piston slap or spun bearing?help!
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On The Tree
Joined: Jun 2007
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From: kingsville, Tx
piston slap or spun bearing?help! hey what's goin on guys? new here on ls1 tech anyway i've either got the worst case of piston slap ever or somethin's real fucked under my hood. only happens first five or ten minutes after a cold start but sounds like HELL! I've had older 350's knock quieter with spun bearings and bent valves. oil pressure is good about 40-45 pounds at idle closer to 70 above 2k, runs a little rough first couple of seconds when i first start it up but after that runs fine. somebody please tell me I'm paranoid or i should buy a new motor.
hows the oil look? need to look for copper. Mine has one cylinder that raises hell when its cold...pulled the pan and all bearings look new so i assume its piston slap. DId the oil pressure change? Keep an eye on that and that will help determine if its a bearing or not. Normally you can unplug a coil pack and the sound will lessen or go away if its a rod bearing on the cylinder you unplugged
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Thread Starter
On The Tree
Joined: Jun 2007
Posts: 106
Likes: 0
From: kingsville, Tx
dude unpluggin coilpacks didn't help at all. it sounds almost llike a stuck lifter. it runs lilke its misfiring when i first start it up. it's not throwin any codes though. i might just tear it down next weekend. I'd feel a little more confident with a rebuild before i spend a few grand on cam and heads.
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Instead of tearing it down check out a company called Blackstone Laboratories. They do oil analysis and can tell you if a bearing is toast. I did one for my TA and they said it was all normal. I then did one for a 200 tahoe and they let me know the bearings were prematurally wearing do to a coolant leak. I was blown away how they picked up and they explained if fixed quickly no problems would arise. So the way I looked at it is spending like 20 bucks on a oil analysis was alot cheaper and less time consuming then the alternative. Although it sounds more like piston slap to me I know how the need to know for sure factor can affect you so I would be thinking like you.
I found out about them through another members modification website. Here is the link.
http://www.xse.com/leres/ss/oilreport.html
http://www.xse.com/leres/ss/oilreport.html
If it's misfiring you may just have a bent pushrod or a loose rocker arm. But it would make noise all the time if that was the case. Also, a spun bearing should get louder as the engine warms up. Pull your valve covers and make sure its not something in the valvetrain before you spring for a complete rebuild.
Originally Posted by Thule
if it goes away when it gets hot it is not a spuned bearing, if its spuned it makes more noise when the engine is hot
The only other thing other than a piston slap that could act like that would be a stuck lifter - it could unstick as the engine warms up. But a lifter will sound a lot different. Much more of a high-pitched, clattering type of noise, where a piston slap will sound more like a knock. Take it to an experienced mechanic and get his opinion. He will be able to tell the difference between a piston slap and a stuck lifter.
