Home made 4 stroke race outboard.

[Instigator]

I like it.

So here we are.
This is my Afghan street mechanic way of doing a highly precision trial fit up.
The idea is to check to see that the driveshaf does in fact pass through the center of the crank main bearings.
Now I'll pull it apart and weld everything.
Then draw file everything that Mother Merc would mill.
Same outcome.Attachment 543600Attachment 543601
This is a 2.5 box but a 3.0L will fit also

[NZ Sidewinder]

This photo is a milestone.
The leg is mounted on the clamp and at the yoke can be seen a new design feature.
The engine can be raised or lowered 2 inches without removing the clamp from the boat.

[NZ Sidewinder]

Back to the details.
Here is the water pump detail.
Because the 4 stroke has an oil sump in the leg, the water tube can't go up vertical.
The driveshaft goes through a tube in the sump but the water can't go that way, so it's piped out the side of the leg and upwards to the powerhead.
On this build, the pump in the lower unit will supply water for idle and slow going, but the main flow will come from transom scoops at speed.
This same system can be adapted to serve the 3.0L gearbox pump as well

[NZ Sidewinder]

This job is moderately difficult.
Ambitious would be to plant a Ford Barra straight 6 on the leg.
The Barra is the Australian Ford 6, around 4.0L
Turbo north of 800hp.

[VkingMike]

The Aussie 2JZ, that would be something.

[NZ Sidewinder]

No substitute for cubes.
2.0L might be a little light on torque, especially since this motor is probably destined for a 20fter.

[NZ Sidewinder]

Here are some photos of work in progress.
The midsection is tacked down to a 40mm plate for welding.
All the welds are full penertration flux core.
I spent a couple of decades welding pipelines so this all comes easy.
The steel is 1/8 corten which makes the mid reasonably light.
The poor man's 15 inch mid is 1/4 inch.

The other photo is the gearbox plate, gearshift and water pump pipe.
The water pump will only be responsible for low speed water supply.
This plate system is what enables the mid to be fitted with either a 2.5 or 3.0L box.
The only significant differences between the two lower units is the bolt pattern and a small detail at the water pump fitting.
The centerline spacing of the forward dowel, forward bolt, shift shaft, driveshaft, water pump outlet, rear bolt and rear dowel are all the same between the 2 units.
Edit.
The 3.0L gearbox I've quoted is actually off a 4 stroke.
They are big solid boxes with 1.92 gears.
I don't have a 3.0L box yet.
Piad 1 dollar for the 4 stoke box

[Greg G]

Paid 1 dollar........I love it! You have now officially gone beyond my range of understanding but I'm still watching this thread like a hawk. Thanks for sharing your work and btw I do know a clean and mean bead when I see one.

[NZ Sidewinder]

A motor like this is destined for 100mph plus and there's no way I'm getting in the boat, or putting anyone else in it without a safety cell.
So in parallel with this job is the construction of a cell.
Cell building makes outboard building look like child's play.
There is some serious engineering going into this part of the job.
It involves mold making ( tooling), wet layup, vacuum infusion and wet vacuum bagging.
Also polycarbonate fabrication and canopy design and fab.
On a difficulty scale 1-10, it's 10.5
Today I mocked up the canopy in cardboard on the actual cell front half.
The back half is currently being fabricated on the mold.
It's a 4mm skin each side of 15mm foam.

[NZ Sidewinder]

Here is the rear half of the cell seen the the previous post, getting it's foam core glued on.
The inside shell is still on the mold and covered in epoxy glue.
The pre shaped foam is placed on and vacuum bagged down.
The clamping forces obtained via vacuum are incredible.
In this case, the total weight of pressure is around 10 ton.

[NZ Sidewinder]

Now the fun starts

[NZ Sidewinder]

I used to buy only 2.5 mercs for parts.
Now it's Hondas as well.

[NZ Sidewinder]

I've been full time on the cell, so work on the motor is on hold for another week or two.
The cell is coming along.
Although today I visited my Merc parts guy and picked up 6 2.5 pistons on 141 rods, a set of rectangle 5 petal cages, a 2.5 bring block and a late model f block.
The late model f blocks are a nice block.
Another photo shows the screen cutting template and the male mold for rge cell roof.
Cell roofs are difficult because the rules say they need to be 4 inches above the drivers helmet.
This makes for a tall cell which is difficult to design.
The result is always contrary to racing lines

[NZ Sidewinder]

I've been busy with the cell, but each day on the way out of my shed I grab the welder and do a bit.
Finished the welding today.
These photos show the mid with the 2.5 and 3L adapter plates.
The mid weighs 44lb and the adapter plate weighs 15lb.
Not light , but not too bad.
The mid is made of 1/8 corten.
It's lighter than the poor man's 15inch mid which is made from 1/4inch mild steel

[Instigator]

Great work all around.

Cant wait to see the motor mocked up!