2003 Argo 6x6 Bigfoot - Repower for work rig

[AZSkibo]

Hey all! Posted an intro but figured best to drop a new build thread here. I’m an aquatic biologist in western Montana (I work all over the PNW) and has been looking for used Argos when this one popped up on the Craigslist outside of Denver last spring (2020).



So a friend of mine grabs it for me for the tidy sum of $3500 and said it looked “kinda clean”. Closer inspection on arrival up here showed this one was likely a very low hours recreational buy that likely saw little to no use in the 17 years prior to me. The wiring had been toyed with at some point so I opted to retire the whole deal to my specifications and intended use as an aquatic herbicide application rig. Understand I don’t mean in swampy or marshy areas (though I see those too); rather, I am frequently on multi-thousand acre properties with multiple water bodies (lakes, ponds, rivers) and the amphibious capabilities of the Argo platform make running from site to site and in and out of the water a breeze. My buddy had an older 8x8 and recently traded up for a 19’ Conquest 6x6 as they 8x8 platform was a little large for his tastes.

So, other than cleaning the frame and chains, regreasing all the bearings, and a total rewrite from stem to stern, I didn’t do a whole lot to her last season. Lol. The pump setup is all controlled via the temporary dash setup. I’m installing a final version when the motor work is complete. On that end, I’ve pulled the worn out 18HP Vanguard and will be rebuilding it for use in a railroad go kart Repower project that is planned for the next time I have a few minutes to kill.








Got the old 18HP out...



Noted that I still need to reposition the bilge pump. I upgraded from the stock (broken anyway) to a 500gph. It’s a simple swap other then getting at the bulkhead fitting in the hull.

Ordered a new motor based on a LOT of surfing the threads here as a visitor...



This Briggs & Stratton Vanguard 31hp came from www.smallenginewarehouse.com with the muffler (more on that later) and the canister air filter (more on that later). It also came with the stub shaft (top secret), beefed up stator, and whatever. Oh! It’s a 1 1/8” 4” shaft. Which, who gives a **** because the footprint requires me to make an adapter plate.






So it’s off to the metal shop on the ‘Morrow to source a piece of 6 1/2” x 11 1/2” x >1/8” plate steel. Thought process: As I won’t be using the old fan ducting, I have more than enough room to offset mount the bigger motor to keep the clutches aligned. Open to suggestions but I’ll likely just go with the 6X6Parts offerings for both driver and driven, along with a new belt. Oh, and a caliper rebuild of course. I’ll likely go ahead and do the winch mount (rescue line) now as well since it’ll be a much bigger pain in the ass once the big block is mounted. I’ll keep you posted if you care.

[dirtdobber]

Welcome and congrats on your 6x6. This is an interesting build you have going. Be careful in the water with all the extras you have, particularly a full chemical tank. Don't get overloaded or top heavy.

I'm curious about your chemical application setup. That looks like way too much pump for the two spray nozzles on the back of the machine, or the spray wand. What's the rest of the story?

[AZSkibo]

Haha! Yep. BUT, it’s the smallest pump I could get with electric start. Benefit is I can charge my handgun reel to 150psi without problem and the bypass regulator keeps everything in check. I usually just apply out of flood nozzles from the rear.
You can get all different sizes, so I just dial in my application rate as needed between pump pressure and nozzle selection. Pretty standard stuff. Pump generally runs at idle so wear is near zero. I can fill the tank (30 gal, sits between the frame rails) in about 30 seconds. With bypass regulator set and nozzle discharge at 30psi, it takes me about 3 minutes to drain it. I mounted the tank down as low as possible to get as much weight as possible at or below the water line. I still need to be able to clean it out as needed, so a true in bottom of frame setup won’t work here. The added weight of the bigger motor should even everything out nicely. As was (?), it was fairly stable in the water with the 18HP motor.

[trevorakm1]

interested to see this motor installed. I have an 01 bigfoot. I replaced the 18 hp motor with the B&S 23 horse motor. Easy bolt up and go. I just barely fits under the hood height wise. I'm glad Idid it. here's what I noticed trail riding: it didn't go any faster and I realize it's a transmission issue. The more noticable issue is fuel consumption. The 23hp drinks more, not drastic but noticable. I wonder how much the 31 would guzzle. something to consider if going out into nowhere.

keep us updated, love to hear a driving report and pics of the final install.

[AZSkibo]

In case you wondered just WTF a rail kart was; it’s this.



Currently pedal powered on a direct drive axle with coaster sprockets and with no brakes! I’m going to use my old 18HP vanguard after a rebuild. Likely a simple direct drive chain clutch. Should be capable of going way faster than is reasonably safe. ��

[AZSkibo]

Just a quick update. Between shoveling snow and keeping the cabin warm, spare time has been at a minimum (skiing has been great though!). Got the exhaust system mostly done up. Using the factory muffler as a template, I liked the idea of retaining the factory muffler support for the header pipes to provide better support and less stress to the exhaust bolts in the cylinder heads. Years of experience with steel bolts in aluminum heads made this an easy decision. So the old muffler was cut aaay from the support and new 1 1/2” DOM exhaust tubing was welded up by my local fab shop (no welder at home) based on my sketches. In short, it occupies essentially the same space as the previous muffler with the exit flange face at approximately 10” away from the cylinder head. I still need to final sand the surface, VHT coat and bake the pipes, and then wrap the tubing with insulating fiber tape (header wrap in the auto world) and secure with 18g mechanics wire. I’ll run a piece of 2” flex out the body to the external muffler. My hope is to get as much heat out of the engine bay as possible; and as much fresh air IN as I can. More on that to come.

[trevorakm1]

I was able to still use a bigfoot hood so that was good. I had fabricated a vent/ scoop that I could open and close based on weather conditions temperature wise. It provides more outside air into the engine compartment. I did it to help the previous motor but wasn't enough. I then fabricated a bracket to mount on the screen where the muffler exits the body that held a couple of computer exhaust fans to draw the heat out and awaqy from the exhaust pipe and muffler. This remedy helped a lot but the fans eventually died, not made for this much heat. I just reeently replaced them with atv radiator cooling fans. Same size as previous but stronger and made for this type of application. They work great aren't loud and move air. I set up the original fans with a 3 position switch, off on, on. first on is for the exhaust fans I installed and the second on then adds the brake fan. This allows me to if at idle to draw out engine heat and puts a lower load on the battery if rpms aren't high enough to charge battery. When ready to travel I then add the brake fan. It all works great and in the hottest months I never have to run without the hood, especially in the water where high rpm/ heat and slow foward movement limiting engine scoop vent air flow.
How is the height of this motor? will it require a new fabricated hood?

[AZSkibo]

Great ideas! Height may possibly be ok for the stock hood but I won’t know until later this week when I get the motor mounted. I had assumed it wouldn’t fit and planned either to modify my hood or to go to one of the aftermarket units that seem to have a little greater vertical clearance. I’m going to run the new air cleaner mounted on the hood surface to reduce intake air temperatures. I’m not convinced the brake fan setup actually does anything useful and it’s in my way with the bigger motor, so the plan is to utilize the existing brake cooling screen as an intake for an electric radiator fan (ATV/UTV size) to pull air in to the engine bay. I’m still toying with the idea of an external oil cooler that will submerge when swimming to allow even greater heat exchange, but I’m not sure I want to go that far just yet. I’m already going to run a remote filter setup on the Vanguard for slightly greater capacity as well as cleaner oil changes.

Noted that my transmission is an HU unit so I should be able to utilize a little of the extra HP from the new motor while driving. I wasn’t aware the Bigfoot could be had with anything other than the low range transmission, and as I won’t be running tracks I don’t need the bottom end anyway. Still thinking about what tires to run; missed out on a set of NOS runamucks last season. If I can find some this year at decent price, I’ll make the switch then.

[Canadian.Trucker]

Very nice! I’m super jealous of the 31hp. My ‘03 conquest has the 20hp and I feel she’s a little tired.

[AZSkibo]

I had to go and make mine all complicated with a rewire and the addition of my sprayer system in the back. So far other than getting alignment correct, the upgrade isn’t really that hard so far. My clutches arrive from Roy at Quality Drive on Tuesday so I’m hopeful to have everything bolted down sometime later next week

[AZSkibo]

Quick update before I get her finished up. I took the motor plate out and machines my engine mounting holes to allow for lateral adjustment when setting clutch alignment. You can see these slots in this picture:



You can also see the hood latches mentioned recently in another thread; thanks for the info! Ok, I mentioned earlier about a new hood in the works; well, here it is.









Plenty large to accommodate the increased block height as well as future plans for an AMR500 supercharger. I also mounted the air filter onto the Argo body. It sits just behind the muffler tunnel and routes underneath the bodywork directly to the intake. With the header pipe now glass fiber wrapped, heat shouldn’t be nearly as much of a concern even with the significantly larger motor. I also took the opportunity to install the winch mount kit from Richard’s 6x6 which was super easy to do. Now I’ll have a rescue line available should I need one. With this Argo being used for pond/lake work, that’ll be kind of nice insurance to have in hand. Plus it looks cool.

Next up in the “details nobody will ever notice” department is a revised cooling duct setup. I can’t use the stock blower setup due to the larger engine so I set about revising it to fit the new setup. My plan is to use twin 3” inline bilge blowers. I’ll set these to run manually on the dash and they should be adequate to draw cooling air into the engine bay. The hood design should also help this too I hope. My replacement piece has two 3” stubs for attaching the heat resistant silicone scouting I’ll be using.



Factory screen fits inside...



And mounted up is almost invisible. I’d paint it but I don’t care that much. Plus it looks cool.



Here’s a shot of the motor, now bolted down and the clutches from Quality Drive Systems are now mounted.



Clearance is great all the way around. Tightest point is between the engine cylinder head and the brake caliper mount, but there’s enough clearance that everything is totally happy as is with no further modifications needed. I did remove some spare brackets from the motor and I will be mounting the vacuum operated fuel pump on the motor cover sometime. If I can figure out the wiring harness color code, I should be able to get her started in the very near future.

[AZSkibo]

https://youtu.be/AqU1juJ10wM

[AZSkibo]

https://youtube.com/shorts/y73crWtIMR0

[trevorakm1]

waiting for the driving videos. sounds good. who fabricated the hood and the exhaust plumbing?

[AZSkibo]

Hood was done at Metalworks of Missoula; I hit it with some metal etching primer, some olive drab green paint, and satin clear coat. It’s pretty close to the subfaded Argo green. Manifold was done over at J&K Customs using the stock Vanguard muffler from the new motor as a template. I wanted to retain the support brackets on the original muffler for stability and stress relief on the cylinder heads. I’m going to make an outer support with some expanded metal and a pair of 2” washers. Supertrapp diffuser disc muffler with an extra set of plates should keep her quiet. As much as I like the open header sound, 10 hours of that a day will get old quick. I’m going to redo my dash now that I have the motor setup. Pics of that next.