rmdhawaii

iTrader: (4)

From the NitroKB.com archives: Stripping 2nd Gear?

Below is some information and best practices to help identify, correct and potentially avoid a problem with stripping the 2nd spur gear.

Why the 2nd spur gear might strip:

• Engine is not parallel to the 2-speed shaft, causing the gears to be meshed at an angle
• Gear mesh gap is too loose (too much gap) or too tight (no gap)
• Engine or engine mount shifts during an accident or because the engine screws get loose, causing improper gear mesh
• 2-speed shifts too hard into 2nd gear, because there is too much of a gap between the 2-speed shoes and the 2-speed housing
• 2-speed shaft is bent, causing the spur gears to wobble (inconsistent mesh)
• Bearings are worn (bulkhead and/or clutch bell), causing the spur gears and/or clutch bell to wobble
• Pinions or spur gear(s) are worn out, causing too much of a gap and/or improper meshing of the gears
• Crankshaft has too much side-to-side play at the front bearing, causing the clutch to wobble
• Car goes airborne and comes down while on-throttle, which may cause the chassis to flex enough to cause the gear mesh gap to be too loose or too tight (If the car goes airborne, get off the throttle!)
• Collision while on-throttle, which may cause the chassis to flex enough to cause the gear mesh gap to be too loose or too tight.
• Track debris gets caught in the gear mesh

Make sure the…

… engine mount(s) are perpendicular to chassis center line
… engine is parallel to the engine mount and 2-speed shaft
… carburetor is not touching the brake disc
… 2nd gear hub is not touching the clutch bell
… 2nd gear hub is not touching the side stiffener
… clutch bell and/or flywheel is not touching the chassis
… ends of the top and bottom engine mount screws are not touching each other
… side stiffener is attached before adjusting the gear mesh
… screws on the radio plate are not loose
… tuned pipe is not attached to the engine when you adjust the gear mesh
… engine doesn’t move when you apply the brake or throttle
… clutch endplay is not more than 0.3mm
… difference in tooth count between the spur gears and pinion gears is the same

Initial gear mesh adjustment:

1. With the engine mount out of the car, mount the engine to the engine mount. Ensure that the engine is mounted straight onto the engine mount(s).
2. Mount the engine with engine mount into the car, with the engine screws slightly loose. Be sure to put thread lock on the screws.
3. Turn the engine so that the piston is in the middle position (not top dead center or bottom dead center)
4. Remove the e-clip on the 2-speed shaft and remove the 1st spur gear
5. Align two 2nd spur gear teeth with the one 2nd gear pinion tooth so that it fits perfectly together – then back off the pinion gear from the spur gear so that there is a very small gap. If you hold the pinion steady and rock the spur gear back and forth, you should notice a very small amount of gap between one spur gear tooth and the one pinion gear tooth.
6. Tighten the bottom engine mount screws, ensuring that the engine mount is perpendicular to the chassis.
7. Turn the spur gear and check the mesh at 90, 180 and 270 degrees from the current position. If the mesh is too tight in one particular spot, readjust the mesh for that spot and check all the positions again.
8. Rotate the gears and make sure the gears are not binding. If they are, readjust the mesh.
9. Put the 1st gear spur and e-clip back onto the 2-speed shaft. If the 1st gear spur is binding on the 1st gear pinion (the mesh is too tight), it means that something is not right.
10. Inspect the gears from the top of the car and ensure that the pinion and spur gears adequately overlap each other when the clutch bell is pushed in and pulled out. If necessary, repeat the entire procedure ensuring enough overlap before tightening the bottom engine mount screws.
11. With the wheels mounted on the car, push the car backward and forward and make sure the gears are not binding.

Checking the gear mesh:

• Turn the engine so that the piston is in the middle position (not top dead center or bottom dead center)
• Remove the e-clip on the 2-speed shaft and remove the 1st spur gear
• Align two 2nd spur gear teeth with the one 2nd gear pinion tooth so that it is centered. If you hold the pinion steady and rock the spur gear back and forth, you should notice a very small amount of gap between one spur gear tooth and the one pinion gear tooth.
• Turn the spur gear and check the mesh at 90, 180 and 270 degrees from the current position.
• If everything is okay, put the 1st gear spur and e-clip back onto the 2-speed shaft. If not and nothing appears to wrong (see "Why the 2nd spur gear might strip" above), you have two options:

1. Loosen the engine screws and remesh the gears. Check that the engine mount has not shifted (check the position of the screws) and the engine is parallel to the engine mount and the 2-speed shaft when tightening the screws.
2. Remesh the gears using the bottom engine mount screws. Check that the engine has not shifted out of position on the engine mount. Be sure to reapply thread lock to the bottom engine mount screws.

Proper 2-speed clutch shoe adjustment:

Instructions for properly adjusting the 2-speed shoe prior to and after installation: (Attached)

Additional things to consider:

• Purchase a one-piece engine mount. It makes it easier to ensure the engine mount is perpendicular to the chassis.
• At a minimum, check the gear mesh before starting your race day and before running your Main.
• If the 2-speed hub is touching the side stiffener or clutch bell, add a 0.1 - 0.2mm shim on the 2-speed shaft between the pin and the bulkhead bearing. Another option is to trim, sand or file the side stiffener where it is touching.
• Change the rear bulkhead screws that fasten the bulkhead to the chassis from 3x8 to 3x10mm. This will help hold the bulkheads better.
• As per the instructions, use lock washers on the top engine mount screws.

Note: The information above is based on a compilation of posts from the MTX-4 thread at RCTech.net and my experience with the MTX-4.