Piston Slap - questions

[XH29N0G]

Can I get people's thoughts on piston slap. 

My 383 was rebuilt by Muscle Motors with a 3.9 stroke crank, forged diamond pistons and 6.700 rod.  They broke it in and ran it on their dyno before shipping it back.  The shop that installed the engine said that there was some piston slap, but that was not uncommon with forged pistons.  The engine pulls well, starts right up, and there are no indications of problems.  When the engine starts it sounds like a diesel.  The piston slap does not go away when the engine is warmed up but is reduced. 

My question is whether there is information I should know, or anything I should do to reduce it.  I have heard that changing oil weight can change it.  Would this be a good or a bad move?  Is there something else I should keep an eye out for?

Thanks in advance for any feedback.

[flyinlow]

I have SRP forged pistons. They make some noise for 1-2 minutes on a cold start.  I assume it's the pistons. With headers, no valley sound deadener and fiberglass hood ,there is more noise than a stock set up.  Dose not sound like a diesel.

[XH29N0G]

Diesel - not really loud diesel (late model vw diesel) - but knocking like a diesel nonetheless.  The person doing the restoration said he had heard others like it. 

[cdr]

i am sure its ok,call & talk to muscle motors

[AKcharger]

I had the same thing with my 470 kit from 440 Source. It's a diesel for the first 2-3 min then it's fine.  I've put about 5,000 miles on it and it's fine, I just make sure it's warmed up well before I romp on it.

Only concern is there is STILL noise AFTER it's warmed up...that doesn't sound right    ...at least mine quiets down

[XH29N0G]

i am sure its ok,call & talk to muscle motors

Thanks for the suggestion.  I'll do that.  It is also my impression that it is OK, but I thought I would ask since people on this forum have so much more experience than me.  I also did not know if there were certain things that I should be doing.  (I am making sure that it is warmed up before driving for one.)

[justcruisin]

What is the cam? Fast rate cams can kick up noise that could be described as a diesel engine noise.

[don duick]

sorry to be a killjoy but my friend who works in a machine shop told me this is not good the piston is too small and will only get worse. You will have to pull the engine and check bore size and piston skirts you might get away with having the pistons coated . If you don't want to do this guess it wont hurt to try heavier oil might slow you down at worst.

[XH29N0G]

justcruisin - I could be wrong on the source of the noise, but am attributing the piston slap diagnosis to the folks who installed the engine.  They have more experience than me but are not a Mopar-focused shop.

The cam is a hydraulic one they listed as .519/.511 236/246@50 (I think 280/296 is the advertised duration) with 112 LSA.  The rocker arms should be the stamped steel rockers.

I have had lifter noise before and it sounded a little different to me, but this cam is more aggressive than the one I had before.    Is there a way to tell whether it is valve train noise vs piston slap?  

Don - thanks for the heads up.  More to ask about.

[myk]

Piston slap was a "standard feature" on GM's LS1 series of engines for over a decade.  If their motors can have that flaw yet perform as well as they have over the years, maybe piston slap isn't such a bad thing?   

[John_Kunkel]

Forged piston slap is not only caused by a different expansion rate but also a different pin offset than cast pistons.

"It's better to hear it than smell it".

[John_Kunkel]

Forged piston slap is not only caused by a different expansion rate but also a different pin offset than cast pistons.

"It's better to hear it than to smell it".

[firefighter3931]

Without hearing the noise in person it's near impossible to diagnose.  Forged pistons are installed looser than hyper or cast slugs to allow for thermal expansion so a bit of noise on startup is normal. You might have a combination of lifter noise and piston slap occurring at the same time. 

What type of oil are you using ? Synthetic ?


Ron

[BSB67]

If the block was properly clearanced for the piston for street use, it should not slap once it is fully warmed-up.  With that said, unless the sound really bothers you, it will probably be fine. 

[XH29N0G]

Ron,

Thank you.  I still have to call the folks at MM.  I do not believe it is synthetic.  I am using the oil that they put in.  MM put in Shell Rotella Blue Label.  I think the people who put the engine in changed the oil, but do not recall the brand.  I know they use a high ZDDP oil.   I will try to see about starting it tomorrow and warming it up and figuring out how to record it if that would be sufficient for a long-distance diagnosis.  

[fy469rtse]

I was waiting for you to kick in Ron ,
I think with all the alloy we are putting on these engines also amplifying engine noises too,
Just the differance needle roller rockers compared to the bushed type
Considerably noisier, are we just hearing more of what's going on ?

[firefighter3931]

Ron,

Thank you.  I still have to call the folks at MM.  I do not believe it is synthetic.  I am using the oil that they put in.  MM put in Shell Rotella Blue Label.  I think the people who put the engine in changed the oil, but do not recall the brand.  I know they use a high ZDDP oil.   I will try to see about starting it tomorrow and warming it up and figuring out how to record it if that would be sufficient for a long-distance diagnosis.  

Hey XH, see if you can post a few vid clips of cold start and after warmed up to operating temp so we can help diagnose. 


Quick story :

Awhile back, a memebr changed from mineral based lube to synthetic (Royal Purple racing) and the engine sounded like a sewing machine.  I asked him what he'd changed and he said new synthetic oil was the only change. I was quite surprised at how much valetrain noise suddenly appeared. I recommended he go back to dino oil and as soon as he dumped the synthetic lube the noise went away. I'm a big fan of Brad Penn Racing oil....it has lots of zinc/phos for flat tappet cam protection.



Ron

[Challenger340]

If it is a MM Stroker Kit... very high probability that they used a more expensive Forged Piston Alloy being "2618"... as opposed to cheaper 4032 Alloy Pistons more commonly found in cheaper Kits.
The downside being;
the more expensive 2618 alloy can be slightly noisier, as they typically call for a little more clearance when fitting the Cylinders.

Are you warming the Engine right up to 190*F ? That will help fully expand the 2618 to round and fit the bores.

Synthetic oils are GREAT !... but that said... if there is one thing about them that lacks, it is pour point "Mass" at operating temperature, that they lack as a sound deadener.
Basically "piss water" at temperature ? If you have some Piston slap.... thicker DINO oils are best to shut them up.

just my opinions

[XH29N0G]

Thank you Ron and Challenger340 for your thoughts.  

OK,  Here are the videos.  I am not sure they are clear enough to really show the difference.  There is a difference once the car is warm, but the sound persists.  If I slow the idle to 700 RPM it becomes more pronounced.  I assume I should set the idle higher (per discussions on the forum)

http://youtu.be/gu18c9hpwaI is of a cold start at about 1200 RPM

http://youtu.be/dY-2M7VvYA  Cold start about 900 RPM

http://youtu.be/vUBqikxDSQ0 Warm engine idle at about 900 rpm

http://youtu.be/40pFbx4Xnro Warm engine after oil change to 20-50w at 1000 rpm

[cudaken]

While faint, I can still hear the diesel like sound at idle warm. I have to guess this is not a good thing. 

[Challenger340]

Yeah, If it was one of mine, and it rattled like that ?... I would probably be hearing about it from the Customer ?
So,
if it WAS one of mine(it ain't)... my first question would again be;
1.) What brand, type, and weight of Oil do you have in that thing ?
quickly followed by...
2.) not "warm"... but what is the ACTUAL temperature in degree's Fahrenheit that the Engine is running at ?

The easiest thing to do... is look at the Specification/Build Sheet that comes with the Engine ? It should have the Piston to Wall clearance recorded there, as well as the Piston part# to check if a 4032 or 2618 Alloy ? That would help lots here ?
Reccomended Oil should also be there ?

It's Piston Slap allright.... just dotting I's and crossing T's to see why ?
and,
as long as the pistons are still providing a stable enough ring platform to maintain Compression and Sealing, not a big worry ? just sounds like a RACE Engine !

The thing got any blowby... with.... and without.... the PCV plugged in the Valve cover under light brake stall ?

[XH29N0G]

Challenger340 I don't know enough to understand the details of your post, but let me see if I understand what a possible next set of steps might be.

1) Oil.  I do not know, but I can change it and check again.  I believe it is 10w40, but do not know the brand.  I can try Ron's recommendation of Brad Penn (what weight would you suggest).  
2) The engine temperature (read off the factory gauge) was 200 or slightly higher.  I had driven the car for about 5 miles after warming it up and then did the second test.  I do not know how accurate the factory gauge is or what thermostat is in the engine.

I am looking at what I think is the build sheet and I do not see a piston part number.  They told me that they changed the piston choice mid build because they originally planned to use another supplier, and did not put the number on the sheet (I can make a guess- but I think I should ask them directly).  I also do not see the piston to wall clearance (although it may be here and there are other measurements).  I can contact them, but this build was done about a year and a half ago (the rest of the car took longer than expected).

If the engine has blowby, I have not noticed it.  I see no oil on, or downstream of, the pvc.  I do not completely understand the blowby test.  (If it makes a difference, the car has a manual transmission).  Are you suggesting putting a small load on engine and testing to see if air comes out the pvc or vent on the other side oir dipstick when the pvc is disconnected from the intake and plugged?  I can do that test.

As far as a plan of action: Are you suggesting that I should do the oil change and blowby test first and see what I learn and then contact MM for more information? 

[flyinlow]

I have had good luck with Mobil 1  15w-50 which has higher zddp levels in our current 446 and 452 engines both with forged pistons, but you are trying to go back to conventional oil.

On a former 440 build ( 30 years ago, when men where men and oil was oil ) I used  Valvoline Racing 20W -50 with Speed Pro forged pistons. Relatively quiet and good engine life.

With both Ron and Challenger 340 talking about conventional oil I  may have to rethink my choice of oil.

[firefighter3931]

I would try some Brad Penn 20/50 and see what happens....i bet that settles it down.   

Ron

[Challenger340]

I would try some Brad Penn 20/50 and see what happens....i bet that settles it down.   

Ron

YEP !
First things FIRST !