Lightweight billet pistons

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Having a try at Billet pistons made from low expansion 4032 alloy (allows sightly tighter installation clearance than 2618 alloy). The advantage of billet is that you are not dependent on an existing forged shape. So you can have them designed anyway you want. The result in this case is the lightest Norton piston so far. The 73.5mm piston in the image below tips the scales at only 177 grams. Note the efficient box shape and the underhead milling keeping the crown thickness uniform around the intake pocket (at bottom).



No dead weight left on this shape.
 
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In an aluminium forging, you have better grain flow - which determines the way the piston grows when it is heated. Also the way it behaves when it cops a beating. You would never make a billet piston as light as a Mahle. Perhaps you should have a talk to a metallurgist in the aircraft industry ? Japanese two-stroke pistons are spun-cast, then forged in a machine - one process. That is the reason most ordinary guys cannot make them. Back in the early days Jack Findlay was racing a TR500 with a pair of factory pistons. After he had finished successfully racing the bike, Suzuki reclaimed the pistons.
 
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In the early 1960s, my friend with a 500cc Manx provided the main competition for Ron Toombs with the 4-valve Henderson Matchless. Alex Henderson showed my friend one of his pistons which was much lighter than the ones my friend was using. My friend was having his pistons cast and running them at 14 to 1 comp. They used to do all sorts of strange things - such as collapsing under the inlet valve. The piston in the Henderson Matchless was magnesium and they used to rebuild the motor in the pits between races. I don't think Ron ever raced overseas - he was killed at Bathurst in about 1978 while making a come-back with a TZ350. But he was faster than any Wayne Gardner or Mick Doohan. There is almost no video of him racing, but he was the best.

https://trove.nla.gov.au/newspaper/article/110940820
 
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lcrken

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Very nice looking pistons, Jim. Good to see more experimentation going on. For those interested, below is a good summary comparison of different material choices for pistons, from some magazine or on-line article, but I don't recall where.

Ken

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Hypereutectic

Cast hypereutectic pistons have several benefits in OEM applications as well as some performance applications. Most OEM modular engines with the exception of the extremely high performance
models have been using cast hypereutectic pistons since day one, including the current Coyote 5.0. According to McFarland hypereutectic alloys are highly resistant to expansion, and wear extremely well. This allows OEM manufacturers, or builders in the aftermarket to construct an engine with extremely tight piston to cylinder wall clearances since the piston will not expand enough to cause a problem. These alloys also have a high resistance to scuffing which improves their wear resistance. The biggest downfall to a hypereutectic alloy is its high silicon content. The high silicon content makes the piston more brittle, and under violent detonation, such as that which can occur when things go wrong in a nitrous or forced induction engine, these pistons can be catastrophically damaged.

Eutectic 4032

With new piston designs creating a physical model for test fitting and final design verification is a key part of the final design process.
Eutectic alloys should not be confused with hypereutectic alloys. 4032 is the most common eutectic alloy used in pistons. It does contain some silicon content, however it is much lower and more tightly controlled than in a hypereutectic piston. 4032 pistons are also forged, rather than cast, further eliminating the larger pockets of silicon found in many hypereutectic pistons.
According to McFarland these alloys don’t typically need hard anodizing for the ring areas or the rest of the piston, as they’re strong enough to resist micro-welding in many cases. They posses good wear characteristics, and McFarland says their combination of strength and wear resistance make them well suited for a variety of applications where a forged piston is necessary.
Many high performance engines run pistons with this alloy including endurance racers, forced induction applications, and even some OEM applications. “This is an ideal choice for modern engines with tight controls on the fuel system and ignition timing, where detonation is not an issue,” says McFarland.

2618 X-Material

2618 is the racer’s alloy, also known as X-material. This alloy contains no more than .25 percent silicon. It is strong, yet under heat and pressure it becomes malleable. According to McFarland that malleable characteristic actually allows the piston to distort under extreme conditions without fracturing, or failing. This can save other engine components during extreme detonation.
There are drawbacks to using 2618 pistons though. According to McFarland that distortion which saves the engine, may require the pistons to be replaced as part of periodic maintenance. We’re not talking about after every race, but where racers running a milder setup with 4032 alloy pistons might perform a ring and seal replacement between seasons, a racer with a 2618 alloy piston may need to replace their entire set of rings and pistons.

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Think about it - Forged or billet the piston design software would cut you the same profile, so would be very near identical in weight. With modern methods, it does not matter what forging you use providing there is sufficient material to start with. Machine time and waste material are the difference, ideally both should be minimised, unless the customer is prepared to pay.
Using billet to cut a piston and justifying it by not using an existing forged blank, is not an advantage, it is a compromise.
 
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Mad
Yes but I have been paying attention to billet pistons in Nortons and they do work without issues. Otherwise I wouldn't go there. Not saying that I am going over to billet pistons. Only that I'm trying out a pair. I'm also bringing in 4032 forged pistons in larger quantities which have been working out well as shown below. The quality of Wiseco pistons is hard to beat and its taken a long time to get them produced and available for Nortons (you wouldn't believe the hassle). But in the case of a forged piston you also make a compromise by using whatever forgings are available. Its too expensive to design your own ideal forging.

Med CR 850 wiseco piston below weighs only 204 grams bare.

 
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lcrken

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@lcrken - what was the alloy that you and Steve Maney used for your J&E forged pistons?
We used (and still use) 2618. At that time, that was the only alloy in which JE had suitable forgings for making Norton pistons. It was also the alloy JE recommended for race use, and that was the primary use we were offering the pistons for. I think that 4032 is probably a better choice for most applications. I'd still stick with 2618 for really high stress use, like supercharged bikes, or running on nitrous or nitromethane, or even some of the more extreme high rpm, high horsepower race bikes, but that's a personal choice.

Jim deserves a lot of credit for the effort he puts into looking for applications of modern technology to our old Nortons. I know from experience how difficult it can be to get piston manufacturers to work on new designs for such limited interest products. I'm impressed that he managed to get Wiseco interested. I still get along OK with JE, but after they were acquired by Wiseco, it's become a bit less satisfying. Maybe that's why Jim started working with Wiseco? Attitude in the sales force and engineers counts for a lot. I originally had Norton pistons made by Venolia, and they were very willing to work on one-offs and odd stuff. I only switched to JE because they had more modern technology and manufacturing machinery, and really high quality control. And because I knew the sales rep, who was a motorcycle guy and went out of his way to help me get started with them.

Ken
 
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Thank you. I think you could reduce weight a lot more as I just compared to my homemade pistons which are 234gr for 80mm size.
 
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Thank you. I think you could reduce weight a lot more as I just compared to my homemade pistons which are 234gr for 80mm size.
It gets harder to lose more weight (diminishing returns). My 81mm JE pistons are 240 grams. If JSM pistons were 80 mm they would be 230 to 235gms. JSM 78mm 4032 alloy Wiseco pistons are only 204 grams. You can finesse maybe another 5 to 10 grams off with skirt drilling, underdome milling, shaping the pin boss etc but it adds more expense.
 
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Jim Schmidt's 12 to 1 comp. pistons have domed crowns. Is that achieved without much increase in weight when compared with a standard comp 850 piston. ?
 
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Found this photo in my files and it might be the piston Weal is talking about. Nice shape but not enough skirt left in the high wear area to last long enough for the general public. Not enough distance/material between the top ring and the crown - with valve pockets it would melt between the top ring and the pocket unless the fuel mix was rich and black (might work with a big bore but not with smaller bores where the rings are closer to the pocket. Would be nice to see more photos and specs - skirt, crown and pin wall & pin length etc to understand how such minimal weight was achieved. And race testing to see if it lasts.

Regardless whether or not it works for everyone its an incredible accomplishment on Weal's behalf.

Here's another photo (don't know who it came from if not from Weal).


Its a Wossner piston. Single ring and thin oil ring. I had some wossner pistons made but they refused to meet my specs in favor of their own heavier specs (by about 8 grams).

Acotrel - the domed pistons are underdome milled. They weigh about the same as JSM Hi CR pistons.
 
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Just saw this thread this morning
..., all I can say it that we are a lucky bunch for sure..... Awesome!!
 
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The AN standard 850 Omega forged HC piston, with full skirt, is lighter complete with rings, pin and circlips, than a original Hepolite and GPM cast flat top standard piston.
It was decided to use full skirt on the advice from the same design team that designed the first Panigale pistons. Slipper and semi slipper would work, but the life of them using standard rods would be considerably reduced.
Not sure if anyone has attempted to lighten further.
 
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Jims pics are not of my pistons, mine were milled from solid billet from Mahle, Germany´s well know piston producer and look a bit different. Sorry, i am unable to send pics right now as I am on holidays for the next two weeks. But I think I should have a couple pics of pistons and my own steel conrods at 339 gr each on my home computer. If so, I send them. If not you have to wait for the next tear-down after another dyno run ;-)
 
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