Spun Main Bearings?

[Run_em_Hard]

What causes a spun main bearing. Had them replaced two years ago. I have a 509 ci with a Vortech, intercooled. 10qt Hardin Marine oil pan and a high flow oil pump. I had good oil pressure. I was cruisin at 4800ish rpm. Its a steel crank. Any advice? I am getting sick of fixing shit:mad:

[502 JET]

If clearances are too tight you can burn up the bearings.
Not saying this is your problem just something to look into.

[ck7684]

oil on the backside during install can cause this...thats just one thing...

[steelcomp]

Initial tolerances/clearances could have been off...these need to be checked or verified during the build up. Also, using a standard bearing instead of a performance bearing can lead to this. Performance brgs, even with the same clearance, are designed different to prevent this from happening in higher hp applications.

[gn7]

or a junk oil pan

[Run_em_Hard]

Thanks guys:)

[cfm]

What was your oil temp when this happened ?

[BrendellaJet]

whoever rebuilt it last time, shouldn't do it the next time.

[WishIknew]

Crap in the oil cooler?????????

[Run_em_Hard]

whoever rebuilt it last time, shouldn't do it the next time.
I have already decided this...

[Run_em_Hard]

Crap in the oil cooler?????????
I will have to look into this.

[Run_em_Hard]

What was your oil temp when this happened ?
To be honest I don't know. But my engine temp was pretty low. Lake water temp was about 72 degrees and I run a big offshore oil cooler.

[ck7684]

Well, the oil should be warmed up plenty before hittin' it also...

[adjones419]

I'd say clearances during assembly or an oiling problem.

[BrendellaJet]

thing is, if it was a clearances issue it probably would have made itself known pretty quick unless you hardly used it for the 2 years after being built...Could be a bunch of stuff. Pay the money to have someone knowledgeable build it. pay once, cry once...

[Moneypitt]

thing is, if it was a clearances issue it probably would have made itself known pretty quick unless you hardly used it for the 2 years after being built...Could be a bunch of stuff. Pay the money to have someone knowledgeable build it. pay once, cry once...
All it takes is one too many romps with cold oil, like pushing molasses through the motor. 3 to 5 seconds without oil will weld the bearings to the crank, and wa la, they spin. Spun mains are a lot less common than spun rods, but it happens for about the same reasons.......Also cranks that flex are hard on bearings. The sides flex down to "flash" the oil off the edges of the bearings, which then burns across the rest of the bearing. Heat cases the tolerance to shrink, the crank grabs the bearing, and away they go.........MP

[Willis]

What causes a spun main bearing. Had them replaced two years ago. I have a 509 ci with a Vortech, intercooled. 10qt Hardin Marine oil pan and a high flow oil pump. I had good oil pressure. I was cruisin at 4800ish rpm. Its a steel crank. Any advice? I am getting sick of fixing shit:mad:
Hello People,
First off, I want to say if you run the boat hard all the time, like I did, things will fail really quickly.
I use to have that problem bad, spinning main bearing.
Went through several cranks until I decided to increase the bearing clearance from .0025 to .0035.
However, the increase in bearing clearance will make the oil pressure real low at idle.
To solve this problem, I installed a high volume oil pump with a 1/16 shim behind the spring.
My oil pressure is some what high, but “No Spun Bearings”.
I developed distributor gear problems. I’d rather change distributor gears every other year than to build the engine.
:messedup:
Just my point of view.