Piston slap anyone??
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Mountain Pass
Joined: Jan 2003
Posts: 136
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Piston slap anyone??
Fellas,
I'm starting to notice what I think sounds like piston slap on my motor when I start it up on a cold morning (teens or lower for temps). Just wondering if anybody else is experiencing this phenomenon.
I'm starting to notice what I think sounds like piston slap on my motor when I start it up on a cold morning (teens or lower for temps). Just wondering if anybody else is experiencing this phenomenon.
Cargo Master
Joined: Dec 2003
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From: Sunny Florida
If you only hear it at start up then you have a bad bearing. If it's there most or all of the time then you may have a bad wrist pin or bad piston. Does it make noise when warmed up and you free rev it?
Postmaster
Joined: Jun 2003
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From: shepherd
i have a mustang that does it now. well i was told it was a piston skirt broken or a slung bearing. it is a 5 spd when i push the clutch to shift the gears you can hear it and then it quiets down. you can have it idleing and hear it barely and all of a sudden you hear a knock and then it sounds like it was before. i was told by 2 mech. that it was a slung bearing.
Cargo Master
Joined: Dec 2003
Posts: 2,735
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From: Sunny Florida
A spun bearing will more than likely knock all the time and it's not a good thing if it is spun. Either way you have a very serious problem and it should be taken care of. Its also hard to determine the problem with out really hearing it first hand. good luck
Postmaster
Joined: Jun 2003
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From: shepherd
ok update on the stang. it just got way worse today while going to the mechanic. and yes now it does it all the time it sounds like a helicopter going down the road at 25 mph. good thing it did not throw a rod. i was told today that it could be also a rod bearing.
Elder User
Joined: Sep 2003
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If you only hear it at start up then you have a bad bearing.
Piston slap occurs when the engine is cold, and goes away when the engine warms up. This is because the aluminum piston grows more than the cylinder walls with heating, and the slack is taken up.
An engine can run a long time with mild cold piston slap, but it will eventually get worse, and will at some point bust a piston skirt.
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Laughing Gas
Joined: Dec 2003
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From: Ford, WA
I have an 86 Bronco with a 302 that does the same thing.. It also has alot of blowby and pumps out a little but of blue smoke when I accelerate. I thought it was a rod bearing at first but now i'm sure it's piston slap..I have no idea how many miles it has on it.. hoping to replace it with an EFI 351W soon..
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Elder User
Joined: Apr 2003
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the sounds are different - a rod has a double knock and wont run very long i.e. minutes not hours before it throws the rod while a piston slap is worse when cold and lessens as the motor warms up and has a single duller knock and may run for years.
Junior User
Joined: Nov 2003
Posts: 64
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From: Peabody
ya i got a 302 in one of bronco's thats has a piston slap for two years and i have beat it pretty good....she's also got some oil pressure issues but i stopped worryin and just drive it .....its a ford...it'll be fine...but it does get quieter when the truck warms up..seems like u already had enough help...just wanted to throw in my 2 cents
New User
Joined: May 2004
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RTM I have free rev knock
Originally Posted by RTM
If you only hear it at start up then you have a bad bearing. If it's there most or all of the time then you may have a bad wrist pin or bad piston. Does it make noise when warmed up and you free rev it?
Postmaster
Joined: Jun 2003
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From: shepherd
Originally Posted by daerhldgs2
Probably piston slap. A rod would be out of the block by now , when rods get loud enough to hear they don't last long, minutes not hours and days, a wrist pin has a sharper sound and will knock for a long time.
Cargo Master
Joined: Dec 2003
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From: Sunny Florida
Well I would take a piece of wood and try to pin point the noise if you really want to know what it is but when there is that kind of noise it can only mean something is wrong so at this point you drive it until it breaks or you replace the engine now before it leaves you stuck some where.
Even if it's a rod bearing the rod will more than likely need resized which requires you to remove the complete piston and rod together.
If its a main bearing then you may get away with turning the crank and installing new bearings.
Just remember if it is something you can save now driving it longer only increases the chances of a major fix and not a simple one and even simple fixes are some times just a band aids.
Even if it's a rod bearing the rod will more than likely need resized which requires you to remove the complete piston and rod together.
If its a main bearing then you may get away with turning the crank and installing new bearings.
Just remember if it is something you can save now driving it longer only increases the chances of a major fix and not a simple one and even simple fixes are some times just a band aids.