Full Suspension Big Block Mini-Buggy Build

SquidBonez

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Got the steering together!
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I used a 22" 5/8" go kart steering kit off of Amazon. The steering supports are made from 3/4" ID 1" OD round tubing. The bushings are 5/8" ID 3/4" OD bronze flange bearings I found at Ace Hardware and they work great. I plan on using this same tubing and these same bearings on the pivots of my front A-arms. Also of note is that the entire steering system is removable in the event anything needs to be serviced/replaced.
 

SquidBonez

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Quick update, just got my NEW Predator 420 hemi out of the box aaaaaand...
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That being said, I just ordered a Duromax 440. I'm not buying a third 420.
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On a brighter note, here is a quick mock-up of what the tires look like in comparison to the size of the frame. The fronts will be farther forward for sure, this is just to give a rough idea.
 

madprofessor

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Wonder if the people involved in the shipping of that 420 can spell goofy as easily as they can demonstrate it. That would be a hefty drop of the box to snap that corner off, was there any apparent damage to the box, like wrinkled cardboard?
BTW: Big fan of the use of locking collars and bolts to make the steering completely removeable.
 

SquidBonez

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The new Duromax 440cc just came in! Also picked up some Champion rockers (same ratio as stock I believe, just a lot tougher) and some chromoly pushrods to match. I want this engine to be super strong. According to dyno sheets I've been seeing, I'm looking at somewhere around 20 - 23 horsepower and 35+ ft-lbs of torque once this engine is built. Aiming for 5,500 to 6,000 RPM, but no more than 6,500 RPM since I will be keeping the balance shaft in it (they are apparently safe up to about 6,000 RPM, pushing them into 7,000 is a gamble). Stock cam will be staying in it since I'm using a 40 series which is only rated for 18 horsepower. People push them far past that number by using kevlar belts (which I have two of) but again, I want this whole setup to be reliable.

My one gripe with the Duromax 440 is that I doubt the stock horsepower rating. A Predator 420 is rated at 13 horsepower and has been reliably confirmed to be around 13 stock. How are they finding another 5 horsepower out of only 20ccs? A Predator 79cc is 3 horsepower. Regardless of the questionable horsepower rating, I'll happily take that extra 20cc.
 
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SquidBonez

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Got the billet flywheel installed! This is probably the only stock engine you'll ever see with a billet flywheel lol
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The engine is noticeably more difficult to start due to the lightweight flywheel but I still got it running pretty easily. Once it's hard-mounted on the frame it should be much easier.
 

SquidBonez

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Got more work done on the engine. I took the head off to install heavy duty valve springs (50lbs). A bit tricky to get the retainers to sit right but thanks to a valve spring compressor tool it was way easier than doing it by hand. One concern I did have was that I noticed either oil or gas sitting on top of the piston. Is this normal? I did run the engine to break it in, mind you. Also keep in mind I'm using Royal Purple 10w30 so I'm convinced it's gas as the oil is quite literally purple.
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After getting the head together I installed a thinner MLS head gasket rather than the stock fiber replacement to get a boost in compression/power. I hope this doesn't make the engine much harder to pull over - or rip the cord out of my hand like the Predator 420 did.
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Next was the throttle linkage. I replaced one of the springs with a piece of coat hanger to get a more immediate and snappy throttle response. It works great and fit perfectly. The throttle always returns to idle as well.
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One quick thing to note is that Duromax engines do NOT come with the clamp/barrel nut for mounting a throttle cable. Luckily I had some left over from my 420. I also put a nut on the throttle stop screw since I had to turn it in more than the spring would allow. I just did this to keep the piece of coat hanger from flexing if you pull on the throttle too hard.
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Last but not least I removed the electric start and blocked off the starter motor hole with a block off plate from NRRacing. It looks great!
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Now I have to wait for my new pushrods to come in (I need longer than stock since I'm using Champion shaft rockers). After that I'm going to test run the engine again to make sure everything works as it should and then remove the governor and put in the billet connecting rod. Once that is done the motor is complete.
 

SquidBonez

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How big of a cam do you have to need that much pressure?
It's the stock cam. And I have 50 pound springs because that's the lowest most parts stores sell. They sell 50 pound single valve springs and 65 pound double valve springs. I know Vegas Carts has 35 pound springs for sale but only the 50s and up fit the hemi head on my 420, which is where I'm reusing these springs from. No point in buying another set when these are brand new.
 

SquidBonez

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Got the next part of the engine build completed - the head. I had to wait for my longer pushrods to come in because the champion rockers - despite being stock ratio - require longer pushrods. First try on starting the engine was a dud. It didn't really want to start and would occasionally pull the rope out of my hand (not as hard as the 420, mind you). So I re-did my valve lash and now it starts much easier.

Only one problem - it will idle just fine but when I press the throttle lever on the engine it stalls out. Just out of curiosity I tried pulling the throttle open on the carb itself (little black piece), and it revved up just fine. I think it may be the governor to blame since I replaced the one spring on the governor arm with a solid piece of coat hanger. The governor operates through tension on said spring I'm pretty sure. Plus it sounds like it's revving higher than 3600 RPM, which is when it's supposed to kick in. We'll see if the issue is resolved after I remove the governor. I also have to change the ignition coil because the one that comes with the Duromax doesn't fit my aftermarket spark plug. Just going to use one off of a Predator 420.
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Even with the governor still in it it sounds mean! It was shooting flames from the exhaust when I let off the throttle.
 

madprofessor

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It was shooting flames from the exhaust when I let off the throttle.
Yeah well, nothing new there, but multiple choice, and possible multiple causes. Running too rich may get some unburned fuel into the exhaust because it didn't ignite after the butterfly suddenly closed off the airflow, but ignited in the hot header pipe.
My guess though, you didn't advance the timing on that motor yet. You can get some sho nuff unburned fuel all the way to the exhaust like that if it's already running a little rich.
I think it may be the governor to blame
...............only if the idle screw is set so low that a piece of linkage pushing it all the way back starves it to a stop. If that were the case then it should starve to a stop at idle in the first place.
 

SquidBonez

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Yeah well, nothing new there, but multiple choice, and possible multiple causes. Running too rich may get some unburned fuel into the exhaust because it didn't ignite after the butterfly suddenly closed off the airflow, but ignited in the hot header pipe.
My guess though, you didn't advance the timing on that motor yet. You can get some sho nuff unburned fuel all the way to the exhaust like that if it's already running a little rich.

...............only if the idle screw is set so low that a piece of linkage pushing it all the way back starves it to a stop. If that were the case then it should starve to a stop at idle in the first place.
Timing is stock because the cam is stock. Plus I heard big blocks have a tendency to shear offset keys. Idle screw is set in the stock position and it idles just fine so I think it has to be the governor, especially when it will rev out when I open the carb butterfly itself rather than just moving the linkage.
 

SquidBonez

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The engine is now fully built and running! The best part? It doesn't try and rip my arm off like the Predator 420 did. Just a note to anyone building a 440 or any big block for that matter - if you add a billet rod you will most likely have to do some internal clearancing to get it to fit. There is a little ridge on the back of the block that the connecting rod bolts will hit if you don't ground them down (Duromax engines seem to be pre-notched to fit this but I still ground part of it down just to be sure). You will also need to clearance the counterbalance shaft slightly. I used a sanding disc and took off little by little until it just cleared to avoid weakening the counterbalance too much.
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Another interesting note about Duromax engines is that they seem to come stock with rod bearings. I don't remember seeing any on the Predator. That and paired with a 10 bolt sidecover versus the 8 bolt on the Predator and, of course, the extra displacement, these 440s seem like better engines than the 420s for exactly the same price.
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One issue is that the engine still does not rev off of idle. It just dies anytime you try to rev it up, but I believe it's because I might have installed the emulsion tube in the carb upside down. I'll have to check tomorrow and go from there.
 

SquidBonez

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Had a pretty productive day today. First off, I got the engine running much better. It will now fully rev up. The issue was not the emulsion tube. Turns out the 0.42 jet was way too lean, so I drilled out the stock jet with a 1/16" bit and it worked perfectly. Max RPM I recorded was 5280 but it has more in it, I just didn't want to rev it too high without a load on the engine.
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I also got the floor pan/brush guard made. I used 1/8" thick ABS plastic sheets. It's very light, durable, and easy to work with. I'm going to cover the top side of the floor with skateboard grip tape to provide extra grip on the floor so my feet won't slide around.
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I also drilled out my spindles/pitman arm to take a 1/2" bolt for extra strength. My one concern is that now the hole in the pitman arm is too big and it will crack (which would be very dangerous at speed), so I'm going to weld around the outside of the arm to add more material and grind it smooth.
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Finally I began making the steering linkages that will be put in place to reduce bump steer. The larger holes will be the pivot holes and have a bronze flange bushing to prevent wear. The smaller holes are where the tie rods will connect. I drilled two holes so I can adjust steering angle/effort if need be. I still need to round out the edges, but they are mostly done. The dots on the outside of the larger hole are just there to remind me which one is the left/right one after I paint it (dot faces out from the buggy).
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All in all this project is going pretty well. It's far from perfect in terms of absolute precision but this is my very first ground-up project and I'm building it with basic tools. I'm kind of using KGN Metal's buggies (search them on YouTube) as inspiration. They look rough but are very functional. Anything that breaks can be fixed fairly easily. Function over form is the name of the game here.
 

Denny

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Do me a favor please, don’t use ABS plastic for your floorboards. A stick could go through that and spear you quicker than you can react. I know on my karts the steel floor pans have saved me. I always had a ton of dents pointing from the bottom up. Knowing what I know I would be leery even using aluminum under 1/8” thick.
 

SquidBonez

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Do me a favor please, don’t use ABS plastic for your floorboards. A stick could go through that and spear you quicker than you can react. I know on my karts the steel floor pans have saved me. I always had a ton of dents pointing from the bottom up. Knowing what I know I would be leery even using aluminum under 1/8” thick.
Well the good thing is since the floorpan bolts in I can replace it with any material I want. I could always change to steel in the future. I just used ABS because some sprint/dirt track guys use it. They use 1/16" thick, and since mine is going to be off road I went with double that.
 

SquidBonez

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Got the floor pan covered with grip tape and installed. Feels much better now and it's pretty rigid. Super light as well! Also have the pedals on it just to check for clearance. If I ever need to reinforce the floor to protect from sticks as Denny suggested, I can cut an additional metal skid plate to put under the plastic one.
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SquidBonez

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Had to re-make the pitman arm. As I mentioned before I was going to try welding on the outside of the pitman arm to add material and strengthen it. Unfortunately I blew right through it when I tried welding it. So I cut the old pitman arm off and made a new one out of 1/4" flat iron. Not as pretty but way stronger.
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The more I work on this thing the more imperfections I notice. Mostly small things like something being an 1/4" off from center or slightly crooked. While this bugs my OCD I am mostly concerned with strength and functionality. I'm sure it will look much better once it's fully constructed and has tires.
 

madprofessor

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That steering setup deserves that 1/4" iron for the pitman arm, as it's the best arrangement I've seen to date. To repeat myself................I'm a big fan of the removeable components config, and of using double-split collars to facilitate that.
 
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