Bad Bearing? Mechanic says I need to pull the eninge

bmay1909

Active Member
Nov 11, 2018
155
Lake St. Clair/MI
Boat Info
02 Sea Ray Sundancer 380
04 Sea Ray Sundancer 320 (sold)
Engines
Twin 8.1 Mercury Horizon V-Drives

Twin 6.2L MPI 320-HP V-Drives
Last week while out I lost oil pressure (went down to 20ish PSI). When I start the boat it will increase back to 35ish but continue to lose pressure the longer the engine was running.

So the mechanic came out to the boat today to see if he could figure out what's going on.

He believes its a loose/bad bearing of some sort (mentioned cam bearing, rod bearing and a few other types of bearings). When he increased the RPMs to 2300 he heard a lot of knocking.

He's telling me we're gonna need to pull the engine and tear it down to see what exactly is causing this.

Let me know what other info you may need

Any suggestions?
 
Worn Cam bearings usually contribute to low oil pressure, they aren’t notorious for “knocking”

Rod bearings take the most abuse. When worn, you get a knock every time the piston changes direction. Not quite a metallic sound, but more like a dull knock.

Crankshaft bearings are pretty sturdy and last a long time as long as they have a good supply of oil.
 
Sorry, but yes. You are going to have to pull the engine and completely disassemble and measure everything to find out where out of spec. Or you can go down the road of a rebuilt short block. Get your checkbook ready.
 
Sorry, but yes. You are going to have to pull the engine and completely disassemble and measure everything to find out where out of spec. Or you can go down the road of a rebuilt short block. Get your checkbook ready.



Obviously, there are a lot of variables. But roughly how much do you think this will run me?
 
Obviously, there are a lot of variables. But roughly how much do you think this will run me?

Does the knocking get louder when you snap the throttle closed from 2500 rpm?

Rod bearing knocks tend to get louder for a brief period as the engine speed rapidly drops.
 
Obviously, there are a lot of variables. But roughly how much do you think this will run me?

I blew a motor this year, 350 TBI, $6500 for all labor, haul out, rebuild and dyno motor, reinstall, launch, sea trial. That included a new alternator and distributor as well. I didn’t have the time or energy to do the work myself

The only thing we reused was the crank which we balanced and polished. Bored the motor 30 over on a dipped block, pistons, rings, valves, etc. all new
 
Obviously, there are a lot of variables. But roughly how much do you think this will run me?
I think I have seen guys talking about swapping rebuilt short blocks for about $7K each(ish)
Obviously, there are a lot of variables. But roughly how much do you think this will run me?
Strecker basically answered your question. I think it depends on your location. His numbers seem low for everything he was able to do. I estimated $7Kish. Keep us posted
 
I wouldn't pull an engine until I confirmed the low oil pressure with a mechanical gauge. I don't trust electrical gauges when it comes to making decisions involving several boat bucks.
 
Does the knocking get louder when you snap the throttle closed from 2500 rpm?

Rod bearing knocks tend to get louder for a brief period as the engine speed rapidly drops.



yes it gets a bit louder when increasing RPMs
 
I wouldn't pull an engine until I confirmed the low oil pressure with a mechanical gauge. I don't trust electrical gauges when it comes to making decisions involving several boat bucks.


Definitely! We did test with a mechanical gauge as well with the same results....low oil pressure.

Boat is getting hauled out today so hopefully I will have more info once he gets working on it this week
 

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