cookie Posted February 21, 2006 Share Posted February 21, 2006 No piston slap is not the same as valve tap. Sometimes it's hard to tell the difference though. Piston slap is the psiton hitting the cylinder wall and valve tap is excessive clearance in the valve train. Anybody got a link to how it works for this person? Quote Link to comment Share on other sites More sharing options...
jimkasper Posted February 21, 2006 Share Posted February 21, 2006 I have a '98 Outback (2.5) that I purchased used in 2002 with about 38,000 miles on it. Piston slap when cold since purchase. I now have about 53,000 miles on it and although it still sounds like an old Mercedes diesel when cold, I have had with no problems to date. jimkasper Quote Link to comment Share on other sites More sharing options...
nipper Posted February 21, 2006 Share Posted February 21, 2006 I have a '98 Outback (2.5) that I purchased used in 2002 with about 38,000 miles on it. Piston slap when cold since purchase. I now have about 53,000 miles on it and although it still sounds like an old Mercedes diesel when cold, I have had with no problems to date. jimkasper i have a 97 outback with 182,000 on the car with piston slap. The car runs like a top. Its all original. i had a 98 legacy that got smashed. At 180K that had slap too and no problems. Its just a subaru thing. nipper Quote Link to comment Share on other sites More sharing options...
dxrflyboy Posted February 22, 2006 Share Posted February 22, 2006 I have my doubts that the short skirt design is there for fuel economy, or at least not entirely. As Subaru has added longer strokes and overhead cams to their engines, they have become wider and wider, to the point where there is no more room left between the wheelwells. In order to make an engine that still fits in the car, they've had to minimize rod length and piston height. Short rods create more sideloading of the pistons, while the short pistons are more likely to rock in the cylinder bore, especially when combined with larger bore sizes. The upside is the short pistons reduce reciprocating mass, allowing higher RPM operation. The slap is a problem for cylinders 2 & 4 because sideloading occurs on the top side of the cylinder, so the pistons shift from the bottom side to the top side during the power stroke. Revising the piston can minimize the noise, but the pistons will always shift to some degree during the power stroke in cylinders 2 & 4. Quote Link to comment Share on other sites More sharing options...
nipper Posted February 22, 2006 Share Posted February 22, 2006 I have my doubts that the short skirt design is there for fuel economy, or at least not entirely. As Subaru has added longer strokes and overhead cams to their engines, they have become wider and wider, to the point where there is no more room left between the wheelwells. In order to make an engine that still fits in the car, they've had to minimize rod length and piston height. Short rods create more sideloading of the pistons, while the short pistons are more likely to rock in the cylinder bore, especially when combined with larger bore sizes. The upside is the short pistons reduce reciprocating mass, allowing higher RPM operation. The slap is a problem for cylinders 2 & 4 because sideloading occurs on the top side of the cylinder, so the pistons shift from the bottom side to the top side during the power stroke. Revising the piston can minimize the noise, but the pistons will always shift to some degree during the power stroke in cylinders 2 & 4. From an automotive engineers persepctive (mine) the shorter skirt is there for several reasons. It is there for gas mileage and for more power. When you reduce the engine mass, you reduce the Horsepower that is required to turn the guts of the engine. The engine revs faster. It is also there for emissions, as less mass means the piston warms up faster. It is also done to reduce NVH (noise vibration and harshness). Pitson slap can be reduced by slightly offsetting the wrist pin, why they dont to this (its done in motorcycles) i dont know. When one says it is there fo gas mileage, its not there for the individual owners benafit, but its there for the fleet benafit (cafe rating). that .2mpg gain may mean nothing to you, but it means a lot to the manufacturer. Also the other thing that blows your opinion out of the water, is that ALL engines have smaller or non existing piston skirts for the same reasons. The reason why it is so much more obvious on a subaru is because the engine lies on its side, and gravity has some say in the matter. Again for the 20th time a link i post with topic Worst case scenario and a cool test http://www.pistonslap.com/whatisit.htm WHy http://www.canadiandriver.com/articles/jk/020320.htm Parts of a piston http://www.hastingsmfg.com/Service%20Tips/piston.htm Excellant picture http://www.drive.subaru.com/SubaruDrive-Sum02/Piston-Cranky.asp and yes they did remove too much material on the skirt (im shocked, first good picture ive seen of it). nipper Quote Link to comment Share on other sites More sharing options...
Setright Posted February 22, 2006 Share Posted February 22, 2006 nipper, the EJ engines do have offset pins. My source is Subaru's own tech material. In fact, I can't think of any engine that doesn't have offset pins. Almost any skirt design will slap if the pins are centered. Similarly, pistons aren't round when they're cold. These are basic "musts" of a piston engine, I doubt very much any engine is without them. But still, the later EJ's slap when cold. Piston length and wrist pin height within the piston are the cause. I am leaning very much toward Dr.Outback's view on this. If you're engine doesn't slap when warm, relax and enjoy the drive. Quote Link to comment Share on other sites More sharing options...
nipper Posted February 22, 2006 Share Posted February 22, 2006 i meant the proper offset, sorry. i have always agreed with that, it goes away when warm, just drive the car. i never even started thinking about it untill the threads appeared more and more. Basically my cars gone 180K with slap, at the next 180K ill worry about it. i'm more upset that my heated drivers seat isnt working right then piston slap nipper Quote Link to comment Share on other sites More sharing options...
Setright Posted February 22, 2006 Share Posted February 22, 2006 I had a busted heated seat in a old Legacy. Took the seat out, removed the cloth cover (held on by copper clips) soldered the broken bit in the element, and presto! Quote Link to comment Share on other sites More sharing options...
nipper Posted February 22, 2006 Share Posted February 22, 2006 I had a busted heated seat in a old Legacy. Took the seat out, removed the cloth cover (held on by copper clips) soldered the broken bit in the element, and presto! cool wonder if it works the same with leather (dont mean to hijack the thread .. sorry) nipper Quote Link to comment Share on other sites More sharing options...
ctoth Posted February 22, 2006 Share Posted February 22, 2006 My '04 impreza ts has it. It has about 35,000 on it and it didn't really start until about 25-30 thousand. Mostly when it's below freezing outside. What ever though, when it's warn it goes like a bastard, so I don't care. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.