Piston Slap
15 April 2006, 10:18 AM
#1
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Piston Slap
Which cars did this affect?
I seem to remember it was the 1996 cars mainly?
Does it appear in the latter cars at all?
How does it manifest itself? I assume it appears when cold only and a Top End tap?
Pete
I seem to remember it was the 1996 cars mainly?
Does it appear in the latter cars at all?
How does it manifest itself? I assume it appears when cold only and a Top End tap?
Pete
15 April 2006, 10:25 AM
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Originally Posted by struv
iv heard mainly 98 cars
Apparently it is due to the piston diameter being slightly too large for the bore, and as a result the piston ovalised upon usage causing piston slap as a design error. Although I stand to be corrected.
Robin.
15 April 2006, 10:49 AM
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Originally Posted by pslewis
Nowt to worry about though, is it??
Nothings going to break??
Pete
Nothings going to break??
Pete
15 April 2006, 10:52 AM
#6
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Is 'my' car special then?? 
I am being asked questions ......
And it seems that the noise disappears after about 30 seconds of running and only appears under load - not there when idling, but after about 30 seconds not there at any time?
Pete
I am being asked questions ......
And it seems that the noise disappears after about 30 seconds of running and only appears under load - not there when idling, but after about 30 seconds not there at any time?
Pete
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15 April 2006, 10:57 AM
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Originally Posted by pslewis
Is 'my' car special then??
I am being asked questions ......
And it seems that the noise disappears after about 30 seconds of running and only appears under load - not there when idling, but after about 30 seconds not there at any time?
Pete
I am being asked questions ......
And it seems that the noise disappears after about 30 seconds of running and only appears under load - not there when idling, but after about 30 seconds not there at any time?
Pete
Robin.
15 April 2006, 11:00 AM
#13
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Originally Posted by TonyBurns
Could be those dodgy oil changes you've been doing also Pete? 
Tony
Tony
Pete
15 April 2006, 11:07 AM
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I have a variety of noises from my engine bay, I have eliminated my tappets, and I havn't any piston slap.
I know that I have a clicking noise from my boost solenoid (on drivers side suspension bulkhead in engine bay), and this is only apparent at about 1500 rpm and above, wether under load or not.
And I believe my cam belt tensioner/idlers to be worn (car is over 100,000 kms), and they seem to cause a sporadic ticking noise at times, on idle-not sure about under load.
Hope this helps
I know that I have a clicking noise from my boost solenoid (on drivers side suspension bulkhead in engine bay), and this is only apparent at about 1500 rpm and above, wether under load or not.
And I believe my cam belt tensioner/idlers to be worn (car is over 100,000 kms), and they seem to cause a sporadic ticking noise at times, on idle-not sure about under load.
Hope this helps
15 April 2006, 11:48 AM
#19
96-to end of 98 (so may include early reg 99 cars )IIRC.
It is a highish, rapid "clinking" noise, sounding from the middle to upper end of the engine towards the cylinder heads in time with the engine rotation. That is very prominent when cold, and increases in intensity on acelaration or when you lightly rev the engine.
It was about the time Subaru started using their fancy ceramic and molybdenum coated pistons.
Due to differentiating thermal expansion properties of alloy pistons and steel cylinder liners. Pistons are sized accordingly to fit correctly when HOT to prevent scuffing, wear and at worse - seizure. So this can mean the pistons are excessively undersized when they are cold, thus allowing them to rattle around in the bores (piston slap).
Subaru got the calculations a bit wrong, where they considered it to be too excessive and potentially could cause problems at the latter stages in the engine's life. I personally think it was an overreaction from Subuaru addressing customer's whose engine's "funny noise" were causing them concern.
As long as it stops completely when warm (within 30mins absolute max...norm is 10mins). It should not really ever cause any problems. But eventually, due to the contact of the piston skirt with the bore, it will scuff off the protective coatings, and the bores will wear excessively oval (all piston bores on any engine eventually wear oval due to nature of a piston's movement), causing piston ring sealing problems and an increase in oil consumption, blow by gasses and reduction of cylinder compression. By this time piston slap would probably be very persitant. And maybe present until the engine is completly warm (well over 30mins) or still persitant when hot (although not always nessecerily the case).
So to sum up: Long term effect is the engine's overall life span is reduced. But your talking well over 100,000 miles, probably 200,000miles at a guess. Which I'm sure the big ends would have long gone before then
It is a highish, rapid "clinking" noise, sounding from the middle to upper end of the engine towards the cylinder heads in time with the engine rotation. That is very prominent when cold, and increases in intensity on acelaration or when you lightly rev the engine.
It was about the time Subaru started using their fancy ceramic and molybdenum coated pistons.
Due to differentiating thermal expansion properties of alloy pistons and steel cylinder liners. Pistons are sized accordingly to fit correctly when HOT to prevent scuffing, wear and at worse - seizure. So this can mean the pistons are excessively undersized when they are cold, thus allowing them to rattle around in the bores (piston slap).
Subaru got the calculations a bit wrong, where they considered it to be too excessive and potentially could cause problems at the latter stages in the engine's life. I personally think it was an overreaction from Subuaru addressing customer's whose engine's "funny noise" were causing them concern.
As long as it stops completely when warm (within 30mins absolute max...norm is 10mins). It should not really ever cause any problems. But eventually, due to the contact of the piston skirt with the bore, it will scuff off the protective coatings, and the bores will wear excessively oval (all piston bores on any engine eventually wear oval due to nature of a piston's movement), causing piston ring sealing problems and an increase in oil consumption, blow by gasses and reduction of cylinder compression. By this time piston slap would probably be very persitant. And maybe present until the engine is completly warm (well over 30mins) or still persitant when hot (although not always nessecerily the case).
So to sum up: Long term effect is the engine's overall life span is reduced. But your talking well over 100,000 miles, probably 200,000miles at a guess. Which I'm sure the big ends would have long gone before then
Last edited by ALi-B; 15 April 2006 at 12:01 PM.
15 April 2006, 04:35 PM
#25
Sometimes piston slap isn't there immediatly you start up, but becomes apparent after 20 - 30 secs as expansion differential starts. Obviously this is not always the case but can be one scenario.
There were occasional problems with cam belt tensioners at cold start up, allowing it to "bounce" slightly against its stop. This sounded just like piston slap, and like slap, went away as the engine warmed. (I had this on my 99my - yours is a 2000my I believe?)
JohnD
There were occasional problems with cam belt tensioners at cold start up, allowing it to "bounce" slightly against its stop. This sounded just like piston slap, and like slap, went away as the engine warmed. (I had this on my 99my - yours is a 2000my I believe?)
JohnD
Last edited by JohnD; 15 April 2006 at 04:39 PM.
15 April 2006, 05:04 PM
#27
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CockLink is all quiet, thanks .... I was told to adjust it until it never shows RED - it's really only there to impress the Chavs at MacDonalds
Thanks for all the posts .........
Pete
Thanks for all the posts .........
Pete
15 April 2006, 06:05 PM
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wouldn't worry about it tbh
mine had a rebuild after i did an **** oil change and the pistons were checked and said to be in good order so they were left alone
noisy before it was rebuilt and is noisy afterwards, tbh it does not bother me in the slightest
mine had a rebuild after i did an **** oil change and the pistons were checked and said to be in good order so they were left alone
noisy before it was rebuilt and is noisy afterwards, tbh it does not bother me in the slightest
15 April 2006, 07:05 PM
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Originally Posted by pslewis
CockLink is all quiet, thanks .... I was told to adjust it until it never shows RED - it's really only there to impress the Chavs at MacDonalds
Thanks for all the posts .........
Pete
Thanks for all the posts .........
Pete
Sorry - you are joking aren't you? Have i missed the great PSLewis getting a knocklink?
