Found this in the archives..hope it helps explain
Primary Oil (synthetic) - Harley Davidson Community
Synthetic oil or "energy conserving " dino oil in the primary is not a good choice here in big twins. They contain friction modifiers and a clutch with some miles on it could be prone to slippage from using these oils.
The synthetic oils are a great choice for the engine as they will reduce friction between the moving parts, this however it the opposite of what the friction disks need in a clutch.
Most 10/40 or 20/50 without friction modifiers will work fine or you can use the HD formula + lubricant in the primary.
Primary fluid ??? - Harley Davidson Community
Re: Primary fluid ???
--------------------------------------------------------------------------------
Now there ya go, you answered your own question
Actually a light oil in the 10/40 would work well in there and that's about what the older HD primary fluid was. The key here is not to use a synthetic oil or an energy saving oil like 5/30 or so in the primary mainly because of the additive packages in them.
The heavier the oil, the more it will be prone to clutch plate dragging when the clutch lever is pulled in. The heavy weights actually cause the plates to spin a bit from the "drive" that the heavier oil is causing which will cause hard/noisy shifting and problems finding neutral.
Synthetic oils are designed with additive packages to reduce friction and clutches NEED friction to operate properly. I think you can see where this is going.
Some use synthetics in the clutch/primary area and report no problems at all but as the clutch wears, the problem begins then when the friction is reduced and the clutch then slips.
1,000 mile service on 08, electronic throttle, synthetic oil - Harley Davidson Community
Performance and Technical information on clutches and clutch components for Harley-Davidson motorcycles.
Motorcycle Clutch
The major working component of a motorcycle clutch are the friction plates. The friction plates take the abuse and wear of daily riding. Designed as a consumable item, they wear out and need to be replaced. You can do several things to extend the life of your clutch. They are:
Make sure all components are properly adjusted.
Maintain proper lubrication of your wet clutch. Change your clutch oil at regular intervals. Always use a good quality oil, at the proper viscosity, in your clutch.
Adjust your riding style to eliminate excessive slipping, which causes excessive heat resulting in rapid wear.
When clutch components are replaced, always use the best parts available and replace all worn components. High quality clutch components will save money in the long run.
Drive Train/ Clutch FAQ's - Harley Davidson Community
Frequently Asked Questions about a motorcycle clutch...
Q: What type of lubrication should I use in my clutch?
A: Follow the manufacturer's recommendations for viscosity. Use only good quality oils and lubricants. For Harley-Davidson Big Twins, use the HD primary chaincase oil or a good 5-30W - 10-30 or 10-40 oil that do not contain friction modifiers.
Q: What is the purpose of the oil in a 'WET' clutch?
A: The primary purpose of the oil in a wet clutch is to act as a coolant. The oil in the primary chain case flows around the clutch plates and friction plates, cooling them. This results in smoother clutch action and prolongs clutch life.
Q: What causes my clutch to stick or drag?
A: There is no single cause of a sticking clutch. Some more common reasons for a sticking clutch are:
- Clutch controls are improperly adjusted. Clutch cable is collapsing.
- Clutch spring tension is to tight, spring binding.
- Too heavy an oil has been used in the clutch. A thick viscosity oil can cause the plates to stick, especially when cold.
- Clutch oil is 'worn out' or burnt. The oil has been in the clutch to long, clutch plate wear is excessive causing slippage, or a driving style that slips the clutch. Changing the oil in a clutch often improves the situation.
- Clutch plates are warped. Friction plates or metal plates may be warped.
- Improper adjustment on primary drive chain/belt.
Q: What about using Synthetic Oils in my clutch?
A: Synthetic oils, by their very nature of better heat resistance and improved lubricating properties, would seem to have an advantage. This is an advantage when it comes to lubricating an engine or transmission, but turns into a disadvantage when used in a clutch. This increase in lubricating properties (they are slippery) can cause an old, worn out clutch to fail. The purpose of the oil in a wet clutch is to cool, not to lubricate. The more 'slippery' an oil is, the more likely a clutch is to slip, resulting in increased heat and creating excessive wear.
While most high performance clutches are designed to work with synthetic oils, it is not recommended that they be used by most clutch manufacturers. Synthetic blends are usually considered acceptable.
Q: What causes my clutch to slip?
A: Some of the more common reasons for clutch slippage are:
- Clutch controls are improperly adjusted. Improper cable adjustment.
- Insufficient clutch spring tension. This can be due to excessive wear or in highly modified engine, to much power.
- Worn or warped friction plates or steel plates.
Q: What causes my clutch to chatter?
A: Some of the more common reasons for clutch chattering are:
- Clutch controls are improperly adjusted. Frayed or stretched clutch cable.
- Burnt or glazed friction plates.
- Worn or warped friction plates.
- Diaphragm clutch spring does not have enough tension. Too flat or worn out.
- Clutch hub liner friction plate rivets loose or broken.
Q: Why is it hard to shift my transmission?
A: Some of the more common reasons for a hard shifting transmission are:
- Clutch controls are improperly adjusted. Cable adjustment is improper or worn cable.
- Improper adjustment on drive train chain or belts.
- Clutch has too much drag.
- Improper oil in primary chaincase for wet clutch.
- Transmission or gear box problems
- Primary chaincase needs cleaning
Q: I have installed a high performance cam in my Harley-Davidson. Do I have to add a high performance clutch for the extra power the engine puts out?
A: The stock H-D clutch assembly will handle up to 80-85 horsepower, provided the clutch plates and springs are in excellent shape. Depending upon your driving style, bolt-in cams will not cause you to change your clutch. Highly modified engines do require changes to the clutch. Additional friction area needs to be added by use of an 'extra plate' clutch pack assembly or changing to plates with additional friction area. Several vendors can provide high performance clutch components or a replacement clutch. Barnett's extra plate clutch with a heavy duty spring is an excellent choice for a street bike.
