How is this caused? what are the symtoms? longgevity of motor shorter?
any experts?

ps I have this problem on cold start on my '97 EJ22 with 65k so I'm just wondering.

I cant be arsed to type loads.. lol

Basically it due to a large bore clearance between the piston and the cylinder wall.

Either the piston has distorted.. the cylinder has.. or it was machined incorrectly in the first place.

Basically the piston is tilting allowing the base of the skirt to impact/slap against the cylinder wall... it could even be the top of the side of the piston.

Basically each slap will leave a mark on the wall and the piston itself...eventually you will start to loose compression (the rings wont seal against the damaged wall)... you might find that the piston will fail too.

Slap can vary.. and its magnitude will determine the life of the engine.

Slap is common when you fit forgies..as these expand more with heat.. hence you have to run larger bore clearances.... once warm they are fine, but at cold they sound baaaaad... and do the most damage.

J.

ok then, maybe I will save up for a new shortblock? Is it my fault I have piston slap? or is it subaru's?

From some of my own research, I can tell you SOME piston slap is inevitable. You may not even be able to hear it. A thinner oil in your engine can even cause piston slap. I hear a little slap in mine when it's cold, but that's about it. On my next oil change, I'll got from 5w-30 to 10w-30. Winter months here in colorado just make it a good idea.
Another factor in our engines with piston slap is the boxer design itself. This is JUST A GERALITY FOLKS. SPARE ME THE FLAMES! Places of load bearing are different for boxer engines, inlines, and v's. For a v8, it was a certain angle in the 360 degrees of the rod bearings that was JUST ONE place of concern. Chevy drilled an oil feed hole in the bearing at that exact location to relieve pressure and aid in cooling. In-line engines like to chew crank bearings. For us boxer freaks, it's the piston rings that recieve the most frictional load. Part of our engines being naturally balanced, is that the vibrations are distributed throughout the rotating assembly. Bottom ends on a boxer are slightly more "tortured" than others engines by design...I think. I'll stop the generalities there, 'cuz you could write several books on this stuff.
The point is, every engine has a part that likes to wear out first. For chevy 350's, it was the front oil bearing. For my old suzuki inline 1600, it was the number one piston's rings. To each his own, I guess.

Gary

Following on from the above comment about angles of the dangles...

Phase one engines have central gudgeon pins...where as Phase II have offset pins.

The use of the offset design helps to minimise the piston slap.

Yes, oil viscosity can affect piston slap.. but it is so minimal.

I have never seen/heard of a piston pin failure.. and I have never seen any excessive wear.

If anything its the big end that suffers (due to the differences in design).

J.
J.

You probably won't need a new shortblock. Assuming the piston slap is still at reasonable levels, you should be able to get the block re-bored or re-sleeved and that'll take care of all the grooves. You'll have to get new pistons of course (ones w/o grooves) http://www.i-club.com/ubb-files/wink.gif
When I rebuild the engine in my old mustang the #5 cylinder had such bad piston slap that I could stick a dime in the grooves on the piston, and the top compression ring came off in about 30 pieces. http://www.i-club.com/ubb-files/eek.gif That could be why I was only getting about 8 psi. of compression in that cylinder. http://www.i-club.com/ubb-files/wink.gif But it only got that bad because it was driven way past the point that it should have been rebuilt, and the car would run hot in the summers.
Good luck

Oh dear... on Nov. 21 I drove my '99 550 miles on I-5 and parked it at my mom's house. The next morning (20 degrees F ambient) I started the car to an awful clacking noise which lasted about 2 minutes then tapered away to nothing. I gathered that this is piston slap and hoped it would not return once I returned the car to the Bay Area. Unfortunately when I went to start the car tonight the noise was present, although not as loud as before. It's only in the middle forties, though, not cold like before. Prior to last Wednesday I had never heard anything like this at startup.

So... what's next? I have a feeling that it will get worse. My only engine mods are an intake and a UR pulley. Do I wait until it's unbearable? Would Santa Cruz offer to replace the engine if it develops "bad" slap? What is bad? Five full minutes on a 40 degree ambient startup from cold? Present all the time? When the compression starts to fail? I am pretty disappointed, seeing as my RS has only 23000 miles and has always had clean oil, mostly Valvoline Synthetic and Mobil 1. What should I do?

I talked to the guys at Santa Cruz... they said the only real solution is an engine shortblock swap if it gets bad. Omigod... would it ever run right again? Will they freak out when they see my suspension mods? I guess the only things I'd have to remove are the Field unit, pulley, and intake. I don't know if I can even get the car down there. Why me? Why my RS?

All piston slap is not created equal.


http://caselaw.lp.findlaw.com/scripts/getcase.pl?court=il&vol=app/2001/1994079&invol=3

Just thought I'd put this here for posterity since I've been researching piston slap and this is interesting. It's about Chrysler, not Subaru but I think the the issues are the same.

Here's the most relevant bits in case this link goes away:


Dr. Asmus, a senior research executive at Chrysler, engages in engine research. He testified on behalf of defendant regarding the "piston slap," which occurs in all four-stroke engines as a result of the forces acting upon the piston. He explained that there are several types of piston slaps. One is the "conventional" piston slap, which refers to the lateral movement of the piston from one side of the cylinder liner to the other. Conventional piston slap causes the most concern to engineers because at this point the oil film which protects the piston from the cylinder liner is relatively hot, oil viscosity is relatively low, and the gas pressure force in the chamber is high. Furthermore, the gas force on top of the piston slap is very high, and the cylinder liner at the point of impact is very hot. Asmus explained that conventional piston slap is most audible under a heavy load when gas pressures are high and cylinder piston temperatures are elevated.

Another type of piston slap is "early" piston slap, which occurs at approximately 45 to 50 before top dead center during the crank shaft rotation when the cylinder pressure changes from negative to positive. Asmus testified that, unlike conventional piston slap, early piston slap during idle is not a concern to engineers because the forces involved are very low and the gas pressure forces are low. He opined that the oil is more robust and thicker, thereby allowing the piston to be cushioned during the impact. Although early piston slap does exist in all throttle spark engines, it may or may not be audible because the audibility depends on the nature of the translation and other sounds that may be emanating from the engine structure.

He further testified that a throttle spark engine is not defective because it exhibits a conventional or early piston slap at idle, nor is it defective because there is an audible conventional or early piston slap at idle. He stated that the audibility of a piston slap is very subjective and is one of the many things about an engine that is audible. He explained that attempting to reduce the audibility of the piston slap subjects the engine to great risks of serious failure.

Jay_UK seems to better understand piston slap causes than some "suby specialist" It has nothing or little to do with the engine configuration ie in-line, flat or V. Piston pin off-set is determined by the bore centerline and crankshaft stroke together with combustion pressures as part of the equasion as to the forces applied.

Holy dead threads batman....

before you go out and have someone tear the engine apart check the timing belt tensioner. These are common to make some noice on a cold engine.

This thread is old as dirt, but I think the original guy might have been hearing hydraulic lifters clicking because of the cold weather, not piston slap.

:huh: Back from the dead?

Anyway, piston slap and lifter noise on cold start is natural for Subies. If it goes away when the car warms up then it's perfectly normal.

What about thrust bearing wear/ crank endplay. Could that have a (ahem) bearing?

ALL subarus have some piston slap.

I consider myself to be a phase I engine guru. With piston slap in that type of engine the skirt of the piston is hitting the cylinder wall. This can be fixed by upgrading the piston "head" to the newer version....In think they are $70 a piece. You dont have to take the engine apart as there are access holes to get at the piston head, you will need to take of the heads though. That being said....phase II engine with piston slap you can pull the piston heads off and take a look at the skirt and actually see where the metal is scored in most cases, if its not scored look for other issues. In fact it makes sense to look at the above mentioned other issues before internal surgery in all cases.

Stu