I read a lot about piston slap in this forum. I have a 2004 Outback Wagon with the 4 cyl engine. (wanted a 5 speed trans).

 

Can I expect this car to piston slap or have they changed design to prevent this in the 2004 model?

 

Also, while I am asking...I read about head gasket problems. Has Subaru fixed this problem for the 2004 models?

 

Dave

Check out this thread:

 

http://forums.nasioc.com/forums/showthread/t-453210.html

Your engine will most likely be quiet while it 's brand new and the pistons and wrist pins fit tightly. My '02 with around 26,000 miles started to get noisy this winter during cold starts.

The noise is a by product of extremely short piston skirts. As little as 1/2 of one thousanth of an inch of piston skirt wear will cause the noise.

Dino oil, synthetic oil, heavy weight oil, light weight oil ; knock yourself out. Try them all. It won't do any good. Once the cold piston clatter starts, it's there to stay. I use Castrol 10W30 in mine. It seems to like that oil the best.

I don't worry about it much. Every japaneese car that i've owned has had cold piston clatter for hundreds of thousands of miles with no problems. Subies are no different.

Okay I hear you, but when is this noise something else. Subaru dealer has already used this example of noise on our engine. Now the sound does not go away, after a 16 mile drive, (half hour) especially when you give it some gas, sound more like a rattle. I had an independent Garage/Owner who deals in Foreign autos, he says that it's sounds more like loose Rod (piston or other I'm not sure). This car hass 22K miles under warranty till 36K I'd like this to go away before then, is that unrealistic?

stop making the noise when warm (if it ever gets warm in Alaska)

I would be back to the dealer and if it was not fixed a SOA rep.

I live in CA and mine still slaps until warm.

Tensioners for the timing belt also have a rep for rattles.

Thanks for your comments....

Not sure SOA Rep though. We're taking into the dealer tomorrow and I have a list of suggestions they should be looking at since reading this forum.

 

Bottom line they need to clear this secondary sound, I accept the engine has to make a running sound but the background knocking does not sound right.

 

I have a lot of faith in this independant Mechanic, who reckons that it should be fixed by Subaru.

 

Should I just ask them if we could have a new engine?

 

What's involved there does it have to blow up first? Surely it's covered by the warranty, I let you know how I get on.

 

Cheers again,

 

BTW I'm in USA largest temperate rainforest USFS Tongass.

I know that there are a few bad timing belt tensioners out there, but piston slap sounds like nothing else but piston slap. It always seems to start with #4 cylinder for some reason.

 

Replacing the belt tensioners in hopes of getting rid of the noise is wishful thinking in most cases and is usually a waste of money unless Subaru is picking up the tab under warranty.

 

Are "counter measure" pistons still being used for people that complain about the noise? I haven't heard anything about them in awhile.

the folks who were really adamant got new short blocks.

I just got off the phone with my BMW rep as I am trying to get a new belt tensioner that does not make noise before my warranty ends.

It sure is not easy to convince folks that you want it right.

If it is only the tensioner for the timeing belt it would be cheap for them to fix.

If it does not go away when it is warm it is a problem.

Originally posted by Scoobaroo

SNIP

It always seems to start with #4 cylinder for some reason.

SNIP

 

Interesting. I have some cold slap and it' s always sounded like only one cylinder making noise.

I have a 2003 Outback/4cyl/auto with 42,000 miles. The piston slap noise started this winter and it's getting worse. Under warranty, the dealer replaced the timing belt tensioner and the nose remains. I now have an appointment with the zone rep coming up soon. And this car is a replacement for a 2002 that was returned as a lemon.

 

I also have a 1995 Mazda 626 with 226,000 miles and that engine doesn't make a bit of noise. So Subaru has a big problem here.

 

Back in the 60's, when I was in high school, only worn out engines had piston slap.

Back in the 60's, when I was in high school, only worn out engines had piston slap.

Back in the 60's, pistons weighed a ton and had giant piston skirts. Now the skirts are incredibly short, and pistons are very light. And if they are forged (no idea), they have to be given more clearance because they expand more than a cast piston.

Subaru installs New Short Block

After only 22k on our 2002 Forester, we had some really loud slapping, due to wrapped cylinders. She sounds like a *****cat now! No instructions for 'running-in' period though?

One thing to note, the noise from the timing belt tensioner should be mostly apparent at idle, it's a intermittent knocking sound. Piston slap should be a consistent knocking sound, which increases in proportion to throttle increases.

My 2000 outback has no piston slap, however it did have a leaking tensioner, which the dealer replaced under warranty. The car has 90,000 km.

I have an '05 Baja that started knocking at less than 9,000 miles. Rep says "that's normal". Maybe for a worn out piece of crap, but it shouldn't be for an almost brand new car. They replaced the timing belt tensioner, and it got better, but it still sounds like it's going to blow up on bitter cold mornings for about the first 10 to 15 minutes. No one can explain to me what is so different about this engine that causes this problem. Oh well, I've got about 38,000 miles left on my warranty, we'll see what happens.

I have an '05 Baja that started knocking at less than 9,000 miles. Rep says "that's normal". Maybe for a worn out piece of crap, but it shouldn't be for an almost brand new car. They replaced the timing belt tensioner, and it got better, but it still sounds like it's going to blow up on bitter cold mornings for about the first 10 to 15 minutes. No one can explain to me what is so different about this engine that causes this problem. Oh well, I've got about 38,000 miles left on my warranty, we'll see what happens.

 

It's horizontal "boxer" configuration with small pistons skirts for increased fuel economy. Any comparisons to a 60's vintage motor (other than VW or Porsche) is just plain wrong.

 

It's been proven that these motors can run for years with piston slap if it goes away quickly once it's warm. If that the case the stop worrying about it. If it still slapping after that than you might have an issue.

Recipe for piston slap:

 

Take an inspired design like the 2.2, then lengthen it's stroke by moving the crankpin further out from the centerline so it swings a wider arc as the crank rotates.

 

This drags the piston down further into the bore at BDC (tHAT'S oK, jUST cHOP sOME mATERIAL fROM tHE bOTTOM oF tHE sKIRT) and pushes the piston out of the top of the deck at TDC (nO pROB, jUST pUSH tHE pISTON bACK iN sO tHE cROWN iS fLUSH wITH tHE dECK aND hAVE tHE wRIST pIN pOSITIONED hIGHER oN tHE pISTON).

 

Garnish with moly coating in an attempt to mask the noise through the warranty period. :-\

Blitz soon you will be able to put your skill in electronics to good use. As Subaru owners age a switch on the hearing aid would be very handy for this issue.

How 'bout Active Audio Knock Cancellation (AAKC) as part of the car's audio system to improve the S/N (signal to knock) ratio?

 

**** ******!

Ermm. Blitz, I like the idea, and the moly coating thing is SO true.

 

However, moving the gugeon/wrist pin "sideways" won't increase the stroke??????

 

The crank needs alteration to change the stroke length.

moving the gugeon/wrist pin "sideways" won't increase the stroke??????

 

The crank needs alteration to change the stroke length.

Straight from my post:

...then lengthen it's stroke by moving the crankpin further out from the centerline so it swings a wider arc as the crank rotates.

I make no mention of moving the wrist pin sideways. In order to keep the piston crown from poking out above the deck, the wrist pin had to be relocated HIGHER on the piston (closer to the crown).

 

In order to keep the skirt from contacting the crank at BDC, the skirt had to be trimmed.

I like your electronics idea Blitz, sign me up for the first prototype.

As for the piston what did raising the piston top and wrist pin achive? Less friction? I have always assumed that they got the slap when they cut the skirt, but I've never seen the pistons side by side to compare.

I like your electronics idea Blitz, sign me up for the first prototype.

Last week I repaired Kim Wilson's (Fabulous Thunderbirds) famous Red Bassman ...now I'm thinking about developing an "active" wheel that changes shape in anticipation of road irregularities for the purpose of smoothing ride quality and improving handling. Cool huh?

 

The 2.5 is a bored & stroked 2.2 ...it's a stretched design. If you stroke a 2.2, the piston moves farther at both ends (TDC & BDC). The crown pokes above the deck at TDC and the skirt contacts the crank at BDC.

 

The wrist-pin position was raised relative to the crown ...or alternatively: the crown was lowered relative to the wrist-pin position. What it accomplished primarily is that it keeps the top of the piston from poking above the deck at TDC.

 

The skirt was trimmed back to keep it from contacting the crank at BDC. The latest Sube brochures show cutaways of both the "streched" EJ-25 and the more normal-looking EZ-30. The EZ-30 piston looks more sane to my eye.

Ah, now I see what you mean. I was not think of comparing it to the 2.2 it came from. It probably saved a lot of money not raising the deck as you could use all the same machinery. basically it is just a 2.2 with the typical hot rod tricks.

I'm glad you got a famous amp back on the road where it belongs!

I think an active wheel might very well work these days. They have done a lot of interesting things on trains you might look at.

IMO, it was greed for displacement on-the-cheap. Bad gamble, and I hate to say it ...but it reeks of "GM-think".

 

Only kidding about the active wheel, but it wouldn't suprise me to something like it someday.

I think they have been putting suspension in high speed rail wheels and working on sensors to tell when the track has a ripple. You aren't far off.