Build a Kart Racing Engine

This article is a step-by-step guide to help you build a stock class Briggs and Stratton flathead for kart racing.

Steps

  1. Have a clean, dry area to disassemble your engine.
  2. Remove the stock exhaust from your engine. You can get rid of it because you won't be needing it again.
  3. Remove the carburetor from your engine. you will not be able to use this either unless it is the flip-choke type with a screw-on air filter.
  4. If your carburetor is one like mentioned above, keep it. if it is not, find one.
  5. Remove the sheet metal cover from your engine, you will need this later so keep it.
  6. Remove the flywheel from your engine.
  7. Remove the cylinder head from your engine. The gasket might break but don't worry, you will replace it later.
  8. Remove the crankcase from your engine. Make sure you have drained the oil out of your engine first or your clean, dry area won't be so clean and dry anymore.
  9. Check the bolts on the connecting rod. They should have a 3/8" head. if they don't, find the right socket.
  10. Take the rod bolts out and remove the cap from your connecting rod.
  11. Push the connecting rod and piston out of the top of your engine block.
  12. Remove the crankshaft and the camshaft.
    • Two lifters should fall out of the block. this is okay, you won't be re-using these.
  13. Use your valve spring compressor to compress your valve springs and remove the keeper from the valve.
  14. Remove the valves from the block.
  15. Use a wire wheel or some sandpaper to remove the remaining gasket material now that the block is bare.
  16. Soak the block in your favorite degreaser.
  17. Rinse your block out with water and dry it to prevent it from oxidizing.
  18. Clean the rest of your parts the same way.
  19. Order a higher lift cam for your engine, billet lifters and valve springs to match your cam of choice.
  20. Order a racing exhaust pipe for your engine.
  21. Use your valve lapping tool and valve lapping compound to lap your valves in. you will know they are finished when you see a cut circle all the way around the valve and the valve seat.
  22. Wipe the valve lapping compound off of your valves and valve seats.
  23. Start assembly of your engine by putting your valves in.
  24. Install your billet lifters followed by your camshaft and your crankshaft.
  25. Consider installing your connecting rod - it is easiest at this point.
  26. Compress your piston rings and slide the rod and piston into the block.
  27. Using your torque wrench, torque your rod bolts to {{safesubst:#invoke:convert|convert}} pounds
  28. Go up in torque by {{safesubst:#invoke:convert|convert}} pound increments until you hit {{safesubst:#invoke:convert|convert}} pounds.
  29. Recheck rod torque.
  30. Install the crankcase. a slight tap with the handle of a hammer will help it go on.
  31. Install the crankcase bolts. Don't worry about torquing them, just make sure they are tight.
  32. Use your flat file to take material off of the bottom of your intake valve stem until a feeler gauge of the recommended thickness (valve lash) fits snugly under the valve.
  33. Do the same for the exhaust valve.
  34. Install your valve springs and keepers.
  35. Put the valve cover back on your motor.
  36. Install the head back on your engine and torque it to {{safesubst:#invoke:convert|convert}} pounds in a cross pattern.
  37. Recheck head bolt torque.
  38. Install your carburetor.
  39. Install your racing exhaust.
  40. Install your flywheel.
  41. Install your sheet metal side cover.
  42. Put oil and fuel into your engine.
  43. Make sure it will start up.
  44. If it starts up, go racing and have fun.

Tips

  • A billet rod will be less likely to fail than a stock rod, if your connecting rod breaks, it will take most of the other parts with it.
  • If your karting organization's rules state you have to run alcohol, then drill out the holes behind the fuel jet. Drill the smaller hole out to 0.026" and drill out the larger hole to 0.062" and buy an alcohol jet.

Warnings

  • Always wear proper safety equipment when operating a go kart of any kind! That includes an approved suit or jacket, driving gloves. An approved helmet and neck brace! The pros do it. You should always do it too!
  • Don't do any kart/racing kart without proper instruction and supervision. Inexperience and carelessness in operating any machine can result in serious harm or even death!

Things You'll Need

  • an inch-pounds torque wrench
  • a valve spring compressor
  • a set of feeler gauges ranging from 0.002" to 0.025"
  • a 1/2" socket with the same drive as your torque wrench
  • a 12 point 1/4" socket with the same drive as your torque wrench
  • a 3/8" socket with the same drive as your torque wrench
  • a piston ring compressor
  • a 0.025" precision drill bit
  • a 0.062" precision drill bit
  • a valve lapping tool
  • some common sense
  • a flat file
  • a whetstone
  • money for high performance parts

Related Articles

References

  • arcracing.com - arc racing is a source where you can buy billet rods for karting engines
  • dynocamsstore.com - a manufacturer of high lift karting cams, billet lifters, and high tension valve springs.
  • 4cycle.com - if you ever need any karting help, this is one of the best websites out there.
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