Your rods are not likely to go through a forging process so this is probably overkill.

[andy198712Participant @andy198712]

So it depends on the metal a lot in terms of the age hardening, but can vary from 5-10 days depending, and this normally ends you at T42 temper state. (The T is temper, the first number is the state and the second number is the amount of solution heat treatments it’s had)

 

to get to T6 see you would artificially age at a lower temp normally around 190*c ish depending on metal and for anywhere from 8-16hrs. Again varies on type of alloy.

 

 

the first treatment is SHT solution heat treatment where is high temp (like 500*c) for a shorter time (30 mins varies on thickness) and is then immediately quenched (this is very time critical)

 

the metal is then as soft as an annealed peice for a short period of time. It age hardens quickly. You can hold this state by freezing it. And then depending on what T state you want, begin your Precip…..

 

 

I could bore you for ages on this. We do a lot of sheet metal work on aircraft and do a lot of this. Many variables depending on metal and thickness and what you want to do with it….

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