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Old 14-02-2016, 16:19   #16
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Re: Rebuilding 2 stroke outboard

That Yamaha will have stainless bolts going into aluminium castings which after 3 decades will be a nightmare. Been there with a V4 Yamaha, we couldn't get the thermostat out without snapping a bolt which then had to be drilled and tapped and so it went on.

Is the engine worth it? if there is something wrong with it not running properly then its going to be carbs, reeds and ignition.
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Old 14-02-2016, 20:18   #17
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Re: Rebuilding 2 stroke outboard

I will keep my 2 strokes as long as I am able. They are tanks unlike the 4 strokes of today. They are easy to service and rebuild if necessary. To the OP: check your compression in each cylinder. If there is less than 20% difference between cylinders, you do not need a major rebuild. If there is, get a service manual and do it yourself.


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Old 14-02-2016, 20:52   #18
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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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Your kidding! The cost to rebuild a small 2 stroke outboard is only a couple of hundred at most! No way will a 2-stroke rebuild cost as much as a new 4-stroke unless you replace the whole power head!
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Old 14-02-2016, 21:20   #19
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Re: Rebuilding 2 stroke outboard

I'd start with a compression test. If it good, go for fuel pump, filters, water pump. Check the prop shaft to make sure its not bent. Inspect the lower gears. Check out the electronic bits & replace anything dodgy. Replace fuel hoses & give it a go. This much you will do no matter what else you choose to do.


As the others have noted, OBs have to be run hard & abused to get serious damage. I have had several oldies over the years. Some have bounced off the transom while running. All I had to do was get the water & sand out in order get them going again. The real old ones found in barns & boat sheds needed points condenser & coils & nothing else.


If you have to go deep on this get the rebuild book and parts list. - perhaps an easy download from the internet. I don't know how the Yamaha is built, but my old 1950's Mercury had cast iron sleeves bolted into the aluminum block. These could be replaced outright with new pistons & rings - no oversize or milling. Connecting rods may have needle bearings so be careful when you remove the rod caps & keep the caps & rods matched as they were originally installed.
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Old 14-02-2016, 23:32   #20
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Re: Rebuilding 2 stroke outboard

I recently rebuilt my 8hp Yamaha 2 stroke of the same vintage.

What I found was extensive corrosion in the joint between the crankcase and lower unit, and also where the exhaust manifold attaches to the crankcase. A previous owner had attempted a repair with about a 1lb of bondo to fill in the gaps. Several bolts were siezed and had broken off in the crankcase casting. The crankcase was a write-off.

However, all was not lost. The crankcase casting was available for $350, so I bought a brand new one.

The other issue I found was that the lower crankshaft bearing was noisy and worn, and quite rusty looking. This one gets damp, I think, from proximity to the exhaust manifold.

More good news : the crankshaft bearings are pressed-on roller bearings. No machining required to change them, just a press.

As I was getting a new crankcase (with new honing), I changed the piston rings.

I took the opportunity to change the outboard from a 6SF to 8SF, which means changing the carb and exhaust manifold.

If you have a lot of noise, I would suspect either exhaust leaks from the manifold / crankcase joint, or worn main bearings.

Total cost for crankcase, rings, every gasket in the outboard, carburettor, exhaust manifold, thermostat, bearings, about $800.

I now have the only new 2 stroke in the US! It runs like an absolute champ now.
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Old 15-02-2016, 19:41   #21
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Re: Rebuilding 2 stroke outboard

Ok thanks everyone, that's very useful. I get it, i was over complicating it. Its not an inboard or a diesel. I'll see what I get once i open it. Perhaps just honing. But I do fear the SS bolts into aluminum casting. Ive had my share of those. Its the winter up here, and now is the time to do it. I am in no rush. I can soak the stubborn bolts in WD40, or torch the aluminum and work them off slowly. I see a lot of spare parts, block, crank, pistons etc on ebay. So parts are plentiful and at a reasonable cost. carb and ignition are new on it. Ive been also keeping a spare carb and ignition. That pretty much keeps me on the water. The engine runs fine, its just very very loud. And if it wasn't the off season, i would probably not do it. But cheap parts and loud noise are making me want to take a peek inside.
I dont like the 4 strokes. too heavy. (but indeed very quiet).
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Old 15-02-2016, 19:55   #22
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Re: Rebuilding 2 stroke outboard

BTW, For parts I found iboats.com to be pretty good. They have parts diagrams for most models and years. Worth taking a look just to see how it comes apart.
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Old 16-02-2016, 13:29   #23
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Re: Rebuilding 2 stroke outboard

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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 . . . .

Yes, way better than puking oil into the water just running it.
All of the energy used in the production of a new motor, is controllable source pollution, if it's done properly.
Better yet go electric.
All production, causes pollution.


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Old 16-02-2016, 14:47   #24
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Re: Rebuilding 2 stroke outboard

Better yet, if you want to reduce your impact, sell the boat & motor, move into a tent and ride a bike.

Arguing about the environemtal impact of a hobby that inheriently consumes signficant resources is as silly as yuppies driving hybird cars to save the world...while they consume 100x the resources of the average of the rest of the world's population.
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Old 18-02-2016, 19:42   #25
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Rebuilding 2 stroke outboard

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Originally Posted by belizesailor View Post
Better yet, if you want to reduce your impact, sell the boat & motor, move into a tent and ride a bike.

Arguing about the environemtal impact of a hobby that inheriently consumes signficant resources is as silly as yuppies driving hybird cars to save the world...while they consume 100x the resources of the average of the rest of the world's population.

Nothing silly about trying to do your best to lessen impact on the environment.
What's really silly is doing nothing, and talking others out of doing something!
Maybe because giving up is better than trying?


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