Piston Slap - What year was problem solved or was it?

[H]

I have a 2004 2.5XS Forester. This morning I started up as per normal. The
vehicle had been sitting since Friday (long weekend). Upon starting I heard
a dreadful slap type of noise... so loud I immediately shut off the engine.
Upon restart the noise was less severe.
There is ample oil in the engine. It was changed 1400km ago at its first
6000km service.
There has been no repeats on subsequent restarts throughout the day.

I have heard of the dreaded "piston Slap" but thought it was more in the
1997-98 models with excessively short piston skirts. Has the problem been
addressed in recent years?

Thanks in advance.

Harry

 

[Jim Stewart]

I have a 2004 2.5XS Forester. This morning I started up as per normal. The
vehicle had been sitting since Friday (long weekend). Upon starting I heard
a dreadful slap type of noise... so loud I immediately shut off the engine.
Upon restart the noise was less severe.
There is ample oil in the engine. It was changed 1400km ago at its first
6000km service.
There has been no repeats on subsequent restarts throughout the day.

I have heard of the dreaded "piston Slap" but thought it was more in the
1997-98 models with excessively short piston skirts. Has the problem been
addressed in recent years?

My '99 will do that occasionally if I don't
drive it every day. I think the oil filter
check valve doesn't seat and the oil drains
out of the valve buckets. It only lasts
for a second or 2, right? I think piston
slap usually lasts at least until warmup.

 

[Spudster]

I have an '02 OBS and it started doing something around 8000km. Not sure if
it is piston slap, but it makes a knocking sound at cold start in the winter
and goes away after about 5 min. Took it to the dealer last winter and,
wouldn't you know, the car would not make the sound when it was there. They
said I would have to leave it overnight which I couldn't do. I will reassess
the severity of the noise this winter and decide if I'm going to push the
issue or not.

If this is piston slap, I can't believe they haven't resolved the issue
after all these years of knowing about it. This problem could kill Subaru if
they keep ignoring it and word spreads.

Personally, I would never buy a used car that knocked on startup. Maybe this
has not been a big issue because Subaru owners tend to keep their cars
forever and never end up on the used car market?? Do we take the bad to get
all the good?? I dunno.

Steve.

 

[Ross]

I have heard of the dreaded "piston Slap" but thought it was more in the
1997-98 models with excessively short piston skirts. Has the problem been
addressed in recent years?

Anyone care to explain what piston slap is to me? Im pretty well up on
mechanical stuff but never heard of this before???

Ross

 

[Voja]

This is very good link that explains what is "piston slap".

http://www.butkus.org/subaru/piston_slap/subaru_piston_slap.htm

Another good one:

http://resnet.uoregon.edu/~dwhite/pages/subnoises.html

Voja

 

[Scott Marcy]

I don't know if they've addressed it since, but my 2000 OB received a
brand new short block at just over 50K miles because of piston slap.
Thankfully, it was covered under warranty.

-Scott

 

[Don]

I had a case of piston slap in my 1949 Ford back in 1953. Pistons had been knurled
to reduce oil consumption and the knurling wore off rapidly causing one piston to
rattle. There ain't nothing to prevent a piston from rattling if the skirts are
short or not up to diameter specs. It's a simple lever arm, the ratio of the
distance from the wrist pin to the top of the piston where the detonation takes
place off center compared to the distance to the bottom of the piston.

Same here on our 1998 @ 50K miles under warrantee. Our 2003 OB started doing
it early on, 3K miles. It's the same ole malady, slaps when cold, OK after
a warm up. The 1998 OK seldom got OK.

Don

I don't know if they've addressed it since, but my 2000 OB received a
brand new short block at just over 50K miles because of piston slap.
Thankfully, it was covered under warranty.

-Scott

Username munged by FixNews

 

[GW De Lacey]

Anyone care to explain what piston slap is to me? Im pretty well up on
mechanical stuff but never heard of this before???

Actually, while it still exists, it's not as common as it once was.
The slap, that is, not the actual problem that causes the slap.
Bores that have worn oval cause pistons to fit sloppily. In the days
of cast iron pistons the sloppy fit of the pistons in these
circumstances would result in a distinct slapping sound at certain
RPM. Of course, this would be accompanied by all of the other problems
resulting from loose pistons. Modern pistons are not prone to the
noise, but the other problems are just as prevalent as in the old
days.

-- GW