Piston Slap and PTV clearance

My 2000 Legacy GT wagon has had piston slap for a couple years now. It only happens in the cold. It used to make a faint sound like the drumming of a coffee can. It went away in a few minutes of driving.

 

So I know that the common wisdom is don't worry about it. But lately it's started to sound like this.

 

[ame=http://www.youtube.com/watch?v=7NVjR4CYrCw]Subaru EJ25 Piston Slap - YouTube[/ame]

 

That's not my video, but my wagon has that clicking noise. It's pretty loud but it goes away just like the piston slap. But if it's cold out it lasts for a pretty long time. If I accelerate it gets a lot louder and if I decelerate it goes away. It gets fainter and fainter as the engine warms up, and eventually goes away.

 

So I'm afraid that a valve is smacking a piston. I just put new head gaskets on a couple years ago and it's run without a hiccup until lately. Before I rip the passenger side head off and look for witness marks etc I was hoping that someone had some experience with this symptom.

 

I know where this is going if my hunch is right. Considering that at least one piston had been slapping around in there for a while the smart money might be a short block or long block. Any valves that have hit pistons would of course have to be replaced too.

 

This engine has 107,xxx miles, runs smooth and gives great power, and doesn't even use any oil at all.

 

So thanks for reading.

Piston slap is the movement of the piston laterally in the bore as the skirt is very short.

It stops as it warms because the metal expands and now fills the bore.

Not a valve to piston issue.

Am sure a mechanic on here will add, especially as to the long term effects of such.

 

O.

I know exactly what piston slap is. I understand why it goes away when it warms up too. I have built a few engines in my years, but I have never built one of these.

 

I saw on youtube an EJ25 engine that had been driven so long with piston slap, that the pistons rocked enough to smack the cylinder head. I also saw where a guy showed the witness marks on his piston and valve, and then was able to rock the piston - a lot - by hand at TDC. But this video I provided illustrates the same noise I'm experiencing - only louder and mine doesn't have the knock.

 

I don't think I'm being unreasonable with my concern over PTV clearance issues, but I might (I hope) be a little paranoid.

 

If it's just Scoobie noises, I won't worry about it. But if the engine is getting ready to drop a valve, I want to know about it.

 

Thank you for responding.

Osei is correct. Piston slap (and the noise that you hear from such a thing) is not a result of the piston contacting the valves, it's a result of the piston making contact with the cylinder walls.

 

I know that. I am concerned about the piston slap becoming bad enough to cause clearance issues. I know that this happens in extreme cases. PTV contact can in fact be the result of advancing piston slap issues.

 

Remember that this noise started out as typical piston slap - a muted coffee can drumming sound that went away within a few minutes every time. It's just since the weather turned cold that this new noise came up. It was 10 degrees with 30 miles an hour wind the other day and when I started the car, the sound was really sharp and loud. I didn't hear it on the expressway but when I got off, I heard it again. But today with 25 degree mild conditions I only heard the tapping for about 5 minutes.

 

If the car is running fine and has been making the noise for a long time, it may well just be injector noise.

 

This noise is new and it's definitely not injector noise.

 

If you're pistons are making contact with your valves you'd likely be seeing significant compression issues over time, if not immediately.

 

I know this very well. I haven't done a leak down but first day off I will. Time will tell as I'm still daily driving the car.

 

If I have to fix it or (gasp) get rid of it, I want to be able to start planning. Plus I don't want it to take a dump when I'm 25 miles from home and it's super cold out.

Are you hearing lifters that have worn to out of spec, or a hydraulic lifter that isn't pumping up to stay in adjustment ? I know the 97 Outback I had suggested shim changes at 100k. Is the 2000 similar ?

If the piston had worn to the point where it could tip to hit the valves, you've got a huge problem even without the valve contact. You would likely have lost compression, or damaged the piston. I don't believe that with the oil coating on the cylinder wall that that wear would be significant enough to cause valve contact.

It's got a non-hydraulic valvetrain. Everything was adjusted two years ago with new head gaskets.

 

If it's just some valve noise or piston pin noise, I will not worry.

 

I saw pics of a piston that had worn enough to rock and hit the cylinder head. Since my car runs so good, makes good power, and doesn't even use any oil, I doubt the piston wear could be so severe.

 

Thanks to all. I have something to think about.

I know the 97 Outback I had suggested shim changes at 100k. Is the 2000 similar ?

Does my head have shims in the pedestal? I did not remove the cam; I just cleaned everything up with brake clean and used lots of compressed air (I have a rubber tipped blow gun). I blew all the gunk out of the oil galleys and disassembled and cleaned out the rocker shafts. The head was very flat (fire rings hadn't failed; all they had was weepage at the bottom) so I cleaned the deck up with a 14" long block sander with emery cloth. I pre lubed everything with assembly lube.

 

What I did not do was check any clearances(except for valve lash adjustment of course). I do know how to optimize a valvetrain geometry because I have installed custom valevetrain parts on old school V8 engines. You must always adjust rocker arm height for a small contact pattern on the valve tip that is centered for maximum performance and even more importantly, longevity. Then you must check that all lifters can bleed down a certain amount and also check for bleeddown times. These engines were (still are) adjusted with adjustable rocker studs and adjustable guide plates. And you must always check clearances with a custom setup. I use the "clay" method where you assemble and adjust everything and assemble with a small lump of clay on the valves; then you turn the engine over a couple of times by hand and disassemble and check thickness of clay for approximate clearances.

 

But - I did none of this with my Subaru engine. I just reassembled it (along with a new timing kit, water pump, and tensioner) trusting that it would run great because it ran great before I even disassembled it. I did turn it over by hand a couple of times and it did not bind, so I finished the installation. It started right up with zero drama and ran without a hiccup for two years and 12,000 miles. And it uses not a drop of fluids.

 

Is it possible for my piston slap to evolve into this clicking noise? Check out this ej20 piston slap

 

[ame=http://www.youtube.com/watch?v=F2H_13231-8]subaru impreza piston slap ej20 wrx/sti - YouTube[/ame]

 

How bad is that? Did the car engine still run good?

 

I'm used to piston slap from high performance engines I've built. Aftermarket forged pistons are almost always louder than stock pistons; even if the stockers are forged. But it always used to go away within a few minutes and my Subaru used to be the same way.

I would check the timing before pulling a head. If timing is on then move onto a compression or leak down test. If a piston were rocking that heavily in the bore (to cause valve contact) I can't imagine it would not show low compression readings with rings tilted to that degree.

Agreed Mike. Leak down test is Sunday (first day off).

 

I am convinced that it is in the bottom end, because it is load dependent. Did everyone look at the rocking piston video? It made a clicking noise.

 

If it keeps running right I may never know, because I intend to drive it. It is my work car. If I thought it was an easy fix (like replace the rocker shaft) I would knock it right out in a couple hours.

 

Thanks to everyone for their help.

I'm positive the 97 was shim over bucket. If I remember correctly, there was a somewhat different adjustment on the next generation. I'd defer to the 'vacation pics' to verify the process.

Pics would be appreciated.

 

I just put everything together the way it was when I took it apart. I know that poor valvetrain geometry can cause accelerated wear and early failure of components. I suppose that this sound could be that, but why would it be load dependent?

 

If one of the front pistons is bad, I'm thinking of just slipping one in there quick and dirty, without removing the engine. If it's one of the rear, no dice.

 

I can't help but wonder what kind of maintenance this car had. I bought it 9 years old with 89000 miles. It had some recent repairs and of course I had to do some more. But the back hatch wad dirty and worn out. The plastic pieces were scuffed and cracked. It looks like someone hauled a motorcycle or greasy machinery in the back. That's OK because I bought it as a work car; the cargo space is great and the rack is handy too.

Leakdown "cold" showed passenger side front cylinder leaking past the rings a little more than the other three. (Sorry guys no numbers; I do it by "ear.") I drove it around for a few hours (usual routine errands) and checked again. It was much more uniform.

 

I hardly heard the noise the last few days. If I do it goes away within 15 seconds of starting. But once it gets below 15 degrees, the noise is terrible and it takes a long time to go away. There is a cold snap right around the corner (been pretty mild the last few days) so maybe I'll do a "cold" test when it's real cold out.

 

My fear is that I will wear something out driving it in the frigid weather. It won't go away idling if it's really cold out, even if the temp gauge is all the way up. Plus I think it's pulling timing when it makes the noise because it feels a little sluggish. (I just repaired the knock sensor wiring; and when it threw the code, it ran bad and used a lot more gas.)

 

I have noticed a couple of Outbacks with the exact same noise lately. It must be something that's been dealt with before.

Just curious, what weight oil are you running ? Is it synthetic ?

5W30, non synthetic. Changed twice a year at 3000 miles.

 

Think 0W30 might help? It's early for an oil change but if it's going to help with winter performance I'll do it.

considering the cost of oil vs. time/effort of pulling it apart, I'd give the oil a try and see if that changes things.

Well Mr. Wheelbuilder, thank you for your input.

 

I have some interesting observations. If you just drive it easy like in "warmup mode" (which I tended to do when it was still knocking) the noise never goes away. If you drive long enough to bring the temp gauge all the way up (couple of miles tops - thermostat and cooling system work great) and shut it off for a few minutes, the knock is completely gone; even if the temp gauge goes way down. If you warm it up for a few minutes with easy driving until the gauge goes over the first line and then accelerate briskly a couple times, the knock goes away. If the outside temp is over 50 degrees f, you don't hear it.

 

It was zero degrees f after my shift tonight, and I started my car and went and sat in the (nice and warm) truck for 10 minutes before I left. When I got in, I drove it out of the driveway and the needle was over the first line. I gunned it and the knock went away. Even the transmission (terrible morning sickness in cold weather) performed without a hitch. I was surprised.

 

I think everything points to piston slap. I will change the oil once it warms up and try 0W30. I also have cardboard in front of the radiator (completely blocked off now) and it definitely helps it warm up faster. It also helps with awesome heat when you need it.

 

I was going to put a "shift improver" kit into the trans to see if it helps. I think it will but I also think the 3rd gear clutch is pretty worn out. I asked the dealer about clicking when shifting into 3rd and they said it was "normal." I asked about slipping when shifting into 3rd and he asked "is it throwing a code" and I said "no" and he said "then it's not slipping." But it has a nasty flare when shifting into 3rd when the trans is cold. So faster warmups seem to help with this a lot too.

I'm glad that you didn't end up having to tear into the engine.

 

As far as the transmission - have you changed the fluid (drain and fill) lately ? My Outback loved new fluid, but I can't say it slipped ever. You might see about the band adjustment as well, I never ended up adjusting the OB, but I think it was simple enough. This from a guy not under a car at the moment, and away from the manual...

I did a drain and fill a couple of years ago. I also changed the spin on filter. I used Dextron III, which is supposed to be OK. I probably should have used Subaru fluid.

 

Which band can be adjusted? Do you have a quick link?

 

 

The engine is still screwy, but I'm not going to tear into it while it's running so good. I've learned how to get it to warm up quick and that will do for now.

 

Thank you for your help.

Those can really sound disturbing, I've heard some that still slap a bit when the engine is warm. Part of the problem is the design of the piston, not having skirts. Just drive it, don't fix it until it breaks.

I like to stick to no more than 30,000 mi. on a trans fluid change. Dexron was fine up to the mid/late 2000's. My 09 uses the odd Subaru only stuff, the 97 was Dexron III. You used the right filter on the trans ? It isn't an engine oil filter. I think there are a couple manufacturers other than Subaru. I'll try to dig up my manual and see where the band adjustment is. You can search this site for 'vacation pix' That should have some useful detail as well.

I put the right filter on. It is a Wix. I don't think it's a problem. Trans is OK when warmed up.

 

So tuner, think it's going to break? I've seen pics of some nasty EJ25 pistons, but I think they were from turbo engines.

http://allwheeldriveauto.com/subaru-piston-slap/

 

My car does it too and its more noticeable the colder it is outside.

When I first got the car I did an oil change Mobil1 5w30 and the noise was pretty loud.

Last month I changed the oil again with Penzoil 10w30 and it seems the noise is not as loud as with the 5w30.

Yes, that video is a good explanation. I was hoping to hear it on the video.

 

I keep noticing Subarus with the exact same noise as mine. While it is certainly loud, I don't care as long as it keeps running good. It doesn't even use any oil at all.

 

American consumers have been conditioned to expect whisper quiet, effortless to drive cars. When I was young, an American car making a noise like this would have been rejected by consumers and probably subject to a massive recall. Everything was smoother, quieter, more powerful. I remember the power steering that required zero effort to turn. It's pretty boring actually; you feel detached from driving, like you're operating a simulator.

It was very cold last night when I left work. Warming it up in the driveway for 7 minutes helped a lot. The noise went away in a mile of driving and even the trans did a lot better. It's a pain in the ass, but it works.

 

It was so cold that the suspension felt super stiff. I've experienced this on other cars and I always wondered if it increased wear on struts etc. I remember when it was 20 below and my tire rolled right off the rim when I turned right. Being stranded in my car is a big fear of mine in this frigid weather. I'm not so young any more.

 

I work 2 jobs and need my car for both of them. I haul a lot of stuff (hundreds of pounds) when I do electrical work. That's why I bought a wagon. I love doing electrical work because I love solving problems with old buildings and houses and I am very good at this. But working for people is another story. The guy I worked for for 2 years hasn't paid me in over 3 months. I bounced to another gig and he is furious. He feels betrayed and says he is going to charge me $100/day for every day I don't come to work when he calls. I told him to go take a business class. I know he just doesn't want to pay me (and he still expects me to come to work for him!) because he said this when I told him to just pay up or else the judge will tell him to pay, plus court costs. I think he thinks employees are actually slaves.