Do crankshafts require polishing???

When rebuilding an outboard, is it required to polish the crank or service it in any way before assembly?? Trying to figure out if the marina just wants to scare me into purchasing an assembled powerhead from them. They have been a great source of information when I needed help in the past, so Im not really complaining about their expertise. Im on a budget, but want to do everything correctly. My opinion is that if there is no damage or strange marks on the crank, then nothing more is necessary. Anyone have some experience with this? Thanks again.

Re: Do crankshafts require polishing???

If a crankshaft has slight blue markings, usually those can be polished out with #600 wet/dry black sandpaper and mineral spirits without fear of a failure. If however, one of the throws is burnt a dark blue or pitted, scored, gouged, reusing it could prove disastrous.

What is the condition of your crankshaft?

Re: Do crankshafts require polishing???

Normally you'd polish the crankshaft journals by hand, with crocus cloth along with a light lubricant. I like to use Marvel Mystery Oil but whatever your preference.

Now, if the shop is saying their "machine polishing" is better, well maybe just a bit since it's done by machine and may be a bit more consistent than hand-polishing, but you can certainly do a serviceable rebuild without machine-polishing the crankshaft!

As you say, very important the crank journals have no chatter marks, bluing (signs of overheating), etc. You can measure the journals to make sure they are within factory specs.

Very telling is the condition of the rod journals and the old bearings as they came off the crank. Any problems are gonna show up with nasty/rough-looking surfaces.

If all the bearing surfaces were clean & smooth, no discoloration, a simple hand-polish along and renewed bearings (always good shop practice), along with a careful reassembly, should get you a reliable rebuild.

No doubt the shop is highly-motivated to sell you their powerhead, and I'm $$ure they're very proud of it, too!

HTH...........ed

Re: Do crankshafts require polishing???

The powerhead is off the lower unit but I haven't disassembled the crank yet. Thought I should get an idea of what to look for once I do inspect. I have a manual and will mic where needed. Motor ran great and had no issues before the #3 cyl compression dropped from wall scoring. I will post results of what I see on the crank. Should be within a couple days. In the meantime, thanks for the great advice

Re: Do crankshafts require polishing???

Make absolutely sure you keep the connecting rods and caps together and in the right end to end sequence. And if you are using roller (or needle) bearings, keep them in the proper end to end sequence as well. If this is an OB it all is very important. Some folks even mark them before removal to get them back in the exact same places. If this is an IO you probably would replace the bearings (sleeve insert type) anyway... Just a thought!

Re: Do crankshafts require polishing???

What year and hp is this motor. It does make some difference in what is serviceable condition for its intended use.

Do not panic if you find some pitting. The key is how much bearing surface is available to support the needle bearing as it crosses.

Re: Do crankshafts require polishing???

Sorry neglected to say its a 1986 Evinrude 90 HP outboard. Originally thought to repair #3 cyl only but everything has to be disassembled anyhow. Decided it made more sense to refresh the entire power head with a good rebuild kit. Just in the beginning stages of tear down and cleaning. Should be a fun project if I don't rush anything. Power head is still together. Carbs and electrical already removed. Even with the manual I still took about 100+ pics with my smartphone to make reassembly easier. The marine version of "measure twice, cut once".... except no cutting!

Thanks for the great replies. This will be my first (hopefully not last) outboard rebuild project. I have an 18' Starcraft eagerly awaiting power for Lake Erie and my nephew to catch his first walleye.