I recorded a few sound clips of my '86 2.5 (which will soon be replaced or rebuilt), and like the topic asks, I am wondering if this is a knocking rod, or "just" piston slap. A little background on the motor: '86 2.5, 169k miles, definately had carbon buildup, and I don't think it was given the best (or worst either) treatment.

First, this is what it sounds like cold (about 2 minutes of running):
http://www.cosineaudio.com/fiero/coldeng.wav

Then this is what it sounds like after about 10 minutes and 5 miles of running time:
http://www.cosineaudio.com/fiero/warmeng.wav

I know the timing gears are making noise (pretty obvious! ), and about 2/3 to 3/4 of the way through the clips, when then sound gets dramatically louder, that was taken from the right rear of the car under the facia.

Just wondering what you think that tapping is.

Oh, and if anyone is wondering, that is the stock exhaust with the cat replaced with a straight pipe

No speekers co can't hear it.

Piston slap is worse cold and goes away as it warms up. A rod knock will get louder as the engine heats up and the oil thins.

not meaning to sound sarcastic.. good luck with your situation.. As far as im concerned piston slap only pertains to that $$$35000.00 GMC truck i have sitting in my garage next to my 86 GT fiero.. Look 18 years later and they still cant build a strong motor...

pc...

out

Electrathon, I'm leaning towards piston slap for the very reason you mentioned; it quiets down when the motor warms up. I'm really just kinda wondering what to expect in a teardown, and what other people think it is. I've never really experienced either sound before, and I'd like to know for my own knowledge.

Trying to decide if I will rebuild the bottom end, or just skip it and get another short block.

PCGamer, don't worry I hear where you are coming from. My Dad was told that it was normal that his brand new trailblazer knocked a little when it was cold, and that it was also normal for the valvetrain to be a bit noisy!!! Also gotta love the crazy "oil change required light" reset proceedure: turn the key to the run position but don't start the vehicle, and the floor the throttle 3 times ( i think ). Kinda makes you wonder if there are any easter eggs hidden in there somewhere!

Often times it is very tough to see if a piston is just a couple thousandths loose. The solution is to have it bored and oversize pistons. If it is a rod knock, which is much more common in a 2.8 you will have to have the crank turned too. As a general rule the solution for either is a bottom end rebuild.

If you have the money just prepare yourself for a quality rebuild.

Sounds like the usual 2.5 with 169K miles on it. Nothing out of the ordinary IMHO.

------------------
Tim
Red 88 Formula Auto 2.8 100K+ Miles - Hypertech - No Cat - No EGR

Murphys Law - "Nothing is as easy as it looks, Everything takes longer than you expect, And if anything can go wrong - it will, At the worst possible moment!"

I guess I missed the point. The engine has the sounds of an engine needing a rebuild. Could be rod bearings. Could be piston slap. Could be piston pin slap. Could be worn timing gears. Could be valve train noise from collapsed lifter or broken spring. Could be oil pump not keeping up and letting lifters lose their prime. I don't think it is the worn valve guides or worn valve seats or burned valves. Could be the worn main bearings or worn cam bearings dropping oil pressure causing the lifters to collapse. Could be a bent push rod rattling around.
You'll need to rebuild in any case. You'll want to bore the cylinders enough to get past the uneven wear on the cylinder walls and get the proper size pistons and rings. You'll want to replace the bearings and possibly replace the crankshaft or have it turned down .010" You'll want new timing gears and cam bearings. The old springs need replacement. Valve seals and seat resurfacing should be done, too. Water pump and oil pump might as well be done now unless you just did it.
Don't let your interest in the strange sounds displace an important part of Fiero ownership, wrenching. Enjoy!

Better not be a valve spring, as I just put a rebuilt head on it after it blew the head gasket The pushrods are fine, and it holds good oil pressure. I know the timing gears are part of the sounds there, as they get real bad around 2500 rpms. I guess I was more curious than anything else. I know the motor really needs to be rebuilt or replaced, one of which will be happening in a couple weeks. The duke is a fairly new motor to me, and I was just wondering what I was hearing.

Just a few cents of random info. I had a Pont Transport van that had piston slap from the factory, it ran fine for 115000 miles till i sold it. They even had a recall. Ive never known anyone to rebuild just the top or just the bottom and not have the other blowup in more than a few months. You make the head better, and lower end goes, rebuild the lower and top goes. The more miles on the engine, the greater the risk too. To me, if it needs a head, I still get a reman. I will however replace a blown head gasket and not mess with the head itself other than cleaning.

grrrrr... I guess sooner or later I'd wind up with a double post... may as well be now!

[This message has been edited by SpideR W (edited 04-08-2004).]