Full Suspension Big Block Mini-Buggy Build

SquidBonez

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Well, after quite a bit of planning and parts hoarding, I've finally begun on my project. What I'm building is (as the title suggests) a full suspension big block mini buggy. I currently have a Predator 420 hemi built for this buggy. Mods include a stage 1 kit, billet rod, billet flywheel, 50lb valve springs, chromoly pushrods, thin head gasket, and governor removal. I plan on keeping the stock cam. I may even upgrade to a Predator 670cc v-twin in the future. Aiming for 50 - 55 mph top speed but mostly focused on torque. I also have a Comet 40 series transmission with red driver springs and medium roller weights for a higher engagement (2600 RPM).

The tubing I'm using is 1/8" wall (11 gauge) 1"x1" square tubing simply because it's easier to work with than round tubing is. I'm using a Chicago 125 Flux welder from Harbor Freight. It has worked well in the past, especially when you get better wire for it. Very easy to use, although the welds usually aren't very pretty and you have to clean the slag/spatter off. That, and this is my first time welding on a project...so that may be part of it.

The suspension will be single a-arm in the front (with adjustable camber) and swingarm in the rear. Simple yet effective - and very light. This buggy will be designed to be easy for a beginner like myself to build and as light/compact as possible to help maneuverability and acceleration. It will be 50" wide at it's widest point, which is the standard width of an ATV trail. Tires will be 20x10-8 in the rear and 16x6.5-8 in the front.

I made a very basic 3D model of what I'm planning the finished product will look like (subject to change of course):
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SquidBonez

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I started with the box where the seat will go. The seat is just a cheap polyurethane bucket seat from Summit Racing. I was originally going to do seat sliders so basically anyone would be able to ride it but in order to save weight/complexity it will just be hard-mounted to the frame through the 6 holes you see in the middle.
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After this I made the front box where my legs will go. I ordered a pedal kit from GoPowerSports and that's where the little brackets at the end are from. Very similar to the old Manco Dingo I had. I still have to connect the front piece to the rear and add supports/gussets. That's what I'll do next.
 

TNThomas

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Nice, very similar design to the Grand Daddy from spider carts. Those little flux welders are great, ive got the Titanium 125 flux, and it has been great! Good luck, im in basically the same boat as you, just doing 2 seats, and the Duromax 440 here. I want to do the 670cc, but I cant justify the price increase. What are your thoughts for shocks?
 

Oldsman

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I want to do something similar. I plan on using the BDX a-arm kit/bulkhead for a Yerfdog. Post updates when you can. Thanks.
 

SquidBonez

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Nice, very similar design to the Grand Daddy from spider carts. Those little flux welders are great, ive got the Titanium 125 flux, and it has been great! Good luck, im in basically the same boat as you, just doing 2 seats, and the Duromax 440 here. I want to do the 670cc, but I cant justify the price increase. What are your thoughts for shocks?
For now I'm using 12" general go kart shocks. May upgrade to the nitrogen shocks with the remote reservoirs in the future.
 

SquidBonez

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Finally got some time to work on this project again. After realizing my engine block had a crack in the cam journal essentially rendering the whole block useless, I decided to go back to working on the frame. Today I added some side supports between the seat box and the main frame to strengthen it. Also prevents the seat box from getting hung up on any sticks or stumps in the event of an accident.
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Also of note is that I drilled two more holes in order to move the seat forward in case my girlfriend wants to have a go. She's 5'5" and couldn't reach the pedals with the seat in the original location considering I built this around my 6'1" body.
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However, this does mean I am going to have to rethink the design of the roll cage/shock mounts. I might get rid of the hoop in between the foot guard and the main roll hoop and just have two bars coming down directly from the roof rather than connecting the the leg hoop like in my original models. Something like this (with the exception of the double a-arms):
Screenshot_20210828-190701_Samsung Internet.jpg
I believe this will actually be lighter, easier, and make getting in/out of the buggy more comfortable. As for the top shock mounts, I may run a peice of tubing from the frame and connect it to the cage (like in the model above) or just have 2 bars that are not connected to the cage but instead are just reinforced with 45° cut pieces of tube. The latter will be easier but the former will be stronger. We shall see once we get there.
 

USAMAC

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Your project is very inspiring. I can see the benefits of the focus on it being light weight, but I'm not so sure sacrificing decking is worth it. You might also consider going with carriage bolts on the bottom as well. I'm sure like anyone else, you're going to want to run through the woods with it at some point. It's only a matter of time before you get impaled from the bottom up by stick. I look forward to more updates, how's the motor progressing after finding the 420 was dead?
 

madprofessor

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Here's a couple of pics of a way overbuilt front end shock support "tower" using Monroe MA775 Max-Air air shocks. Before and after pics, first is with homemade upside-down rack and pinion, second is after cutting it all off and using chaindrive with tensioner to lower steering to pitman arm level.
Shock tower remains the same the whole time, no diagonal bracing required besides the little pieces inside of it. Why? Look at the vertical aspect of the shocks when raised up for offroad. They lay out more when lowered for track racing, but the biggest factor remains, they push against each other, which refocuses the energy upwards.
 

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SquidBonez

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Your project is very inspiring. I can see the benefits of the focus on it being light weight, but I'm not so sure sacrificing decking is worth it. You might also consider going with carriage bolts on the bottom as well. I'm sure like anyone else, you're going to want to run through the woods with it at some point. It's only a matter of time before you get impaled from the bottom up by stick. I look forward to more updates, how's the motor progressing after finding the 420 was dead?
The main frame (where my legs will go) will have a floor to protect against sticks, and the seat itself covers my butt so I'm not too concerned about not having a floor on the seat box. Also the foot gaurd will have a piece of sheet metal that will keep sticks from coming in from the front. Funny you mention that, because I got a piece of wood stuck in my thigh right below my butt when I was driving my old Dingo. Driving over a pile of sticks at 40mph seemed like a good idea at the time...

As for the motor, I finally managed to get my hand on a new 420. Seems like there's a huge shortage on engines right now. I'm going to break the engine in first BEFORE modifying it this time.
 

madprofessor

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I'm going to break the engine in first BEFORE modifying it this time.
?????? Not understanding that, Squid. You're going to do initial wear on the crank journal and wrist pin, then replace OEM rod with a billet one?
And is new billet rod going to be overlength than OEM? Using new ring set with the rod? I'd worry about "lipping" the cylinder wall, then pushing past it with the new rod.
What am I missing here? What's the advantage?
 

Denny

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Don’t worry. Start and break in the engine first to make sure it runs all right and jetting is optimized for your current set up. Too many times I see on here people who know nothing about engines modify them out of the box. Then whine for help because it won’t run right, when they don’t know if it ran right out of the box. Heck bolt it on and drive it first and then see if the modifications you made even did any good. They may have less of an effect then hoped for.
 

SquidBonez

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Don’t worry. Start and break in the engine first to make sure it runs all right and jetting is optimized for your current set up. Too many times I see on here people who know nothing about engines modify them out of the box. Then whine for help because it won’t run right, when they don’t know if it ran right out of the box. Heck bolt it on and drive it first and then see if the modifications you made even did any good. They may have less of an effect then hoped for.
That is my plan. The 212 I modified was broken in before any modifications. That engine is still doing just fine on my friend's minibike. I want to make sure the damn thing actually runs before I do anything to it.
?????? Not understanding that, Squid. You're going to do initial wear on the crank journal and wrist pin, then replace OEM rod with a billet one?
And is new billet rod going to be overlength than OEM? Using new ring set with the rod? I'd worry about "lipping" the cylinder wall, then pushing past it with the new rod.
What am I missing here? What's the advantage?
The rod is going to be stock length. The advantage is the peace of mind in knowing the engine works right. And if something goes wrong, I know at which point it started going wrong and what I need to check/undo to get it running right again.
 

SquidBonez

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New update. Today was spent just fixing any mistakes and fabricating parts for the steering system. I have pieces for the steering shaft supports and angle iron that will be used to mount the steering linkages. I also have a foot guard built but not welded on the frame yet.
20210919_142656.jpg
I stripped the paint off of my CVT plate that I got from OMB warehouse (I want to paint it black). I also pressed in some bearings for the jackshaft. This plate is a really nice piece, and works with both 30 series and 40 series pulleys.
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The steering shaft also originally came with two pitman arms welded on, but I'm only going to be using one of them so I cut the extra one off, welded and scores I made in the shaft, and then sanded it down so it was flush. Just wanted to make sure I didn't lose any strength in the shaft.
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I also noticed that when I drilled the extra holes to move the seat forward so my girlfriend could drive it, that the seat would be too far forward to fit the steering shaft supports. So I welded the holes shut and ground them down. Turned out really well, can't even tell that they were there. Unfortunately this means she won't be able to drive, but that just means I get to build something else in the future.
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The last thing I did was mount all 4 tires. Rears are 20x10-8 Carlisle Turf Savers, and the fronts are 16x6.5-8 Carlise Turf Savers. I wanted a tire that would provide decent enough grip but still allow for some sliding.
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I also managed to get my hands on another Predator 420cc hemi. Still has yet to be started; all I did was take it out of the box.
 
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SquidBonez

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You are going to weld that rigid rollcage in the cad drawing to that flat frame, yes? Hope so, or it's going to bend in half like wet cardboard.
Yes it will be welded to the base frame. Honestly this design would be more than ok on a rigid frame kart, perhaps with more gusseting, but the roll cage will be apart of the frame as a whole, sort of like a unibody car.
 

Denny

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You did not make any mistakes. You just made learning opportunities! :thumbsup: You should have left the the 2 pitman arms on the shaft. They tried to build in Ackerman for you.
 

SquidBonez

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You did not make any mistakes. You just made learning opportunities! :thumbsup: You should have left the the 2 pitman arms on the shaft. They tried to build in Ackerman for you.
Luckily the spindles i have seem to have built-in ackerman. Even if its not perfect it's better than nothing. Plus the extra pitman arm was getting in my way. As I build more you'll start to see what I'm talking about lol
 
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