420 predator

[Dfish1247]

Hey folks, have a yard kart with a 420 and 40 series tq, red springs and heavy weights in the driver, 10/50 gears. Live axle with 13” slicks.
Engine is stock as a 2x4 and runs great, just hits the governor.

Since I’m opening up the case to remove the governor, would I need to replace the connecting rod and flywheel on the other side? Never found a straight answer unless putting 50lb valve springs so valve float stops. Then yes for sure.

If not, I’d just put a header, jet, and air cleaner on and be done.

If the flywheel and rod need swapped regardless, valve springs, cam, and a carburetor. If I go this route, I’d like something that pulls hard from driver engagement(2600rpm allegedly) to around 6000, is that a realistic option?

Thanks in advance.

 

[panchothedog]

with 13" tires and the mods you mentioned that should not be a problem. I have never built a 420 but those numbers are very realistic with the 212 and the 420 makes more than twice the torque. Should be a walk in the park.

 

[madprofessor]

The upgraded rod is a plus even if you don't remove the governor. Warranties are there for a reason, one of which is a piece of the rod's cast metal breaking off or just flat out snapping in half. After that, valve float with the factory valve springs is reasonable as a limit before replacing the flywheel. Now that I see that in print, oops, jinx, it's gonna disintegrate. Get a billet rod for any engine with the governor modified/deleted, and a billet flywheel anytime the valve springs are upgraded.
Why a new carb? You can get bigger jets for the factory carb dirt dang cheap, huge performance for the money. Just absolutely must get tons of free-flowing intake and exhaust to use it.
Choose a cam carefully, talk to the dealer first. You don't need a cam milled for low/mid torque power, you have that already with a 420cc. Especially with those little 13" tires.

 

[Dfish1247]

Well, the governor is going away. Might as well just put a rod, flywheel, and springs. Flywheel and valve springs aren’t hard to change from what I’ve seen. Looks like one of the Briggs flathead spring compressors will squish the springs enough to pop the locks out.

Connecting rod, I’d like to try dropping the piston down as far as possible in the cylinder and changing the rod that way vs pulling the head. Reason being is the crank needs to come out to break that shelf thingy away and clean the aftermath out so the rod bolts don’t hit. With the crank out, I may have enough room to pop the retaining clip out with the piston coming out. If I can’t do that, I’ll pull the head and pop a new gasket in.

I was thinking around the 275 cam size, but I’ll ask for sure to see how it would work.

 

[panchothedog]

Having never been inside a 420 I guess I really don't know, BUT changing the rod without removing the piston from the block sounds like it could be difficult.
Other than the price of a new gasket pulling the head isn't that difficult. Also if you are going to be cutting something out of the block (that shelf thingy ) there are going to be aluminum shavings to be washed out. Trying to do that with a oily piston sitting in the bore and making sure none of them into the cylinder sounds VERY risky. Good Luck.

 

[Denny]

How will you know if you want to put a longer rod in if you don’t pull the head?

 

[madprofessor]

I personally would absolutely pull the head off if for no other reason than to put it back on with a thinner (hopefully stainless lip) head gasket for higher compression. With thinner head gasket, over-length rod, ratio rockers, different valves or pushrods, different cam, any combo of things, it's always a good plan to do a squish test with Play-Doh or similar to verify valve-to-piston clearance.
That means................pull the head off, apply squishy, R&R, check clearance. See why a stainless gasket is good? Repeated on/off.

 

[Dfish1247]

Why a longer rod? is it to push the piston more towards zero deck or to help lower piston speed? Usually longer rod means a new piston to match due to compression height, bad bad news if you get it wrong.

Was hoping to keep with regular or maybe mid grade gas, hence no mention of a thinner head gasket, or advance timing key.

Im after what most would consider the basic intake/cam/carb/header deal on a car. It runs better, makes more oomph, but it’s not a temperamental pain to drive. Hope I worded that correctly.

 

[Denny]

Getting the piston closer to 0 deck will increase compression slightly. Decreasing quench area will aid in mixture mixing in the combustion chamber. Slightly reducing fuel octane needed while quickening the burn rate. All of these things combined increase the efficiency of the engine. You have to learn for everything you do there is a consequence weather it is a good one or a bad one is up to you. For each and every action there is a reaction!

 

[madprofessor]

For each and every action there is a reaction!

Oh, how I wish my ex-wives could be so easily reminded of that! Dfish, watch the first 8 minutes of this linked video to see all of that stuff explained....................honda gx390 build part 1 ...using clay to check valve clearances - YouTube

 

[Dfish1247]

Thanks guys.

I watched the video, glad to see the same stuff applies here as the v8s. I ordered a rod, flywheel, valve springs, stage 1 kit, carb adapter piece for the air filter horn, side cover gasket, and a couple advance keys 4-8 degrees, and .018 head gasket. I’ll see how this does before trying a cam, this may be enough to scratch the itch. I’ll see what works with 93 octane on timing.

Ive watched a couple videos on assembly, is there any reason I couldn’t reuse the governor arm to fill the hole? It has a ball on it before it bends, I figured just cut it of under the ball and that’ll keep it from coming out the top, and the clip on top keeps it from falling in. And, why couldn’t I just weld the hole in the stud where the low oil sensor wire comes through? I’m failing to see a real reason to tap and loctite, and all that mess to fill a hole. Granted, not everyone has a welder, so you do what you have to.

 

[panchothedog]

For the governor arm I have on 5 builds used a 1/4 x 28 bolt, grade 8 or stainless ( something hard ) and just let it cut its own thread. Diameter is close enough, no tap, no shavings and no problem. Have never had one come loose.
For oil sensor I have always tapped hole, 7/16 x 20 of I remember correctly. I don't have the equipment or experience to weld the hole shut. I guess if that
seems easier for you it would work. It does create shavings to tap the block
but it is empty so clean up is easy, besides you are already going to have shavings from cutting out that shelf thingy you mentioned earlier. I was told by the shop that mills and ports my heads that the aluminum used in these engines is extremely soft. You might want to consider that. Does it take longer or add more heat to weld up a larger hole as compared to a smaller one. I really don't know, just throwing it out there.

 

[madprofessor]

is there any reason I couldn’t reuse the governor arm to fill the hole?

Not going to dampen anyone's spirit of discovery here. Just relating that my first effort at leaving the governor shaft in place and counting on that clip to keep it out of the block FAILED MISERABLY! It slipped into the block later, got hit by the crankshaft counterweight, and jammed the engine tight. Get every governor part and appurtenance out of that block.

 

[Dfish1247]

I am asking about the bolt itself that the oil sensors wire goes through. Weld the open end shut on the bolt itself, then reinstall with the nut to hold it in place. I see where you’re coming from, if I’m going to have shrapnel to remove from the shelf removal, what’s some metal shavings.

I do understand why people put bolts in however, it’s the second most secure plug there is, welding being first. Only reason I thought of chopping and leaving the upper end of the arm is cotter pins are used to hold the castle nut in place on the front disc/drum of 2wd trucks and cars on the spindle. Being that’s on the unsprung side of the suspension, it sees all the shock of the road plus the castle nut fighting the cotter pin to loosen. Those last near forever, usually the vehicle rusts away before that cotter pin needs replaced.

 

[Denny]

The wheel spinning down the road on a car or truck is not trying to remove the wheel bearing nuts. If you notice the washer between the bearing and nut in the center is a key. The key fits in the key way and blocks the washer from spinning. The cotterpin is a safety measure. A backup. And cotterpins should be replaced each and every time they are removed for maintenance.

 

[Dfish1247]

The key blocks the washer, not the nut. That nut isn’t cranked down either, if it is, the bearings get torched. And yes, the pins should be replaced at any bearing repack or change, but they’re usually changed when their bent over and then snap.

Anyway, was just wondering any ill effects of using the chopped arm vs a bolt.

 

[madprofessor]

any ill effects of using the chopped arm vs a bolt.

The main ill effects are felt by OCD people like me. I'd probably wake up at night from nightmares about whether or not that was a good idea.

 

[Denny]

The key blocks the washer, not the nut. That nut isn’t cranked down either, if it is, the bearings get torched. And yes, the pins should be replaced at any bearing repack or change, but they’re usually changed when their bent over and then snap.

Anyway, was just wondering any ill effects of using the chopped arm vs a bolt.

No the key and washer combo blocks the nut from the bearing.

 

[Dfish1247]

The main ill effects are felt by OCD people like me. I'd probably wake up at night from nightmares about whether or not that was a good idea.

I’m there on the ocd. Have head and main studs on an engine that’ll never see 6k rpms. Ain’t coming apart though,lol.

 

[Dfish1247]

Got the engine back together. I put an .018” head gasket in vs the stocker and an 8* key. I cannot pull start this engine, once it’s on compression, the cord won’t hardly budge. I pulled the spark plug and everything turns super easy. Is this normal?