Leopard Clutch and Drum Maintenance

[Bryan W. Joplin]

Below is another Tech Tip. Please excuse the formating, these are typed in Word and copied in. Since these papers are so long, I decided to enter each as a new topic. This also allows a continuing dialogue on each subject. I was surprised no one questioned why a 10 tooth driver with an 80 tooth axel produced more torque than an 11 driver and 88 axel. They are both 8.0 gear reductions?? Maybe this was address on Ekarting??

The clutch and clutch drum bearing should be inspected and serviced every hour of run time. That’s a full race day including pre-race practice.
1. Remove and Inspect the Clutch Drum
a. Remove the drum holding nut. A #2 phillips screwdriver stuck through the ring gear and against the case, will keep the crank from rotating. ( #1 phillips, if you have the newer ring gear) Inspect the inner and outer washers for wear and replace if damaged. If the washers are not lasting 15 or more hours, chain alignment is an issue.
b. Clean and inspect the drum and needle bearing. A properly lubed needle bearing will last the life of your driver.
2. Inspect and clean the clutch.
a. Do not spray any cleaner/degreasers on the clutch pads. Acetone contained in most cleaners dissolves the pads and will result in premature failure of the clutch. If the pads are black with carbon from excessive greasing of the drum bearing, remove the carbon by wiping the surface with 100 grit sand paper. The carbon will sand easily and restore the pads to almost original surface and color. Do not be aggressive and remove any significant clutch material. Clean up any debris from sanding, especially the bearing surface on the PTO end of the crank.
3. Ring Gear Inspection
a. Before reassembly, carefully inspect the starter ring gear. The gears are prone to cracking between the lightening holes and teeth. Inspect the ring gear each time the clutch is serviced. A cracked ring gear will come apart at high rpm and cause significant damage to the starter bendix, case half and PTO end of the crank. (See gear failures belowl)
4. Clutch Drum Installation
a. Reinstall the inner washer (remember they are directional). Put a small amount of high temperature automotive wheel bearing lube on the drum needle bearing. Work the lube in the bearing. Too little lube, you risk the chance of bearing seizure. Too much lube, and you grease the clutch surface. (the clutch will be slow to lockup, out of turns)
b. Install the bearing, drum, outside washer (its directional) and nut. Insert a phillips screw driver through the ring gear to hold the crank, and torque the nut to 27 ft lbs. Loctite (blue) is optional. Achieving the correct torque is important. If your starter fails, and you use an external starter, when the starter disengages, it will remove an improperly tightened drum nut . If the drum comes off, the clutch pads will expand, causing extensive damage to the engine.
5. Ring Gear Failures

When I experienced my first ring gear failure, I asked around and found the problem to be common. Virtually every Leopard owner had had a failure, a crack at one of the lightening holes in the gear. The results in some cases were extensive damage to the engine, including case damage, starter bendix and PTO crank half. The nature of my failed gear looked like a defect, so I contacted IAME in Italy. IAME would not discuss the issue direct, but referred me to the U.S. importer, Russell Karting. According to Russell Karting, they had done research into the gear failure. The problem was not defective gears. Russell had found that the gears were being damaged by track debris. Due to limitations in the bearings and crank dimensions, the gears were very light weight and easily bent. Their testing showed that a slightly damaged gear would break, when exposed to high rpm (16,000-17,000). IAME was working on a redesign, and as everyone knows, the 2009 Leopard was introduced with modifications to the PTO end of the crankshaft. IAME has also slightly modified the ring gear for the 2008 and older engines. I have a new ring gear with slightly smaller lightening holes. In the old gear, the lightening holes extend into the machined radius at the transition to the gear teeth. In the new gear, the lightening holes stop just before the radius. This leaves more material at the point of past gear failures. When purchasing a gear, you should check to see if you are getting a new gear or old stock. An easy check for a new gear is to stick a #2 phillips through a lightening hole with the clutch drum installed. If the #2 phillips passes through the hole, you have an old gear. If you are running an old gear, give consideration to replacing it.

There appears to be a simple work around for this failure. I have had two gear failures, each occurring after an incident, where I was off the track. So, if you go off the track, check the gear carefully. The gear should also be checked during routine maintenance.

As I said, I have had two failures. The first time, I did not know about the gear problem. After the first failure, I designed a shield to protect the gear. On the track and while off roading, my gear is protected, and I have had no gear failures. At a SWRC race I was instructed to remove the shield. According to Tech at that time, it represented an engine reliability advantage. By the end of the day, I had a broken gear. I continue to run the shield and have not had a gear failure, while the shield was in place.

The shield is a piece of ¼ in. masonite fitted between the clutch cover and crankcase. The masonite is cut to the shape of the engine, with a hole just large enough for the clutch drum. If you are interested in installing this shield, stop by my pit on race day. (pre 2009 models)

Bryan