Spun Bearing Cause

[TeamHoss]

I own a 2003 Centurion Cyclone (v-drive) with a mercruiser 350 MAG MPI (5.7). I have approximately 380 hours and do not drive the boat aggressively. I dropped the boat in the water in early June and was running back home to beat a storm. During the initial run I noticed the boat was starting to run rough and ultimately the engine stalled at which point I noticed smoke coming out of the engine compartment. Turns out my mechanic did not hook up all the hoses after witnerization and it fried the wet exhaust system. My mechanic owned up to the mistake and replaced all of the hoses. I dropped the boat back in the water in late June. I ran the boat for exactly one tank of gas. Literally after filling up I noticed a knocking in the engine as I accelerated and that knocking continued to get louder the faster I went. I pulled the boat out of the water and brought back to my mechanic. He tells me I "spun a bearing" and that he reccomends a rebuilt replacement motor.

I asked if the spun bearing was related to the overheat issue and he said "no they are independent issues". I am not a mechanic, but I have to beleive that the overheat may have caused this or be related to this issue. Thoughts?

 

[04fxdwgi]

Re: Spun Bearing Cause

I own a 2003 Centurion Cyclone (v-drive) with a mercruiser 350 MAG MPI (5.7). I have approximately 380 hours and do not drive the boat aggressively. I dropped the boat in the water in early June and was running back home to beat a storm. During the initial run I noticed the boat was starting to run rough and ultimately the engine stalled at which point I noticed smoke coming out of the engine compartment. Turns out my mechanic did not hook up all the hoses after witnerization and it fried the wet exhaust system. My mechanic owned up to the mistake and replaced all of the hoses. I dropped the boat back in the water in late June. I ran the boat for exactly one tank of gas. Literally after filling up I noticed a knocking in the engine as I accelerated and that knocking continued to get louder the faster I went. I pulled the boat out of the water and brought back to my mechanic. He tells me I "spun a bearing" and that he reccomends a rebuilt replacement motor.

I asked if the spun bearing was related to the overheat issue and he said "no they are independent issues". I am not a mechanic, but I have to beleive that the overheat may have caused this or be related to this issue. Thoughts?

The overheat probably added to an already existing weakness in the engine by thinning out the oil so thin that it didn't lubricate as it should. The oil not only lubricates, but acts a cushion between the main / rod bearings and crankshaft journals and cools the bearings by pulling the heat away from them as the oil is returned to the pan and actually cooled by running across areas of the block cooled by the water. If too thin or the block is too hot, the cushioning and cooling effect is not as good as it should be, jeopardizing the bearings (and every other friction surface in the engine). What type of oil are you running in the engine?

 

[moetr]

Re: Spun Bearing Cause

Definitely! After a long cruise my oil pressure at idle drops way down around 10 psi on boat gage. It comes back to 20 psi after short time. It is because the oil is hot and thin, 15W40 Rotella with low hours. That tells me that hot oil reduces oil pressure. If it gets too hot not enough pressure to protect the bearings and it can break down. Now how was the oil pressure before this engine got hot? If you changed oil regularly and pressure was very good that tells me bearings were most likely in good shape. I have seen these motors, Crusader version, with over 3000 hours with great oil pressure. Did you see pressure drop when it overheated? Should also be using heavier oil in boat like straight HD 30 or 40 or Mercury 25 W 50 or maybe as low as 15 W 40 diesel oil.

Saying the overheat can not be related is not correct. It may not be but overheating can easily ruin a bearing from both low oil pressure and oil breakdown, lack of lubrication. (This is where synthetic shines but should not be needed on a boat.) As always not an expert just my opinion and some common sense.

 

[littlebookworm]

Re: Spun Bearing Cause

Was the spun bearing caused by the overheat? Possibly. Give Mercruiser a call. Both of the previous postings give a fairly good explanation of the situation. You will need more than those postings and my statements to get anywhere; you will need documentation from a certified authority. Most of my experience is with car engines. A spun bearing on a car engine is usually caused by high mileage and poor mainteance, including using too thin an oil. Severe overheating will also be a factor. Marine engines aren't that different, but I'm no expert in their intricacies. Are you going to have other problems with this engine after the spun bearing is repaired? Probably. Engines do not like high heat. There's the possibility/probability of a blown head gasket, warped cylinder heads, loosened freeze plugs, warped valves, overheated electricals. You may be looking at an engine replacement rather than a rebuild. From your posting, it seems the mechanic is taking no responsibility for the spun bearing. You may have a lawsuit on your hands. Sorry. Good luck. Hy

 

[TeamHoss]

Re: Spun Bearing Cause

I appreciate the reply. Franlkly, I am not certain what oil is put in the boat as the same mechanic has winterized this boat 7 different times and always includes an oil change as part of the winterization. The overheat was pretty severe (enough so to melt wet exhaust hoses). He is suggesting a new engine (re-built engine) and is looking at prices, etc. Unfortunately, I beleive this will be a $5k expense which I currently don't have. He is a good guy and runs a very honest busienss, but it is a small marine business which makes him eating this repair a big deal. I think I am in a pickle becasue I don't think I can definitively say the two incidents are related although very likely based on what I have read.

 

[etracer68]

Re: Spun Bearing Cause

I would say the operator of the boat, is somewhat at fault here too. Your gauges should have shown you, that you where over heating. Any time I run my boat, Im always looking at the gauges every few minuts. I do understand that sometimes people forget. I dont mean to put the blame on the operator, but you should at all times know whats going on. As far as over heating causeing a bearing to fail is not that common, it had to have pegged the gauge. I have been racing small block 350's for years, and have had cooling problems, that seen well over 300 deg, and never hurt a bearing, and run 20w-50 oil, which is a 20 weight oil. Im not saying it couldnt happen, but it had to run for some time at high temp.