Engine Disassembly

Bob Evans

Grumpy Old Admin
Staff member
Engine disassembly will vary a bit from motor to motor depending upon your starting point. The new Briggs Raptor class of engine is my favorite to work with as it has been assembled by the factory with racing in mind. It comes with the specific parts needed for stock class racing and has been evolving for the last 4-5 years(Raptor I, II and now the III). Each model has brought improvement to the basic design and will in the end save you money looking for the right part when compared to a stock tiller or ‘Fun’ kart motor.

Before starting to disassemble the motor, be sure you have the needed workbench space and the proper method for fastening the motor to the bench. The easiest method I’ve seen involves using four 5/16 wood studs. These have a wood screw bit on one end and a standard 5/16 bolt pattern on the other. This enables you to screw the four studs into your wood bench in the pattern of the four bolt holes for mounting a Briggs. You can then place the engine onto these bolts and fasten it securely to the bench. You will need to do this to effectively work on the motor. You will also need a small parts bucket or box to keep up with everything.

1. Remove the 3 to 4 bolts that retain the flywheel cover. These are 1/4” X20. For the newer motors use a 3/8 wrench or socket. Older motors use a 7/16”.

2. If the motor comes with a kill switch mounted to the flywheel cover remove it from the coil and side cover.

3. Remove the spark plug and save it for your lawn mower as it’s useless for methanol racing.

4. With a 1/2” socket remove the 8 head bolts. On older Briggs there were 3 longer length head bolts used over the exhaust side than from the rest of the head. Note the position of these bolts. On the Raptor series of engines all head bolts are of the longer design.

5. With a 3/8 socket remove the bolt retaining the bottom of the tank bracket to the block.

6. If the motor comes with a governor loosen the nut holding the governor arm. Then pry the lever off with a screwdriver. Also remove any ground wires a this time.

7. Now remove the 2 bolts holding the carb to the block. On older motors these were 7/16 bolts. Newer motor use Torx headed bolts. If you don’t have any Torx tools you can most likely use an curved allen wrench to loosen the bolts. Once you have them out gently throw them into the trash or used bolt bin as we will replace these with standard 3/4” allen headed bolts. The carburetor and tank will come off as one piece.

8. If your motor has a muffler remove it now and discard it.

9. Using a 5/16 socket remove the 2 valve cover bolts and valve cover.

10. Remove the 2 5/16” coil bolts and the coil. Be careful not to bent the coil vane as this must remain as stock and is a tech item.

11. Remove the nut holding the flywheel or the starter ratchet on older motors and the new Raptor series. You will need a special wrench available at kart shops or your local Briggs dealer as well as a flywheel holder. When using the flywheel holder be sure and not engage the aluminum fins surrounding the magnet.

12. Using a flywheel knocker, remove the flywheel. The method here is to screw the knocker onto the crankshaft in place of the starter ratchet and then back it up 1/2 turn. Then strike the knocker sharply with a hammer. This will loosen the flywheel and enable you to easily remove it. It will almost fall off. Do not hit the flywheel or attempt to pry it off as you will damage the motor or flywheel. REMEMBER, this flywheel will be spinning at around 6000 RPM when we are racing and you don’t even want to see one come apart! USE THE RIGHT TOOL.

13. Using a valve spring compressor or the special valve spring tool available at most kart shops remove the valve springs and retainers. If you use a valve spring compressor, the feet must go between the retainer and spring, lifting the spring up so you can flip the retainer off the valve. If you chose to use the special valve spring tool the trick is to align the small notch on the retainer toward the open portion of the valve spring pocket(away from the cylinder). The spring tool can be used to slightly lift up on the retainer and twist it around a bit at a time. Once you have the retainer pointed this way lift up on the retainer and spring using the tool and then pull backwards. The retainer will come loose and the valve spring can be removed.

14. Pull the valve out the top of the motor. On a used motor you may encounter resistance to a valve coming out. STOP. What is holding the valve up is a burr on the valve stem from the continuous beating it takes during operation. Push the valve back down and using a small file remove the burr from all sides of the valve stem. Again the valve should come out easily. A gentle hand here may save you the cost of a new valve or valve guide.

15. Remove the six bolts holding the side cover on. These are either 3/8 or 7/16”.

16. Remove the side cover by gently tapping on it and pulling at the same time. If you have a motor that came with a governor remove the nylon gear. Behind the gear is a flat metal washer that must come off. Look closely, as it’s there!! Remove the governor arm and discard it. The hole remaining can be plugged with a 1/4” x 20 screw that will almost self tap it’s way into the hole.

17. Remove the two rod bolts and pull the bottom of the rod cap off with the dipper. These bolts can be either 7/16, 3/8 or 5/16 in size depending upon model year. If the motor has a separate dipper thrown it away as we will replace it with an after market nylon or billet aluminum one not subject to failures.
18. Reach in and push the rod and piston up out of the cylinder in one motion.

19. Remove the crankshaft.

20. With a small set of needle nose pliers remove the two circlips that hold the wrist pin in the piston.

21. Push the wrist pin out of the piston with a straight sided 5/16 socket or a large Phillips screwdriver. Be careful not to damage the wrist pin hole if we are going to use the piston again.

22. Remove the bearing from the crankshaft on the power tack off side(PTO). On the new Raptor series the crankshaft has been clearanced for easy bearing removable and the bearing will just pull off along with the crank gear. Be careful not to lose the woodruff key on the newer style crankshafts that holds the gear in place. On other motors the bearing is a press fit and can be removed by the use of a gear puller or by a bearing separator. We will clearance the shaft later for future easy removal.

Now you have a box full of parts. Next let’s take a close look at these and determine what is usable for a racing motor.