Confirm rod knock

[AZmike]

Shortly after changing the oil (less than 60 seconds after restarting the engine) I noticed that my engine has developed a new noise. It's much louder than the valve clicking sounds that I'm used to. At any engine speed below about 1500 rpm I can hear it. It's most noticeable at idle. I've never heard rod knock first-hand before, but that's my best guess. Those few seconds without oil pressure after the change may have finished off one of the rod bearings. It sounds like a knock: not quiet, not really loud, but very noticeable, even with the hood down. The noise doesn't really change when disabling individual cylinders, just slows down with the engine. I used a breaker bar and listened at different locations around and on the engine. I wasn't able to pinpoint anything--it just sounds like it's coming from the block, or maybe the head (I can't think of anything in the head that could ever sound like this though). Can anyone think of any other possible causes for the noise to develop immediately after an oil change? The filter is the same brand as I was using previously and the oil is the same weight. Any advice is appreciated.

[88Accord-DX]

First thing you need to do is spend 20 bucks for a cheap stethoscope at the auto parts store or if you are going to do this.
Remember that diagnosis of engine noises is nothing more than splitting possibilities down to only one.
Try to track the noise down with the stethoscope tip or the end of the hose suckered onto the engine surface, sealing the end. Spend a full ten minutes putting the hose all over the engine, not just where it is loudest.

Rod knocks are loudest at higher speeds (over 2500 RPM) Feathering the gas pedal may result in a distinctive back rattle between 2500 and 3500 RPMs.
Bad rod knocks may double knock if enough rod bearing material has been worn away allowing the piston to whack the cylinder head in addition to the big end of the connecting rod banging on the crankshaft rod journal. It will sound like a hard metallic knock (rod) with an alternating and somewhat muffled aluminum (piston) klock sound.
Wrist pin knock in modern engines is very rare today but is a favorite for the misdiagnosticians.

Determining which cylinder contains the noisy parts may be aided by shorting out the plug wires one by one.

If the noise is changed when the plug wire is shorted to ground, you can figure that the problem is in the reciprocating bottom end parts. (piston, wrist pin, connecting rod or connecting rod bearing)

If the sound doesn't change, look at parts other than the reciprocating ones. In many cases of rod-knock or piston slap, more than one is banging so even if you eliminate the noise from one rod the other one will still be a-banging away with a different, similar tone.

There is a real nice yet little known test for piston slap.
When the engine is cold, the aluminum piston is small in comparison to it's iron cylinder. Therefore the rather hollow slapping noise will be loudest first thing in the morning.
So, the test is this:
First thing in the morning, start the engine up and run it for 15 seconds while you listen carefully and memorize the sound and it's intensity. Shut it down quickly, pull the spark plugs and put two squirts of motor oil into each cylinder. Reinstall the plugs, fire the engine up again and listen.

If you have piston slap the noise will have been greatly reduced or even eliminated…..for 15 or 20 seconds that is, and then your nightmare noise will come back.

Valve train noises generally are loudest up to 1500 rpms. Include;worn camshafts, low oil pressure, worn rocker pivots, very loose valve guides, worn rocker arms…..

Deeper clunking noise is the main bearings knocking.

Hope that helps some.

[AZmike]

Thanks for the reply, but I found the same information googling before posting here.

I tore the bottom end apart after work tonight and found the problem. All of the rod bearings looked ok, but it looks like the lower third main bearing is completely gone. I also found a few aluminum pieces in the oil pan along with a mess of copper chips. Is there some sort of cap over part of the the dip stick hole in the block? There is a step in the dipstick hole that look like it could have held something. I can't think of any other source for the mystery debris. The valvetrain looked intact.

The three middle crank journals all look ok, so I guess the next step is to pull the tranny so I can drop the crank and check the upper half of the third main bearing. Are standard size replacement bearings close enough to the correct size to use as replacements? The factory service manual assumes I can try all sizes until I find the one that fits correctly.

[88Accord-DX]

Yeah, I found the above info. on a search.

Standard bearings has the original dimensions specified by the engine manufacturer for a new unmachined crankshaft. Get some Plastigauge to measure bearing clearance to see which bearings you need. There are specs to see if you need oversized ones. Also , if your replacing the mains, replace the rod bearing too, & rear main seal. Check crankshaft end play to see if you need a new thrust washer. (Only if you have a dail caliper to check that)
If you pull your crank out, if you have a outside micrometer, check the taper & out-of-roundness on the crank & rod journals. That will tell you if your crank is shot & need a new one. Regrinding is an option. Check rod side clearance before or after replacing componants also.
I'm not sure on the dipstick part your talking about. Re-building my motor later this year.

*editing some & add on* Not sure if your taking out your crankshaft. You can take out all the rod & main bearings (top side) from tapping them out from one side and slipping them around the journal.

[Oldblueaccord]

Thanks for the reply, but I found the same information googling before posting here.

I tore the bottom end apart after work tonight and found the problem. All of the rod bearings looked ok, but it looks like the lower third main bearing is completely gone. I also found a few aluminum pieces in the oil pan along with a mess of copper chips. Is there some sort of cap over part of the the dip stick hole in the block? There is a step in the dipstick hole that look like it could have held something. I can't think of any other source for the mystery debris. The valvetrain looked intact.

The three middle crank journals all look ok, so I guess the next step is to pull the tranny so I can drop the crank and check the upper half of the third main bearing. Are standard size replacement bearings close enough to the correct size to use as replacements? The factory service manual assumes I can try all sizes until I find the one that fits correctly.

Since your that far into it I would also use plasti guage and check all the tolerances and buy the bearings that are closets. Honda actually does that from the factory thast why they last.
You get a 350 made on friday second shift the bearings will be all the way on the outside of the tolerance. They just slap the same size in all week long.

Good luck its time consuming but I think you saved the motor. As far as the dipstick I cant remember whats in there its been a while. Be wierd if something did break off but it should not get into the oil pump past the screen anyway

wp