# A " Boxer" Question.



## BRIAN (Nov 7, 2014)

Something to mull over during tea break.

As I understand it some boxer type engines tend to wear pistons more on one side of the engine than the other.

Why ??

Brian.


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## chuckorlando (Nov 7, 2014)

Dont know nothing about boxers. But maybe it's the angle or offset the cylinders have on that side.


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## Bill Gruby (Nov 7, 2014)

Boxers are opposed cylinder motors Chuck. Hence the name "Boxer" Think of two human Boxers fighting. The pistons are like their gloves one against the other. I would think it might have something to do with lubrication and Gravity. At start up the oil will all be on one side of the cylinder. I need to think on it a little more.

 "Billy G"


http://www.youtube.com/watch?v=L2aGqmmS0gs


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## hermetic (Nov 7, 2014)

I think it is also because Boxer style engines tend to suffer cooling problems, in that some of the cylinders run warmer than others. All engines wear the bores on the axial thrust faces (the faces at 90 deg to the gudgeon(wrist) pin. I once had a Rover 105 car that had wedge top pistons that were offset, now that did cause very uneven bore wear, but it had done nearly 200,000 miles and still ran perfectly, apart from oil consumption being a bit high;-) Thinking about it a bit more, if the cutouts for the valves on the piston crown are unequal sizes this could have a very similar effect.
Phil


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## BRIAN (Nov 7, 2014)

OK for boxer think VW --  BMW bike-- Lycoming aero eng etc. 

Bill and Phil are on the right track .

brian.


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## Karl_T (Nov 7, 2014)

BRIAN said:


> OK for boxer think VW --  BMW bike-- Lycoming aero eng etc.
> 
> Bill and Phil are on the right track .
> 
> brian.



The old VW bugs certainly had this issue. But at least they were very easy to work on.

Lycoming at the other end of the scale. My dad had one in his Cessna 172, one great engine.

Any design his inherent weakness. the question is, how well did the engineers solve the issue?

Karl


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## JPigg55 (Nov 7, 2014)

I'd heard that too years ago and that it was due to gravity as the pistols/cylinders were horizontal causing it to ride heavier to the "DOWN" side.
That said, I bought a couple Subaru's about 4 years back. Subaru's have used boxer engines forever and my research before buying showed them to be reliable, long lasting engines many going 300K to 400K miles.
I've wondered if some of this was due to the symetrical drive system keeping an even torque on the engine.
I've got over 160,000 miles on my Legacy currently with no issues. Definitely love it for these Illinois winters.


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## BRIAN (Nov 7, 2014)

Getting warmer, that's part of the problem.

B


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## Ebel440 (Nov 7, 2014)

It may be because in vws they use splash oiling so gravity would keep the oil on the bottom. On vws #3 cylinder was more prone to wear as well due to the fan shrouds design it had less air flow


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## compsurge (Nov 7, 2014)

The traditional *turbo* Subaru implementation uses an "inefficient" unequal length exhaust header design (this is also the cause of the boxer rumble).  This tends to leave the #4 cylinder with more heat soak since the exhaust gasses do not escape as quickly.  Since the air/fuel metering occurs downstream of the collector for the 4 cylinder exhaust runners, it is averaged across all 4 cylinders, potentially running #2 and #4 in a non-ideal A/F ratio. Combined with the pistons metallurgy, a large enough knock/pre-detonation event has lead to the infamous #4 piston ringland failure.  This is a common problem, but it has not plagued all of the turbo cars. 

Proper oiling is not really a problem with the Subaru implementation of the design.

The non-turbo cars do not exhibit this failure mode and have a different engine and heads.

/2005 Legacy GT owner


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## BRIAN (Nov 7, 2014)

Leaving individual design problems to one side.
For a start, why would gravity only affect one side of the engine and not the other.
 perhaps Phil has the answer to this part?
B


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## John Hasler (Nov 7, 2014)

My guess (and it is a guess as I am not familiar with these engines):  For one cylinder the axial thrust face is on the top, for the other it's on the bottom.  The bottom face will get better oiling if the oiling systems are the same on both sides.  Thus the cylinder with the axial thrust face up will get more wear.  This could be mitigated by the oiling system design.


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## BRIAN (Nov 7, 2014)

Ok that's the basic problem, now to make things worse. if you look from the front of the engine one bank is high and the other low how will this affect the problem.
 B.


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## BRIAN (Nov 7, 2014)

Jut to help I will give you a diagram of a common lay out. note the right side is slightly lower and the left higher on this engine.
But remember the question is why? I offer no cure .
Compsurge mentions the "rumble" this is also part of the problem.




Brian.


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