2002 Mastercraft 5.7 harmonic balancer moving in and out

[Scott Danforth]

I feel like at 3500 rpm under load this wouldn't be a long term solution

About a 20 revolution event

 

[nola mike]

About a 20 revolution event

The lifetime of a theoretical sub atomic particle...

 

[Grub54891]

Seen two break just forward of the main bearing over the years, one blew the pulley off, the other still ran but the pulley wobbled like crazy. Ugly stuff!

 

[Bt Doctur]

The one I had was quiet as a mouse, no rotating noise. Only when the bearing cap was removed did it fall from the block

 

[jchandu]

Well Bt Doctor, you were close. See attached video
View attachment 30F009D0-C53C-4E93-8771-375986930B2E.MOV
View attachment 30F009D0-C53C-4E93-8771-375986930B2E.MOV
View attachment 30F009D0-C53C-4E93-8771-375986930B2E.MOV

 

[Grub54891]

Well never saw them break there!

 

[Bt Doctur]

Its very hard to believe you can crack a crankshaft in half and still have it turn and have the motor run.

 

[jchandu]

Looking for some suggestions going forward. My initial thoughts are to replace the crankshaft, and bearings only. My concern is metal fatigue on the connecting rods and wrist pins from the forward and backward vibration.

The engine has 970 hours.

What would you do in this situation?

 

[flashback]

Its very hard to believe you can crack a crankshaft in half and still have it turn and have the motor run.

Actually says a lot for how the crank is mounted I think..

 

[jimmbo]

A complete Teardown and Inspection is needed. If new Pistons, Rods, Piston/Wrist Pins, Crank, and Bearings are what will allow you to sleep better, so be it.
Also inspect/Magnaflux the Caps that hold the Crank in the Block for Crack/Fatigue

 

[Scott06]

Looking for some suggestions going forward. My initial thoughts are to replace the crankshaft, and bearings only. My concern is metal fatigue on the connecting rods and wrist pins from the forward and backward vibration.

The engine has 970 hours.

What would you do in this situation?

I would tear it completely down and have a machine shop check rods pistons etc before reusing, get a new crank, do a valve job and go.

if time is short and money is no issue a new marine 5.7 base engine is $5k https://www.michiganmotorz.com/5-7l-350ci-vortec-base-marine-engine-1996-current-replacement

you could swap it over in a day and be back on the water vs waiting on machine work and parts

Would verify the correct flywheel and balancer is on engine

 

[todhunter]

What would you do in this situation?

I'd be buying a Scat 383 rotating assembly and taking the block to a competent machine shop, letting them know the situation so they can inspect for any damage.

 

[jimmbo]

I'd be buying a Scat 383 rotating assembly...

And you would need to take/send the ECM out for a reprogram because of the Displacement change, and perhaps a different intake to flow more Air, for the same Reason.

 

[Scott Danforth]

I would be building a stroker

 

[jchandu]

Just some pictures of the broken crank.

 

[jimmbo]

That Crank was cracked for a while, likely dropped on the factory floor, and put back into Inventory by an Employee who didn't want to get yelled at.

 

[jchandu]

I would be building a stroker

It may already be a modified “stoker” setup from Indmar. The engine is rated at 350hp plus has a SCAT crankshaft.

 

[Searay205]

I would replace crank and bearings. put oil pan back on and take my chances. Option two go with short block from OEM. There are no crafts in the world anymore, machine shop, not worth the wait or headache....

 

[Scott Danforth]

call indmar with your serial number

measure the stroke. 3.48 is stock 350 cubic inch. 3.75" stroke is 377 cubic inch. add .030" oversized pistons and you get 383 cubic inch

if you have to build a stroker shortblock, get a new crank. have the local engine machine shop inspect the rest. if the rods are bad. a whole SCAT/PC rotating assembly is about $1100

 

[RaceCarRich]

Its very hard to believe you can crack a crankshaft in half and still have it turn and have the motor run.

This 496” BBC ran and idled fine. But you could hear the clanking a mile away. No other damage.