Fancy Pants Pistons

We've discussed fancy Commando pistons a lot here, skirt length, closeness of gudgeon pin to bottom ring, drilling of skirts, etc.

I was in Mahle Germany recently and saw some awesome looking pistons! Unfortunately they were for OEMs, and a lot were for diesels. Nevertheless, look at the attached video link to see where current thinking is going, of most notable interest is the skirt design...

https://www.youtube.com/watch?v=QXkLP9hfq7Y

Thanks Nigel, those Duramax pistons look awesome, I wonder if JS or other vendors will give something like a try in a performance Norton>
Regards Mike

What the heck is it?
My wife has some shoes that look a lot like that, I've even thought of trying them on.

I'm now ashamed of the pistons I'm planning on using in the 920. They are an old design, just lumps of aluminum with some internal steel bits holding them together plus big old skirts like square dancing ladies in a Roy Rogers movie.

Glen

Being made out of steel, I doubt if you could ever get a Norton piston in that style down to the weight of even the heavier aluminum pistons we use now.

Ken

Brooking 850 said:

Thanks Nigel, those Duramax pistons look awesome, I wonder if JS or other vendors will give something like a try in a performance Norton>
Regards Mike

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I think that they already do by way of extra lightening/lubricating holes fore and aft on the already reduced short skirts.

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Any substantial reduction in piston weight will usually give a noticeable improvement in a bike's acceleration. The main consideration is probably the fatigue life of aluminium con-rods with the lighter pistons. I've seen Mahle pistons out of two-valve Jawa speedway bikes where the bottom of the skirt has actually bent inwards without breaking. Forged pistons are always better than cast ones. And I believe the two stroke pistons are machine-made spun-cast then forged to get the grain flow right to stop seizures. If there are Mahle pistons for 850 Commandos, would you please post any identification numbers ?

This steel piston is made for todays high output truck diesel Engines because they have way higher comustion pressure than any petrol Engine.
It looks fancy because it needs to be as light as possible but they are still heavier than comparable alu piston.(and much stronger)
They are not usable for our Engines or of any benefit.

Sten

this is not necessarily true. there is a LOT of factors that go into what type of piston is BEST for a certain application. example is today's auto engines pretty much all use a cast type coated piston as it allows a super close clearance. a 5.4 ford V8 runs as close as .001, try that with a forged piston.

acotrel said:

Forged pistons are always better than cast ones.

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Brooking 850 said:

Thanks Nigel, those Duramax pistons look awesome, I wonder if JS or other vendors will give something like a try in a performance Norton>
Regards Mike

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What makes the Mahl piston intresting is the window between the skirt and the rings - the upper portion of the skirt is removed. For this to work the upper portion of the piston above the rings would become a primary load bearing surface wearing on the cylinder and that area is above the oil ring and rubs with less lubrication. Mahl may be getting away with this by using their coating. Mahl has some trick shit for sure. The closest I come is by drilling the skirts - it lightens the skirt while retaining the skirt length. Another option is to taper bore the pins (see below). You get diminishing returns - cutting those last few grams gets expensive - but every little bit counts.

The window of the Mahl piston would allow more oil to get in there and lube the skirt - this is one advantage of drilled skirts.

This monotherm design is possible because of high strength steel but still heavier than a alu piston, steel having much higher density weight.(sorry if I repeat myself)

The hole in your piston skirt is clearly no problem and looks structually ok to me but I think a monotherm designed alu piston would break into pieces immediately in serious use.

But why not go ahead and ask JE pistons? If i am wrong I would not be unhappy at all.

Sten

billet said:

.......The hole in your piston skirt is clearly no problem and looks structually ok to me but I think a monotherm designed alu piston would break into pieces immediately in serious use.....Sten

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That seems about right to me (and probably everyone else here too), but ya gotta admit Sten that the light weight pistons and longer rods from JS Motorsports are a thing of beauty and probably about as close as you can get to fitting an updated more modern type of piston/ring/wrist pin into our old aircooled engines.

Yes, I do not only admit but i totally agree with you about his piston/rod design (having bought his Product myself)

I just felt the need to point out how wrong the monotherm design is for alu pistons

Sten