The "Howdi Engineering"
Starter Sprag Clutch
A roller and ramp type has been developed to overcome the inherent problem with the standard Ducati sprag clutch and flywheel assembly. The original Ducati bearing was not designed to accommodate engine kick back. The bearing was made by numerous manufactures originally used in thermostatic cooling fan drive clutch/bearing for trucks and earth moving equipment and automatic transmissions for cars. Ducati adapted the bearing for their use. However the "Howdi" sprag clutch has been specifically designed for Ducati motorcycles with simplicity and practicality in mind.
Features
Australian designed and manufactured using heat-treated alloy steel & fully CNC machined.
Eliminates starter motor and sprag clutch damage with engine kickback.
Motor runs smoother & main bearings last longer, due to fully machined, balanced and polished flywheel.
Cannot be damaged with high compression or lightened crankshaft motors.
Inbuilt oil sludge eliminator.
Available in your own desired weight flywheel.
You have the advantage of retaining your own primary gear.
Only 5 moving parts, as against 22 on a standard Ducati starter clutch.
The Flywheel
The next design improvement of the "Howdi" sprag clutch. After numerous tests on bevel drive flywheels, it was found that a variation of up to 5% of the correct balance factor was found, due to some unmachined sections of the original cast flywheel. This imperfection has been eliminated in the "Howdi" sprag clutch, and replaced by a fully machined flywheel and clutch, assembly affording a better balance to the crankshaft and main bearing.
Sludge Removal
With the insertion of sludge removal holes placed at the highest point of the ramp, the sludge and excess oil is centrifuged from the clutch and removed with each oil change. This eliminates the chances of these impurities tracking through the crankshaft and into the sludge galley and the conrod bearings, causing premature wear.
The Drive Rollers
Designed to completely disengage when idling and that eliminating any contact with the ring gear after start up. This doesn't apply to the original sprag bearing as they always have contact with the ring gear spigot at any one time. The rollers used in the "Howdi" clutch are custom made, as there are no commercially made rollers available in the diameter and length used. The size and weight of the roller is critical because it has to have the correct mass to disengage the sprag clutch at the correct rev range. This is 150 - 180 rpm above starter speed. These are made from heat-treated alloy steel with high core strength.
The Ring Gear
Improved by increasing the driving spigot diameter to the largest possible diameter to give the greatest mechanical advantage on the rollers when engaged. This reduces the point loading on the rollers and eliminates the crushing effect on the standard needle roller bearing which is retained in the "Howdi" clutch.
The Springs
The ones used in the "Howdi" sprag clutch have been computer designed to compress and disengage the clutch at the 150 - 180 rpm above starter cranking speed. They are made of a heat-treated chrome/nickel steel, and will not loose their tension under normal engine
operating temperature.
|
click images for larger views
|
|
Howard & Diane Scaysbrook
Howdi Engineering Pty Ltd
PO Box 8, Woy Woy
New South Wales
Australia 2256
Phone/Fax: 61 2 4342 1594
Mobile: 0409 42 1594
Email: howdi@tac.com.au
|
|
