Yamaha Pro 50 Outboard 2 Stroke With A Melted Piston. How Did This Happen?

[@GPOldMarineShop]

Good video! Rebuilt plenty of melted piston two stroke 3 cylinder to V-6 outboards all brands oil injection and premix some years back. According to OMC tech people at the time (1990s-2000S) low octane gas was the biggest cause of rings getting stuck coking.They had an experiment where they demonstrated in their classes about low octane gas 87 on how dirty and abrupt it burns compared to 89 and higher octane. But for melting issues and stuck rings for me personally rebuilding all the carbs( to avoid a lean condition), new fuel pump or pumps and waterpump,thermostats, full throttle timing checks & also removing oil injection back to premix insured my warranties. I never had one motor come back.Your analysis on the bad oil injection is definitely a possibility ......

[@hunterbaxley3197]

Instead of just honing over the aluminum, it works really good to take some muriatic acid and a cue tip and applying it to the aluminum spots, also known as transfer spots. Then take a scotch Brite and scrub the aluminum off. The acid softens it up really well. If you just use the Hone without doing that first. It gets annoying because the stones tend to get gummed up with aluminum.

[@bigjimar77]

Always used muratic acid to take off aluminum from end mills.

[@evyc2537]

That’s awesome!!! You were able to diagnose the problem so quickly 👏

[@fox-body]

Thanks😘

[@michaelh7527]

I just got done about a month ago getting an old 1990 Yamaha 40hp 2 cylinder running. I got it for free from the neighbors trash pile. He is the type that really doesn't take care of anything. He said the motor overheats, charging system doesn't go over 11.8v, it stutters over half throttle, and it's hard starting..... Whew 😂😂😂. Compression was surprisingly perfect on both cylinders. I pulled the head and water jacket cover which was just packed with mud, salt corrosion and thermostat was locked up. I cleaned all that out, new gaskets and Thermostat. I then just pulled both carbs, rebuilt, and replaced all fuel lines, plugs, and filter. I took it out for a test run. Sure enough at half throttle it was surging and charging was 11.8v. I replaced the rectifier and no difference. All wires looked good. I did notice a little grayish dust under the flywheel. I pulled it and discovered the magnets were worn down. The stator base retainer ring was broken and causing the stator base to wobble and contact the flywheel magnets. I ordered a good used flywheel and stator base assembly. I replaced the retainer ring with a new one..... That motor now fires up like brand new!! It runs perfect at all throttle ranges and charges around 13.5volts 🥳🎉🎉🎉🎉. I have now ordered a Yamaha paint kit and full set of stickers. Free motor, moments of pure frustration 😂. But roughly 10 hours of labor, and 300.00 for a great running motor 😁

[@fishydubsfishing6516]

I'm a industrial maintenance mechanic from years gone by I have the 4.2 Yamaha four stroke and I can't believe the prices on parts

[@thegunnut221]

Great helpful video. I have a premix yammy 60 so I know exactly how much oil the engine is getting. The Yamaha Mechical oil mix system is one of the best but can obviously fail.

[@AN-kg4ei]

easiest thing to overlook on this job is that boat plug... 👍 Great job!

[@elijahslater5999]

Awsome video mate thanks, gave me a bit of confidence !

[@ct1762]

telescoping gauge isnt accurate enough. but that piston most likely stuck a ring, allowing hot exhaust to get pumped back into cylinder causing detonation from lack of decarb maintenance. nothing to do with the ultra reliable oil pump. this motor is going to measure atleast .003'' over anyway so all should be bored properly it wont last long or have nearly the power without doing the job right. cheap out and you get crap results.

[@roderickhagan9040]

Hey I like that foxbody in the back

[@fox-body]

Me too. 😁

[@Restored_2strokes]

If it were a possible oil injection clog. Then it’s plausible to say that particular oil injection for that piston should be inspected first no leakage due to the clog still there.

[@tomswindall7456]

Do u have a video of how u got the pistons out?

[@fox-body]

Sorry I didn’t video that.

[@catlifeoutdoors6369]

That motor was terribly tired. Look at the compression passing the rings. I would bet that compression should be 130+. On all the 3cyl yammies I’ve wrenched on 130 is about normal. I would suggest punching all 3 cylinders and new pistons. Like it or not it’s tired. Just my opinion.

[@donsscooters]

Dang brother,, Have you watched you video. Please consider moving the camera slowly or not at all. This could be a valuable video if we could not get motion sickness watching it. Don't stop making them, just consider those that watch next time. Thanks,

[@fox-body]

lol. My bad. I’m not great at videoing.

[@cobuscarstens6417]

You did great. Very informative. Wish I had someone like you around to teach me. However your videos makes a world of a difference! Thank you

[@doowrath]

Do you have a parts list i have a 1988 pro 50 and am not sure if the 50 in the same parts or exactly what i need to fixmine middle cylinder melted

[@fox-body]

Sorry I don’t. I actually sold that boat.

[@NXGena]

Hello guys, I bought a boat with an old Yamaha outboard 2-stroke engine built in 1983 50HP Model: 6F4 and I can't find a parts list or repair instructions. This engine is not listed anywhere. I'm desperate, someone please help me. Thanks in advance

[@frankk533]

What year is that engine? Thanks

[@fox-body]

90

[@jeroenbastian]

What are the differents from a pro50 and normal 50?

[@fox-body]

Not really sure.

[@Puzkajuzzi]

Tried to look into this, some people say that pro version had 849cc block when normal had 600cc. However I compared part numbers and it shows same part number for the block in normal version and pro. Also the heads part number, pistons etc. are the same. One guy said that the pro version would only have slightly advanced ignition timing, which would make sense as the part numbers look the same.🤔

[@timsussenbach5376]

The difference is... its a 60 hp... they share the same block as the 70 hp

[@evyc2537]

That’s good it wasn’t anything super expensive 🙇‍♀️

[@fox-body]

Yep😁💵