Trying to narrow in on mysterious noise for a long time

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  #1  
Old 08-04-09, 09:55 PM
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Trying to narrow in on mysterious noise for a long time

I have a 92' Ford Ranger with 2.9 V6. The engine was replaced June 2008. It seems to perform well. But I notice when I rev the cold engine that I hear a few faint rattles or knocks just after the rev winds down to an idle. It doesn't do this when the engine has warmed up.

I have heard other faint subtle sounds on and off since last year. I have had the mechanic listen, but he says he doesn't hear anything that concerns him. I had someone listen today and they heard the sound too, which is a more recent development. It is definitely irregular. I hooked up a scanner for trouble codes. It returned code 11 for system pass both times.

Anyone have any ideas on this? I am sort of wondering why he did not do any simple diagnostic tests all this time. Couldn't he have tried a mechanic stethoscope at least? Or maybe not all mechanics subscribe to this method?
 
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Old 08-04-09, 10:13 PM
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light knocking or rattle on cold start up is most likely piston slap...esp if the engine has coated pistons. when the coating wears off, the piston is allowed to shift from major to minor thrust surface on the skirts and then back again each time the piston is at BDC or TDC (when the rod angle changes) as the pistons are cam ground when manufactured, when it heats up (the piston) the piston to cylinder wall clearance diminishes and the noise leaves.

I have a 2000 chevy tahoe with over 160K on it that rattles like marbles when started cold...been doing it since 9K and has never worsened...bottom line is piston slap is normally disregarded.
 
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Old 08-05-09, 07:44 AM
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Well, what causes piston slap? It is a rebuilt Jasper engine, which is supposed to be the best. Is this considered a defect from engine not being rebuilt to correct specs? Will it cause faster engine wear?

Thanks,
Dave
 
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Old 08-05-09, 08:22 PM
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My dad has a 92 chevy 1500 with a 350 has had piston slap since it was new now has 170k on it and still runs great I would not worry about the slap if anything let it warm up good before you stand on the gas.
 
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Old 08-05-09, 08:43 PM
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If it has piston slap, there is something wrong,, The piston skirt has cracked or the guy that punched the holes in the block had a hangover Monday... With todays technogly if an engine has piston slap when cold,, Get it fixed... Yes it may run 200k miles yet,, But its not right....Too much piston to cylinder clearance can never be good... Roger
 
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Old 08-06-09, 12:24 PM
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hmmm...if it can go 200k, how would that be bad.

it's not an uncommon problem in today's engines because many pistons have a teflon coating on the skirts...when the coating wears off, the clearance increases ever so slightly and some noise at cold startup may result. as I stated, my 2000 tahoe started the noise at 9K...it now has 165K on it. still makes the exact same noise, no better no worse than when it started. i still maintain that if the posters noise truly is piston slap, which is what the description sounds like, it won't be a longevity issue.
 
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Old 08-06-09, 01:11 PM
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Hello Blues, I have a 96 jeep grand cherokee and had same problem I went to 20 w 50 in oil changes with slick 50 treatment every 3 changes and have incredible luck using this routine hitting 300.000 as of now just a suggestion hope this helps
 
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Old 08-06-09, 06:40 PM
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If you're happy with pistons slapping around in the cylinders, each to there own... If it were any engine I've built,,(or bought) It would be fixed as the slap indicates excessive piston to cylinder clearance..no matter what kind of coating they may have told you they put on the pistons... If you want the skirt of you're piston hammering on the bore of the engine & think,,, this is normal???? Just my thoughts....Roger
 
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Old 08-08-09, 07:53 PM
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Thanks for all your input. So I paid about $4900.00 including tax to buy and install an engine with pistons flopping around? It seems that some people would overlook the defect and others would insist on repair or replacement. I'm with the second camp.

How many of you would insist on repairs and how many of you would leave it alone? But better yet, how do you prove that it is piston slap? I read about this method that involves removing plugs and squirting oil into the combustion chambers.

I don't know why people are ok with this. If this turns out to be the problem, it won't be acceptable to me. From what I have read, manufacturers often play off piston slap as a minor defect to be ignored. I don't buy into this. I hope I don't get into a beef with the mechanic and manufacturer over warranty, rental car reimbursement, etc. This could be a major inconvenience, and I only have this one truck.
 

Last edited by bluesbreaker; 08-08-09 at 08:20 PM.
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Old 08-08-09, 08:15 PM
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There is a very thin line here .....Key word being "EXCESSIVE" clearance.


As the engine heats up , things expand....Normal...You cant change physics.

In theory, if you tightened things up to minimize clearance...when the motor heated up , it would sieze.....A certain amount of clearance is essential...and if this clearance falls into a range that allows a piston skirt to "Kiss the wall" when cold...so be it.

On a lighter note, 3/36 warranty, and a reputation to protect, after cash like that, your installer should at least humor you.....Instead of dissmissing it.
 
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Old 08-08-09, 08:24 PM
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Well, look at it this way. The original engine never had piston slap
before it finally failed from a blown head gasket. But maybe I'm getting ahead of myself before the mechanic listens to the noise this Monday. I've kept a written record and even photos since June 2008 installation.
 
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Old 08-09-09, 12:47 AM
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Why do I keep thinking the noise is related to oil circulation? There was a time in the past when people would pour products like Risolone (blue color) into the oil to try and find a quick and cheap solution if this was the case. I knew people who would use this stuff instead of regular oil even. I do know that GM had a lot of piston slap issues around their pickups and large SUV's 10 years ago, as well as with their Northstar Caddy engine back a few years ago also. Northstar engines early on in addition to slap seemed to use alot of oil right off the lot also. At one time due to variable cylinder bore dimensions and loose tolerances in the block casting, engine assemblers at GM plants for instance would need to measure and fit each piston separately from a selection of piston sizes they carried at the work station. Amazing right? Toyota 20 years ago learned how to make a block casting right and only needed to use one piston size and the other OEM's followed their lead. Are you sure the problem could not be around delayed lubrication at cold startup?
 
  #13  
Old 08-09-09, 04:21 PM
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Oil circulation could be a possibility. I have read that insufficient valve train lubrication was a design flaw seen in late 80's early 90's 2.9 V6 engines.

I am using 20W-50 oil currently because of the oppressive summer heat here in Arizona. When it cools off, I'll switch to 10W-40.
 
  #14  
Old 08-20-09, 07:56 AM
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Noises

It needs to be kept in mind that only the owner has heard the noise in question. Perhaps before we throw the baby out with the bath water a qualified mechanic should hear and diagnose the problem first hand. There can be a number of things that go bump cold and not warm. A chain tensioner or perhaps a belt tensioner not to mention the bearing on the turbine wheel in the torque converter. An accurate diagnosis needs to be made first.
Bill
 
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