For 10 years, The Cylinder head Shop has been on the leading edge of cylinder head technology - leading the field in the application of racing materials and specifications to road and classic racer cylinder heads. We have questioned many of the "pre-sets" that govern current thinking about materials and procedures. We have been correct and our work has one races and return very high mileages. 

The Nucleus Sports Elite range of Valves was expanded to include new concepts in Guide design. Our Power Guide range suitable for road or race.

Examine closely the details of your current valves and compare them to the Power Guides. The majority of heads use cast iron guides. A decision made by accountants in the 50s and not engineers in the 90s. Top manufacturers will be using phosphor bronze but now look at the design and tolerances of each guide.

Is the inlet the same shape as the exhaust? Most are. Why? Are the gases doing the same thing on the way out of your combustion chamber as they were on the way in? Does the design allow for the best flow? Does it take into consideration the tremendous heat of exhaust gases forcing their way down onto the tip of the guide? Is the tolerance between the valve stem and the guide the same as it was in the 60s? Why? 

Ask your self, would you chose to run around on 60s tyres? Has engine manufacture techniques improved in the last 40 years? Likewise lubrication and carburettion? Then ask yourself why the standards of your guides have not. Ask why heads wear out in 20 or 30,000? What does this add up in your mind?

We looked not just to racing for our inspiration, because the perameters for racing are different to that of road application, but also to aviation. In aviation, high mileages, low servicing and utter reliability are necessary. The material we chose to make our both out inlet and exhaust guides from was Colsibro.

Colsibro, a copper-nickel-silicon alloy, possesses a remarkable blend of physical and mechanical properties not found in any other material currently available on the market. Equally importantly, it is not "exotic" in terms of price, which is in a similar range to more conventional bronzes. Its cost compares favourably with its closest rival, copper-cobalt-beryllium, but without the potential toxicity hazards. It is technically superior to silicon bronze, now almost impossible to source.

Colsibro alloy develops its unique performance by heat treatment and is stocked in its fully precipitation hardened, heat-treated condition. Other tempers are available to special order when, for example, the alloy is required to undergo extensive deformation. Heat treatment is then applied to the finished component to develop the fully hardened properties. Something not possible when sizing guides to individuals heads or valve sets.

It is important to remember that some alloys have a short "shelf life" that makes them fine for racing not optimum for road use, such as some titantiums. Colisbro is always fully stress relieved in the hardened condition which means that close tolerances can be held and a complete freedom from stress cracking.

Typical uses of Colisbro: 

The combination of strength, corrosion resistance, high conductivity of heat, wear resistance, softening resistance, spark resistances, cryogenic properties useful in the presence of liquid gases, and numerous other attributes has found use in every engineering field but made a name for its self in cylinder head application in high performance engines. And this includes air cooled and motorcycle engines that are generally much more efficient, and stressed, than automotive engines.

Each bar comes certificated suitable for aviational purposes.

In addition to Colsibro, for even more demanding customers, we also keep a stock of a rare alloy called Trojan which is of an even higher specification and can make guides to order only. Both alloys machining beautifully, holding their shape and close tolerances through out the processes. All guides are made in small batches and those fitted by ourselves hand finished to perfection.

Additional Features: In addition to the materials we chose, the finish and design is important. Features you will find on Nucleus Power Guides make them unique.  The first thing you notice is that the inlet and the exhaust are different shapes. The inlet tapered to allow for a good flow and less resistance, the exhaust has a stub nose finish to prevent damage from heat of combusted gases. Then you notice how closely the valve fit. Almost a sliding fit. We work to tolerances of .5 of a thou on our road bikes and .2 of a thou on our racers. This will make the eyes of a traditional engineers roll, but it works. Materials are not everything. Design is important.

Look closely and you will see other features. 

• Where manufactures fit circlips to stop guides slipping too far into the heads, we machine shoulders.
• On the top of the guides we put a surface that takes oil away from the valve not leave it to flood the guides.
• We shorten the guides top and bottom as much as possible. Thanks to the close tolerances we work to, this is safe and allows for more flow in the ports and high left cams etc. about the head.
• We use radius corners instead of square edges that perform badly under heat.
• We fit inlet stem oil seals where none were fitted before.
• Oversizes, specials, internal diameter changes are stock in trade for us.
• And so on, each guides is a work of art.

Close tolerance work is our signature. we work to standard other cannot. What we have discovered are a number of benefits in performance and longevity. For example, standard guide to valve clearance is 3 to 4 thou on classic European vehicles, sometimes even 4 to 5 thou on classic Americans. We work down to 0.5 on the inlet and 1 thou on the exhaust, except on our racers where we work to even a closer fit.  In addition, we have found that;

• Heavy oil seepage  is not drawn into the combustion chamber allowing for a cleaner burn and less carbon build up.
• The fuel air mixture is kept more constant as air is not drawn down the side of the guides.
• Valves do not rock back and forward in the guides wearing out seats and guides under the angled action of the cams or rockers.
• Vacuum in the inlet port is increased improving charge and performance.