Author Topic: Diecut pistons  (Read 734 times)

Offline Tarsier79

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Diecut pistons
« on: 27.08. 2016 08:02 »
question\replies moved from Pictures, Stories & Introductions

The A10 still has an Iron head, but the pistons came in a separate box. They are marked Diecut Y.Alloy 724QM, and the other 70M4Q. They look very similar, but are not exactly the same. It looks like one has been drilled, I am guessing to match the weight? Are the markings to do with the weight? and should they ideally match exactly? Also Should I just replace the rings just for the sake of it?


trevinoz:
Mate, I wouldn't even consider using Diecut pistons. Rubbish made from old saucepans or such.

Tarsier79:
Thanks for the reply. What would you suggest?

Peter in Aus:
I think Trev is right I use JP Pistons (South OZ) some say there rings are no good but I have not had any problem with them.
Peter
A10 Swingarm.

Offline BSA_54A10

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Re: Diecut pistons
« Reply #1 on: 27.08. 2016 11:26 »
Y Alloy was a registered eutetic Al-Si alloy made by Sims Metal.
It is a secondary foundry alloy made as some have mentioned from 100% scrap metal.
There was absolutely nothing wrong with the metal. I made thousands of tons of it.
However a lot of the castings made from it were not degassed properly so suffered from Hordenitis ( continually grew in use )
It was the cheapest secondary foundry ingot available used to make the castings as cheap as possible so I would probably use them as a conversation starter or table orniment.
Bike Beesa
Trevor

Online RichardL

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Re: Diecut pistons
« Reply #2 on: 27.08. 2016 13:49 »
Trevor,

I thought that salvaged aluminum has the potential to be as pure as originally smelted. With the emphasis on "potential", is this incorrect?

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Offline Tarsier79

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Re: Diecut pistons
« Reply #3 on: 27.08. 2016 21:04 »
Ha ha, table ornament it is.
A10 Swingarm.

Online trevinoz

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Re: Diecut pistons
« Reply #4 on: 27.08. 2016 23:15 »
I have used GPM and Taiwanese pistons with no problems.
I have avoided JP because the ones that I first saw were very heavy but I have seen some recently which look as good as anything else.
There have been anecdotes stating JP pistons need large clearances because of their tendency to grow but I cannot comment on this.

Online olev

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Re: Diecut pistons
« Reply #5 on: 28.08. 2016 04:16 »
I've had a JP piston and rings in a greeves 250 for about 4 years.
It has thrived on a diet of brutality and lack of love.
I have to recommend them.
cheers

Online groily

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Re: Diecut pistons
« Reply #6 on: 28.08. 2016 07:33 »
A pair of 8.5:1 +20 JPs I put in a 650 AJS three years ago have been good.
I ran them in carefully because of scare stories, but no problems so far.
I think skirt clearance provided was 3.5 thou on a 72mm bore - but not 100%certain on that. Weights were 24-ish grammes heavier than a standard bore AE / Hepolite if I recall correctly.
Brand new crankshaft plus new rods dynamically balanced to 61%, and the result is very smooth at most rpm.
I'd use them again based on this experience.
Bill

Offline BSA_54A10

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Re: Diecut pistons
« Reply #7 on: 28.08. 2016 09:22 »
Trevor,

I thought that salvaged aluminum has the potential to be as pure as originally smelted. With the emphasis on "potential", is this incorrect?

Richard L.

No way Hos'e.
Aluminium is a very reactive metal thus it is almost impossible to purify it.
Mg , So, Ca & to some extent Zn can be thermally refined .
Apart from them, once it is in the metal it is in the metal for good.
Even worse all the elements you add to extrusion alloys are poison to rolling and casting alloys.
Everything you add to wrought alloys are poison to casting alloys and everything you add to casting alloys are poison to both wrought & extruded alloys.

Thus when impurities get too high the only thing you can do is to dilute with pure aluminium like wire , saucepans or bottle tops.
However the companies who extrude wire also want old wire to add to their batches so scrap wire is very expensive.
In fact scrap wire is more expensive than Y alloy so we were spending 40c/kg to melt scrap that was $ 10/kg to cast ingots that were $ 5.00 / kg so in many cases it is cheaper to tip the entire furnace out ( up to 20 tons ) and make known composition scrap ingots than to dilute the 20 tons back into specification.
This was the principle thing that killed aluminium can recycling.
All the morons who shove steel or lead washers into the cans.
The steel washers sit on the bottom of the furnace slowly dissolving into the melt and can not be removed so can contaminate thousands of tons of ingot.
So you melt cans in a rotary furnace, then tip that into the alloying furnace so you can melt it quick before too much iron dissolves into the aluminium.
However lead which in  theory should burn actually melts under the aluminium and then runs down between the cracks in the brick lining where it build up .
Then either one of 2 things happen, the lead conducts heat from the melt directly to the furnace wall which glows red hot then collapses or even worse it floats the bricks so they fall out and then the lining collapse into the melt without warning.
In both cases some one usually ends up dead and even more end up with disgusting burns from hundreds of litres of liquid aluminium at 800 C pouring all over them
Bike Beesa
Trevor

Online RichardL

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Re: Diecut pistons
« Reply #8 on: 28.08. 2016 16:42 »
Trevor,

Thank you, that is a great explanation. I know I have heard adverts for conservation talk about aluminum cans being able to be put right back into new products when recycled, but the complications are not known to the ad people. We are quite fortunate to have your metallurgical expertise in these areas to lean on and set us ('me") straight.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Online Peter in Aus

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Re: Diecut pistons
« Reply #9 on: 29.08. 2016 01:01 »
Trevor,

Thank you, that is a great explanation. I know I have heard adverts for conservation talk about aluminum cans being able to be put right back into new products when recycled, but the complications are not known to the ad people. We are quite fortunate to have your metallurgical expertise in these areas to lean on and set us ('me") straight.

Richard L.
And me
Peter

Busselton West Australia
49 A7 longstroke
58 A10  SA

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Re: Diecut pistons
« Reply #10 on: 29.08. 2016 06:30 »
I'm firmly in the avoid JP's like the plague camp (had several sets of serious grief from around 10 years ago  *problem* ) , but recently MikeB fitted a pair of +80's and has had no problems with them so perhaps they have improved  *dunno*.
I still wouldn't touch them if I could find anything else...
Touch wood I've been lucky enough to find nos BSA pistons in the right OS and compression todate but this does involve time and some forethought to collect them when they turn up at swap meets or on ebay.

A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Re: Diecut pistons
« Reply #11 on: 29.08. 2016 06:43 »
Why do people put steel or lead washers into Coke cans?

Offline BSA_54A10

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Re: Diecut pistons
« Reply #12 on: 29.08. 2016 11:14 »
Why do people put steel or lead washers into Coke cans?
Cans are bought by weight.
So the really big shonks put the steel or lead into some cans then squashed them and tossed them into a sack full of mixed crushed & uncrushed cans.
The government funded can recycling purchase price was nearly twice the actual scrap value so you could make a lot of money.
The do good charities were the worse offenders sad to say , I suppose they thought the new dialysis machine was worth the deception & I doubt they realized the potential fatal consequences of their actions.

The final attempt down here was to only accept uncrushed cans then run them over a magnet & down a spiral seperator to weed out the "funny " cans.
You also get rocks, gravel, all sorts of stuff to make them heavier.
However this was very slow, caused all sorts of arguements & fights and for the sellers was unprofitable as a 10 x 6 x 6 trailer load of crushed cans goes about $250 but the same volume of uncrushed cans goes about $ 60.
Cans are painted both sides and the paint can go 10% by weight but typically was 3-5%.
Being paint, it burns well before the Al melts and as it burns it takes some of the can with it.
We have all tossed a beer can in a fire and you don't end up with a plug of solid Aluminium sitting in the bottom of the fire.
SO they have to be plunged under the surface to avoid paint burning ( no air under the melt ) but when you do that any liquid trapped in the can explodes ( steam explosion ) so in reality can recycling is a money loosing exercise.

Steel cans suffer a similar fate.
Because of the solder they can only be used in malleable iron casting and because adding carbon to steel to revert it to cast iron is very difficult you can only add a small amount which you balance by adding pig iron.
And you still can end up with the solder seperating with the tin going into solution and the lead  dropping to the bottom of the furnace.
The "no tin" solders are even worse so regardless of what you read or hear most steel cans go to the tip .
When they were made with tin plate you could recover the tin with a caustic bath.
the detinned cans are then left out rust to nothing, the rust is then ground and magnetically seperated then pelletised and sent to blast furnaces.
The seams with solder in them get burned then used in fertilizer.
However now 3/4 of the cans are zincalume coated with renders them totally unable to be recycled and even worse the zinc coating has a very short shelf life which sort of defeats the purpose of canning in the first place.

No more now, I can feel Musky's  breath over my shoulder. finger poised on the delete button.
Bike Beesa
Trevor