TOPIC: Tell me to step away from the cylinder hone!

The tear down is complete on the '57 RD-19 I picked up last week (my earlier post). I pulled the head yesterday out of curiosity and found scoring in the bottom cylinder. So I completed the tear down tonight only to find this mess on the piston. You'll see the gaps between the ends of each ring in the picture, but you'll also see a gap in the piston between two of the rings. Yes, there's a chunk of piston missing. For a few minutes I stood there telling myself it wasn't that bad... I could find a replacement piston and hone the cylinder and maybe oversize the rings. But someone tell me it'll be easier just to find another power head. And what am I looking for now? A '57 or '58 35 hp? I'm assuming the 2 RD-18 30 hp motors aren't going to help in this regard, except perhaps as trades, correct? Ugh.

You'd have to take the block apart and send it to a machine shop that specializes in boring & honing outboard blocks. They would bore-out then finish-hone the cylinder to the next oversize. However, I have no idea if oversize pistons & rings are even available for these.

There's no way you could fix the scoring by honing the bore yourself and fitting bigger rings, it'd be virtually impossible to hone it by hand and get even cylinder walls. It'd be so tapered & irregular that it probably wouldn't seal properly.

These motors are so common, however, that you should be able to find a replacement block or even a complete, serviceable powerhead. Likely there are plenty of these on Craigslist or even eBay Motors.

HTH.........ed

davesinvader,

IF it was my BigTwin, I would have a competent machine shop to bore out both cylinders to fit 40HP pistons/rings & put it back together.
(It's NOT a complicated deal, though boring it out is NOT something that you would want to try yourself.)

NAPA auto supply stores have the pistons/rings for CHEAP, as SIERRA PARTS brand.
(I LIKE CHEAP.)

yours, satx

Hi satx. I like your idea. would I need a different crank or bearings or carb or anything besides rings and pistons? And what sierra or napa pistons were you thinking of?

davesinvader,

The standard size 40HP rings/pistons will fit your OB & NAPA sells them. - Ask your NAPA guy/gal for a Evinrude OR Johnson (1961-65) standard 40HP pistons/rings/gasket set.
(I cannot see any good reason to change anything else, unless there is other CONCEALED damage to the powerhead.)

Also, EBAY will be a source for an OMC workshop manual for your model Gale. - If I remember correctly, I paid 10 bucks for mine plus postage.

NOTE: Changing out the water-pump impeller, both coils, condensers, plug-wires, sparkplugs, etc and REBUILDING the carb will be a GOOD THING too.
(You'll end up with a CHEAP/TOUGH OB that will likely outlast you, with minimal care. = BigTwins are OVERENGINEERED.)

BEST WISHES on your project.

yours, satx

Thanks again satx! Yep, I already have the impeller, coils, plugs, wires, condensers, points etc on hand, which is why I'm motivated to stick with this darned motor! I'm heading to Napa this weekend to see what they say.
Dave

davesinvader,

I asked "LaShauna" (the computer guru) at a local NAPA store about that model Gale (I just bought a '57 Buccaneer 12S13B and will need a few things.) and she said that SIERRA makes every part for the 1955-1963 Gale OBs except the cowl, exterior engine castings and the bare block. - She said that the same is true for all the other OMC engines to 1970.

yours, satx

Stax - have you done this before? I tossed a 1958 35 HP block on my scrap heap just this morning due to a deep score in the upper jug. I held a 40 piston up to the block and just eyeballing, it looked way, way too big. I don't have the spec's in front of me to know the difference in cylinder dia. between the 35 and the 40. I would think that there'd be nothing left of the 35 cylinder liners after boring enough to fit the 40 pistons. If this can be done, I'll pull that block off the scrap heap & save it.

Thanks,

Bruce G

Bruce Gerard,

The actual difference in the bore is 2.875 & 3.060, according to my #1300 SELOC manual, Page A4. - It's the SAME block through mid-late 1960.
(I'm NOT a machinist but I had this "modification" done by Murphree's Machine Shop in Pittsburg, TX about 20 years ago & it worked out FINE. = That BigTwin was still running fine years later, when I sold the boat & I know of NO reason that Shawn Murphree would have lied about what he did to that old Johnson BigTwin.)

Before you junk that block forever, you should "mic it out", as I have NO way of knowing how badly scored your block is.

yours, satx

satx, thanks for all of the help so far, if can indulge me a few more questions:

iboats lists the Johnson RDE-19 35 hp I'm working on as a 3.06 bore with 2.75 stroke.
boatspecs.iboats.com/Johnson__RDE19__35hp__1957/bpe/57e13028

You mentioned using pistons & rings for 61-65 40 hp. According to iboats, the RD-23 40 hp is 3.19 bore with a 2.75 stroke (in fact all 40's up to 1969 have the same specs)
boatspecs.iboats.com/Johnson__RD23__40hp__1961/bpe/57e10633

So if I'm looking at this correctly, I need to bore the cylinders from 3.06 to 3.19, correct?

I ran over to Napa this morning with the block. The machine shop guy confirmed that the score was too bad to hone out. He measured the cylinders and said they were at 3.059 (at the top, not the damaged area), which would be the 3.06 listed above. He did say that it wouldn't be a problem to bore it to 3.19 and said he'd done that type of work on boat motors lots of times. So I think I'm good there.

My problem is now finding the pistons. The Napa parts guy wasn't that helpful. He just handed me the Sierra catalog and said to tell him what I needed. But the Sierra catalog they had is pretty vague. It lists 35-60 hp for the same piston, with a bore size of 3.187, number 18-4125. Is that what I'm looking for? The guy quoted me over $100 each. Does that sound right? Not exactly my idea of cheap, but if it includes wrist pin and rings it's probably ok. Just wanted to confirm before I dump $$$$ into this. Also, I can find that part number online for cheaper but it shows they're flat top cylinders, does that make a difference? Pic attached of the Napa Sierra page. Thanks a ton for the advice!

I glanced at the 1961 RD-23 parts diagram at marineengine.com, and got the piston part number for the 40hp: 378274. I see three of them $25 and under on eBay. Or you could contact Dan Gano ( www.ganotech.com ) and see what he has: he'll give you good advice, and a great price on parts!

I'd study the parts diagrams between your year and 1960/61 and see what else changed. You're essentially making a 1960/1961 40hp, and some people think the crankshaft was undersized for 40HP. OMC beefed it up in 1962.

While I won't argue it feels great to bring something back from the dead, I might also look to see if I could find a parts motor with a serviceable head, or if someone has a head for sale... You could post on the AOMCI's "Webvertize" page:
www.aomci.org/cgi-bin/yabb2/YaBB.pl?board=Webvertize

Or post your original question(s) on "Ask a Member" for more advice. There are plenty of people there with OMC lubricant in their veins!

I don't remember seeing what variants of the 30HP and 35HP models you have-- the towers came in two flavors: super quiet (with a two-wall housing) and a plain-old version. If you have two of the same flavor the heads should exchange (the two flavors have different base gaskets). Again, studying parts diagrams should tell you. You'll lose 5 HP but you'll save on gas!

davesinvader,

YEP. 3.060 to 3.190 for the "boring project".

I would check ebay for NEW pistons/rings/gaskets. And if not there, the aomci.org webvertize section.
(100.oo each sounds like highway robbery to the "friendly neighborhood cheapskate".)

I've recently seen NOS pistons on ebay for 20 bucks each. - Rings/gaskets are not expensive.

BEST WISHES, satx

silver-bay,

ONE of the VERY few things that I disagree with "Max W" on is the '60/'61 OMC 40HP.
(I started "messing about in boats" at age 14 (in 1960), when my late father bought me a Lone Star twin-cockpit tin runabout with a 1957 Evinrude 35HP OB. - I had a ski-boat for 2 years before I had a car, as I grew up on a large lake & actually went to JHS & 2 years of HS by boat. In all these years since, I have NEVER known of a BigTwin breaking a crankshaft OR ever saw one "worn-out in service". - The BigTwin is ridiculously over-engineered.)

I also like boat/OB/trailer rigs that match in year model & wouldn't "part-out" or junk a BigTwin that was the right year for my hull, unless it was irretrievably "trashed" & I had another OB of the same year to replace it.

just my opinion, satx

That piston / ring chart does not cover the old motors at all.--Chart covers the newer 35 HP that came out in 76 in no compatible with " old 35 hp " of the late 50's.

One of many issues here is cost. First you have to find a shop to do the boring, new rings and pistons, gaskets, seals, it all adds up. Don't forget to have the compression ratio calculated as well, and the piston crown to head clearance must be checked. Me? I wouuld just find another block, tons of them out there for cheap.