Turning (polishing) crankshaft YES-NO ?

[WaltCorwin]

Lost #4 connecting rod on my '84 Merc 200 V6. I am attempting to rebuild it myself. There is no evident scoring of the journal, but it is kind of black. Mechanic I've been talking to (who has been very helpful so far) says the crank MUST be replaced, as it cannot be turned to polish the journals. If I do it, I'll be looking at another rebuit within a year, guaranteed. Would anyone care to offer a second opinion?

 

[mjestey2000]

Re: Turning (polishing) crankshaft YES-NO ?

He's right, any friction in that area will cause a fatal breakdown in a very short period of time. If you are worried about cost, you can get used cranks in good condition for low cost. Reconditioned ones for a little less than new. Polishing a crank would most likely wear even more of the crank down leaving slop in the connection. Bad news too. My guy down in Fla helped me out big time for my rebuild. 150 or so for the used crank. I got it and it was in fine shape and the engine is now running great. address follows.... <br /><br /> http://www.stuartfla.com/outboard/ <br /><br />mike

 

[WaltCorwin]

Re: Turning (polishing) crankshaft YES-NO ?

Thank you Mike. I've rebuilt a couple of car motors, and simply turning the crank and fitting new bearings has always been pretty standard procedure. My mechanic guy said ya can't do that on an outboard (something about how the metal 'rolls'). He was adamant about it. I appreciate your reply, as I was hoping to hear from folks with experience on these motors. I don't have any!

 

[Paul Moir]

Re: Turning (polishing) crankshaft YES-NO ?

FYI, 2 strokes usually run rollers directly on the crankshaft throwes instead of plain (automotive), due to the lack of lubrication. This requires a bearing quality finish and hardness on the surface of the throw to slow wear. Usually the throw is hard chromed (thick chrome plated) to achive this hardness. I suppose they could be case hardened though. <br />I would expect that if your chrome is burnt then you would have to have it ground off and rechromed (ie, rebuilt).

 

[kenimpzoom]

Re: Turning (polishing) crankshaft YES-NO ?

Your confusing polishing with grinding. They are two different things.<br /><br />Grinding down the crank significantly changes the diameter of the journal requiring new special sized bearings.<br /><br />Polishing removes very little metal.<br /><br />Ken

 

[Hooty]

Re: Turning (polishing) crankshaft YES-NO ?

Use some 1200 grit wet or dry with WD40 and see if it won't polish the dark off the crank journal. Mic the journal and if it's still in spec and not scratched, run it.<br /><br />c/6<br /><br />Hooty

 

[WaltCorwin]

Re: Turning (polishing) crankshaft YES-NO ?

Thanks for your replies and advise. I'm gonna take Hooty's suggestion and maybe get lucky.<br /><br />Walt Corwin<br />DeBary FL<br />'82 Chris-Craft 213 CC 'EndorFin'<br /><br />Ps: She ain't exactly been livin' up to her name!

 

[jim dozier]

Re: Turning (polishing) crankshaft YES-NO ?

Use a crocus cloth. It is a very fine abrasive cloth, like emery cloth only finer, used for polishing crank journals.

 

[ledgefinder]

Re: Turning (polishing) crankshaft YES-NO ?

Merc tech school materials say use 320 grit emery cloth on crank journals & if that'll remove the scratches/discoloration, run it.

 

[Hooty]

Re: Turning (polishing) crankshaft YES-NO ?

I've known of using 320 grit but it always sounded to aggressive so I like the 1200 grit / WD40 thing. It'll polish out and it makes cracks easier to spot.<br /><br />c/6<br /><br />Hooty

 

[adam12]

Re: Turning (polishing) crankshaft YES-NO ?

I'm with Hooty - buff it up let 'er rip..

 

[WaltCorwin]

Re: Turning (polishing) crankshaft YES-NO ?

You guys have provided some very helpful info. Maybe I should have opened this motor all the way up before I asked any questions, though. Pulled the crank last night and found a big hole in the cylinder block that I could not see before. The #4 connecting rod had beaten a hole in the wall under the #3 piston. It may be ouside the compression zone, but it's a BIG hole, and looks like new powerhead time to me.

 

[Walker]

Re: Turning (polishing) crankshaft YES-NO ?

Even though the hole may be outside the "compression zone" doesn'tmean anything. In a crankcase scavenged motor the piston creates crankcase pressure on the down stroke thus forcing fuel/air mixture into the cylinder through the intake port. On the upstroke the piston creates crankcase vacumn thus pulling fuel/air mixture from the carb into the crankcase. Each piston and its associated crank journal is isolated in the crankcase buy crankshaft rings. So, if you have a hole in the crankcase, that particular piston cannot create the pressure/vacumn pulses to move the fuel/air mixture from the carb to the crankcase to the cylinder.

 

[G DANE]

Re: Turning (polishing) crankshaft YES-NO ?

It may be too early to throw the towel yet. <br />Some holes can be welded if they are not in the sleeve area. Be sure both housing parts are bolted together and turqued while welding, and maybe even better put cranck and bearings in too.