MJ's Blown Piston

[macojoe]

Ok just for kicks, I took the head off today, here is what I found

http://syncboard.com/albums/Boat-Tackle-Box/Picture_015.sized.jpg

http://syncboard.com/albums/Boat-Tackle-Box/Picture_014.sized.jpg

http://syncboard.com/albums/Boat-Tackle-Box/Picture_018.sized.jpg

Also something you can't see, there is a small hairline crack in the bad sleve of the middle piston.

[msbhammer]

OUCH ! :-/ :'( :'( :'(

[Vic]

Oh man sorry to see that MJ. I'm sure you'll have her going in no time.

[macojoe]

shes done Vic!! I have not the time or cash or no how to repair!!

I am looking to get a motor from Blue-Runner now.

[bigshrimpin]

MJ - That doesn't look bad at all from the pics. Take a shot of the hairline crack in the cylinder wall for me . . . I've never seen one of those before. There's some nice aluminum skuff and maybe a little scoring from the ring in the middle one?? Can you catch your finger nail on the groove?

[macojoe]

yea I can catch my nail easy.

I tryed to get that crack to show, its way in when the piston is in. I will try again tomorrow.

[Skools Out]

yeah that one would need a boring. then see if it's a threw crack if no use it and bore the rest.

[Blue_Runner]

I must say I was expecting to see something God aweful, but it doesn't look terrifying in the pic. I'm sure the old digi-cam probably can only do it about 30% justice compared to the naked eye though.

Crack kills.

[76GMC1500]

That's a microseizure tansitioning to a full on seizure. *The metal on the cylinder is obviously aluminum from the piston being transferred to the cylinder wall. *Microseizures are generally caused by lack of lubrication, but can be caused by overheating. *Overheating localized to one cylinder is caused by lean fuel/air ratios, detonation, and advanced ignition timing. *This is a carbureted motor where oil is mixed in the carb? *I will say that the problem was caused by the carubretor. *If you do plan to reuse these carbs, REBUILD the one from the bad cylinder and have the others checked out before installing them on a new motor or you could end up in the same position.

Now, you want to get back on the water for cheap? *You have here what is a mostly good motor short of one cylinder and one carburetor. *How mechanically inclined are you? *You could strip the motor down to a bare block and take the block to the best machine shop in town. *You will get the best rates at an automotive machine shop, the process is the same regardless of application. *Any hotrod shop that deals with newer engines will be the best. *To sleeve a cast iron engine block, parts and labor come to $90 per cylinder. *Of course, your engine being an aluminum cast in liner engine can add some complicatoin and can add a little to the price of labor and the liner cost is going to be sky high. *If the liner is thick enough, they can just bore inside of the liner and install a sleeve just like on an iron block. *If the liner is thin, they have to bore the old liner completely out and start from scratch. *This is a little more costly. *For the best deal on a replacement piston, go to Wiseco. *They make drop in replacement pistons for a lot of engines. *If the failure is lubrication related, *you may want to replace the adjacent main bearings and connecting rod big end bearing. *You will certainly want to replace the connecting rod small end bearing as there is a good chance it was overheated. *Your wrist pin will probably come out blue and gold from the heat.

On further examination, I take back what I say about lubrication related. *That is definately an overheat failure. *Lubrication microseizures take place low in the cylinder where the piston skirt transmitts connecting rod thrust to the side of the cylinder. *The majority of the material is located at the top of the cylinder where the piston shouldn't make contact with the cylinder wall. *What appears to have happend to me is that your piston ring failed (causing the low compression readings you got earlier in the season). *The failed piston ring allowed combustion gasses to blow past the piston and heat it up to the point of seizure. *I feel confident in telling you that your ring failed because if it were still intact, it would have scuffed much of the aluminum deposits off of the cylinder wall.

[Repirts]

Hi MJ,

It has been a long time since I last posted but I feel that you need some encouragement with this. As you will remeber I blew my 175 Merc a couple of seasons ago and was really bummed out. But, all has turned out ok.

Get the manufactures manual and a lot of plastic baggies for parts, pull the power head and take it down the basement. Tear that sucker down to the block. It's a 2 cycle- hardly any parts at all! Get it to a machine shop and get an estimate- might not be too bad!

I did it with my engine. No experience necessary. Did mine in just a few nights.

Go for it! What do you have to lose?

Go for it

[Skools Out]

MJ's getting a LIKE NEW Yamaha 150 from BR

[bigshrimpin]

MJ - Stick to your plan . . . . Tear it down, part it out, and sell everything. Buy BR's and don't reuse your carbs unless you rebuild them first. Leave the oil injection off too. You'll have some fluke/bass money after a few trips to buy another parts motor.

Your more than capable of rebuilding that motor, but the smartest/quickest path to the water is BR's Yammie!!

[macojoe]

Ok I want to thank all for your help!!

1. I do ot think it was a oil issue cause I was using oil, the level was lower then when I started.

Yamaha does ot mix oil with gas it is a derict oil injection.

2. Carbs?? If the middle carb runs the middle cylinders then why is one at 0 and one 120 ??

3 *yes it over heated big time!! *But why?? *Water was pissing, and the thermostas check out ok in a pot of water boiling at 180*

So if not oil, carb, or water then what?? *I still think there was a internal break down of some kind??

So I agree, that it was the ring!!

I also think that fixing 1 of 6 cyl will be nothing more then problems with the remaing 6, on a 18 year old motor.
I would only fix if I was going to sell it!

If I had got the parts motor I might have tryed over the winter to build it and then sell in the spring??

But since it that did ot work out I will sell the parts and go with BR motor!

[Geekie1]

MJ, I was expecting a hole in the piston!! Could be a broken ring, however, I think that the most likely problem is a bad reed. Running lean can cause a reed to burn up which would also give you zero compression on that cylinder. You can check the reeds by pulling the center carb and look down the manifold barrels to check the reeds on the bad cylinder and comparing them to the good cylinder next to it. To get a better view and a little more work, you can instead pull the intake manifold with the three carbs still bolted to it. You will need to disconnect the fuel lines to the carbs, oil lines to the manifold, disconnect the carb linkages, not a difficult job. If the reeds are damaged, you will definitely see it when you pull the manifold, carbs, reed as a unit!! Reeds perform a similar function as valves on a 4-stroke. To repair the reeds is a job in the lower hundreds of $. The cylinder wall does look a little screwed up though so some work on that cylinder will probably be necessary. If the reeds look good, you most probably do have a broken ring. Yamaha oil fuel/oil is not mixed in the carb but in the intake manifold. I think the oil system on the Yammie is pretty simple and bullet-proof. If the oil level sensor lights on the helm instruments is working (self test when starting) and if you get low in the main tank or the small tank on the engine, you should get a yellow or red light and the rpm's of the engine will drop to 2000rpm. There is an article in Bass and Walleye magazine that explains the whole thing. Monday I will post the URL that has the article. Although an oil pump could fail, I have never heard of one failing on a Yamaha. But I guess I haven't heard of alot of things.

[macojoe]

Thanks Geek,

But all oil systems were go!! oil level was down in the tank at end of day.

as stated above, this is a dead thread as I am not going to be fixing the motor at all.

I will ck the reeds as I plan on keeping the carbs for spares on BR's motor, they have the same numbers.