TheBigBlueBoat

Does anyone have a rough idea as to the clearance between the crank counterweights and the oil pan, particularly at the front?

Background: Yesterday I started getting a knocking noise from my freshly rebuilt 455. I initially thought it was top end noise, due to the higher frequency (relative to revolutions) as well as it didn't have the deep tone of a typical rod knock. I tried listening to the top end and didn't find anything, then got under the car and I could feel it in the pan. But while I was under there I noticed a dent in the front of the pan above the tie rod. I knew one of the mounts had bit the dust last week, but apparently the other wasn't far behind. It has liberated itself from its iron bounds, the engine is nearly sitting on the crossmember. I've had one friend have an issue with counterweight clearance to a windage tray, and it did produce a similar sound to a broken flexplate or rod knock.

Either way I'll be testing oil pressure, pulling wires to see if I can narrow it to a cylinder (or not), and eventually dropping the pan. I'm just curious if this is even a possibility or if I need to just suck it up and prepare for the worst.

While we're at it; has anyone dropped the pan in-chassis? Any tips or tricks on that?

TheBigBlueBoat

Picture of the dent in the pan:

It was tough getting a good measurement on the base of that versus the pan rail.

cutlassefi

Your knock is most likely not the dent in the pan, sorry.

TheBigBlueBoat

Is there that much clearance between counterweights/rod bolts and the pan in the front? It's a solid 1/4"-3/8" dent, and who knows how much the overall pan has been pushed in hitting the crossmember; it's pretty much sitting on it now.

Oh well. I guess it's coming out.

wr1970

It isn't the oil pan.

TheBigBlueBoat

Pulled the engine. Dropped the pan. Found this on the other side of the dent. Those two wear marks are from rods 1+2.


I measured the clearance and they were seeing about 3/8" interference, comparing distance from the rod bolts to the pan rail, and the pan bottom to the pan rail. That would explain the drumming sound, feeling the noise in the pan but not the block.

Rod caps were removed and inspected. No damage to any of the bearings.

Root cause: driver's side engine mount failure due to prolonged oil exposure from the old engine. The driver's side mount came out in two pieces. Failure of the driver's side mount likely over-stressed the passenger side resulting in its failure, and the oil pan contacting the crossmember/tie rod, resulting in our bottom end noise. All that headache for $10 of parts. Replace your motor mounts at the slightest hint of failure.