My 90 745 apparently has piston slap during warm-up. From what I've read, I'm assuming this is a mechanical condition that can't be fixed with engine additives or better oil, etc. So IF that's true, my next thoughts are: Does it get worse or just keep on slappin forever? -Because the car needs a new rack and struts. Do we spend this kind of money and time (DIY) on a car with piston slap? If it does get worse, How much quality time do we have left together?

My '87 740 turbo developed cold temperature slap on #4 piston when it was about 5-6 years old. Noise disappeared after warm up. After about 10 years, I had it in for a timing belt replacement and the mechanic said that the slap was excessive and we should replace the piston. Did that (and all the associaed stuff) which fixed the piston slap - for about one and a half years! Same noise was back, goes away when it warms up, hasn't got any worse in the last ten years,engine runs just fine.

I was talking to another good Volvo mechanic about the problem. He said it was a fairly common problem. Volvo used a low friction piston design on some of the engines to improve gas mileage. The piston has either a shorter skirt or a slipper style skirt. Net effect, it is really sensitive to rocking if the clearances open up a bit. He sid don't sweat the noise if it goes away when warm. End result, I wasted about $1000 on the piston replacement.

Thanks guys. Now I can move foreward with confidence.

You can always get good info here at the BB!

Greetings,

Maintain your car as if it didn't have the piston slap, turn the radio up a bit and you will be surprised how far that noisy engine will take you.

Three of our four cars on the road presently, have piston slap and the one that is the loudest gets driven the most. 1987 744, 315K, still runs real well, slaps like a fiend when cold and sounds like a diesel when warm.

Car had the slap when we got it 100K mile+ ago and may have gotten a little bit louder but shows no signs of dying anytime soon.

Back to work, rcs

Before you get too involved and intimidated by this, i have one thing you can check. Sometimes an exhaust manifold leak can sound like piston slap. When the engine is cold, start it up and run your hands around the manifold to see if a leak could be causing the noise.

best of luck -
Brant
--
89' 744ti, 106K miles, slushbox : 87' 745ti, 229K miles, m46!

I tried to blow up the 88 760 several times to have an excuse to throw the noisey engine away. I finally swapped it out with an N/A 230F from an 86 240 and cured it.

Apparently the piston slap is only annoying and not an indication of imminent failure.

Regards,

--
Will Dallas, www.willdallas.us, www.willdallas.org, www.willdallas.com, www.dallasprecision.com 86 245 DL 222K miles, 93 940 260K miles, 88 765 GLE 152K miles

My 87 has it big time, I also drive the crap out of it and have put 20K or so on it in under a year, it'll be fine. Do plan on a motor swap one day if you intend to keep it, but that isn't a big deal in one of these cars. The later motors were not prone to piston slap, 90 seems to have been a bad year for it for whatever reason. If it's not rusted, keep the chassis maintained, and keep an eye out for a wrecked 92 or 93 and up doner car.

Where I live (northern Virginia) these cars have recently become MUCH harder to find than they once were, (and a lot more expensive when you do find one, especially 240s) so I would recommend keeping yours if the body and interior are in good shape. If you get rid of it, there will come a time when you wish you hadn't. (unless, of course, you can find a super-clean low mileage car for cheap to replace it with, and even those can have problems that don't become apparent right away)

Unless it suddenly gets A LOT louder, the piston slap, while annoying, does not represent a reliability issue. Try using 15W40 "diesel" oil (not synthetic) which may help quiet things a bit.

Struts and a rack are both fairly easy DIY tasks. The only special tool you will need is a spring compressor. If there are any junkyards in your area with 740s, a good used rack shouldn't be too hard to find. Crawl underneath and pull back the boots from the body of the rack. If it's clean and dry inside (there may be a few blobs of grease from the inner tie rod ends) it is likely to be a good one. If it is an oily mess, fluid everywhere, you don't want it. It doesn't matter what brand the replacement rack is---they are interchangeable as complete assemblies.

My mother had a 90 with piston slap.The only thing that made it worse was when I decided to switch to synthetic oil(it got much worse)I would suggest changing the oil often and stick with what ever type of oil is in it now.My 89 780 has had piston slap since I bought it three years ago with 185,000 miles on it.It is loud when first started in the morning and then quiets upon warm up although the noise never completely goes away,the wife drives it every day and we often take it out of town.Yes it can be fixed,the repair is expensive.Hope this helps

Our 90 740 with 178,000 miles has been doing it since before the 100,000 mark.

Did the advent of Piston Slap coincide with using the rope trick for the timing belt?

What is it exactly, loose rings or wrist pins?

Bill

I've never used the rope trick on that car.

My understanding is that it is due to the piston(s) being ever so slightly undersized for the bore diameter, whether from wear, incorrect original spec, or a combination of both. This loose fit allows it/them to wobble slightly from side to side at certain times, instead of going smoothly up and down, causing the rattling noise. The noise is more pronounced when the engine is cold, as the clearance is greater then----aluminum expands more than cast iron as it warms up, so the piston actually "grows" slightly, relative to the cylinder bore, reducing/eliminating the noise as the engine reaches operating temperature.

I suspect that running the engine hard before it is warmed up is a major factor in which engines develop piston slap and which don't. Avoid doing this.

Hi Blue Horse,

That doesn't make sense to me since the piston doesn't contact the cyl bore
at all. The rings are in contact.
Perhaps the noise is rings chattering for some reason.
I wonder if you can have good compression and bad rings?

Something I found out with a corolla that sat for a long time was that it
burned oil like crazy, maybe a quart an hour/60 miles until I was doing a clutch job on that car and soaked each cylinder with a healthy dose of good old
Mystery Oil for two days. That must have freed up the stuck rings because it stopped gulping oil. Maybe slap can be treated that way too?

One hint though, before putting the plugs back in, put a pile of newspapers
by the plug holes and crank the car to spit out most of that oil.
The newspaper gets the oil instead of the engine area.
Mystery oil won't be great for the cat converter and O2 sensor I'd guess.

Bill

Piston skirts do contact the cylinder wall, hence the wear, and then the slap.
Volvo made the skirt too short, the piston rocks, and they never fixed it which still ticks me off. I don't consider putting oil squirters on it a fix, though it's as close as it gets. The B23 did not have any of this sillyness.

The piston slap is caused by the very short skirt on the B230 piston which does not tolerate the wear that a regular skirted piston does. From what I have been told, the slapping can start within a few hours of assembly or many thousands of miles later. The tolerances for assembly are very tight (within a few ten thousands of an inch)to compensate for the short skirt. Slapping will not generally hurt the performance of the engine but is kind of annoying. It was probably something the old vikings did to keep warm and carried over to their engines. :)

Regards,
--
Will Dallas, www.willdallas.us, www.willdallas.org, www.willdallas.com, www.dallasprecision.com 86 245 DL 222K miles, 93 940 260K miles, 88 765 GLE 152K miles

Thats right, short pistons are prone to slap, they might have gone short to reduce the reciprocating mass. Longer aftmkt pistons can cure it.
But who cares. Not I.

I've been led to believe the shorter skirts were an attemt to reduce friction.

It was an attempt, along with the small thrust bearing that wore out on manual trans cars, and the small rods that broke left and right, they slowly fixed these things over the years. The oil squirters were the last thing to be added in 92 or 93.