420 engine

Ted Hamilton

Design Drafter / Racer
So, I like the idea of an open 420 torque monster. What's the cost to build a mild open, and what target RPM for survival? I was thinking a "budget open" build, medium aggressive cam, bigger valves and seats, mild port and polish, small flywheel, on gas. I figure 6500 rpm to live? What are the costs for a critter like this? And other than weight, any cons? Pros? GX390 better? I hear the built 305s snap cranks....not my cup of tea. Haven't seen much discussion on industrial open builds. What say you?
 

ECkarter

Member
A well built 342 at weight would be tough to beat. Third bearing on flywheel is recommended. They're as reliable as a race engine can be, until you start throwing stroker cranks into the mix.
 

oldloco

Member
440 with all the rotating assembley has been balanced
 

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What are you going to do with it? Lots of things can be done without too much cost, if you can do the machining yourself or know a friend that can help you. We built 2 mild 390's but, used genuine Honda parts.

I've got videos too!

Brian #89

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Ted Hamilton

Design Drafter / Racer
Why do they need a 3rd bearing on the flywheel side? Seems like a lighter flywheel would be in order if that inertia is twisting/snapping cranks?
 

nobozos

Member
Brian was that you behind the wheel? Par for the course the leader gets taken out and goes to the rear what's wrong with that picture.later Chuck.
 
You can wrap up a LOT of money in a high end industrial build.
I prefer the genuine Honda blocks and cranks for sure.
Just about everything else ends up aftermarket.

They will conservatively make ~30-32CHP. Beyond that they certainly get a bit less reliable.

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Here's one that I recently finished up. I did take a bunch of pictures throughout the build with the intention of putting them all up on our Facebook page, but have just been too busy to get that done yet.

They are torque monsters, as you say. You'll want a jackshaft set up. A 4 disc on the crank won't last long (1, maybe 2 races if you're lucky.) Then it's $100 for friction discs every time you turn around. Move the clutch back tot he jackshaft and you can get away with a 2 or 3 disc clutch that should last the whole season (depending on number of races.)

Because of all the torque, they're not real driver friendly for rookies or on dead slick tracks.
Definitely a fun engine to drive.
We've built quite a few of them over the years but their popularity has waned since the MX stuff got so popular and is considerably more reliable.

-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
32 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 

Ted Hamilton

Design Drafter / Racer
That's a really nice looking engine, Brian!! Do you run a "single side" jackshaft (both pulley and clutch on same side) since the engine PTO is already inboard? Or do you run a belt driver on the flywheel side to the j/s? If you took that flywheel retaining shaft, turned it to 3/4" and milled a small keyway in it, that would be a really slick stub for a 3/4" bore 8mm belt driver...
 
That's a really nice looking engine, Brian!! Do you run a "single side" jackshaft (both pulley and clutch on same side) since the engine PTO is already inboard? Or do you run a belt driver on the flywheel side to the j/s? If you took that flywheel retaining shaft, turned it to 3/4" and milled a small keyway in it, that would be a really slick stub for a 3/4" bore 8mm belt driver...
You can do that on a mild built, but you'll break the crank if the engine's got any testosterone.
I have a 3/4" crank here if you choose to go that route.

The jackshaft is kind of a hodgepodge.
The one on my kart works outboard like a 2 cycle.
The Burris jackshaft & big block mount won't work as it comes on most karts. I just went through this with a 390 customer -- I think he ended up getting a shaft from Kermit to use in his Burris j/s kit. That way he has keyway rather than spline shaft, and keeps both the driven and clutch to the left side.
Nothing drives off the flywheel side. I just had the cover off to change the coil in this picture.
Belt drive can be done with a belt drive conversion on the clutch. The crank is PLENTY long and can be cut shorter if need be - some large seats require it.
I've got another road race customer going with a belt drive clutch on his animal engine.

There is nothing "off the shelf" about this as every kart and engine/clutch combo is different.
I "think" that's why guys will buy "kit" 460 or Vegas engine packages, so they don't have to do all the homework and source all the parts (which can be a real pain, especially with this covid mess.)
 

Ted Hamilton

Design Drafter / Racer
I'd be mounting mine on a Buller j/s, making a custom plate to bolt the engine to. I think I'd go with #40 / 420 gears from the crank to the j/s primary, then run the clutch "inboard" (toward seat) of the j/s gear. Standard #35 to the axle via clutch. You'll have to post some more pics of the finished product...
 

Jim Moore

Member
I have a VC 460 and cant find the engine mount plate to use on my ultramax mount. No luck getting in touch with vegas carts or bullfrog and they used to sell them.
 
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