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Old 09-02-2016, 07:59   #1
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Rebuilding 2 stroke outboard

Hi I am thinking about rebuilding a 15HP Yamaha circa '84-86. Ive done this numerous times with inboards (diesel and Atomic 4s). Usually I would take the engine apart and bring head, crank, and block to machine shop for pressure testing, acid bath, boring, re-surfacing the head/block etc. Im sure machine shop would recommend some of the stuff, but I want to go in requesting services specific to an outboard and not general automotive or inboard stuff.
So What are the recommended machine shop services done on a 2 stroke outboard rebuild.
Oversize/hone cylinders (if needed)
Acid tank and pressure test head and block
re-surface block and head(if needed)
Turn journals
Magnaflux crankshaft

Is this too much, should i do some of this myself or am I missing anything?
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Old 12-02-2016, 09:17   #2
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Re: Rebuilding 2 stroke outboard

Are you sure you need to do this? I inherited. 1969 Evinrude 55hp sitting in a field for 5 yrs. I changed the plugs, ignition power pack and rewired it. I didn't need to disassemble anything. Oh yeah. I also replaced all the old fuel lines.


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Old 12-02-2016, 15:46   #3
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Re: Rebuilding 2 stroke outboard

technically, not, but the engine is very very loud. And i've been told that its due to general wear. And i buy it. Worn bearings, pistons would likely make it louder then usual. i use the dink to go far and spend quite a bit of time in the open ocean with the it.
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Old 12-02-2016, 16:23   #4
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Re: Rebuilding 2 stroke outboard

Unless you have unusually high hours, I doubt a rebuild is going make any difference in noise. Outboards, however unreliable, tend to run for decades. I recently gave away a 1959 that never was overhauled but still running as well as outboards run.
Piston slap or loose wrist pins probably can't be heard over the normal noise. If the engine runs, the head and crank are probably ok. Milling the heads will result in a higher compression ratio and possible unreliability.
You could take it apart and check those items and put in new seals and gaskets and hope you don't damage something.
For noise you might line the hood with foam or lead sheeting would be better.
I've rebuilt at least dozens of engines. In all that time I only had 2 cranks that had cracks. One was a racing engine and the other was a aircraft radial involved in a crash. My 1947 & 48 Detroit mains have the original standard cranks.
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Old 12-02-2016, 16:28   #5
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Re: Rebuilding 2 stroke outboard

I used to race two stroke motorcycles for suzuki back in the day! We never did half the stuff your being "charged" for. You can actually just Hone the cylinder to get .010 , .020 , or .030 , oversize. if your going to let them do all that go ahead and port the intake, bore the carb, add boyeson reeds and turn it into a 30hp at 9000 rpm's.
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Old 12-02-2016, 17:27   #6
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Re: Rebuilding 2 stroke outboard

First, tear it down...outboards are not aliens to your previous experience. Could be that it was overheated and a bearing went...decide from there...if it's trash, it's trash...just lost time for tear down...or some nice garage time...cheers!


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Old 12-02-2016, 17:34   #7
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Re: Rebuilding 2 stroke outboard

I had an ex Florida OB mechanic help me rebuild my Yam 15 in Trinidad. It took us less than 2-3 hours . I bought the parts down there. However, as I remember, there was one main bearing we could not get at without special tools, or something, so we left it.
What are your symptoms? Mine had a bad main bearing, all of a sudden the engine wouldn't rev up under load.... probably due to harmonic vibration.
I think it was an early 90's model, but may have been late 80's.
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Old 13-02-2016, 19:07   #8
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Re: Rebuilding 2 stroke outboard

Upgrade to a 4 stroke, the cost of your 2 stroke rebuild will cover the cost of an upgrade.
And the environment will thank you!


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Old 13-02-2016, 19:46   #9
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Re: Rebuilding 2 stroke outboard

Quote:
Originally Posted by Boatyarddog View Post
Upgrade to a 4 stroke, the cost of your 2 stroke rebuild will cover the cost of an upgrade.
And the environment will thank you!


Sent from SV Cloud Duster
So mining the ores to get all the different metals, cracking the oil to get all the plastics, firing the ceramics for the plugs, chopping the trees for wood and board packaging plus paper for pages and pages of warning notices that sometimes include instructions, melting the metals to make alloys and copper then fed into moulds and into mills to make castings and wire, injection moulding the plastics to make covers, running the factories to assemble all these bits into an outboard, then shipping it half way round the World to Main Agents, then shipping again from the importers to the distributors, shipping again to the dealers, who then have to dispose of the packaging, etc., is somehow 'better for the Planet' than a quick repair job for a fuel efficient engine that burns synthetic sugar based oils in its fuel?

Well I'd never have guessed . . . .
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Old 13-02-2016, 20:40   #10
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Re: Rebuilding 2 stroke outboard

Better make sure you can pull it apart first. Some of those outboards that have lived in salt water all their lives can be a nightmare to disassemble thanks to corrosion - the poor man's loctite.

Another possible issue with Yammies of that vintage is corrosion of the water jacket, especially in areas where it gets hot and the gunk collects up around the heads.
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Old 13-02-2016, 22:48   #11
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Re: Rebuilding 2 stroke outboard

Quote:
Originally Posted by phorvati View Post
Hi I am thinking about rebuilding a 15HP Yamaha circa '84-86. Ive done this numerous times with inboards (diesel and Atomic 4s). Usually I would take the engine apart and bring head, crank, and block to machine shop for pressure testing, acid bath, boring, re-surfacing the head/block etc. Im sure machine shop would recommend some of the stuff, but I want to go in requesting services specific to an outboard and not general automotive or inboard stuff.
So What are the recommended machine shop services done on a 2 stroke outboard rebuild.
Oversize/hone cylinders (if needed)
Acid tank and pressure test head and block
re-surface block and head(if needed)
Turn journals
Magnaflux crankshaft

Is this too much, should i do some of this myself or am I missing anything?
I'd investigate the price of parts and labour. It may not cost much more to simply buy a new motor.
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Old 14-02-2016, 05:45   #12
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Re: Rebuilding 2 stroke outboard

Quote:
Originally Posted by Ribbit View Post
So mining the ores to get all the different metals, cracking the oil to get all the plastics, firing the ceramics for the plugs, chopping the trees for wood and board packaging plus paper for pages and pages of warning notices that sometimes include instructions, melting the metals to make alloys and copper then fed into moulds and into mills to make castings and wire, injection moulding the plastics to make covers, running the factories to assemble all these bits into an outboard, then shipping it half way round the World to Main Agents, then shipping again from the importers to the distributors, shipping again to the dealers, who then have to dispose of the packaging, etc., is somehow 'better for the Planet' than a quick repair job for a fuel efficient engine that burns synthetic sugar based oils in its fuel?

Well I'd never have guessed . . . .
You left out the spares costs, with the huge difference in the parts count. All the extra parts that have to be manufactured etc. and shipped to dealers to support four strokes. The inventory, packaging, and transportation costs. Special tooling.

The most popular engine here is hands down the Yamaha 65's. The local fishermen wouldn't use anything else. One of them told me he can rebuild his outboard on his picnic table on a Sunday afternoon using common tools, and be back on the water on Monday.
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Old 14-02-2016, 06:07   #13
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Re: Rebuilding 2 stroke outboard

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Originally Posted by Canibul View Post
You left out the spares costs, with the huge difference in the parts count. All the extra parts that have to be manufactured etc. and shipped to dealers to support four strokes. The inventory, packaging, and transportation costs. Special tooling.

The most popular engine here is hands down the Yamaha 65's. The local fishermen wouldn't use anything else. One of them told me he can rebuild his outboard on his picnic table on a Sunday afternoon using common tools, and be back on the water on Monday.
Thats the great thing about the Enduros (I assume Y65 Enduro). Basic engine, easy rebuild. Had my Y60 Enduro rebuilt in Guatemala for about Q5,000 (~US$660), thats total parts (genuine Yamaha) and labor. This was a "minor" rebuild (not as extensive as what OP is considering), but still hard deal to beat. Back on the boat in about week (parts delays), running great, years of service life for $660!
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Old 14-02-2016, 13:26   #14
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Re: Rebuilding 2 stroke outboard

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Originally Posted by Boatyarddog View Post
Upgrade to a 4 stroke, the cost of your 2 stroke rebuild will cover the cost of an upgrade.
And the environment will thank you!


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That doesn't really answer the OP's question, does it?

My guess is, a new outboard is going to cost a lot more than rebuilding what he has. The extra weight of a 4 stroke may be an issue, both with portability and with the trim of his boat.
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Old 14-02-2016, 15:29   #15
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Re: Rebuilding 2 stroke outboard

The parts to rebuild mine were very low cost actually. But then... I was in Trinidad...
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