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Old 03-03-2003, 12:58 AM   #1
RhinoRex
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Question Uneven piston wear in flat fours?

It seems to me that the flat four has the potential for worse engine wear than other engine configurations. As you all know, a good deal of engine wear happens when you first start up. In a flat four, you would always have the pistons' weight resting on the same side of the rubber piston rings. I would think that one side of the ring (the down side) would wear faster than the other sides. In general it seems like gravity would cause problems in flat fours that inline engines don't face and that Vs face much less.

I'm sure there's a way that this is deal with. How do they do it?

For those of you who have rebuilt horizontally opposed engines, do you notice uneven wear on the rings?
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Old 03-03-2003, 01:27 AM   #2
Gethin
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The engine has bee in development for over 30 years and is one of the most reliable designs you will see.

The pistone design is very light and IMHO the gravity effect would be negligable.

http://www.mypersonaldrive.com/Subar...ton-Cranky.asp

I have seen pictures before of engines stripped down and never seen any wear as you describe resulting from the gravity effect on cold start.

Anyone else had hands on experience examining the bores?

Gethin.
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Old 03-03-2003, 02:05 AM   #3
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Quote:
Originally posted by Gethin
The engine has bee in development for over 30 years and is one of the most reliable designs you will see.
more like 60+ if you include light airplane engines, which really haven't changed in over 50 years
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Old 03-03-2003, 11:01 AM   #4
RhinoRex
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I am not at all questioning the reliability of the flat four. It's more that this problem occurred to me and I am now curious about how they solved this engineering challenge.

That is, this question is more curiosity than heresy.
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Old 03-03-2003, 11:14 AM   #5
Eric SS
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There is more than enough oil in the cylinders at startup to prevent uneven wear.

What are you talking about when yo usay "Rubber piston rings"???
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Old 03-03-2003, 01:08 PM   #6
RhinoRex
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When I wrote that, I was thinking of the compression rings and the oil control ring. I knew as I wrote it that they aren't made of rubber, but I figured that people would know what I meant.

Thanks to the link that Gethin posted, it seems that the piston skirt is more relevant to what I was thinking of.

That article is pretty interesting.

So is that the answer? There's enough oil left in the cylinders and gravity introduces no special issues? Naively (which is the only way I operate in engineering) if I imagine moving an object back and forth inside a horizontal cylinder by hand and then up and down in a vertical cylinder, it seems like there would be more friction in the horizontal.
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Old 03-03-2003, 01:56 PM   #7
Eric SS
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Quote:
Originally posted by RhinoRex
When I wrote that, I was thinking of the compression rings and the oil control ring. I knew as I wrote it that they aren't made of rubber, but I figured that people would know what I meant.

Thanks to the link that Gethin posted, it seems that the piston skirt is more relevant to what I was thinking of.

That article is pretty interesting.

So is that the answer? There's enough oil left in the cylinders and gravity introduces no special issues? Naively (which is the only way I operate in engineering) if I imagine moving an object back and forth inside a horizontal cylinder by hand and then up and down in a vertical cylinder, it seems like there would be more friction in the horizontal.
The parts are light enough for gravity to not have much effect compared to the outward force the rings are putting on the bore.
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Old 03-03-2003, 02:21 PM   #8
North Ursalia
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Indeed... the pistons weight about a pound with rings.


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Old 03-03-2003, 11:38 PM   #9
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Yikes! One pound! The Scooby Engineers did a great job!

Gethin.
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Old 03-04-2003, 01:02 AM   #10
gjhsu
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Quote:
Originally posted by RhinoRex
if I imagine moving an object back and forth inside a horizontal cylinder by hand and then up and down in a vertical cylinder, it seems like there would be more friction in the horizontal.
Also consider that the bore and piston are made to pretty exact tolerances, so the friction cause by weight should be darn near even throughout the circular shape. I could imagine your problem if there was any sort of gap between the top of the piston and the cylinder, but I think they are manufactured tight enough to avoid that problem. For the record, I'm no mechanical engineer, but that's just what I am observing.
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