Parts Inspection

Bob Evans

Grumpy Old Admin
Staff member
Even if you have a new motor, go over each part and inspect it visually for flaws. Remember this motor was built to be run at a maximum RPM range of 3600 not the 6000 we’ll be running. You are looking for casting flaws or cracks. If you are dealing with a used motor be sure and do this on each part.

1. Crankshaft. Using your 1” micrometer measure the rod journal thickness. New crankshafts are between .999 and .998. Anything less than .996 and you are asking for trouble. Frankly I suggest using the crank for a fun kart if it’s less than .996. The new Raptor II and III use a induction hardened journal that will wear quite a while before needing replacement. Some of the older Briggs crankshafts were also heat treated and seem to never wear out. These can be identified by a bluish color around the journal left from the heating process.

2. Piston. Use only a new piston, as it takes quite a bit of abuse in a racing motor. Two styles of pistons are made for the 5HP motor. For aluminum cylinder motors(cool bores) a chromed piston is available to keep scuffing to a minimum. Steel bore motors(I/C) used to come with an un-chromed piston. On all motors we now use only the Chromed piston. This keeps parts inventory down and simplifies matters quite a bit. The new Raptor III motors all come with the chrome piston. As I write this, a new piston is available on the Raptor III motors in 1999. This piston was designed specifically for racing and should eliminate the occasional problem of pulling the wrist pin from the bottom of the piston. When this happens you generally can kiss the motor good bye. A major improvement. All of these new pistons will be chromed.

3. Rod. Again here we are not going to re-use an old part. Use a new rod as this is the current weak link in the motor. The rod comes in two styles. Older rods came with a separate dipper which was a stamped steel part on factory motors. As mentioned earlier throw this away. They have a nasty tenancy to crack and break off leaving you with NO oiling system at all. Bad news. Several after market dippers are available ranging from nylon to billet aluminum if you choose to stay with this style of rod. Personally I have moved to the newer style of rod that originally came with the RAPTOR II. It is part # 555207 and comes with an integral dipper thus eliminating additional expense. While many people were skeptical of this design it has proven itself over the last few years to be quite reliable. A simple test can be performed on any new rod to check for casting flaws. With the rod cap firmly attached(100 in. Lbs) hang the rod by a small piece of string through the wrist pin hole. Take a small socket extension and give the rod a firm tap. You should hear a sharp ringing sound that lingers a bit. If you hear a thud or the ringing stops quickly suspect a bad rod or miss threaded bolt holes. Replace it!

Head. Not much here, other than cleaning a used head up of all the carbon that has accumulated. Several methods exist for doing this the easiest being a sand blaster if you have availability to one. Spray oven cleaner can also be used to loosen the carbon, BUT be careful not to leave it on very long as most will eat aluminum. Scotch Brite with Carb cleaner will also work pretty well. Just be careful not to scratch the head up as the tech man will frown upon this. For sandblasting the head is legal in both WKA and IKF.

Carburetor. For racing purposes only one style of carb is allowed. It will have a removable brass jet and not have a pull choke built into the carb. The ones with a plastic choke are legal. Legal carbs come on all RAPTOR motors.

Valves. If the motor is new, retain the valves as they can most likely be used with our new camshaft we are going to purchase. If we have used valves the area to inspect is around the spring retainer area. In racing, this area gets beat up quite a bit. If this are looks too abused replace the valve. You don’t want the retainer coming off while racing. Also inspect the valve stem area for wear and replace as needed.

Valve Springs. Most valve springs can be reused in our racing motors as long as they meet the current rules on minimum height. Currently WKA minimum is 1.300 for an exhaust valve and 1.240 for intakes. Maximum exhaust length is 1.500. Generally we will be using an exhaust spring on the intake side for most stock class engines. Intake springs can be used in the restricted classes. This is legal in WKA. Exhaust springs must be used on the exhaust side.

Camshaft. The stock camshaft that comes in all motors(RAPTOR included) are useless today. Rules now allow for after market ground camshafts to be used. These are more precise in their timing and should always be used in place of the stock cam where rules allow.

Flywheel. Inspect the flywheel carefully if you are dealing with a used motor. Discard if it appears abused in ANY way or has missing fins. Remember, you don’t want this thing coming apart at speed. The flywheel cover is useless in this situation. Minimum weight for a flywheel is 6lbs.(6 lbs 4 oz FOR 2001) Most newer ones are well over this limit. Older Flywheels were a bit lighter than the current design and can be used on short tracks where acceleration is important.

Coil. The coil should be tested with an ohmmeter for plug wire resistance between 2000 and a max of 5,000 ohms. Most new black coils have around 2600 ohms.

Valve Cover or Breather valve. Breather should be in stock condition. It actually functions like a PVC valve(one way valve). Check this by attempting to blow into the grommet. It should have a good bit of resistance.

Block. If the block is used, check the block for any cracks or holes from past failures. Be sure and check the cam boss inside for any cracks. Check both the intake and exhaust ports to be sure they are within stock class rules. The entrance to the intake port can not be over .880 and the exhaust entrance max. Is 1.005. Non issue on new motors. Also check the area around the lifter holes for cracks.