Could I get a good explaination of piston slap, and I also wanted to know if it is good or bad (probably bad). And if there are different degrees of it. I also wanted to know if once it starts, if the engine will be dead soon. Or is it kinda like rings on the engine slightly getting worn out after the engine sees a few miles.

thanks,
Kevin
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1980 244DL, 1982 245GL, 1987 744GLE, 1991 245SE, 1996 855GLT, 2001 V70

If you have an affected B230F* block, you can actually move the cold piston around in the cylinder by hand (head removed). Of course when it's warm that doesn't happen, but when cold you can re-create the noise by rocking the piston around.

--
1992 940 wagon, 72k
as well as others.

Volvo's attempt to lighten the B230 engine resulted, among other things, in a design that included shortened piston skirts. Piston skirts normally hold the piston straight and parallel in the cylinder bore. This is important because the forces are asymmetric, so a piston has a tendancy to rock back 'n forth when the loads on it change -- such as going from intake to compression to power strokes.

Keep in mind that the Volvo block is iron while the pistons are aluminum -- and aluminum expands twice as much as iron when heated. Thus, the design must include a SMALLER piston, when cold, so that it will expand to properly fill the bore at normal temperatures.

As the pistons work up 'n down in the bores, the aluminum skirts wear. If they're already short 'n light when new, then a small amount of wear can produce a surprising amount of clearance 'tween skirt and wall, particularly on a cold engine. Excess skirt clearance allows the piston to rock, and each time it rocks, the skirt "slaps" the cylinder wall. As the pistons warm and expand, they fill the cylinder bores, the rocking is reduced, and the "slapping" goes away.

It is not dangerous and it does not mean the end is near. However, when you hear tapping from a cold B230 at idle, you should be sure it's piston slap and not a bad bearing or worn wrist pin (not common in Volvo engines).

My '91 740 has piston slap (230k miles, or so). When wife leaves the driveway on a cold morning (always at about 150 mph and accelerating...) I can hear the piston slap for about 5 miles, which, at her speed, doesn't take long...;-)

Personally, I like to drive the cars VERY GENTLY for the first 2-3 miles, allowing the block and pistons to equilibrate to operating temperature. This advice is totally lost on wife.
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Don Foster (near Cape Cod, MA)

If the pistons are rocking back and forth, does that effect the ring wear?
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Regards,

David
1991 744 NA 139+K Miles

Good question, and appropriate.

From a practical standpoint, I'd guess that the rings or the lands do not sustain any increased wear beyond the normal amount. The pistons ALWAYS move side-to-side slightly because of the cyclic loading on the piston crown. In the case of piston slap, the pistons are also rocking slightly, but perhaps only a few extra ten-thousandths of an inch. My opinion is that this would mean nothing at the mid and top regions of the piston. And don't forget that the rocking is minimized once the engine reaches operating temperature.

Keep in mind that the dimensions we're discussing are tiny -- on the order of a few wavelengths of light, and much less than the thickness of human hair, even mine.
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Don Foster (near Cape Cod, MA)

Don,

Thanks for the excellent explanation regarding the piston slap noise. Is there a way to distinguish between the noise of piston slap and the noise made by valves needing adjustment?

I haven't seen much on the board about adjusting valves on the B230F and I was curious as my '93 and '86 240's both make a slight tapping noise at startup, and like you, I try to baby them until they are warmed up.

Regards,

TomD

Dunno what's up with your 93, as that is the year that the B230 engine recieved some changes that pretty much got rid of the piston slap problem. For one, the piston skirts are longer.

Checking valve lash is not difficult, if it has been more than 50k miles or so, you might want to check it. Not absolutely necessary, of course.

Greg

"Is there a way to distinguish between the noise of piston slap and the noise made by valves needing adjustment?"

Sure. Piston slap diminishes or disappears after a few miles, as the engine reaches temperature. But even more important, piston slap is very sensitive to throttle and load. It comes and goes dramatically as you lightly nudged the throttle of your cold (slapping) engine. Valve noise is entirely independent of engine load. Moreover, valve clatter is a clicking (not to be confused with injector ticking), whereas piston slap is a deeper tapping sound (not to be confused with rod knock).

• Injector noise is a ticking sound.
• Valve noise is a clicking sound.
• Piston slap is a light tapping sound.
• Rod knock is a deeper hammering sound.

My understanding is that it is a metal dilatation issue caused by fairly short (cold) pistons in steel cylinders. Later models apparently have longer pistons.

I'm told by a Volvo dealer that pretty much all older Volvos have it to a degree and that they will keep on driving like that forever. Since the problem goes away once the engine heats up I presume that the usual advice of driving gently until the engine heats up (i.e about 20 minutes no mater what the coolant temperature gauge shows) applies even more here.