Some of you know I work in a marina as a mechanic. We also have a rental fleet I maintain.

From time to time, I have to rebuild one of the outboards.

This one suffered from a seized piston resulting in a broken connecting rod destroying the block.

I was able to salvage two con rods and the crank from the short block. I had another con rod

from a previous motor salvage and we ordered a new block and all the bearings and seals.



New block
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First thing I do is to install the main bearings and shells on the crankshaft.

Here's one of the main bearings with it's shell and clip ring to hold the shells together.
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These little thin rings go on the crank in the groove between the bearing rollers.
The rings seal each cylinder from each other. Critical for a 2-stroke engine.
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I put some needle bearing assembly lube on one shell half and stick the rollers to it.
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Then I slide the shell under the crank journal and use a wadded up paper towel to hold it against
the journal.

More assembly lube and place the remaining rollers on top.
Install the other shell half and install the clip to hold the whole thing together.
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Part 2 coming soon!

Part 2, pistons and rods.

Here is a piston/rod assembly dis-assembled with brand new std bore piston

needle bearings,  wrist pin, circlips and thrust washers. The rod was reclaimed from the blown motor.
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To begin assembly, count out the 29 needle bearings and place them in a nice row.
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Then I squirt a bead assembly lube on the row of needles. It's like greasy tooth paste.

Sorry I didn't get a pic, but the next thing you do is roll the needles up onto the assembly mandrel.

Thats the short metal tube next to the wrist pin.

Insert the needles and mandrel into the small end of the rod. Next I use more lube to stick

the thrust washers onto the four pads on the rod small end, one per side.
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Using a hot air gun, heat the piston top quite a bit. So hot you can't touch it.
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After heating, insert the small end of the rod complete with needles, mandrel and thrust washers into the piston boss.

Quickly insert the wrist pin through the pin boss pushing the mandrel out the other side

and keeping the thrust washers in place.

Lastly, insert the circlips into the piston pin bores using the "special tool". Done!

It's quite a trick, but after you've done a few you get the hang of it.
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More in part three.

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Part three.

After cleaning the new block I oil up the cylinders and piston assemblies with 2-stroke oil

and insert them into the block. Since this engine doesn't use a typical cylinder head

the pistons have to go in through the bottom.

Then the crank is laid in making sure all the dowel pins in the main bearing shells lock into place.

Pulling the first rod up to the journal and inserting the roller bearing. Repeat X 3.
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Crank and rods in and preliminary torque on the rod bolts.
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Case halves together and all bolts at final torque. (note white out on rod bolt heads).
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Reclaimed reed plates with new reeds.
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Intake installed and ready for some Phantom Black!
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Building an outboard is very labor intensive, but I love it!

I thought you left that job???

I did, took last summer off to explore other options. They called me back in September and I went back. Now I'm the service manager.

ETA - The pics are from over a year ago. I was going to write this then, but didn't. Now it's time.

I'll help ya the best I can




Nice work Mr. Mechanic

Thank you! Part 3 is complete and posted.

Cool thread.

What make and model?

Did it die while a renter was out on the water?

It's a 2008 Mercury 50 90hp 2-stroke. Yes, it broke when it was out being rented. Had to be towed back to the dock.

Op, if a little is good is more gooder?

I run exactly 13 oz TCIII oil per 5 gal, this is around 2.7 oz per gal for a 50:1 mix. This is what OMC specs for this engine. The old timers tell me I should run at least 3 oz per gal. I run engine tuner every year too. They say I'm wasting my time and money on that "Snake Oil". I don't listen to them.

Who's right?

As I recall, and it seems to make sense, with a 2-stroke, more oil equals less gas equals a leaner fuel/air ratio equals high cylinder temps and engine damage.

This is correct. The oil takes the place where gas is supposed to be therefore it will run lean increasing

combustion temps leading to engine failure. Still though, the 0.3 oz per gallon isn't enough to worry about.

Engine tuner can be beneficial for the "cross flow" engines which are typically older units. This design has a tendency to carbon up more than

the more modern "loop charged" engines. The downfall is it needed to be done from year one to keep the carbon at bay.

Using it in an older engine that has bad carbon buildup already can be problematic. What can happen is large

chunks of carbon can be broken loose and find their way under the piston ring. This pushes the ring hard against the cylinder wall

causing scuffing. Worst case is the ring snags a port and rips off the piston crown edges.

Here's what happens when they go lean on fuel overheat. Similar to going lean without the melted aluminum.
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Piston crown torn off and the chunks tried to be compressed when the piston came back up to TDC.

This bent the connecting rod allowing it to strike the crank case..
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2008 90hp Mercury 2 stroke.