piston slap common?

Excessive ?piston slap? occurs because an automobile manufacturer designs and/or manufactures a defective engine in which the clearance between the piston and cylinder bore is too great. Essentially, the piston moves sideways and ?slaps? or ?knocks? hard against the cylinder bore and causes damage to the engine pistons and cylinders, excessive smoke emissions, excessive oil consumption, carbon buildup on piston heads, decreased mileage, and a loud and obnoxious ?slapping? or ?knocking? noise, all of which diminishes vehicle resale value in the trade.

The above is from an internet search for piston slap.

Al

On the 2.2l motor, lifter noise is quite common; a tic-tic-tic that generally lessens as the car warms up.

You could try any of the various oil additives, but in my experience they won't help much, if any.

As long as the noise mostly goes away when the engine is warm, I wouldn't worry about it. Once it gets to the point where it's more of a "clack-clack-clack" that _doesn't_ really go away, you'll probably want to look into servicing the hydraulic lifter(s).

This isn't a difficult job on the 2.2; the hydraulic lifter is located in the cam follower (rocker arm if you will), and this is readily accessible without removing the head from the engine. A pretty simple DIY project as it turns out.

I've found that swapping in a good lifter for the collapsed one generally solves the problem, at least for a while. Get an entire head (a slightly warped one is probably fine, and cheap), or even just the cam follower assembly from a salvage yard. If the problem persists, it's an indication that the oil pump is getting tired. (Or that there is contamination present in the engine oiling circuit; did someone use silicone sealant when replacing an oil pan or oil pump recently?)

You can readily find instructions for this procedure on the web, or email me and I'll send you what I have. Takes about an hour, more or less, with no special tools; 10 and 12mm wrenches and sockets, a set of needle-nosed pliers, and a cup or so of fresh oil.

Another possibility is the timing belt system. I'll assume that at

130+K you have had the belt replaced. Did they also replace the tensioner, idlers, and waterpump? Sometimes a failing idler bearing will start off by making a clicking or tapping noise which may or may not lessen as the engine warms. If this is the case, it will get rapidly worse with time, and should be attended to ASAP to prevent possible engine damage. If you use a mechanics stethoscope to listen to the running engine, the lifter noise will obviously be associated with one side or the other's (or both) cylinder head; the timing belt idlers will sound more front and center. Piston slap, I couldn't say.

If I'm way off the mark, and it _is_ piston slap, there's not too much you can do about it anyway. Drive the car until it fails outright (rare), or gets obnoxiously loud, and then either replace the engine or upgrade to a newer Soobie.

Hope this helps.

ByeBye! S. Steve Jernigan KG0MB Laboratory Manager Microelectronics Research University of Colorado (719) 262-3101

When did Subaru start using hydraulic lifters? Sorry for the top post.

You may try different oil filters as some are more obstructive than others. This seems to make matters worse for piston slap- high flow filter is preferable. I'd use some Marvel Mystery oil in the fuel, 8-10 ounces per tank, and a similar amount in the oil, for 500 miles, or so, to clean up carbon deposits, and then change oil. At you're milage you may use something like 15w-40 diesel type oil to control carbon, and put a NAPA GOLD oil filter (this one has good flow specs, and favourable experience) and see if that makes any difference. Chances are it will.

M.J.

Cold "tap-tap-tap" is very common for 1998 - 2000 Subie 2.2 engines. Could be caused by slap due to short piston skirt, or could be timing belt tensioner. Both can make the noise when cold. I had 1998 Outback, 1999 Impreza, and 2000 Forester, each tapped when cold. Irritating, but not harmful.

Try a can of STP or something similar. It keeps a coat of lubricant on all parts while the engine isn't running. So, when you start a cold engine, it should already have a good coat of lube on the piston and you likely won't hear any noise.

What do you figure carbon deposits would do to cause piston slap ?

VF

I wonder what different oil weight would do? The first #, higher or even lower.

VF

Carbon deposits form on pistons, they contribute to wear and increased space between rings and cylinder which makes for increased piston slap. Also thicker diesel oil cusions better. Works to provide an added coat of film that is good at cold starts. Thin oils drain to the pan fast making piston slap worse- someone mentioned putting some STP, this is essentially thickening the oil for that same purpose.

I think taht my approach of installing a higher flow oil filter, plus controlling for deposits better, plus switching to a thicker diesel type oil, has good chance to help, both immediately, and longer term.

M.J.

I didn't think carbon would form or the sides of pistons, and then removing it would help slap. I think different weight oil might help, but heavier oil wouldn't flow as fast when cold, but thought thicker or thinner might be worth a try. Don't know the flat motors, and was wondering how they lube the cyl bore? Squirt oil to the top/upper side, and let it run to the bottom/lower side?

I have a new 07' Impreza, and am concerned about developing piston slap, since soon after I start driving, I often have to accelerate harder if I get into traffic, so trying to take it easy, especially in the winter.

VF

While I'm sure any newer soob could develop a true problem resulting in something like piston slap, FHI/Subaru had engineered piston skirts which were too short in the 90s, maybe early 2000s. (?) pretty sure that design problem is fixed in newer engines.

Carl

Of course it forms there too, but doesn't have much chance to accumulate on the extreme sides of pistons because it is constantly ground there, wearing both rings and cylindeer walls. Synthetic oil is great in preventing carbon build-up as it does not evaporate at high temps. Very little to no carbon forms in the lower engine, most forms in the cylinder area where temps are high.

This is a very difficult topic. There is a point of equilibrium for thickness. If you start your car just once a month, every start will most likely be a complete 'cold start.' I mean oil will have almost completely drained into the pan, leaving little to no layer of protection. For some aircraft that get used infrequently to protect engine parts from rusting a single weight thick oil is recommended. It sits on parts much longer.

If you start your car daily a slightly thicker oil may also stick to parts longer, at least long enough to cusion piston slap at your next start up.

Experiment, experiment. Take into account the ambient temperatures. Thin oil in hot climates, say summer in Phoenix Arizona, drains into pan within an hour or two, so almost every start is a "cold-start." When using thicker oil try to get a higher flow filter like the NAPA GOLD I've mentioned.

This is really interesting, I think flats are generally better oiled than other engines.

Don't worry, you have a newer Subbie probably less likely to develop slap. I have a 2000 Impreza (original owner) and am located about a quarter to a half mile away from an on-highway ramp, where I also have to step on it, everyday.

I always warm up the car, for at least 5 minutes, and have always since new used Marvel Mystery Oil in gas, this is a relatively cheap upper cylinder lubricant. A few ounces like 4-5oz to tankfull. The engine at 49k miles is in near perfect new condition, by that I mean it is very tight, more like a 15-20k miles old engine

M.J.

I forgot to add, the ramp is on an incline and I see

4500-5000 rpms there regularly, sometimes more.

M.J.