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Piston Slap #2


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14 replies to this topic

#1 wrongturninwv

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Posted 03 October 2005 - 06:17 PM

I read the replies on piston slap in Subaru engines.The question I have is how can you tell the difference from a rod knock and piston slap ??? Isent it the same sound ?? How do you tell the 2 apart ?? Mine sounds like it comes from the center of the engine and when it warms up the sound is its almost gone. I know what lifters sound like cause I had dozens of 80s models. Tell me what the difference is. Thanks

#2 nipper

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Posted 03 October 2005 - 06:43 PM

I read the replies on piston slap in Subaru engines.The question I have is how can you tell the difference from a rod knock and piston slap ??? Isent it the same sound ?? How do you tell the 2 apart ?? Mine sounds like it comes from the center of the engine and when it warms up the sound is its almost gone. I know what lifters sound like cause I had dozens of 80s models. Tell me what the difference is. Thanks


Piston slap is in the morning, and goes away after a few minutes. Rod knock is the reverse. As the oil thins out, it wil make itself more apparent, or never go away.

nipper

#3 Snowman

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Posted 03 October 2005 - 06:47 PM

Does the piston slap sound change under load like a rod knock?

#4 vic/se

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Posted 03 October 2005 - 06:50 PM

I read the replies on piston slap in Subaru engines.The question I have is how can you tell the difference from a rod knock and piston slap ??? Isent it the same sound ?? How do you tell the 2 apart ?? Mine sounds like it comes from the center of the engine and when it warms up the sound is its almost gone. I know what lifters sound like cause I had dozens of 80s models. Tell me what the difference is. Thanks

I don't know what is piston slap ......rod knock, is like you just said, you feel more like a knock .......a kick....the sound is very low pitch

#5 vic/se

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Posted 03 October 2005 - 06:55 PM

when i bought my wagon, a 03 SE and then I started reading about piston slap .....i got scared, what i learned later on is piston slap is commun on DOHC engines so sometimes people get confused!!

#6 nipper

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Posted 03 October 2005 - 06:55 PM

This should explain it

http://remanufacture...s.com/page4.htm

That may be helpful
nipper

#7 blitz

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Posted 03 October 2005 - 06:56 PM

Rod-knock tends to get worse as the engine warms up, piston-slap tends to become less as the engine warms up.

Rod-knock sounds like a regularly-spaced wooden thunk, piston-slap sounds like a plethora of 12 inch rulers knocking on walnut shells.

Piston slap will tend to be more pronounced at one particular rpm and generally no load.

#8 wrongturninwv

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Posted 03 October 2005 - 07:17 PM

This should explain it

http://remanufacture...s.com/page4.htm

That may be helpful
nipper

Very helpfull,think everyone should read this. Thanks Nipper

#9 Arniet

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Posted 05 December 2005 - 06:26 PM

"A plethora of 12 inch rulers knocking on walnut shells"? That's a poetic way of describing it.

Rod-knock tends to get worse as the engine warms up, piston-slap tends to become less as the engine warms up.

Rod-knock sounds like a regularly-spaced wooden thunk, piston-slap sounds like a plethora of 12 inch rulers knocking on walnut shells.

Piston slap will tend to be more pronounced at one particular rpm and generally no load.



#10 the_bard

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Posted 05 December 2005 - 06:38 PM

I wouldn't knock it (no pun intended)... my wife definitely describes her cold engine start-up piston slap as the plethora bit versus the wooden thunk.

#11 blitz

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Posted 05 December 2005 - 08:46 PM

"A plethora of 12 inch rulers knocking on walnut shells"? That's a poetic way of describing it.

Yeah, whereas most commuters are content to debate fuel economy & air bags, I'm stuck trying to decide whether I've got an AWD literary or musical appliance. :confused:

#12 mfilopanti

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Posted 12 December 2011 - 10:20 PM

My brother just bought a subaru from an auction and it has a very loud knocking noise coming from the engine and also the transmission doesnt shift right. Its an 05 legacy. Does anyone have any ideas of what it could be? were hoping its not a blown motor. there is no check engine light on.

#13 the3rsss

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Posted 13 December 2011 - 08:34 AM

I have piston slap in my 2.5 dohc. Cant speak for anyone else but I tried a few oils to see if i can lessen the noise at start up. This motor did not seem to like synthetic in any grade! The knock seemed worst with synthetic. Went with mobile 5000 3qts 5-30 rest 10w-30. That seemed to quiet it down quite a bit. I also use a block heater on very cold nights. Warm car in the morning and cuts down the piston slap alot. I had done some major engine work over the summer, I read all the threads and I know that the slap is harmless (my opinion), I still got an oil analysis done for my own piece of mind. It was cheap 25$, quick 2weeks, And found basically no wear metals in the oil. If you want piece of mind, get it done.

#14 darkducati

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Posted 21 December 2011 - 10:39 PM

That's a good idea. I have some very minor slap that lasts about 2-4 seconds before whirring down dramatically at start up. I still wouldn't mind knowing though.

#15 SchwarzeEwigkt

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Posted 22 December 2011 - 03:49 PM

My EJ25D slaps until it warms up. I've found that running the German Castrol 0W30 seems to help with it. That stuff's impossible to find, though.

Either way, it's just a quirk of these engines. Doesn't hurt anything.

It's like that old saying. "It's like a big rump roast on a pretty girl. A shame." You wouldn't kick her out of bed. :cool:




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