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Piston Slap


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20 replies to this topic

#1 mikec03

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Posted 10 December 2017 - 02:01 PM

I have two 90's subarus that developed piston slap at plus 150K miles.  The slap went away on both cars after 10-20K miles.  I didn't change the type oil or put in any additives.  I just wonder if anyone can explain why it went away?  It was very laud and annoying on my 95.

 

And for extra credit, how is it that no one has posted any problem with piston slap on 2000+ years.  Did subaru lengthen the piston?

 

 



#2 GeneralDisorder

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Posted 10 December 2017 - 02:23 PM

95 would be a 2.2 liter. Those don't have slap unless they get severe skirt wear, etc.

2.5's have piston slap due to very short skirts, poor skirt design, lack of proper lubrication... and it's exacerbated by carbon build up in the oil control rings if they get run with non synthetic. They can't tolerate large amounts of carbon due to small oil drain back holes in the skirt.

2000 to 2004 have pretty bad slap as well. In 2005 they changed the skirt to a barrel design instead of a cone/straight taper. They also reduced the oil control ring width. The skirt design change helped with slap but the control rings are even more prone to carbon blockage.

Don't know what you heard but piston slap doesn't go away. Once the skirt to wall clearance opens up.... Well it's not like the aluminium grows back.

GD

Edited by GeneralDisorder, 10 December 2017 - 02:23 PM.


#3 mikec03

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Posted 11 December 2017 - 09:12 AM

Thanks GD.

 

Both of the 90's subarus in question are 2.2's.  The noise in both was the typically described sowing machine sound.  The sound matches the RPM's and got somewhat quieter when the car heated up. When the first one started to make the noise, I took it to both, a local guy who offered to listen to it, and the best dealership for maintenance in the area.  Both said that it wasn't bearings. 

 

In all the comments about piston slap, I never read about it not applying to the 2.2 engine!  If I had, I would have been much more worried.  I always change the oil every 3-3.5K miles with Penzoil 5w30.  I didn't do anything different in either before or after the sound developed.

 

It's a mystery.  One car now has 170K and the other 250K miles.  They both sound good and ride just fine.  The 95 uses oil but the 97 doesn't use a drop.



#4 GeneralDisorder

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Posted 11 December 2017 - 11:59 AM

Sounds like you probably had some lifter noise.

GD

#5 heartless

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Posted 12 December 2017 - 10:02 AM

my 2002 Forester (EJ251) does have piston slap (also has nearly 235K on it), and yes, the sound is a bit annoying at first start up - especially so as it gets colder out, but it goes away when fully warmed up, so not worried about it.

 

the "sewing machine" noise on a 2.2 would be lifter noise, not piston slap - piston slap is much louder, almost alarmingly so.. :huh:


Edited by heartless, 12 December 2017 - 10:03 AM.


#6 mikec03

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Posted 12 December 2017 - 05:49 PM

the "sewing machine" noise on a 2.2 would be lifter noise, not piston slap - piston slap is much louder, almost alarmingly so..  :huh:

I was going to mention that the noise on my two cars was, indeed, very loud.  You could easily hear it  when someone else was driving the car 100 ft away after starting.  When inside the car, if you kept the radio on, it was tolerable,  after warming up.

 

In regard to the lifters, on one of my cars, the 95, the lifter adjustment is automatic.  But on my 97, they are adjustable with a wrench and screwdriver.  And I did take time to make sure that the gap was perfect.  It didn't any difference.

 

I appreciate the comments.  It's just a mystery.  Especially in view of the post by heartless about the noise level, it has to have been piston slap.



#7 Bushwick

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Posted 12 December 2017 - 06:51 PM

The noise could be the timing belt tensioner. They are hydraulic and transmit a knocking to the block. I run 10w30 full synthetic in my 95' 2.2 and it doesn't use oil @190k+ miles nor tick or make noise. Lifter tick (only the 95') would be louder if fully collapsed, but it still sounds like it's in the head vs. the block. If you unbolt the rocker assembly, you can pull each lifter out (they are tiny) and press it with your finger. If it's not firm, you can try hand-cleaning it. I had to do this with mine at 170k~ some were unable to be corrected, and were replaced. If you prime them in a small cup of oil or a large cap filled with fresh oil, every time you prime it you'll see black gunk exit the hole. Keep priming until only clear. Also, inspect all the rocker assembly oil holes for blockage. If you put a small amount of oil into the lifter cavity on the rocker, then insert the lifter, that will force oil through the feed hole for a reference.


Edited by Bushwick, 12 December 2017 - 06:52 PM.


#8 heartless

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Posted 12 December 2017 - 11:11 PM

i thought about this a little on my way to work this morning... while listening to my poor car's pistons slapping away in 8 degree weather. :wacko:

 

it is possible that there was a partial oil passage blockage to one (or more) of the hydraulic lifters that could cause them to collapse - either partially, or in full... it is also possible that it resolved itself given that it only lasted for a few thousand miles...

 

true piston slap will not come on then completely go away, it will be there every time you start the car from cold - less noticeable in warmer weather than in cold weather - but still there.



#9 mikec03

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Posted 15 December 2017 - 02:17 PM

Thanks for the replies.

 

I notice that Hartless also has a 2.2 engine, a 95, and it is making noise!  Something is causing it.  I agree with her comment that it shouldn't go away if it's piston slap, hence the reason that I started this thread!

 

The 95 has hydraulic valve adjustment so the noise could be a collapsed adjuster, and hence the noise could be from that.   However, my 97 [2.2 engine] does not have hydraulic lifters, and I spent an afternoon adjusting the lash so it was just perfect.  It didn't reduce the noise at all!  Besides the noise from a maladjusted lifter is sharp and metallic which doesn't fit.

 

Here is something from the internet that sounds like the noise that I had on my two subarus. 

 

 

 www.youtube.com/watch?v=7NVjR4CYrCw


Edited by mikec03, 16 December 2017 - 11:07 PM.


#10 1 Lucky Texan

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Posted 15 December 2017 - 03:04 PM

oil analysis might help rule-out piston slap or rod knock - depending on what metals are high?

here's the tensioner noise mentioned above, skip to about 4:30 or so;



https://youtu.be/tAxiFJ2rHBE

#11 Bushwick

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Posted 15 December 2017 - 04:05 PM

Please don't take what I posted as being mean-spirited or even haughty. Chances are your belt tensioner was knocking away. I've seen posts pop up here and there over the years where people get noise at some point after running thinner oils, whether it's coincidence or not, hard to say. The timing belt tensioner is hydraulic though. Lucky Texan's link shows how loud they can get @ the 4:30 mark.



#12 GeneralDisorder

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Posted 15 December 2017 - 05:01 PM

Piston slap DOES goes away as the piston warms and expands to better fit the bore. Piston slap is a way of life for the Subaru forged piston community (modified turbocharged models) and affects virtually every engine we build to one degree or another as well as the factory forged pistons on the EJ207 use in the JDM STI models. I really isn't a concern.

Regardless I've never seen it on a 2.2. They have a shorter stroke and so less side force on the piston skirts as well as a more conventional skirt design that prevents this.

The early second deaign hydraulic tensioners starting in 97 are prone to knocking also. Sounds very much like a rod knock or piston slap. All three are similar sounding.

GD

#13 Stevo F

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Posted 16 December 2017 - 01:48 AM

I've heard where the redesigned pistons on the '97- '98 EJ22 had shorter skirts, hence greater chance of piston slap than '96 and earlier EJ22's. The EJ22 in my '98 wagon has always had a soft tap that goes away when the engine is warm, so I have attributed this to piston slap. The'95  EJ22 in our recently acquired '97 GT doesn't make this noise.



#14 Gloyale

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Posted 16 December 2017 - 01:48 PM

For my 98 Forester, I pieced toghether a rebuilt 93 EJ22 using a set of 97 pistons.  Matched "a" and "b" pistons to bores.

 

Ever since the first fire up there has been a fairly noticable piston slap until warm.

 

If it is average temps. say 40-80f  it will not slap right away, but begins after a min or two and then keeps slapping until engine temp rises to reading on the gauge.

 

But in cold wether it slaps right from the get go.

 

It has done this for 40k miles now, never any shavings or oddities in the oil.  runs like a top and doesn't slap after warmed up.

 

I kinda like it now.  it's got a cool rythm.  I will worry if it ever changes.



#15 mikec03

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Posted 17 December 2017 - 03:20 PM

Thanks for all the replies.

 

I've updated the link at Message 9 on this thread so that it works.  The noise I experienced is very similar to the noise starting at 1:55 on the youtube video.  Notice how loud it is our side the car.

 

I've done some research on the internet.  But it's impossible to figure out anything since everyone contradicts each other, although there are a lot of youtube videos on subaru noises.

 

It can't be tensioner noise since I have heard that myself.  It can't be rod knock because the 97 has put on 20K since the noise stopped, and I doubt that a bad bearing would last that long.  It certainly could be lifter noise especially on the 95 since it has hydraulic adjustment which could get plugged and then later unplug.  But the 97 has fixed lifter adjustment and, as I posted before, I adjusted each valve very carefully, but didn't stop the noise or even tone it down. 

 

In any case, I've been driving the 95 for the last two weeks.  What a great car!  The engine is nice and quiet, at least for a subaru.  It's quick and feels like it has great acceleration.  I'll bet that it accelerates faster then my 2.5 2014.  I'll have to set up a drag race when my son returns with it.

 

I will be keeping these 90's cars for a lot of years and will update this thread in a year or two if anything develops to explain the sound, other then piston slap.


Edited by mikec03, 18 December 2017 - 02:48 PM.


#16 subnz

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Posted 17 December 2017 - 06:31 PM

All my previous / present H4s (EJ251 Ea82s Ea81s)  used to / do knock away intermittantly / quietly,  on idle - didn't worry about it .

(not to be confused with hydraulic lifter noise or the continuous knocking of imminent big end bearing failure)


Edited by subnz, 17 December 2017 - 06:37 PM.


#17 mikec03

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Posted 18 December 2017 - 02:47 PM

 used to / do knock away intermittantly / quietly,  on idle - didn't worry about it

If you read the posts, you would have realized that knocking at idle is not the problem.  



#18 GeneralDisorder

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Posted 18 December 2017 - 02:58 PM

You should probably do an oil analysis. You would be very surprised how long a rod bearing will last. Also they tend to get loose, then tight, then loose again. The bearing insert will collapse inward on itslef and "grab" the crakshaft causing it to be tight and lessening the noise. I know this sounds strange and you probably won't believe me but I've seen it many, many times.

GD

#19 subnz

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Posted 19 December 2017 - 12:52 PM

You should probably do an oil analysis. You would be very surprised how long a rod bearing will last. Also they tend to get loose, then tight, then loose again. The bearing insert will collapse inward on itslef and "grab" the crakshaft causing it to be tight and lessening the noise. I know this sounds strange and you probably won't believe me but I've seen it many, many times.

GD

If that is true  - why haven't I had a big end bearing failure in 25 years with owning 5 H4s?

 

In fact have had NO mechanical  internal issues / failures with any of my Subaru engines.

 

2 reasons why there haven't been issues: 

1/  changing oil/filter at regular intervals   (using mineral oils - NOT synthetic oils)

 2/ flushing the cooling system  (including the heater core)    every 2 years as recommended by Subaru


Edited by subnz, 19 December 2017 - 04:11 PM.


#20 idosubaru

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Posted 19 December 2017 - 02:03 PM

If that is true  - why haven't I had a big end bearing failure in 25 years with owning 5 H4s?

 

Simple - he wasn't talking about your vehicles. There are thousands of EJ's without bearing failures - he's not talking about those. There are also gobs of EJ engines that lose rod bearings, he's talking about that failure mode. 

 

There's no particular vehicle being discussed or taken action on, a wide range of years, and there's a lot of dealing in the past which is always influenced and revised over time and can never be confirmed.  This thread is a big cloudy fog ripe for miscommunication and almost zero chance of quantifiably significant ends.  which is fine - but i wouldn't assume to much from it. 

Sure many people are fine with cars making noises, no big deal.  If someone comes on here asking about noises then presumably it's an issue and they want to inspect, confirm, or investigate.



#21 Gloyale

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Posted 19 December 2017 - 04:00 PM

Thanks for the replies.

 

I notice that Hartless also has a 2.2 engine, a 95, and it is making noise!  Something is causing it.  I agree with her comment that it shouldn't go away if it's piston slap, hence the reason that I started this thread!

 

The 95 has hydraulic valve adjustment so the noise could be a collapsed adjuster, and hence the noise could be from that.   However, my 97 [2.2 engine] does not have hydraulic lifters, and I spent an afternoon adjusting the lash so it was just perfect.  It didn't reduce the noise at all!  Besides the noise from a maladjusted lifter is sharp and metallic which doesn't fit.

 

Here is something from the internet that sounds like the noise that I had on my two subarus. 

 

 

 www.youtube.com/watch?v=7NVjR4CYrCw

 

The car in that video has alot of valve clatter and an exhaust leak.

 

Can't hear anything over that.






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