Building a 50's OMC powerhead, to hone or not to hone?

RogersJetboat454

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Jul 9, 2010
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Looking for opinions from the folks who have put a similar powerhead together.
I've got a '56 Fleetwin that I've decided to build a backup power head for (as crazy as that sounds).

I've got a used block, with some surface rust in the cylinders, but the bores are otherwise good shape.
I have NOS pistons, and rings that will be going into those cylinders.
I purchased a repro shop manual for this engine from Ken Cook, and one thing seems to be decidedly absent from it's pages (or maybe I'm blind and I'm missing it).
That is the discussion of cylinder dress during a rebuild.

It mentions lapping piston rings (on unpinned rings) by using a mixture of Bon-Ami, and oil. But no mention of running a hone in cylinders.
I own a hone, and normally on an iron cylinder engine, I'd be using said hone. But since this manual says nothing about it, I'm wondering if this is something people do anyway, or avoid for good reason.

If I don't use the hone, I will be cleaning the bores with a green Scotch-brite pad to clean out the surface rust, and any detritus that may be present in them.

Thanks!
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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any used block
bore to to make the cylinders round again
hone to spec

then buy pistons
 

tphoyt

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Jun 10, 2010
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To be honest I would mic the cylinders to be sure they a round and bore if needed.
But if your not up for that at the very least hone them.
 

RogersJetboat454

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Jul 9, 2010
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Thanks for the replys.
Both cylinders are within spec when measured with a bore gauge, and mic. This appears to be a low use/low hrs block from a motor that was parted out.

OMC made one OS option for this engine (.020), and the parts appear to be far less common these days then the original STD. size pistons/rings.
It’s for an outboard for use on a lake that’ll be lucky if it’s going to be used two weeks out of a year.
 

racerone

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Dec 28, 2013
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38,411
Hone the cylinders.-----Check ring gap.------If around 0.010" / 0.012" the assemble.-----Forget about any lapping of the rings !
 
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