Piston Slap? - PeachParts Mercedes-Benz Forum

cmp · #1 07-23-2007, 08:40 PM

I've been told this is piston slap. sorry for the poor video, but the sound is somewhat there. Any comments?

1982 300D.

Thanks.

WINGAS · #2 07-23-2007, 08:45 PM

A bit loud, but sounds like a normal diesel idle. I dont know how the heck you;d hear piston slap in a diesel. If the pistons are that loose, a compression check would reveal it.

To me it sounds like an enigne needing some adjsutments as it doesnt clean up as well as it should when revved. Bad injetor patterns? rebuild them, set valves if itheir adjustible, new filters.

I've only had a diesel for three months, so please wait for more replies before you take my opinion to heart. But the clackity clack is actually compression slightly mistimed at idle, not slap. Endemic to the beasts.

Run some pump bio or wingas through it. It'
ll clean up the injectors and quiet it down nice.

TheDon · #3 07-23-2007, 08:45 PM

is it isolated to a single cylinder? if so see if loosening the injector hard line to said cylinder stops the sound

Cervan · #4 07-23-2007, 09:03 PM

sounds normal to me lol.

TheDon · #5 07-23-2007, 09:13 PM

Quote:

Originally Posted by Cervan

sounds normal to me lol.

at work some random customer came running up to me and said my engine sounded like it was low on oil. I merely replied.."It's a diesel.. its supposed to sound like that"

cmp · #6 07-23-2007, 09:31 PM

Well, thanks for the replies. Valves were adjusted a couple hundred miles ago, and fluids changed. It's actually always sounded like this for us (over a year now). Our mechanic mentioned the piston-slap possibility. He claims it's the loudest 300 he works on...

Seems to run fine...just really loud. the same model drove past us on the sidewalk the other day and it was nowhere near as loud. That got me paranoid again.

We're thinking of selling it, but I'm trying to clear up any issues first. It needs an alignment, and 2 new tires...then we'll decide if we're going to sell her.

pawoSD · #7 07-24-2007, 12:55 AM

My engine is louder than the other two we have.....but it has driven 53,000 no-mercy miles with me so far....and no problems to speak of.

I'd not worry about it if its running fine. Do make sure the timing chain and tensioner is in good shape though...sometimes that can cause a slapping sound....

Ara T. · #8 07-24-2007, 01:28 AM

Thats what they sound like, they're noticeably louder when cold.

WINGAS · #9 07-24-2007, 06:38 AM

Well, fwiw, I;ve heard piston slap in a 427 chevy,( diagnosed by a crackerjack mechanic, the best I know, works for the FBI!) adn while its a gasser, it was more of a swishy sound. Many of us have heard piston slap in the GM corporate 3.1/3.4?L engines and its not "swishy" its well defined.

Naw, its a loud diesel is all. Ever run bio or diesel purge through it?

deerefanatic · #10 07-24-2007, 07:29 AM

I say start cracking injector lines one at a time and see if it goes away.... That's really not normal and you just wanna make sure it's not something that can go out and trash you motor later...

A loud clatter at idle is fine, but when you rev it up and it's still distinct, that bothers me a little...

Tymbrymi · #11 07-24-2007, 08:55 PM

Quote:

Originally Posted by deerefanatic

A loud clatter at idle is fine, but when you rev it up and it's still distinct, that bothers me a little...

I agree.

Here are some videos to compare your engine noise to.

http://video.google.com/videoplay?docid=-4524880834772559028
http://video.google.com/videoplay?docid=-9142296006509593880
http://video.google.com/videoplay?docid=-4608337093365325271 (can really hear it at the end)

It turns out that there is play in the #1 rod bearing, and the bottom of that piston has a crack in it.

Hatterasguy · #12 07-24-2007, 10:09 PM

Piston slap is what POS GM engines do. You probably could use a valve adjustment and I'm sure the injectors could use some work. Timing is probably off a bit as well.