'72 Johnson 50hp - Blown to pieces

[MM3Canuck]

So I blew her up. About 2 miles out of the marine at 3/4 throttle she popped, instantly died. Got a tow back to the marine and when I finally had a good look at the damage, I noticed big engine block pieces everywhere. 3-4 holes and numerous cracks. I can still turn the prop, and whatever is left in there still turns.

My question:
How and why did this happen?

(oil mixture is always bang on, fuel and oil were fresh that day)


I have the same motor as a spare, but its corroded inside, as it was sitting outside at the previous owner. Can I rebuilt that one, and swap it back to get my current setup back up and running? Cost estimates?

 

[eavega]

Re: '72 Johnson 50hp - Blown to pieces

Wow. That looked violent. I wonder if we have discovered a weakness on these motors? I have a thread I have started about my 1972 Evinrude 50 that also blew a hole in the crankcase. It was is fourth outing, fresh fuel (in fact, I had just returned from the gas station with the second tank of gasoline for that day), correct oil, I had previously checked the timing and that was spot on, and I was running the motor at 6000 RPM, which is the top end of its operating range. Oddly enough, the damage is almost exactly where you show damage in your second picture.

That is the picture of my damage.

Motor kept running on the top cylinder and got me back to the dock. I'm sure I could probably still start it. I am in the process of tearing it down to see if it is repairable. I did pull the plugs and observe that the piston still moves back and forth when you turn the flywheel, so its not seized, and the connecting rod and wrist pin probably aren't broken. I don't know if it was just the crankcase itself was a bad casting which finally gave way. If it doesn't look like there was any damage to the components, my plan would be to have the crankcase repaired and try it again.

You seem to have had a much more violent event than what I had. Know that the pistons and wrist pins are NLA, so you will need to find someone who has either a parts motor or one of the known shops that might have some NOS.

Good luck.

-E

 

[Al-53]

Re: '72 Johnson 50hp - Blown to pieces

WOW..sorry to hear of your problem..but that motor grenaded bad.....one of the pictures show the casting bent outwards...it looks like something let loose bad....them are some scary pictures....

Al

 

[MM3Canuck]

Re: '72 Johnson 50hp - Blown to pieces

Now that you mention the timing, my dad had just played with the timing before it went back into the water.

It was running really well though while hooked up to the muffs.
What can happen if the timing is off?

Yours looks decent, compared to mine! Propbably even fixable.
Im not sure if mine can even be fixed. Looking at some of the pieces that came flying out, it might even be internal pieces, maybe even from the pistons?

Mine died instantly, I guess all compression was lost.

Not a good way to end the season...