Yamaha 784cc into welded mod-v hull

86tuning
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Yamaha 784cc into welded mod-v hull

Post by 86tuning »

CedarRiverScooter wrote:
31 Aug 2019, 19:30
The latest addition to my boat is a winch mounted at the bow - the last 2 times we went out we ran up on gravel beds (obviously not paying enough attention). Fortunately we were able to lift it off, but next time I am better prepared!
Can't wait to get stuck on gravel bars. Hoping that a slick bottom coating makes life easier. But that will be after the boat gets in the water. And I'm still a long ways from that yet. Still figuring out how to put it together at this point.

Getting some arc time in with the TIG welder has been fun so far. So much more control, but I haven't figured out how to smoothy add filler rod yet. I've got both machines plugged in to separate circuits, so I can use both MIG and TIG at the same time. Both grounds connected to my table. Just farting around at this point with the machines and the process.

The Lincoln MIGPAK 180 has a ptfe liner now, and feeds smoother than ever before. With proper prep work, it's much faster, but the welds don't hold a candle to the TIG welds. Now if I could only see better with my old set of eyes, and dab filler smoother, I might just get this boat together.
the two 220v units
the two 220v units
TIG vs MIG welds, no pre-cleaning
TIG vs MIG welds, no pre-cleaning
I'm excited that I'm finally getting back at working on the boat.

See you on the water,

Brian

86tuning
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Yamaha 784cc into welded mod-v hull

Post by 86tuning »

Well I'm slowly plodding away at the water inlet. In the meantime, I did find the service manual for the waverunner here:

https://www.manualslib.com/manual/10588 ... e=1#manual

And it's been quite useful so far. I'm trying to put the engine as far back as I can, to increase cockpit space in the boat. The plan is to shorten the driveshaft and the intermediate shaft. And intermediate shaft shortening requires disassembly. The service manual is helpful for that. Short story is that the shaft is pressed into the bearing, and the coupler is threaded in place, and retained with pipe sealant.

Also found the parts catalog for the waverunner here:

https://www.yamahapartshouse.com/oempar ... 800z-parts

Apparently the 1100 waverunners use a shorter intermediate shaft. Make sense, as the triple cylinder engine is longer. But the couplers are the same, so I could use the 3-cyl shaft to move the engine back, and not have to shorten my 2-cyl shaft. If I can find a used one. But I may be able to shorten the 2-cyl shaft even further to move the engine further back by an inch or two. But that's a tomorrow problem.

Cheers.

-Brian

CedarRiverScooter
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Yamaha 784cc into welded mod-v hull

Post by CedarRiverScooter »

Sounds like you are enjoying the analytical phase of the project.
Maximizing cockpit room is a worthy goal.
Keep the pictures coming!

turbotodd
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Yamaha 784cc into welded mod-v hull

Post by turbotodd »

A couple musings of that engine (XA800).

They are kind of peaky even with the power valve system. In other words, kinda hard to vary the power, beginning at about 1/4 throttle. From there, you are at maybe 25% power, but at half throttle you may be at 75% power, kind of like an old 2 stroke dirt bike. I always liked them but they weren't real smooth in power delivery in the factory installed application.

Secondly-if you decide to test run out of the water, you get about 10 seconds. Once the spark plugs begin to glow (and they will), it will literally diesel, you can't shut it down. The first time this happened to me on a ski what was started without water in it, I about pooped my pants...brand new unit, couldn't get it shut down, was sitting there running. I pushed the stop button. Then removed the lanyard. Then both plug wires pulled off,still running about 6000 RPM. I had no idea what to do. After maybe a minute, during the time I was trying to get to the air intake to starve it, I reached over and pulled the choke knob out, which then killed the motor. No telling how hot it got. To my knowledge it never did show back up for any engine troubles so maybe it was ok. I mentioned the issue to our then yamaha rep, he said that the 800's and 1200's were susceptible to this from time to time. They also said that the 800's especially were really "peaky" in their design and that some folks would probably complain about it-and they did. But they were fast.

86tuning
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Joined: 11 Oct 2017, 01:49
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Yamaha 784cc into welded mod-v hull

Post by 86tuning »

Todd, thanks for the insight.

Re: runaway engine, I've definitely experienced this. Pulling choke out did shut it down.

I thought I'd have more time to spend on my project, but alas it's been over two years now. At some point I need to finish the water inlet. I probably should have bought a cast unit instead of ghettofabbing my own, but hey, hindsight is 20/20 and is for helping out the next person in the same situation. We shall see.

Cheers,

Brian

86tuning
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Yamaha 784cc into welded mod-v hull

Post by 86tuning »

Boat hull has been yard art for a long time, and I've been procrascinating because I'm stuck with the water inlet still. So I made a jig to hold things while I sort it out. I'll be using the cast pump shoe and grate, but need to make the upper portion out of metal. And the shape is complex enough to stall progress. But simple enough that I'm too cheap to buy a commercially made cast water inlet.
plywood jig
plywood jig
jig2.jpg
Next, I examined the cast pump shoe to determine which portion I need to save, and which portion to delete, and how to go about cutting it. I do have a hack saw, but hand tools are for chumps :o
pumpshoe1.jpg
I managed to clamp it in my vise, and hack it off with the circular saw. I managed to keep all my fingers too.
pumpshoe3.jpg
A lot more trimming is needed, but this at least is a reasonable start.
pump shoe2.jpg
Next step is to mark the outer hull before I get too carried away building the powertrain cassette.
hull1.jpg
hull2.jpg
Then back inside to build the water inlet.
cass0.jpg
Clamping the pump shoe is still tricky. There aren't any strong parallel surfaces for it to be held properly in the bench vise. So I had to improvise, using ancient woodworking technology: the holdfast. With no moving parts, these clamps were designed centuries ago. With it held securely, I was able to use the carbide burr on the die grinder to trim it. Then a vixen file to (hand!) finish the edges.
cass1.jpg

86tuning
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Yamaha 784cc into welded mod-v hull

Post by 86tuning »

So I'm building a flat ride plate under the pump shoe, not the original vee plate from the jet ski. The ski hull is deep-V of about 18deg and my hull is 10deg. A flat ride plate is the simple solution. Many modern jet skis and boats have a flat ride plate. I used a piece of 1/4" plate for this and managed to overheat it and warp it.
cass2.jpg
As you can see, the ride plate has tipped down 5 deg or so due to warping of the assembly after overheating it.
cass3.jpg
Lucky for me, when I cut out the ride plate, the cassette went SPROING and sprung back to flat. So I made another one, and was careful to not overheat it this time. MIG welds look terrible before wire brushing :o
cass4.jpg
Next up, the pump mounting plate needs to be mocked up and cut out of 1/4 plate. During final assembly, when the 1/8" transom is added, the mounting plate will be 3/8" thick and should be plenty strong. More cardboard, because cardboard is easier to cut than metal.
cass5.jpg
Ancient sabre saw with a dull blade. Sourcing supplies is a bit problematic at this time, it would be at least 1/2 hour line up to get into any stores to buy blades. So, just muck around with what I got. Also, I'll be running a bead around the cutout so smoothness isn't a high priority. Plus, I can always clean it up a bit with the die grinder if required.
cass6.jpg
cass7.jpg
All these pieces are awkward to clamp, so temporary assembly and tacking makes more sense. Tack welds are easily cut out to disassemble before final welding all the inside pieces.
cass7a.jpg
cass8.jpg
And now the tricky portion that I was actually stalled at. How to make the curved portion symmetrical? It's hard enough to make out of cardboard and mark up, how the heck can I make this out of metal? Yeah 1/8" stock can be bent by hand but I want 1/4" plate for rigidity and strength. And to deal with future pebbles.
cass9.jpg
cass9b.jpg
Last edited by 86tuning on 22 Apr 2020, 16:38, edited 1 time in total.

86tuning
Posts: 78
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Yamaha 784cc into welded mod-v hull

Post by 86tuning »

Doesn't look terribly complex when mocked up in cardboard.
curve1.jpg
Now to cut out a couple pieces in 1/4 plate
curve2.jpg
To bend it, I considered scoring the outside several times, making a shallow groove and then forming it by hand. Then welding up the grooves for rigidity and strength. In the end, I figured out how to make a press brake using a 2" piece of round stock at the top, and a piece of angle iron for the bottom.
curve3.jpg
One side at a time, running back and forth between the hydraulic press and the inlet jig.
curve4.jpg
Then make the other side, and fit it all together. The interior shape and dimensions of my water inlet closely mimics the shape of the original plastic water inlet from the waverunner hull. I figure, if the engineers spent time to design it, and it works, why re-invent it? Yes, I do realize they had design constraints as well. The plastic hull needed to be easily formed in a mold, and that's why the pump shoe bolts in. But I assume that the overall shape of the water inlet must be optimized for performance already.
curve5.jpg
curve6.jpg
And that's what I've been doing for the past while.

Next, the upper inlet plates, and then disassembling the entire unit to weld the interior pieces and make this into one piece of aluminum. Welding the cast portion is not going to be fun at all. I will be welding, then grinding out the contaminated weld, and re-welding a few times to fuse it properly. Then grinding and shaping it again.

Once it's together, I'll be bolting up the jet mounting plate, then mounting the jet, making the hole for the impeller shaft, the shaft bearing coupler thing, then shortening the impeller shaft and re-splining it, so I can get the engine closer to the transom. Then building motor mounts.... so much more work to do. But at least the tricky part of the water inlet is almost done.

One day I might be able to float test this thing....

CedarRiverScooter
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Yamaha 784cc into welded mod-v hull

Post by CedarRiverScooter »

Nice craftsmanship! I esp. like the forming technique.

86tuning
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Yamaha 784cc into welded mod-v hull

Post by 86tuning »

Thanks Cedar, it took a lot of overthinking to figure out how to form the 1/4" plate. I burned a lot of brain cells working it out. Then finally decided that I just had to "measure once, cut 10x" and try. And it came to me the next evening.

Next step is to mount the pump unit and figure out where to put the coupler. I temporarily hung the mounting plate in place, and marked the thru holes.
pump1a.jpg
Make holes in plate for thru fasteners and fittings. Then secure the mounting plate.
pump1c.jpg
pump1b.jpg
There's a lip on the mounting plate due to the previous location, where the plate mounts under the u-shaped water inlet in the ski hull. Since mine is now mounting through the transom, I need to remove the lip to sit the mounting plate flush with the transom.
pump2.jpg
pump3.jpg
Then re-install the mounting plate. Next, I have to reassemble the pump so I can poke the impeller shaft forwards to see where it sits and where to put the coupler. So I dig through a bin I haven't looked into for about a year.
pump4.jpg
What is this black ring? where does it go? Dunno, will have to look in the service manual and exploded diagram to see where it goes....someday soon.

I manage to partially assemble the housings and slide the shaft forwards for a look. And a pic or two.
pump5.jpg
pump6.jpg
The location of the coupler dictates where the engine can sit. I would like to put the engine further back to maximize cockpit space in the boat. I can live with a smaller rear casting deck and less covered storage if I can have more room for driving and seating and moving around the boat.

I put the original plastic pump housing and stuff next to my metal one to figure out where I can put the coupler. And how much to shorten the impeller shaft. Also, will need to phone around to a few machine shops to see who can cut the splines, because my machinist buddy isn't set up to do splines.
pump7.jpg
pump8.jpg
pump9.jpg
pump9b.jpg
Looks like I can move the engine back exactly 6" so I'll need to either buy a 24" shaft, or have this one shortened from 30" to 24"

This week I need to weld the pump shoe and the pump housing together, and find a machine shop to modify the impeller shaft. Then I get to start the engine mounts.

Cheers,

Brian

CedarRiverScooter
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Yamaha 784cc into welded mod-v hull

Post by CedarRiverScooter »

Looks like you will be getting lots of welding practice!

What will you use for the shaft thru-hull fitting ( AKA 'log' for an inboard)?

One thing that haunted my boat is not getting the pump angle right. If you have power trim, ten it should be no problem.

I just got a pump wedge for mine, I was getting porpoising at anything over 30 MPH.

86tuning
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Yamaha 784cc into welded mod-v hull

Post by 86tuning »

CedarRiverScooter wrote:
27 Apr 2020, 09:10
What will you use for the shaft thru-hull fitting ( AKA 'log' for an inboard)?

One thing that haunted my boat is not getting the pump angle right. If you have power trim, then it should be no problem.
The stock impeller coupler has a bearing and seal. No different than what's done with the ski hull. Only difference is that I'm integrating the pump shoe into the hull instead of the bolt-in style on the ski.

The pump does have trim, and I am concerned with efficiency, but there are too many variables to consider for drivetrain angle. So I'm running 'stock' 2 deg down for the pump. I hope it works. Also, planning on putting the fuel tank in the nose so it can be on centerline. Plan B is to put it inside the centre console, but that makes the console a lot bigger than I want.

The bottleneck is to find a machine shop to cut small splines. Everything is dependent on it. Coupler position, engine position, yada yada.

Cheers,

Brian

eeshaw
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Yamaha 784cc into welded mod-v hull

Post by eeshaw »

Another option other than machining splines would be to cut the six inches out of the shaft and have a sleeve slipped over the cut and secured in place. I've pinned axles like this. You can weld the sleeve or pin them in place, but if you pin it use tapered pins and peen the end so it can't back out.

CedarRiverScooter
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Yamaha 784cc into welded mod-v hull

Post by CedarRiverScooter »

+1 on cut & splice. I would just add that heat shrinking the sleeve on would add some strength. A woodruff key is pretty easy to machine in too.

Probably not germain to a jet ski shaft, but years ago we cut down a Ford 9" differential for use in a sports car (Sunbeam Tiger). The half shafts were cut & resplined. Bad advice from someone, said to use them as-is without heat treat. After about a year I had them out for some reason & clearly they were twisting. I had to pay thru the nose to have them induction hardened. But at least that worked.

86tuning
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Yamaha 784cc into welded mod-v hull

Post by 86tuning »

Haven't done much recently. Have called all the local machine shops to find out who can cut small splines. The machine shops I regularly deal with don't cut gears and splines. The two closest gear shops don't do small stuff. They're all referring me to other shops. MiniJet Inc can cut it, but I would need to ship the shaft to the other end of the country and back again. Would rather spend local if I can. Monday I'll drive around to a few gear shops to see if they can do the job. I'll know in a few days.

I'd rather not cut and weld the shaft, since MiniJet can shorten and respline it, I should be able to get that done locally. MiniJet's website charges cad$200 to shorten and respline the shaft, and there is no mentioning of hardening, etc. I figure I'll just bring the shaft and coupler so they can make sure it all fits back together properly.
shaft1.jpg
These are the smallest drills in the set. 5/64" on the left, 1/16" on the right. Shaft diameter is 20mm so a hair over 3/4"

I have to remember to mark the outer hull for the grate and the ride plate before I weld the whole thing together. Marking it now will be a lot easier. I should probably cut out the water inlet in the main hull as well.

Next, I'll be finishing up the water inlet at the same time. Lots of welding and reinforcement to the pump shoe area. Also need to mount the coupler section, after I reassemble the pump.
inlet.jpg
Cheers,

Brian
Last edited by 86tuning on 05 May 2020, 21:00, edited 1 time in total.

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