Merc crankshaft - Send it or junk?

**Smalltownbassin** · 09-20-2021, 06:30 AM

I just pulled a 2.5L crank from a donor motor with hopes of using it in a build. I noticed some light bearing chatter marks on a couple journals. I did my best to clean it up with crocus cloth but there are still some light markings. At what point would you consider a crank to be not worth the trouble or unfit to use? I went ahead and bolted up some rods with steel caged bearings just to check the movement and everything seems ok. Its smooth as silk with no sign of bearings being effected by the chatter marks so im torn on making the decision to use it or not. I just lost a crank in this same block due to bearing failure. Im not looking forward to that again. These cranks are getting harder and harder to find nowadays and seems like when i do find a good one its priced like its made of unicorn bones so im trying to work with whats available to me. And this is a motor that im keeping so im more comfortable taking chances than if it was for someone else. How bad is too bad to use?

**Jay Smith** · 09-20-2021, 07:00 AM

If you have a motor -builder type machine shop he might could polish it clean and yes they are getting hard to find I use crocus cloth too to take bearing chatter off crankshafts …

good luck

**Smalltownbassin** · 09-20-2021, 07:23 AM

Thanks Jay! Have you ever used one in a personal build that didn't clean up completely? I don't really have a way to accurately measure runout but if I had to guess I'd say there are still some 0.001 to 0.002 dips in a couple of the journals that the crocus just wouldn't clean up without going overboard with it. The chatters aren't the full length of the rollers either so I'm optimistic that they won't hang in a dip under power. At best the crocus just smoothed out the transition between the lows and highs if that makes sense.

**ChrisCarsonMarine** · 09-20-2021, 08:02 AM

Sounds like a doorstop.At 4500 rpm cruise the motor is turning over 75 times a second.Think how many times the needles are rolling,skipping,sliding over that little washboard and I think You'll see that flaws on the journal surface are bad news,Chris

**Smalltownbassin** · 09-20-2021, 08:06 AM

Sounds like the search continues then.

**Jay Smith** · 09-20-2021, 08:33 AM

Sorry to tell you but no , I won’t use an iffy crank in my builds . You’d be amazed what a shop that does crankshaft work could do and still take very minimal material off ..
Just for asking are the marks like oil stains or can you actually feel a positive - negative difference ?
just curious?
Jay
call me if ya like 832 597 2603