One of the most difficult, if not THE most difficult engineering challenges that motorcycle research and develpment people have faced over the years has been the design of reliable steering mechanisms. Various manufacturers have tried such things as caged ball bearings, uncaged ball bearings, and tapered roller bearings. I have owned bikes that used the last 2 types of bearings.
Of the million plus miles I’ve ridden motorcycles since 1955, over 500,000 miles have been logged since 1990 when I began keeping accurate service records on my KLR and DR big singles. Both models, by the way, are equipped with tapered roller bearings which are extremely sensitive to adjustment especially after lots of off-road riding.
I’ll never forget purchasing a brand new 1991 KL650A and suffering steering bearing damage on my very first Baja ride of 500 miles. About 250 miles into the ride I discovered the steering stem nut was loose. As soon as I heard the “clicking” sound at the top of the triple clamp, I went to a small garage in a nearby town and adjusted the steering as best I could, followed by a good nut tightening. I immediately headed from San Vicente, Baja, northbound until I reached my home 160 miles away in La Mesa, California.
The following day I backed the KLR650A on to my Handylift and jacked up the front end until the front wheel barely cleared the table (¼ inch). My inspection revealed that both races were damaged and needed replacing. While I was working on the steering bearings and races I located a “spring” type washer to go under the steering stem nut along with the application of intermediate Locktite applied to the threads. The bearings I packed with Shaeffer’s, the best high pressure moly grease (#2 on top and #3 on the bottom).
I was so traumatized by the whole experience of having my KLR bearings fail that I made an $8.00 phone call (expensive for 1991!!) to Timken Bearing Company and talked to an engineer. He informed me that tapered roller bearings were designed for applications like wheels and axles where they live a long time if properly lubed and adjusted. On the other hand, tapered roller bearings were not designed for motorcycle steering applications due to the constant pounding of the bearing into its race, especially on the lower triple clamp. The engineer also advised that motorcycle steering bearings would live longer if adjusted to the tight side as long as steering is not compromised. Based on this information I have devised an adjustment procedure that allows a slight amount of drag but absolutely no play.
I have two 2011 DR650SE’s with almost an identical 46,000 miles on each of their odometers. One has many more dirt miles than the other and as a result, required that both steering bearings be replaced. The other more street oriented bike still has smooth steering and required nothing more that cleaning, re-lubing and adjustment.
As a result of my conversation with the bearing engineer back east, I was able to devise a very effective motorcycle tapered steering bearing adjustment procedure. The basic premise is any play that one can feel by grabbing and shaking the fork tubes is “too much.” On the other hand if the bearings are over tightened, causing excessive drag the steering will be compromised. It’s called “threading the needle.” Good luck!