Home made 4 stroke race outboard.

[NZ Sidewinder]

I'm building a diy 4 stroke race motor that I hope will compete with the Merc 300 and 400r in circuit racing.
Maybe longer river races as well.
The Powerplant I'm investigating is the 2400cc K series Honda.
Turbocharged.
It's going to be a big job, and will be documented in this thread.
So far I've built the midsection and the mid currently runs Merc 2.5 15.5inch boxes.

Edit update
I decided to build a new midsection specifically for this build and retain the Poor man's 15inch motor as a 2.5L platform.
So this thread documents the build of an entirely new engine.

The mid is set up like an f1 in that it doesn't run an exhaust plate system.
This helps keep the powerhead low on the boat.
The K24 motor is 24inchs from the base to the top of flywheel, so it's tall, something like a v8.

I can't afford a r motor, so this is my way of racing competitively in the future.

Currently I'm studying the oiling system on the Honda outboards which use the k series motors.
I'll use a closed water cooling system

Should be an entertaining thread

[Greg G]

Subscribed!

[aj06bolt12r]

Awesome.. Following! Don't forget to keep us posted!

[DangerNewb]

Tremendous endeavor. Heck, I use up all my mechanical skills just servicing and swapping components to keep things running.

[NZ Sidewinder]

So the mid is done already.
It uses a 20inch Merc clamp that supports a large horizontal flat Aluminium plate that the powerhead bolts down to.
That plate, which I call the platform, is supported by large steel wings that are welded to the origional steering arm boss.
The steering arm is cut short and the boss is machined so that the connection to the steel wings is very strong.
541857
Here is a photo of the platform supporting a 2.5 2 stroke and also a photo of the assembled leg541858
Also, hete is the old broken Honda I picked up to study.541859541860
This is a k23 marine motor, but my intend engine will be the car k24.
The oiling systems are the most important part of the job

[laser_ED]

Following this thread,from your past posts I think we all will be watching this one...

[LakeFever]

Just wait til that Vtec kicks in yo


in all seriousness this is precisely the kind of four smoke boost concept I think the world needs. A smaller initial platform to keep the weight down was my thinking but I can’t argue with the proven power and reliability some of those Honda guys have achieved with those K motors. Going to enjoy watching this come together

[NZ Sidewinder]

Ok, well the process has started albeit in small steps.
First I purchased an early 130hp Honda which is an f series type motor, but the goat was to see how Honda dealt with the oil system.
There was also the possibility that some of the parts from that outboard might be useful in the k24 build.
These 130 hp engines are not the car engine just tipped up put on an outboard leg, they are purpose built outboard powerheads.
So what did I learn from the 140 motor?
Interesting design.
They don't have main bearing caps or a girdle, they have the caps as part of the sump pan.
Sort of combined caps, girdle, pan.
The oil pump is about where a cars clutch is in the bell housing.
It's unlike any pump I've seen.
Flat like a saucer and is driven by a pair of flats on a coupling that drives the main input shaft for the lower unit.
Below all this is the oil actual sump.
Surprisingly the oil pump is able to lift the oil out of this sump without being primed
I can't see any system for holding the pump in a primed state.
This is good news.
Next step is to buy a good k24 3 lobe runner and start working with that.
I paid 500 buck for the 130 motor and reckon that the drive shaft coupling alone is worth that to my job.
I may use the sump and oil pump as well, even if the 130 pump is used only as a lift pump for the k 24541987
541988
These engines have a flat crank and balance shafts.

[NZ Sidewinder]

This photo and the general leg layout is well published already, but for the sake of this thread, here is a photo of the leg and powerhead platform to be used.
The Aluminium base plate in this example is cut to suit a 2.5 merc, but another one will be cnc cut to suit the 4 stroke block.
Those black wing shape things are welded to the turn tube boss after the origional steering arm is cut off and boss is machined etc.
The part that's welded to the boss is 1inch thick and then sets down to 1/2inch where the Aluminium plate fits to it.
Shift shaft doesn't go through the tube, it is 2inch further aft.
The water tube in this example suits the 2.5, but can protrude through the base plate at any appropriate location.
A simple pan is fabricated for the cowl to fit to.
542005542006542007

[Speed Jr.]

Well that went from cool to ahh. The K24 would be something to see if you get it to launch at all. The boosted 600+ HP Mitsubishi that was put on a champ mid wouldn't even start in gear, not enough torque. There's a reason everything new has a large displacement

[NZ Sidewinder]

We don't drag race here.
We circuit race.
The boats hit the
start finish line at full speed and go through the turns at over 70mph with ideal speed in the straights of high 80s.
We already have the big v8s here and know what's required to beat them.

[89LASER]

With the oiling system, would there be a way to dry sump it, having a tank in the boat and running an electric pressure pump to the engine? Just trying to think out of the box a little and save some weight off the transom. You would be able to prime the oiling system before start-up.

[NZ Sidewinder]

I've been thinking about this issue.
The typical honda outboard system is probably the simplistic.
However the Honda outboard pump just acts as a lift pump to feed the stock car version pump.
The car one is typically a k20 pump fitted to the k24.
I'm also most likely going to build a 10 or 12 inch leg instead of using my existing 15inch.
This is so that I can get the powerhead weight even lower and also, this enables us to continue running the 2.5 on the 15inch leg.
The priming of the top pump can be managed in the reservoir system where the lift pump meets the main pump.

[NZ Sidewinder]

Today I picked up a k24 block and head from a wrecker to use as mockup pieces for this build.
When it comes time to get an working engine I'll buy the whole car so that the motor can be tested properly and I'll have all the parts I need.
Wrecking yards here don't want to sell complete engines, they just sell long blocks and people need to use their own bolt on parts or buy them.
So here we go.
As with all this type of builds I do, first is to do a rough concept sketch.
I did this one during dinner yesterday.
The idea is to get the powerhead down very low, but retain a 20inch transom.
So to do this, as was the case with my previous 260 build, I lowered the powerhead by deleting the exhaust plates.
With this build I'll take this idea one step further and set the powerhead back and down, on a 9 or 10inch midsection.
This will place the propshaft around 2inches below the pad when the Merc offshore clamp is hard down on the transom.
That's about as high as a circuit race boat should be.542343542344
These engine parts are only for mockup testing etc but themselves are good for parts
Note; the sketch shows an exhaust snout.
This build won't have exhaust in the mid, it will be dumped straight from the turbo.

[NZ Sidewinder]

I've decided to put this powerhead on its own leg.
The origional plan was to use my diy 260 2 stroke leg, however due to the extra weight of the 4 stroke I've decided to build a new, even lower midsection as described.
It will be along the same lines as the APX and run up to 500hp.
Vee bottom circuit racing in Mod Vp.

[Greg G]

Ambitious is an understatement! Thanks for posting

[NZ Sidewinder]

There's no question that the k24 is bigger than the 2.5, but the diffetence is entirely managable542383

[NZ Sidewinder]

It's now time to move on from sketchy sketches to timber mock up.
Timber is great for this type of prototyping.
We dismantled a mint fresh water single ram, offshore midsection and that will get a second shot at life in the fast lane.
The k24 is set very low, much lower even the low profile 15.5 inch motor I currently run.( poor man's 15inch).
542431542432
I've done some weight numbers.
This powerhead will weigh 120kg and the finished motor will total 220kg.
The Apx 360 is 218kg I believe.
I've trimmed weight in the powerhead by using a k20 oil pump and deleting the water pump and counter balance system
The factory water pump on these motors is very heavy.
It will run on the stock merc pump and also twin transom scoops feeding direct to the motor.

[NZ Sidewinder]

Moving along .
The oiling system is the biggest challenge of this project but there a couple of options.
My preferred option is to adapt the stock Honda outboard
system.
It's an unusual setup.
That flat plate thing that is covering the flywheel is the pump and it's driven by the driveshaft spline coupling that's bolted to the flywheel.
It picks up oil from the sump below and in my project would pump it out through an external hydraulic hose to the motor above.
The returning oil is drained back to the sump by more hoses from the bottom of the sump and rocker cover.
So as it stands this minute, this is option one and option 2 is a full on dry sump system.
That disc shape pump bolts to the underside of the base plate ( that horizontal sheet of ply), and the powerhead bolts on concentrically above.
That hefty looking assembly that's sitting down to the left of the block is the factory K24 oil pump/counter balance shaft system.
It gets deleted
542453
542454

[NZ Sidewinder]

The engineering issues relating to adapting the Honda oil pump to this project are mostly solved today.
The pump, both the feed and return lines, the pickup and the sump are all attached to the powerhead.
This means that when the powerhead is lifted off the base plate, the entire oil system comes with it.
This is good.
The feed into the block turned out to be easy as well.
In this photo, the basic assembly process is set out in plywood.
It was easy but not straight forward, although in the end it was is a simple design.
All the components required are to be laser and water jet cut from cad files I make.
It's a difficult job to get the dowel measured up properly so that they fit the new parts.
Just lots time542464

[NZ Sidewinder]

542482542483542484

Today I dealt with the feed from the external pump to the block.
This was done by cutting up the factory oil pump and retaining the part of the casting that fed the oil into the block.
A piece of 16mm tube was fitted into the new port and extends through the sump in a straight line so that the sump will still fit on and off.
The actual penertration will have a welded socket and olive fitting to seal the penertration.
I'll build this while job on this mockup block, then transfer the design over to a good k24.
That said, this old 200 dollar short block will scrub up ok also

[Greg G]

Nicely sorted. 200 dollars ......amazing

[NZ Sidewinder]

Yeah.
I like creating usable stuff from junk.
Even my race 2.5 powerheads are made from junk.
That said, the fact that the Mercury v6, whether it be the powerhead, clamp, mid or gearbox can be salvaged from the scrap heap and built into a screaming racer, is testament to the genius behind its creation IMHO.

[Instigator]

Ray Neudecker, one of my hero’s, used to say that one of his favorite things to do was dig someone elses junk out of the dumpster, bolt it all back together and beat them with it!

Please continue!

What we need in todays $50k motors is more people like you.

Even if you fail, you still have fans!

[Greg G]

Yes Ray was a legend !! RIP Ray

[NZ Sidewinder]

There is a cost to dropping the powerhead 8 inches from fishing height.
That steel cross member is heavy but in to overall picture it's ok.
I've now decided to make the leg 12 inch.
This puts the propshaft 2 1/2 below pad when the clamp is hard down.
2 1/2 inches down is sort of a NZ standard for race boats.
However, the clamp can be raised if it need to for kilo etc542551
I may need to crank up the boost

[NZ Sidewinder]

Here are the profiles for water jet cutting.
I'm yet to do the lower plate that the gearbox bolts to.
I'll probably make it so that it will fit both a 2.5 and 3.0L gearcase.
This us simple because on this motor the gearbox water pump feeds a pipe that enters the leg from the side rather than down from the top as usual.
The gear shift will be different than standard also.
The drive shaft is the datum.
There is one important profile to do yet.
That's the main flange that the powerhead bolts down onto.
It's sort of like an automotive bellhousing adapter plate.
542562

[NZ Sidewinder]

The profiles are now ready to go to the cutting shop so I've brought out my other project and will work on both through the winter.
This other project is a safety cell for our mod vp circuit race boat War Horse.
About 12 months ago the young fella was driving it at the Nationals and crashed.
He went into the second day of racing first equal on points and knew that in order to win he needed to capitalize on his inside poll position.
His main competitor was faster in the straights, but War Horse was much more nimble in the turns.
Hamish lost the lead at the first turn and was chasing the faster boat into turn 4 when he may a serious mistake.
He crossed the large wake of the lead boat sideways and fell into the hole.
The boat barrel rolled 360 degrees and Hamish was lucky to survive it.
After that, I decided that the boat wouldn't race circuits again until it had a safety cell.
What's more, now the boat will be nudging 100mph and only a crazy man would race it without a cell.
So here we are.
I built the male plug last winter and will build the cell this winter, alongside the 4 stroke motor build.
Today I put some wax on it and will continue doing that tomorrow.
It will be infusion molded in Carbon, Kevlar and Glass with a foam core.
Poly Carbonate screen.
The cell is designed as a module and can be fitted to any center steer vee bottom.

It's a male mold system and this mold could even be used to make a 2 seater cell.
Not that I have any intension of doing that.
This one is principally for my boats.
Sitting on the mold is a scale model
542621



https://youtu.be/W_sW6bKP8y0?si=jIgUhAVU8HjZH1A3

[Instigator]

Very nice!

And smart.

PS, love the name of the boat!

[NZ Sidewinder]

Just one word to describe the setup for vaccum forming foam core items.
Insane.
542727
The foam must be the same shape as the mold, even at the radius corner on the inside.
All that while allowing for 2.5mm layup thickness under that foam.
I've got all winter, but I pity those who are doing it for customers.

[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 along542833542834542835542836542853

[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, 542975542976yes 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.



https://cdn1.bigcommerce.com/n-yp39j5/h9d9z/products/23872/images/47130/DSCN9188__14913.1629423107.1280.1280.jpg?c=2

[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.543095

Here are the profiles stacked as will be assembled.
The pan footprint is probably similar to the merc v8
543101
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.
543130
543131
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
543168
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.
543463543464543484

[NZ Sidewinder]

543575543576
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.543592

[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 inches543595

[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 inches543595

[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.543600543601
This is a 2.5 box but a 3.0L will fit also543609

[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.543600543601
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.543613

[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.543625
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.543918543919
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. :cheers:

[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.543939543940

[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.544007544015

[NZ Sidewinder]

544016
Now the fun starts

[NZ Sidewinder]

I used to buy only 2.5 mercs for parts.
Now it's Hondas as well.544020

[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.544194544207
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]

544403544404544405
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!

[NZ Sidewinder]

Thanks
I need to grind all the welds and power sand them.
Get all the weld splatter off and get sand blasted.
I'll cove some of the internal angles and epoxy prime.
Then the leg can hang on the baseplate.
I still need to make the oil sump etc, but that's all easy stuff.
This mid needed to be carefully build because the line of the drive shaft needs to be almost perfect, especially with a short drive shaft.
The days here are getting longer, so progress will speed up.

[Greg G]

Very cool NZ that you could achieve that alignment tolerance on your midsection. Keep going!!

[NZ Sidewinder]

There is some machining work at the bell housing end ( top) but yes, the challenge is getting the gearbox fitted and located on dowels onto the adapter plate which in turn attaches to the bottom flange of the mid.
Tools like straight edges, scrapers, files, marking blue, scriber, marking out block etc are used.
Probably the most difficult and misunderstood part of precision fitting is drilling holes accurately.
When a random hole is drilled in metal, it's highly unlikely to be exactly where it's intended to be.
Drill bits wander, and getting the hole positioned accurately is a learned art.

[Instigator]

When we did my cut down mid, a buddy who is scientist level did it and he was clear w/what we needed.

I was fearless w/it and would not have been otherwise.



Thanks
I need to grind all the welds and power sand them.
Get all the weld splatter off and get sand blasted.
I'll cove some of the internal angles and epoxy prime.
Then the leg can hang on the baseplate.
I still need to make the oil sump etc, but that's all easy stuff.
This mid needed to be carefully build because the line of the drive shaft needs to be almost perfect, especially with a short drive shaft.
The days here are getting longer, so progress will speed up.

[NZ Sidewinder]

More small steps
544537544536

[NICE PAIR]

"Nice work" :thumbsup:

[LakeFever]

There is some machining work at the bell housing end ( top) but yes, the challenge is getting the gearbox fitted and located on dowels onto the adapter plate which in turn attaches to the bottom flange of the mid.
Tools like straight edges, scrapers, files, marking blue, scriber, marking out block etc are used.
Probably the most difficult and misunderstood part of precision fitting is drilling holes accurately.
When a random hole is drilled in metal, it's highly unlikely to be exactly where it's intended to be.
Drill bits wander, and getting the hole positioned accurately is a learned art.


this is a gigantic understatement. Even with best practices issues can arise. A lot of fab shops have switch to water, plasma, laser cutting because of this. Wire cutting is also extremely impressive if you need a certain fine surface finish.

I have an Altzmettal drill press with a box column. The best drill press in the world imo and even with it I sometimes get some variation on my hole location but I’m not building to this level often so it’s good for me. It’s rated for a 2.5” hole with a single twist bit. You gotta watch it when working with this beast. I have a dead man’s switch but haven’t hooked it up. Now that my son is getting curious it’s time to install it.

Anyways not to derail an awesome thread i just thought it worth the mention that we are all very impressed with your efforts and skill here.

[NZ Sidewinder]

I've pulled down the 135hp k24 outboard I got for 141 bucks.
Bought it as seized but it wasn't actually seized.
I had a feeling that it wouldn't be seized, as how does someone seized a Honda.
I found that the head gasket had been weeping due to corrosion around the dekkck area.
This had caused one cylinder to stick it's rings in storage or a period of no use.
Block is toast though
However I got some really good parts out of it.
4 marine pistons, 4 rods, starter motor, wiring harness, injectors, alternator, oil pump, crank, head, gearbox and leg, which is a story in itself, details in photos,
Clamp, and more.
I'm learning lots about how Honda made this car engine run in the vertical position.
The oil system on the k24 uses a oil pump mounted down below as already covered, but instead of piping the oil up to the top and feeding it into the motor where the car system does, and like I was going to, they feed it externally into the oil filter housing.
So that's what I'll do also.
The k24 crank uses the same thrust bearings in moth the car and outboard, so that's works.
The outboard has a very cool water coolef exhaust manifold tha is a bolt on item, so I'll use that to feed the turbo.
The exhaust runners are very short so not too much efficiently will be lost at the turbo by the cooling.
I'll fabricate the inlet side.
Interestingly the Honda gearbox is a preload type.
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What's really interesting is that this 25inch motor has a 15inch leg system shown in the photo.
The missing section that makes it up to 25inch is the section with the oil sump in it.
This bit shown could easily be made into a really poor man's 15inch motor.
Just bolt that section up to a flat plate like the other 15 I did.
In fact it's less than 15inch.
The clamp and lower mouth are very well engineered also.
Down side is the large diameter of the gearbox and the 2.1 to 1 ratio.
It's all happening.

[NZ Sidewinder]

There's been a lot going on recently with this project.
The 135 k24 donor motor was an eye opener.
Honda filled the outboard k24 motors will the hi performance rotating parts.
So for 140 bucks I got most of what's required to build a 500hp boosted powerhead.
My k24 runner donor motor has good parts also, eg twin vtec
Here is a photo of a mock up to date.
The mid is not yet sand blasted but is now fitted true to the block and box..
That exhaust manifold is from the k24 outboard and is water jacketed.
I'll put a 180deg elbow on the bottom outlet of it and put the turbo up beside the block.
The crazy thing about this project is that there is a easy 600hp right there in the photo.
Just need a merc gearbox that would handle that.544818
One small problem is the throw of the gearshift lever at the box.
It's 8inches which is way more than the typical Morse shift cable can do.

[NZ Sidewinder]

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[89LASER]

Maybe these people can make you one with a longer throw.

https://www.facebook.com/p/Baicour-Design-Machine-100057358753945/

[LakeFever]

Baicour marine makes good product I bought my shifter from them. Good people

[NZ Sidewinder]

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The cell is coming along.

[NICE PAIR]

Looking Good, do you have the plexi or can you make it fit what you've built?

[NZ Sidewinder]

We use Polycarbonate, not sure if plexiglass is the same thing.
For this class it needs to be 1/8 thick.
I have a male mold to bend it over with heat.

[NICE PAIR]

You do some awesome work! :cool:

[NZ Sidewinder]

545002
It's time to take on the oil sump.
Here is a view in from the gearbox end.
The stock Honda pickup is in the perfect spot, just needs to be shortened 1 1/2inch.
That entire open space will have a stainless steel sump fitted in it with the low point being where that pickup is.
So the sump tank will have its main bottom just above the water pump and it will drop down to a small sump at the pickup.
The drive shaft will go up through a doughnut type hole in the sump.
The sump will be conected,( hung) from the top plate that the motor is bolted to.
This means undoing 5 bolts and the whole powerhead and sump can be lifted out as a single unit.
Leaving the main base in place supporting the leg and box.

[NZ Sidewinder]

First trial fit.
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[NZ Sidewinder]

I'll get back onto the outboard soon, although I've already
started on the oil sump.
The route for the oil return was a challenge but I've sorted it now.
The hull and Cell has been a priority though because it needs to start the race season with a poor man's 15inch 2.5L
Today I worked on the cell in the morning and started cutting weight out of the hull in the afternoon
I'm aiming to maintain the hull weight close to what it was before the addition of the cell, but shift the driver position aft at least a foot.
So the dash had to come out
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[DangerNewb]

All I can say is if you ever want to come to the US and give me a hand on some of my junk, you have a place to stay. Almost comical how much you get done in a short time period.

[Rsatch]

I was literally thinking the other day about finding a junk Honda K series outboard to see if parts could be mixed with the automotive K24 to make a more powerful outboard.

[Greg G]

I find it amazing that you can toggle from thought to execution on so many different pieces of the project :cheers:

[NZ Sidewinder]

Lol, thanks
At the moment I feel like I'm making slow progress.
I don't do much else other than work our boats.

[NZ Sidewinder]

Even although the motors have the same in internals, the block and head castings are different.
The outboard already has the good rods and crank.
I'd say that the best option for making a bf150 go fast would be to either super or turbo charge.
Use an after market ecu.
Not a project for a recreational boat.
Probably the easiest route for building a fast small race boat would be to build a 600hp k24 car motor and run it as a surface drive.
100mph easy.
Probably a 18-20ft hull, 800lb bare hull weight

[Greg G]

I would be curious on more of your thoughts on super or turbo choice for that platform. First that comes to mind is the octane rating you would need. Whenever you get a minute. Carry on.

[NZ Sidewinder]

The interesting thing about the K24 motor is that by many accounts it deals well with 10-15psi of boost at 10 to 1 compression or even higher while on good pump gas.
Personally I'd be happier with the 165hp pistons down at 9 to 1 CR.
Strange but true

[NZ Sidewinder]

Here is the mockup of the oil sump.
Most of the difficult aspects have been overcome 545179
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The powerhead oil pump and sump assembly is one unit and can be lifted off the main base just by undoing 5 bolts.
Left behind, still as an assembly is the baseplate, leg and lower unit.
All those 5 bolts are accessible from the outside of the leg.
Really simple

[NZ Sidewinder]

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The feeling is of a cockpit from an alien spaceship.
I'd be comfortable running this thing well past 100mph.