401 Nailhead knock

[Guest buickriv63]

Okay, here's a newbie question again:

Is it possible to inspect/verify crankshaft bearing damages without pulling the engine out? I have a slight knock at low RPM's, most audible when idling. I located the knock coming from the bottom of the engine, at the rear end of the oil pan.

I cannot hear the knock at higher RPM's. Also, the knock appears only after the engine has reached full operating temperature, so no knocking within the first minutes after start. The engine is working well, no excessive oil consumption, not much of a blue smoke. The oil pressure light doesn't glow.

Thanks.

[lrlforfun]

OK Pasi: I am in the process of a rebuild of a 401 from a 65 Riv. My culprit was the oil light came on at low idle. A gauge was placed at the connector fitting at the right side of the block, the car was started up and sure enough.....low oil pressure at idle as well as higher engine speeds. The engine had 150 at each hole and ran smoothly and was whisper quiet. The steering link was dropped, the pan comes off and the bearing cap was removed. There was ever so slight scoring. No need to even plastic gauge to determine if it needs to come out. When your finger nail feels even the slightest imperfection on the crank it's basically over. Sure you can install a set of bearings but after a consensus of several opinions there was no quick way out.

What next? The engine came out, the crank goes to the machine shop and it will be evaluated from there. Look for a re-build with an expensive parts list, an expensive machine shop list and lots of labor. What ever you do make sure the people working on it know what they are doing because you could EASILY spend the money and not get what you pay for. Good luck, Mitch.

[Guest wildcat465]

Check for a flywheel problem before dropping the pan.

[Guest buickriv63]

Check for a flywheel problem before dropping the pan.

Flywheel? Could you explain it, please.

[TexasJohn55]

Yeah, cracked flexplates rattle at idle, You can remove dust cover and roll it around to inspect for cracks or loose bolts to converter. They can also crack right around the crankshaft mating area and be harder to see. You can unbolt the converter and push it all the way back, check to see that you can rotate engine 360 degrees and start it up, UNLESS YOUR RING GEAR IS ON THE CONVERTER. TexasJohn

Edited May 13, 2013 by TexasJohn55 (see edit history)

[Guest buickriv63]

Ok. I'll try to check that flywheel/flexplate first, although the engine doesn't rattle to my ear, more of a steady knock instead. Anyway, Thanks!

[Jim Cannon]

Wait, Pasi, before you do anything.

Does your car have A/C? If so, does it have the fuel return line connected from the fuel filter back to the gas tank?

Does this noise ever stop if you drive the car long enough? Or only get louder?

[Guest buickriv63]

Wait, Pasi, before you do anything.

Does your car have A/C? If so, does it have the fuel return line connected from the fuel filter back to the gas tank?

Does this noise ever stop if you drive the car long enough? Or only get louder?

No A/C. This knocking sound comes after couple of minutes driving and it stays the same, no matter how long you drive (I drove a 150 mile trip and the noise stayed on). Last summer I had damper changed, trying to fix a engine vibration, but it didn't help so much. There's still a slight wobble on the new damper and I wonder if it has got something to do with this knocking noise.

[1965rivgs]

Put a mechanical oil pressure gauge in the port where the oil pressure switch is located (pass side near the top of the bellhousing) and determine how much oil pressure you have.

Tom Mooney

[Jim Cannon]

No, the damper will not create a knock. I agree with Tom, measure oil pressure.

I was hoping you had the "Riviera rattle", because it's easier to fix, but you don't.

[60FlatTop]

To the original question, you can "sound out" rod bearings. I haven't done it in a while, like decades. You take a 10" socket drive extension and hold it firmly against t\each bearing cap. Then give it a light rap with a hammer. I always used a brass hammer. As I remember, the good bearing have a nice ring to them. Excessive clearance makes a dull thud. If you have a bad one and you do eight, you'll know.

Main bearing caps are easy, just drop one at a time.

It doesn't take much to drop a few rod caps. Wipe them off and look for a dull gray surface; any coppery color and they are fried. Sometimes you see a small chunk missing, a little 1/8" triangle or rectangle. That is not a big concern as long as no scoring shows on the shaft.

Our breed of Riviera is half a century old now. They have had opportunities to sit for very long times. The long term storage events are not usually planned. If they were the owner would change the oil so it sat with fresh oil on the bearing surfaces. More likely it just got parked with slightly contaminated oil. The acids suspended in the oil will etch the bearing material over time by oxidating the surface. Start the car up and you can wipe away .001-.0015 easily. That added to the original clearance will get you .004 or .005 and a slight knock.

Remember "What you don't wear out will deteriorate with age." Wearing stuff out is fun. Finding it all shot from sitting is pretty sad.\

I dropped the pan on my Riviera before computer slang made PIA a common term. It is a PIA. You need to raise the engine a few inches. The exhaust needs to be removed. The tranny lines and fan shroud need disconnecting and removal. The four pan bolts above the crossmember are hard to do even raised. I found a 1/4' drive socket with a flex extension best to get those lil guys.

At 50 years old we are pushing the limits on an original engine. Whether it is wear or long term storage deterioration, it is probably time to consider a rebuild. I did mine right around 2000 when a piston disintegrated. That's when I dropped the pan and found it full of Chiclets.

Bernie

Edited May 14, 2013 by 60FlatTop (see edit history)

[Guest buickriv63]

Thanks Bernie (and everybody) for your "engine diagnosis lesson". Now I know what to look for, if I drop the oil pan. But I'll start with the easiest test - oil pressure.