Different style Cummins Pistons-These are for real

[sag2]

I was at one of the community colleges this week and the diesel instructor was showing me two new piston designs from Cummins. One is called an articulated piston. It is made of three parts. The top is cast steel, the skirt is aluminum, and is held together with the wrist pin. The advantages are lower weight and higher strength. There is an air gap between the top and skirt to keep heat from transmitting to the skirt.

The second design is a one piece cast steel piston that is very strong and low weight. I was amazed at how small the skirt was. the piston was used, and the skirts looked brand new.

These are obviously from much larger engines than the B, but this might be a hint of things to come in the future.

 

[Vaughn MacKenzie]

Cool pics sag2. The 2-piece design looks similar to something Cat uses.



Besides higher EGT resistance, iron-crown pistons will wear longer, have less ring groove wear, and cylinder wear. Obviously the trick is doing this and keeping weight down.



I have a 1950 Chevy with the 216 "stovebolt 6. " This little hummer has cast iron pistons. When I tore the virgin motor down at 107,000 miles I found there was ZERO cylinder wear, even though most other parts were pretty worn (rod bearings, tappets, cam). When mic'd the bores there was no taper or measurable wear, which is something considering many of those miles accumulated when oil was quite inferior to now. I attribute part of this to the cast pistons (and the fact it only had like 95hp).



Vaughn

 

[nickleinonen]

articulated pistons have been around for over 10 years now in larger engines, and there is rumor that the marine spec isbe has them [but i don't think anyone has ever proved that they are in that engine] the 2nd image looks very much like the pistons in the new isx's [also avalable for n14 in overhaul kits i believe] and some that are in the newer cat acert cat engines.

 

[mhuggler]

The new Cat BXS and MXS C15's now use a 1-piece iron piston with a coated skirt. There's none in the shop right now, otherwise I'd post a picture. There's a huge gap between the crown and skirt(Funky lookin' thing but tough as nails! :-laf )

 

[ThomasLawrence]

Okay - stupid question time. If the rings are held in the steel portion, what's the purpose of the aluminum skirt?



-Tom

 

[Windscreen]

The aluminum skirt is there to take up the thrust loads and to try to reduce weight over an all iron skirt.

 

[rbattelle]

Great pics, Sag. Should've put this in the General Diesel forum...



-Ryan

 

[Gary - K7GLD]

Okay - stupid question time. If the rings are held in the steel portion, what's the purpose of the aluminum skirt?

Keeps the piston from cocking/rocking in the cylinder - also transfers heat from the piston into the water jacket.

 

[Cigar John]

It's from the N-14+,I have them in mine.

 

[ThomasLawrence]

Windscreen said:

The aluminum skirt is there to take up the thrust loads and to try to reduce weight over an all iron skirt

Gary said:

Keeps the piston from cocking/rocking in the cylinder - also transfers heat from the piston into the water jacket.

Right - in a normal piston, sure. But how does this aluminum skirt do any of that with an air gap between itself and the piston top?



-Tom

 

[sag2]

I assume that the piston top is long enough to not cock sideways in the bore, especially since the wrist pin can't move because it is holding the aluminum skirt. There did not appear to be any contact between the skirt and top, so the design must work OK.

 

[ThomasLawrence]

I assume that the piston top is long enough to not cock sideways in the bore

Precisely my point... the skirt doesn't help in preventing the top of the piston from cocking... it doesn't help with heat transfer, because of the air gap. Since all the sealing is done by the rings in the piston top, what function is the skirt serving?



How would the engine operate differently if that skirt were not present?



-Tom