Piston Slap.. - Chevy Nova Forum
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Old 20th-January-2013, 10:38 PM   #1
JRouche
 
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Piston Slap..

I have a 62 Nova. I assembled the engine (early GM 350) about 12 years ago with parts bought 4-5 years earlier. Not state of the art parts. Just some decent parts at the time. A forged crank and rod setup (prolly eagle or cola at the time). Manley forged pistons and some speed pro file fit rings. All spun balanced (cept the rings). And the block was aligned and honed, its a 30 thou over block with splayed studs (ARP for the entire engine) for the main caps.

So without actually going out to the garage and doing some pressure checks (got a nice tool for that but it SUCKS removing spark plugs on this engine) Im just pissin in the wind.

The pistons would slap a lil during a start up. But they would all chill out after the block and pistons got up to temp.

Issue Im seeing now is I have one cylinder that wants to be a lil loud.

The reason Im posting is because the one piston seems to be slapping even when she is warmed up. All the rest of the pistons are good and never made any noise once warm.

I noticed this piston from day one by the way, was always loud.

So what do I do!! Let the loose piston ride in the bore or rip the engine down and measure it again.

I say again cause I did this already with this engine. I Mic'ed ALL the journals, bearings, bores and pistons AND filed the rings. I made a record of all the measurements and swapped parts around to get the best overall clearance. Kinda like "blue printing" an engine. Yes? I even checked the lifters and bores, its a nice engine.

Some folks dont know, I didn't, but engines are into the tenths (.0001"). Im a hobby machinist and like a thousandth (.001"). When turning metal a thou is a nice goal. Grinding is the 10ths side.

So I needed to be able to measure in the 10ths. Anyway I did. Was a lil new for me but working with tenths became comfortable.

What I didnt like was the Manley forged pistons and fast forward to today (20 years later) I still dont like them.

I just dont like to hear the piston flopping around in there.

There is too much money (which I dont have alot of) in the engine. I dont want to ignore the one cylinder but I also dont want to have to pull the engine. And thats what it will take. I cant hang over another fender working on an engine. My back is trash.

Any advice that does not include pulling spark plugs or the engine would be cool.

Obviously I want someone to say its ok, the piston slap wont kill the engine. Sure I know better, that thing is gonna beat itself to death.

I need to get my but on the video camera and take a vid with sound so you could hear it. Its not loud, Id shut her down if it was. Its just there and I don't like it.

Any opinions are welcome... Thanks Guys... JR
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Old 20th-January-2013, 11:25 PM   #2
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Piston slap

I have a 1966 327 362 block l-79 engine built to 1966 specs. very expensive
bottom end to say the least. forged pistons,moly rings,etc. this engine had
been apart since 1974 all the parts were GM high performance new old stock
that came with the engine. an old family friend machined and assy.on most of
the engine. the engine was balanced from pressure plate to the dampner.
I told him to build to 1966 specs he informed me that would not like what
I wanted!! no pump gas and would be a little noisy at warm up. boy was he
wrong I love it!! it does make a little noise at start up maybe 30 seconds
if that. the engine is about 5 years old not many miles yet is driven hard!!
not sure how noisey your setup is? I know after engine is up to temp it
should be quiet.
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Old 20th-January-2013, 11:39 PM   #3
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Personally I would pull it apart and check the slap might not be a slap now if its doing it warm , could be a rod bearing spun
Cost will be cheaper if you do it now instead of when or if it blows up
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Old 20th-January-2013, 11:41 PM   #4
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How is your oil pressure? A rod bearing going out will usually show a decrease in oil pressure.
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Old 21st-January-2013, 09:55 AM   #5
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Piston slap is common on many vehicles. The MoPar 2.2 and 2.5 litre 4 cyl. engines from the late 70's to early 90's would get so bad that they'd sound like a diesel even when hot and those engines were known to get 200-300,000 miles. Today many of the GM engines, especially the V6's and V8's, are well known for have piston slap but that doesn't seem to bother people.

Piston slap isn't a good thing, as you well know, but in a normal use vehicle it doesn't seem to hurt. Does it get worse over time? Sure! But it usually doesn't grenade an engine, it just doesn't sound good.

Now if the noise is getting louder at a seemingly rapid pace then I'd look into the possibility of a wrist pin going bad. I've seen this do some serious damage.

I hope it all works out for you.
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Old 21st-January-2013, 10:11 AM   #6
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Cool

JR you are in world of hurt here you're backs messed up and you can't get the spark plugs out without grief. Are you close to So.Oc? If so I might be able to come over and give you hand. How many miles are on this motor? A leak down test might tell you which cylinder is causing the noise. RICK
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Old 21st-January-2013, 10:42 AM   #7
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One area to look at is the the wrist pins as most guys never check pin clearance in the pin end of the rod or the pin bore of the pistons, Over the years I have seen engines with noise issues bucause clearances were not check.

They all say it said it was ready to assemble HMMMM
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Old 21st-January-2013, 11:16 AM   #8
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My 454 Motor Home engine went from the West Coast to Florida and back with a burnt piston. After the PIG got back I had it fixed. You just never know, HECK back in the 60's everyone seemed to have piston slap. It was part of the "Forged Life Style" back then. Jackel
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Old 21st-January-2013, 11:33 AM   #9
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I hear a little piston slap in my 5.3 after sitting all weekend or daily in cold weather. As soon as it warms up it is gone.

All the regular small blocks I have built I have never heard any kind of piston slap. This 383 called for .002"-.005" and I gave it .003". These are Probe forged pistons and I never hear them at all.

The 5.3 in 01 Silverado is the first to have the piston slap in all my 35+ years of owning and building vehicles.
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Old 22nd-January-2013, 12:28 AM   #10
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Ok first off I have to say thank you to all the guys that replied. I appreciate the info and the time you took to respond, I read ALL the replies.

This is new territory for me. I need all the help I can get.

Ill try to talk about the the posts.

frogman68: I dont think its a spun bearing. Never had one so I dont know what the sound is but its up high and not a sound from the lower case.

62civa: YES!! I did think about oiling, I have had some cars with low oil that sounded the same. We have plenty of oil and pressure here. When cold it will idle with 60psi and get to 75psi if on the throttle a lil (cold oil). Once she is up to temps (180) she stays at 60psi during idle and all RPMs.

Pandora's Box: ERR!! After reading yer post and some others Im thinking wrist pin issue. More to follow re: the wrist pin.

MBZTECH: Thanks Rick for the offer. Im in Camarillo, Ca. A lil far from OC but to be honest I dont want any help beyond verbal. I dont work well with others. Its MY hangup.. I really DO appreciate the offer. But? There is only ONE wrench turning in this garage, the one my hand is on.

CNC BLOCKS: Sucks but what you said means alot. I DIDNT measure the pin bores or the pins. One of the only clearance parts I didnt check. My fail. I assumed the pins were good and the piston pin bores were good. Unfortunately I see the noise coming from a diff source. A pin knock will show up for the upward and down stroke prolly? This is a constant "hit" that is pretty close to being a one "hit" per revolution. A loose pin might show up as two hits for every cycle. Im not getting that.

And commenting on the other posts. Its not good. Its not a cold piston slap. Its a mechanical failure and the chit of it is I need to pull the engine.

NOT my priority right now. Im dealing with other projects. I REALLY dont want to pull the engine. But might have to.. Thanks for the help guys. Some recording of the "knock" are next. JR
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Old 22nd-January-2013, 01:18 AM   #11
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So here is the best I could do to show the knock. My vid camera was all I had to record sounds. So its a video when I just wanted to publish the sound.

Vid one has a big knock at 2:12 to 3:15 and 5:04. Including 5:37 and big on 6:16.


Vid two. Solly for the long video. Skip to :19, :35 and 1:09 for the knock. You will hear it on decell. Oh, :55 big time.




Dismiss the extra noise, its wind noise and a crappy recorder.

What do you think? Too much piston slap? I dont want to pull the engine unless I need to. Oh? The doggish sound? Its a lil high on the timing. Thats not what Im chasing right now.

Any help is good advice. I like it all!! Thanks again. JR
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Old 22nd-January-2013, 08:03 AM   #12
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Does not sound like piston slap but its hard to tell, Make sure a rocker is not making contact with the valve cover.
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Old 22nd-January-2013, 11:20 AM   #13
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Quote:
Originally Posted by CNC BLOCKS View Post
Does not sound like piston slap but its hard to tell, Make sure a rocker is not making contact with the valve cover.
I had the same basic sound and the above is what my problem was. Two sets of rockers and a new set of valve covers finally fixed it. Hard to really tell from the sound in the video though. Have you put a stethoscope to it yet? By the way, I had no scratch marks on the inside of the valve cover at first. Took a long time for only the smallest of marks to show up...Jack
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Old 22nd-January-2013, 11:56 AM   #14
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I dont think there is interference with the valve cover. They are nice large cast units. http://www.gmpartsdirect.com/results...umber=10185064

Yeah Jackel I did use the handy dandy stethoscope. Did that way back when. I forgot to talk about that. So...

I checked ALL around the engine. The intake, heads, header tubes, block, oil pan, valve covers. You name it, I was all over it. The passengers side is quiet. The #5 (third cylinder back from front on drivers side) seems to be the culprit. Thats from listening to the header tube. Its real obvious when hitting the tubes. No sound at all from the block anywhere. No sound from the pan. The head (drivers side) is pretty quiet but I get the usual ticking from the valve train, no heavy noise. Same with the intake.

I really only hear it on the header tube with the scope.

But... I can hear it 20 feet away when the car is idling on the driveway and Im in the garage.

Thanks again, JR.
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Old 22nd-January-2013, 12:48 PM   #15
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Check fuel pump area for noise!!
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