Home made 4 stroke race outboard.

[NZ Sidewinder]

I found a K24A2 motor that was good so that's on its way.
Also, I've built my vacuum infusion / de- gassing rig.
Things are moving along

[Greg G]

Great thread thanks for the posts. You have some impressive skills for sure.

[NZ Sidewinder]

In New Zealand we have a trade call fitting and turning which also generally includes welding.
Many of us worked for yrs in sawmilling, pulp and paper, oil and gas, and geothermal industries.
This created individuals with a broad base.
Some even went on the become electricians who because of their mechanical skills, got into plc and automation.
There are some very clever people down here.

[NZ Sidewinder]

Today I opened the floor of the boat up so that a foundation for the safety cell could be laid.
Fortunately, even after 30 or more years of use, the boat is still sound down there.
Also today, the k24 engine showed up.
I took the rocker cover off to check that is was indeed a twin vtec, yes it is.

[SOMDRacer]

I'm a little late to the show (Finally clicked on the thread)- but if you're indenting to use some sort of "car-style" exhaust (Header with a muffler attached)- so there is no need to run it through the tower- the easiest and probably lightest mid you could make would be identical to the US "Mod outboard" towers. It's how i make all of my towers for my experiments. Plate on top, plate for the lower- a big steel pipe around the driveshaft, then triangulate the two with smaller tubes. Essentially- think of bracing it like a roll cage. The result is very light and strong. Below is exactly what i'm describing. Everything from 20hp to 200+ or more. This 20hp version doesn't have much, but it's 5/16" steel plate and the center tube is 2"x.100" wall. I have a few of my 50hp towers laying around if you want more pictures/measurements. I'm about to build one for my 235 crossflow with a 8" tower.

The best part about this style of tower- if you want to run the exhaust through it, just weld on some thin Sheetmetal between the two.

[NZ Sidewinder]

Hi
This is cool and we are sort of working in the same field.
Over on the poor man's 15inch thread I've built a 260 mid.
That photo looks like a Force clamp.
I have one here and like the very light construction.
This K24 will be turbo so the exhaust will be very short.
Like you, I also like to work in steel, it's easy, cheap and strong.
Welding steel is reliable.
I have a longer term plan to build the components from Carbon/ Epoxy, basically going head to head with the Merc F1 4 strokes.
I also like these mids because any lower unit can be adapted.
This current one has a flange at the bottom of the trunk and that flange carries a plate that matches individual gearboxes.
In this case, 2.5 and 3.0L boxes.
That did require some white man magic though

[NZ Sidewinder]

Here are the profiles for thr build.

Here are the profiles stacked as will be assembled.
The pan footprint is probably similar to the merc v8

To save costs on the water jet cutting I only cut 30% of the holes in the 3/4 Ali plate.
The rest will be drilled using a steel template that was laser cut in mild steel.
Laser cutting is cheap.


Some trimming required on sump yet.
Not sure how that happened?

[NZ Sidewinder]

This is the underside of the pan plate.
The drive shaft goes through the oil tank which is a doughnut type arrangement.
That slot off to the right is the pump output and goes up through the pan and into the motor.
The white outline is the trunk shape

The black flange is the top flange of the leg, similar to the poor man's 15inch.
This one's 12 inch.

[NZ Sidewinder]

The Aluminium plate components needed machining flat and for thickness.
Also made the first Vacuum infused component for the safety cell.
The cell is made from 15mm thick high density foam with 2.25mm of glass/ carbon/ kevlar on each side.

[NZ Sidewinder]

Massive amount of work in this base for the outboard.
The block is fixed to a flange plate which is in turn fix down to the base plate.
Both 3/4 Aluminium.
It's 6 bolts to lift the powerhead off along with its flange plate.everything is Dowelled and the stock block Dowells fit the collar plate perfectly, which is no mean feat.
All studs are 1mm total clearence in the holes and all bolts are fitted, in that they have no nominal clearence.
That is, a 10mm bolt goes through a 10mm drilled hole.
The only clearence is the factory undersize of the bolts.
The thing will not shake itself to bits.

[NZ Sidewinder]

Here's a mockup of the leg and lower unit.

There will be a snout type curve out to the lower but no exhaust hole as it will exhaust up top.
That piece of wood with the pair of black lines on it are the heights of a 2.5 flywheel and a v8 flywheel above the transom as a comparison
This motor is designed to fit on a 600mm transom (2 ft), hard down with propshaft 2.5 inches below pad.
From there, the holes can adjust it up more.
The actual leg length will be 12inch.
Designed to circuit race.
Natural setback from rear of transom to crankshaft, 14 inches

[Greg G]

Wait, explain the setback a bit more. Good progress for sure!

[Instigator]

I like it.

Here's a mockup of the leg and lower unit.

There will be a snout type curve out to the lower but no exhaust hole as it will exhaust up top.
That piece of wood with the pair of black lines on it are the heights of a 2.5 flywheel and a v8 flywheel above the transom as a comparison
This motor is designed to fit on a 600mm transom (2 ft), hard down with propshaft 2.5 inches below pad.
From there, the holes can adjust it up more.
The actual leg length will be 12inch.
Designed to circuit race.
Natural setback from rear of transom to crankshaft, 14 inches

[NZ Sidewinder]

The nateral setback as I've called it I the distance that the crankshaft is set back compared to a 2 stroke.
Also seen in the position of the shift shaft.
As with the poor man's 15inch motor, the shift shaft line doesn't go down through the steering tube, it's behind it.
Typically, the shift shaft is approx 4 inches behind the top outside lip of the transom and the driveshaft is 3 inches behind that.
So a dactory drive shaft is a total of 7 inches behind the top rear lip of the transom.
On this motor the driveshaft is around 14inches behind the transom so that's double the factory distance.
The motor probably suits a long hull.
Today if I find any of these numbers incorrect I'll edit.

[NZ Sidewinder]

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.
This is a 2.5 box but a 3.0L will fit also