how to get rid of piston slap
05-04-2006, 06:12 PM
#31
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Originally Posted by Black02Z71
Yeah, look at these pictures of my old 5.3L. This engine has 58000kms on it, cold start slap started around 40000kms (lasts for 30 secs at startup). No carbon build up here, I always made sure of that. 
I'd try some thicker oil.
I'd try some thicker oil.
What the hell are you talking about, "no carbon build-up" !!! are you blind??? lood the top of your pistons, I hope that you were being sarcastic.
05-04-2006, 07:05 PM
#32
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Crap... i think some of the Briggs-Stratton motors i've taken apart have had cleaner combustion chambers than that... Thats way too much carbon for a EFI engine thats for sure...
05-04-2006, 11:27 PM
#34
The piston slap, or cold start knock, that is commonly referred to is a different issue than the noise caused by carbon build up. I do an induction service on my truck regularly, and I've boroscoped it to see the results. Most of the noise you hear from carbon build up is the tops of the pistons hitting the carbon build up at the top of the cylinder, and the carbon on the valves slappin against the valve seats.
The old piston slap issue is caused by the pistons rocking in the cylinders until the engine heats up and the parts expand, allowing tighter clearances. As mentioned above, the lack of a skirt on the piston is a major contributor to this. On cold morinings I get the cold start knock for anywhere from 15 seconds to maybe a minute, then it's gone. My issue is not carbon related...I think we may be talking about 2 different problems here...
The old piston slap issue is caused by the pistons rocking in the cylinders until the engine heats up and the parts expand, allowing tighter clearances. As mentioned above, the lack of a skirt on the piston is a major contributor to this. On cold morinings I get the cold start knock for anywhere from 15 seconds to maybe a minute, then it's gone. My issue is not carbon related...I think we may be talking about 2 different problems here...
05-05-2006, 09:47 AM
#36
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As he said in post #22
Originally Posted by slammedS10
I am refereing to a slight piston slap after the engine is warmed up.
This is relating to warm engine noise, not a cold engine before heat expansion has occurred.
05-05-2006, 09:55 AM
#37
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Originally Posted by McKlusky
This is relating to warm engine noise, not a cold engine before heat expansion has occurred.
Jim
05-05-2006, 12:21 PM
#39
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Different descriptions are used loosely (probably too much so), descriptions like slap, rattle, knock, tap, etc. All of the above are open to interpretation and relative to what the person using them has been taught to believe.
The easiest way I know to try and clear this up is in the following :
1. If you have engine noise for 3 or 4 seconds on cold engine start-up until the oil
pressure comes up, that is something unrelated to the points this thread has
been attempting to resolve.
2. If you have any internal engine noise when the engine is cold that lasts for
more than 3 or 4 seconds and gradually diminishes as operating temperature
increases, then that could very well be parts expanding and taking up excess
clearance as they heat up.
3. If you have carbon buildup that is causing noise, how loud the sound is will
depend on how much carbon (how thick) buildup there is on the top of the
piston and/or on the bottom of the head. The sound can also be affected by
how many cylinders the carbon is actually causing noise in. Not all cylinders
in the same engine will build up carbon at the same rate.
4. A quality fuel system service (intake vacuum IV induced) should be done
(properly) as preventative maintenance regardless. So if you have noise on a
regular basis (and have not had the fuel system serviced recently) after the
engine is warmed up, then have the fuel system serviced, it needs to be done
anyway.
The easiest way I know to try and clear this up is in the following :
1. If you have engine noise for 3 or 4 seconds on cold engine start-up until the oil
pressure comes up, that is something unrelated to the points this thread has
been attempting to resolve.
2. If you have any internal engine noise when the engine is cold that lasts for
more than 3 or 4 seconds and gradually diminishes as operating temperature
increases, then that could very well be parts expanding and taking up excess
clearance as they heat up.
3. If you have carbon buildup that is causing noise, how loud the sound is will
depend on how much carbon (how thick) buildup there is on the top of the
piston and/or on the bottom of the head. The sound can also be affected by
how many cylinders the carbon is actually causing noise in. Not all cylinders
in the same engine will build up carbon at the same rate.
4. A quality fuel system service (intake vacuum IV induced) should be done
(properly) as preventative maintenance regardless. So if you have noise on a
regular basis (and have not had the fuel system serviced recently) after the
engine is warmed up, then have the fuel system serviced, it needs to be done
anyway.
05-05-2006, 12:23 PM
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It was good to point-out that there are two seperate types of knock being discussed...it eliminated some confusion.
Slammed was talking about the carbon-induced type. As far as I know,GM hasn't changed the type of pistons.
Slammed was talking about the carbon-induced type. As far as I know,GM hasn't changed the type of pistons.