Broken Pistons

[bradboy]

Is it common for the pistons on a 8-9psi boosted H22 to break between the 1st & 2nd piston ring? I just found 2 or mine broken.

[texan]

Yes and no. What engine management system are you running, and why did you run 8-9 psi of boost on a stock H22?

Ps- Piston ring lands will always break there, that's where the most pressure is being placed on them by the high cylinder pressures. Excessive RPM can break any of the ring lands, but overly high cylinder pressures for the design will naturally break the first land.

[SleeperCivic]

Just for info, are you running an intercooler as well? I find it intersting. Also, how many miles (approx) did you have when your pistons failed? Thanks.

http://home.satx.rr.com/importvelocity/

[ivymike1031]

Originally posted by texan
Ps- Piston ring lands will always break there, that's where the most pressure is being placed on them by the high cylinder pressures. Excessive RPM can break any of the ring lands, but overly high cylinder pressures for the design will naturally break the first land.

Texan, to get our terminology on the same page, when you say "first ring land," are you referring to the second crown land (the land between the top and second compression rings)?

I've always referred to the top land (from the tip-top of the piston to the upper cham of the top ring groove) as the first crown land, and the land between rings 1&2 as the second crown land. Of course I've never intentionally referred to any of the crown lands as a ring land, which is partly why I'm asking for the clarification.

[fritz_269]

Originally posted by ivymike1031
Texan, to get our terminology on the same page, when you say "first ring land," are you referring to the second crown land (the land between the top and second compression rings)?

I've always referred to the top land (from the tip-top of the piston to the upper cham of the top ring groove) as the first crown land, and the land between rings 1&2 as the second crown land. Of course I've never intentionally referred to any of the crown lands as a ring land, which is partly why I'm asking for the clarification.

Interesting, I've never heard them called 'crown lands'; but I do agree that texan is talking about the second land. The top land is the distance from the piston face to the top of the compression ring groove.

[ivymike1031]

Originally posted by fritz_269
Interesting, I've never heard them called 'crown lands'; but I do agree that texan is talking about the second land. The top land is the distance from the piston face to the top of the compression ring groove.

Well, I'm probably just permanantly skewed from talking about articulated pistons, where the crown and skirt are separate pieces (and made of different materials). I suppose it's fair enough to call them "piston lands." I'm just used to referring to the part of the piston above the skirt as the crown, and the various larger-diameter portions of the crown as the crown lands. Perhaps the author of the attached picture would have called them "head" and "head lands?"

[SleeperCivic]

I just call the damn things pistons, but thanks for the anatomy lessons guys. I'm now more knowledgeable about pistons now.

[fritz_269]

Originally posted by ivymike1031
Well, I'm probably just permanantly skewed from talking about articulated pistons, where the crown and skirt are separate pieces (and made of different materials). I suppose it's fair enough to call them "piston lands." I'm just used to referring to the part of the piston above the skirt as the crown, and the various larger-diameter portions of the crown as the crown lands. Perhaps the author of the attached picture would have called them "head" and "head lands?"

Where are you getting articulated pistons? For what engine? What materials? Sounds interesting!

I'm very used to single piece aluminum slugs, that get all manner of different coatings (like an iron skirt for aluminum bores) - but I've never seen a two-piece piston.

[ivymike1031]

well that's odd - I thought I replied to this a while ago, but my response doesn't seem to be here.

articulated pistons are often used on diesel engines, especially highly rated ones. They have several advantages over mono-aluminum pistons:

* crown thermal expansion rate is similar to rate for liner (steel vs iron instead of aluminum vs iron)

* Pin bosses in steel crown have higher load-bearing capacity than those in al pistons

* heat from the crown is not as easily transfered to the skirt, so the skirt retains its shape better

* piston secondary motion can be better

I'm sure I've overlooked some other important benefits, but that's life, eh?

see the second page of this document for a picture:
http://www.cat.com/products/shared/p...f/pehp7039.pdf

[fritz_269]

Really interesting, thanks. Shows you how much I know about real truck engines. I love the idea of complete "cylinder packs" that you can just swap into an existing block. Makes perfect sense.

About how much more would an articulated piston cost over a one-piece unit for the same application? Any reason you can think of why we haven't really seen them in gasoline engines? Is it the slow heat transfer of a steel crown?

What is piston "secondary motion"? Same as "piston rock"?

[ivymike1031]

The articulated pistons are generally used in high-boost, high-BMEP applications, typically in engines with bore size > 160mm. I don't think that they offer a significant benefit in the smaller, lower BMEP car applications, or else we would see them used there. Also, the engines that they are used in are somewhat insensitive to reciprocating mass, in contrast to most automotive applications (mono-aluminum pistons are lighter, in general). To answer your question about the cost, I'd say off the top of my head "15% to 50%, if there was such a thing as a monoblock-aluminum piston that would work in the same application." Usually the reason you go to an articulated piston is that thermal loading conditions, firing loads on the crown, or pin boss & small end bush gross pressures, are too severe to allow the use of a cast aluminum piston.

Piston primary motion would be the up-down stuff that everyone knows about. Piston secondary motion would be the thrust/anti-thrust translation of the piston, in addition to piston rotation about the piston pin axis. Although I've never heard it called this, it follows that "piston tertiary motion" would be translation in the direction of the pin axis and rotation about an axis perpendicular to both the pin axis and cylinder axis. Of course, that leaves rotation about the cylinder axis unnamed... hmmm....

To be completely honest, I don't know whether or not slow heat transfer is a bad thing for a piston - there are certainly companies that sell special coatings with the intent of slowing heat transfer to the piston crown (not the same as from the crown, of course). When I mentioned that there was less heat transfer to the skirt, I was alluding to the fact that the skirt has a small air gap (2mm or so) between it and the piston crown. The crown still cools itself via the rings & via an oil gallery in its underside (supplied by oil jets at the bottom of the liner).

gettin' crazy with the text formatting here, I know...