eliminating piston slap entirely?

[3100]

Would a new set of pistons (and whatever cylinder bore work needs doing) eliminate piston slap entirely on one of these motors?

[TGP37]

Would a new set of pistons (and whatever cylinder bore work needs doing) eliminate piston slap entirely on one of these motors?

Possibly, depends how you size them up. Piston slap is the piston not fitting properly when cold. If you let the engine warm up before putting load on it, the lifespan can almost double. I've heard of these blocks going 500k if allowed to warm up before hammering it.

If it's only piston slap when cold, I wouldn't bother it.

[3400-95-Modified]

I did new 30 over pistons in my old 3400 and it still had noise... those were the sealed power ones with teflon side coating.

[3100]

Interesting. It's more pronounced when it's cold (as in, it's loud enough for me to question how it still runs) but it still knocks a bit when it's warm, though it's as a manageable level then.


It's the worst piston slap I've ever heard, but it runs just fine, doesn't burn any oil either. Oil psi is good. Even the OEM (afaik they're original anyway) intake gaskets are intact

[TGP37]

If the car was driven hard while cold often...i.e. rush to work situation 3-4 times a week..... the combustion chamber can get ovaled from wear over time.

But, it might not be piston slap. Try pulling the spark plug while idling one at a time to see if the noise stops. It could be a bad connection rod cap bolt or bad rod itself, etc. Removing the load on the suspected chamber will stop the noise. I heard piston 6 slaps the most but I am not 100% sure about that.

Anyways, mild piston slap is healthy. And if the engine is allowed to warm up before any load is applied, it will last up to 500k miles. Considering the other fluids and maintainence items are cared for.

[3100]

If the car was driven hard while cold often...i.e. rush to work situation 3-4 times a week..... the combustion chamber can get ovaled from wear over time.

But, it might not be piston slap. Sometimes the pushrods and/or the lifters get clogged up and the rockers start to dry up. Making a tapping sound.

Anyways, mild piston slap is healthy. And if the engine is allowed to warm up before any load is applied, it will last up to 500k miles. Considering the other fluids and maintainence items are cared for.

Yeah, I take pretty great care of it. ~3000 mile oil change (5000 kilometers) and I don't lay into it until it's warmed up.

I know it was well maintained its entire life but knowing the previous owners, I think it was probably driven hard while cold often. The noise definitely isn't mild, though.

[TGP37]

Are you sure it is piston slap? A short video could really help if your trying to diagnos this. If the noise is more noticeable then normal it may not be piston slap.

Don't forget the 100k mile maintainence. Oxygen sensor get old and they create a richer condition, fuel filters are often neglected until they clog up. By then the pump is ready to die (if filter is neglected). And keep an eye out for the dreaded LIM leak.

[3100]

Fairly certain. It doesn't sound like it's coming from the valvetrain but I honestly have not gotten out the stethoscope to pinpoint the noise.

[3100]

I'd much rather it be lifter noise. Popping in a new set of lifters and maybe pushrods when it's apart for LIM gaskets is a damn sight easier than putting new pistons in.

[3100]

Are you sure it is piston slap? A short video could really help if your trying to diagnos this. If the noise is more noticeable then normal it may not be piston slap.

I'm trying to upload a video but it doesn't seem to want to work. Likely a PEBKAC error.

[3100]

http://youtu.be/fhJtlzRE268

sorry for the noise, it is windy. it's pretty evident though, even in the poor video, that it's much louder on one side.


i had not been in the car since yesterday..hopped in, started it, got out and pressed record. it's pretty cold but it's just about as loud now as it's ever been.

[TGP37]

Well, if it doesn't go away when all warmed up I'd be suspicious of some other issue developing.

You couls try seafoam in the oil and fuel. Or another top-end cleaner of your choice. You may just have a collapsed lifter. Are you noticing any excessive missfire? Drop in fuel mpg? Top-end cleaner almost comes off as snake oil, but the stuff works great.

1/3 can in oil, 1/3 can in gas while filling up and 1/3 sucked up a vacuum line (as directed). Drive around until fuel is almost empty and change oil. That's what I do for a seafoam treatment. Can do amazing things for a noisy top end.

If that doesn't work, try pulling spark plug cables while running (carefully). Do not pull the cable to far from the block or you'll get zapped. It will run like crap but if the noise disappears, you found the offending cylinder.

Just some ideas....I'm not a trained professional...yet.

[60dgrzbelow0]

If you have a collapsed lifter, the offending cylinder will obviously not have a power stroke and the extra, unburned gasoline will pass the rings of that piston, weakening the ability of the oil to lubricate the longer the engine runs in this condition. When the engine is off, pull the Oil Dipstick after walking away from the vehicle's other offending exhaust odors...smell the dipstick a bit for the presence of a heavy gasoline odor. If this is the case...what TGP37 is suggesting will take some time to diagnose with trial and error...but that should show you which cylinder is involved. If you have not done so either recently or because the weather is so inclement where you are... make a point of at least getting the oil changed ASAP... when your oil gets thinned from gasoline bypass...it causes accelerated engine wear. The definitive test here is first a Dry Compression Test for a baseline... followed by a Wet Compression Test (Do not squirt more than just a few drops of Oil into the spark plug holes here). If the compression elevates during the Wet Compression Test...it means you have very bad rings caused by the out of round condition of the old and tired cylinder walls. If not... then very bad valves are quite probable here ...leaking enough around their seats and again.. .preventing enough compression for a decent power stroke sufficient to ignite and burn up all that residual gasoline. That piston is a drag on the drive train and can make a racket implying cracked piston rings or a bad connecting rod bearing, too...

"You've got a Good Soul... and I hate giving Good People ... Bad News..." The Oracle to Neo... "The Matrix"

[3100]

It's been seafoamed before (on separate occasions, through the fuel, through a brake booster vac line, and once in the crankcase) with no change to the sound.


I changed my oil yesterday. It's got about 50 kilometers on it now and about 30 clicks as of that video.


I'm aware that fuel dilutes oil but there's no more blowby than normal to report. No unusually strong fuel smell from the oil.


the only problems I am aware of at present are a leaky EGR tube and an intermittent ignition hiccup (I believe it's due to original wires...coils seem fine and plugs are new)


Fuel filter is new...water pump is new....alternator is new...IAC and TPS are new, EGR valve


regarding the power balance test mentioned: pulling spark plug wires on a running vehicle is a bad idea....the spark needs to go somewhere. You ground a test light and "steal" the spark from that particular cylinder by whatever means available - I like to take some strands of copper wire and put 'em on the ign. terminal under the boot before putting the wire on the terminal, this way you're not piercing any wires, but you've got a way to short out that cylinder. touching the test light to the copper wire will short the spark to that cylinder. the hard part here is keeping all of those copper wire strands from touching each other.

try not to short a particular cylinder for too long, lest it foul a plug or converter because it's not firing whatsoever when you do this.



thanks for your help!

[Joseph Upson]

It's likely piston slap (although it's a bit higher pitched than I expected to hear), especially if it gets better as the engine warms up. If it is much louder than usual be nice to it. I bought a low mileage 3100 from a core supplier with some overstock good motors years back for turbocharging that turned out to be a recall motor for piston noise. It clacked on first start. The engine held up well for about 30k miles but the turbo started to get the best of it as evidenced by the increasingly loud piston slap. I got it swapped out just in time. The problem is partly the result of using shorter skirt pistons and too much clearance. Here is a link to pictures of what's probably going on in your engine and what the pistons could possibly end up looking like:

This is a 3100 although it has some iron head parts on it.

http://www.fiero.nl/forum/Forum2/HTML/084972-2.html