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Piston Slap..

16K views 44 replies 23 participants last post by  drm101 
#1 ·
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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#2 ·
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.:yes:
 
#21 ·
Don't immediately discount frogman's suggestion of a rod bearing. It's not too difficult to pull the pan & check:

Similar example:
I have a 1969 Councours Estate wagon, original 350/350.
The block is at the machinist now, being bored .030".

At 125k, I did a cheap garage reassembly, with the original pistons and new rings/bearings. It was fine for 17,000 miles. Then, it developed a seeming piston-slap, distinctly on the driver's side. It got to the level of an intermittent 'screech' as the piston travelled up/down the cylinder wall - worst at idle, less as the oil pressure would go up. I parked it for two years.

Upon disassembly, the #1 wall was scored and #1 rod bearing spun. My nodular crank is toast. It's getting a forged one this go-round.

Also, are you using an oil additive? There's no zinc/phosphorous in retail oil, now. Flat tappet V-8's can't survive without synthetic, or an additive. (Part of my learning curve: I'm on my 3rd camshaft).
 
#5 · (Edited)
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.
 
#6 ·
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
 
#8 ·
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.:devil: Jackel
 
#9 ·
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.
 
#10 ·
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
 
#11 · (Edited)
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
 
#13 ·
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
 
#14 ·
I dont think there is interference with the valve cover. They are nice large cast units. http://www.gmpartsdirect.com/results.cfm?partnumber=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.
 
#31 ·
Talk about piston slap, all the new 110" Harley CVO's have it like there's no tomorrow. My '08 had it and my '09 had/has it big time. Of course MOCO says it's normal...

Anyway, since you may have found the culprit, try pulling the plug wire off on #5 and see if the noise goes away. I had an old mechanic that worked for me at a dealership years ago and he did this a lot and it does seem to pin point the cylinder quite well. Next you have to determine if it's a piston slap, wrist pin, or possibly a cracked piston.

I traded years ago and ended up with a 300/327 in a '66 Vette that had a slapping knocking noise. I drove it for some time, maybe a couple thousand miles and traded it off to my brother. He did the same and traded it to another guy. That guy pulled down the motor and one of the pistons came out in two pieces. So that 327 ran for several years and 1000's of mile with a cracked/broken piston.

Noises are very hard to detmine the cause and being an arm chair mechanic is even harder.

I agree with some of the others, if it's that loud, I'd bite the bullet and tear it down and have a look see.

I guess before I'd pull the motor for a look see, I'd pop the left valve cover off just to make sure nothing top side has run amauk.

Good luck with your noise.
 
#23 · (Edited)
I know this may sound crazy, but I had a big block in my 74 Nova, with almost the exact same noise. After I wiped 3 cam lobes (stupid Erson cam!), I replaced the cam and then broke 2 valve springs, replaced them. After all of that I then found (of all things) a cracked flexplate. Replaced the flexplate, and the noise went away. That may, or may not, be the case with yours, but it's worth a look. Better than pulling the motor! Mine was cracked between two bolt holes, and the harmonics created during decel caused the flopping. Couldn't hear it during steady acceleration, but always heard it at steady throttle, and louder during decel. I have had a couple of different small block heads, pull studs off to one side, and that gave me a similar noise, but it was also obvious when you pulled the valve covers.

FWIW, all of the talk about piston slap with the late model GM engines, is actually normal, and very benign. It's a combination of the new design short piston skirt, combined with the expansion properties of the hypereutectic pistons, which is why it only does it cold. If you've ever looked at the pistons, the skirts are barely past the pin. The newer engines use the shorter skirt to reduce rotating mass, and reduce contact area (thus reducing friction), but at the cost of additional rocking in the bore when the engines are cold. Some people hate it, some not so much, I've found using synthetic oil I don't have it as bad as most, so I don't worry about it, if it blows up I'll fix it that's all. As far as the oil usage, that's due to oil splashing into the PCV system, and consumed through the intake, easy way to fix it is to add a catch can, between the breather tube from the VC to the intake tube. They've been selling kits to fix it in the new Camaros, and LS powered Vettes for several years, and they do work.


Pat
 
#28 ·
FWIW, all of the talk about piston slap with the late model GM engines, is actually normal, and very benign. It's a combination of the new design short piston skirt, combined with the expansion properties of the hypereutectic pistons, which is why it only does it cold. If you've ever looked at the pistons, the skirts are barely past the pin. The newer engines use the shorter skirt to reduce rotating mass, and reduce contact area (thus reducing friction), but at the cost of additional rocking in the bore when the engines are cold. Some people hate it, some not so much, I've found using synthetic oil I don't have it as bad as most, so I don't worry about it, if it blows up I'll fix it that's all.

Pat
Try selling this theory to a customer looking to buy a "gas" powered GM vehicle that "sounds like a diesel"! Ain't gonna happen. :no:

***Sorry for the tempory hijack, but had to get that off my chest.***
 
#24 ·
Could be a rod, but it really didn't sound like it. If it is a rod, pulling the spark plug wire off the plug on that cylinder and running the engine will almost or completely eliminate the knock. To me it sounds like maybe you have a lifter going south, I forget from the original post, but your not running mechanical roller lifters or rockers, are you? Their kinda notorious for falling apart in street engines (mostly the older mechanical roller lifters). And lastly, I ran TRW 12.5/1 forged pistons in my Camaro for 20 years, they were so noisy the engine sounded like a diesel at idle (and no, it wasn't detonating at idle!) :)! I replaced the dist. twice because it sounded like it was coming out of it,but it never made a difference. Anyway, ran the you know what out of that motor, and noisy as it was, it never missed a beat. Sold the car to a buddy, who eventually sold the motor to another buddy, I'm pretty sure that motor ran for 30 years. TRW forged pistons were notorious for being noisy, and Manley is the same company, so it's possibly that as well, but I would have thought they would have always been noisy, not just started all of a sudden.

Kurt
 
#27 · (Edited)
Do some easy diagnostic checks first.

Before you pull the pan, pull the spark plug wire off #5 and see if the noise is less. If it is less, then it's in the rod/piston assembly. If it doesn't, it's something else. Make sure you ground the plug wire so it isn't sparking and making a new noise.
 
#29 ·
It dosent sound like piston slap to me sounds more like valve train. I bought a 1959 pontiac from a friend that bought it new it had piston slap from the day he bought it. He took it to the dealer and they told him they would replace the engine but he would have the same problem so he left it like it was. I had the car for years and never had a problem with it. Im not saying its good to leave it slapping I just didnt want to mess with it. It was an all original car with tri power and it ran like a raped ape. I would sell my 69 Numbers matching 396 375hp Nova SS in a heartbeat to get it back piston slap and all.
 
#30 · (Edited)
Chasing a noise (tick, knock, slap, bang, etc..) can be a major P.I.T.A.!!! The longer you do this kinda work, the more you run into. Here's some noise makers I've dealt with:
Flexplate cracked
converter bolts loose.....even just ONE!!
Block-to-bell housing bolts loose (REALLY sounded like a rod knock!!)
Balancer loose (tore up the nose of the crank as well)
Fuel pump pushrod "Sticking" because of the bolt in the front of the block being too long.
Rods bearings
Main bearings
Thrust knock (that was a wierd one!!!)
Valves "Sticking" in the guides
Rockers hitting the inside of the valve covers (yes, the thicker valve covers seem to have MORE interference issues and will seemingly get worse over time as the gaskets (especially the cork gaskets) will shrink or compress.
Bent pushrods
Broken rocker
Broken valvespring
Accessory bracket bolts worked loose on one. Again, sounded like a knock.
Power steering pump going out (made all sorts of noise but never the typical LOW ON FLUID noise)
Saw one where one of the header tubes was hitting the block and several where a tube was hitting the steering shaft and frame.

And of course......piston slap. Usually slap goes away with a little warm-up, but in severe cases, it can egg-shape the cylinder and/or collapse or break the bottoms of the skirts off of the pistons themselves.
I'm with you on the Manley pistons. I've never been a big fan. Especially when there's so many other great choices out there.

I would try as much as possible to isolate the noise. IE: pull the plug wire one cylinder at a time, pull the accessory belts, check all of the header clearances, check the balancer bolt, check the flexplate and bellhousing bolts, etc., etc., etc...

Also. I've seen high volume oil pumps seemingly cover up bearing issues and not show any noticeable pressure loss until things were REAL bad.

I feel for ya with the back situation. Been there. I've also been the one (Like yourself) that's always had a hard time trusting anyone elses work. "It's tight"..."How tight is tight enough TO YOU? I didn't FEEL it. Is the bolt streatching or twisting?" I'm sure you, like I, have a friend around there that you've worked with before. Even if they just hang around and help with the awkward and heavy stuff, it'll make all the difference in the world.

Good luck!!! Hopefully it's something silly (and cheep!!).
 
#32 ·
sounds like valvetrain speed to me..... Had a loose valve guide once on a 2 month old 're manufactured' (nationwide re manufacturer) engine I installed for a customer.... ended up putting new heads on it, noise gone, customer put another 170k miles on that engine with no further problems before he sold it. I found the culprit by using a straight prying device laid parallel to the valve spring and moving it against and away from the valve spring -- shouldn't move more than a couple to 5 thousandths of an inch .005" -- just be careful you're not actually bending the valve stem and counting that as play.
 
#33 ·
Ok. Im over whelmed with ALL the great replies. THANK you ALL.

Im a lil ashamed with trying to troubleshoot my issue with a simple sound recording. I KNOW its NOT the way to go.

I was trying to capture the sound I hear from 10 feet away from the car and I screwed up and put the recorder right next to the engine (on the radiator support). Because the ear can pick up the sound and it over rides the common engine sounds.

Not so with the recorder. I watched (listened)
the recording and totally get why it sounds like there is some valve train issues or other issues, there is ALOT of noise on the recording, even the inrush of air from the intake on some parts.

The recording amplified ALL the standard noise you will hear from a perfectly running engine along with the road noise. The major amount of sound you hear on the vid is the headers and road air noise.

Exhaust gases hitting the primary tubes is VERY metallic. And will sound like a metal on metal "hit" when recorded up close. MY BUST!! Solly guys.

The engine is smooth and there is NO metallic sound in person. No higher pitched sounds (tick) like what you get with a valve train issue.

And its not a deep sound like its in the bottom end. Its a piston slap sound that for the life of me I cant reproduce with what I have :mad:

I do think I have to yank the engine and thats far from my project list. She was at the top of the list and I did what was essential, so I could drive her.

She has been my project car from 1995. Unfortunately she has moved down some. Other projects now take presidence if an engine overhaul is due. I have a CNC mill thats on the front burner right now.

Ill pull the #5 plug to see if the noise changes. If it does then I know Im in for a tear down. Not a prob. Im retired (have the time, not much money) and would rather yank the engine and find SOMETHING than NOT pulling her out and wait for real damage right?

No way do I want to continue to drive the car as is. There is a problem and I want to find it. Im not into waiting to see if it gets worse then fixing much more.

I already know its not a simple cold start piston slap issue even though it started out as that, things have changed. Shes noisy when warm. That should have been my clue to stop driving the car and investigate.

And with ALL the help from YOU guys thats whats gonna happen. My 62 is side lined till I make the garage ready for a full on looksee.

I really DO thank ALL of you for helping out. Great bunch of folks here.

Ill be sure to post some updates with what I find. It might help others down the road. Thanks SNS members!!!!! JR
 
#34 ·
Although diagnosis via video sound is hard to do, the first thing I'd check is for a blown exhaust header gasket - it's happened to me before and sounds similar.
To verify, at idle, I cautiously feel for exhaust gas puffing out around each of the tubes where they mate to the head - and try not to get burned!

Good luck!
 
#35 ·
Check the easy stuff first before you pull the engine.

True story: A mechanic I worked with showed up one day with a really nice sixties c series red and white pickup. I was struck by the absolutely beautiful condition. I said, "How much did you have to pay for this find?". I don't remember now the exact price, but it was too good to be true. I said "BS".

He said the guy sold it so cheap because after investing thousands into the restoration and engine rebuild, the truck had a persistent knock that drove him crazy. He sold it in disgust and anger to my friend at a tremendous loss just to get rid of it. I said, I didn't hear any knock when you drove in. He said when he checked it out, it was just a loose torque converter bolt! He tightened it up and it ran great.

You are going to kick yourself if you pull the engine only to find it was a leaking gasket or other simple problem as described in the posts above.

Rule everything else out first. If all those are good then you may still have to pull it, but don't be so hasty until you make a list and methodically check them all.
 
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