By David Porter, Customer and Technical Support at The Bonneville Shop
Wear limits of parts on 50, 60, 70 year old bikes should be top of mind. One of many considerations the restorer or engine builder is faced with is whether a part or assembly is rubbish or can be put back into service. Wear limits factors include a preference to retain originality, taking advantage of modern upgraded parts manufacturing processes, and perhaps most importantly, holding to an established budget.
Building Budget Brits
As a former operator of a British motorcycle service shop, I was faced with the task of determining the best way to proceed during an engine overhaul when a marginally worn part or assembly was encountered. I often referred to a guide that was published in an excellent book authored by Mike Brown, called “Building Budget Brits”.
The content of the book shares with the reader how to perform many repairs and various operations on vintage British motorcycles, but moreover shows the author’s affinity for one JB Nicholson, who wrote the iconic “Modern Motorcycle Mechanics” book decades ago. JB, or “Bernie”, as he was known by his customers, was a revered and respected mechanic known for his honest assessment of what was absolutely needed for returning a worn motorcycle to serviceable condition.
“As a former operator of a British motorcycle service shop, I was faced with the task of determining the best way to proceed during an engine overhaul when a marginally worn part or assembly was encountered.”
Nicholson’s Specifications on Wear Limits
The “Nicholson’s Specifications” guide is intended to help the mechanic decide when a part can be reused, and when wear limits require replacement. It is likely that this guide was compiled long before the aftermarket of reproduction parts was available as we know it today. There was a time when spares were simply not available or were only available from suppliers “across the pond” at a premium price, so discretion was used as to how long a worn part could be safely put back into service.
A good example would be the suggestion that valve springs be replaced when free-length measures 1/8” less than the length stated in the factory workshop manual’s “General Data” section. Valve springs that have taken a set of 1/16” may not be appropriate for use on a cylinder head destined for service in a competition engine with high-lift camshafts, but in an engine with other worn components used for daily riding or commuting, reusing the slightly worn valve springs may make sense for the individual using the motorcycle, when other more critical expenditures are called for during the repair.
To some degree, these decisions are still being made today for the same reasons. For those who don’t need to follow a budget with respect to their motorcycle maintenance, this guide will be of little use, as the practice of replacing anything and everything suspected to be worn in any way is followed. I found this guide to be very useful, however, and with full disclosure, I often conferred with the customer regarding where to allocate funds to maximize the value of the repair work done. I hope you enjoy this practical guide.