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1.3:1 Ratio 'Cast' Cooper 'S'-type Rocker. Without adjusting screw and nut. [See AEG167, screw (regular) or C-AEA692 (long); FNN605, nut]
Reproduced using the very latest casting methods employing a special aircraft release EN8 steel. The valve pad is hardened to 54-56roc. Correctly profiled pad reduces side loading on valves to a minimum. Particularly effective on small bore engines. Use recommended valve clearances.
The new generation of short period, high lift cams have been developed to give the best results in large bore engines when used in conjunction with 1.5 ratio, hi-lift rockers. For the small bore range, the stock 1.3 ratio is optimum. In certain instances ratios of 1.7 to 1 are of benefit - but is really only applicable to fully developed race engines.
Extra lift of around .030" can be obtained with the bushed rockers by using offset bushes, supplied as a set of 8. If these bushes are used, before and after alignment of the rocker pad to valve and stem must be checked and corrected. Invariably in the 1.3 rockers a special set of steel posts are required. It is possible to fit the bushes to the 1.5 rockers, however other means of realignment must be used if correction is required. The easiest way is to drill out the stud holes in the pillars to the next size (i.e. 11/32 inch and 25/32 inch) and push the pillars backwards prior to tightening head and rocker post nuts. It is, however, not recommended to go more than 2 oversizes. To enhance valve gear rigidity and reliability, especially in high-revving engines, there is a super-thick wall rocker shaft available. Heat treating rocker shafts is now no longer done as it greatly accelerates wear of the rocker bushes. It is cheaper and easier to replace a worn shaft than a set of worn bushes; the bushes require reaming to size once fitted.
To help rocker pad to valve stem tip alignment and reduce friction the standard springs can be replaced by spacers and shims. The spacer set is sold as a set of 3, the shims are so individually.
Although there has been a carbon-fibre push rod available for sometime, it is in 5/16" diameter. This somewhat over-engineered size meant that awkward and time consuming alterations to cylinder block and head had to carried out so that they can be a) fitted, and b) work without breakage caused be rubbing. Basically a good idea, but little consideration to fitment, and seemingly no R & D. The number of inquiries we have about the use and fitment of carbon-fibre push rods has been steadily increasing, however sales were limited because of fitting hassles. This prompted us into looking into just why 5/16" diameter rod was necessary, bearing in mind the standard steel item is only 1/4". Somewhat strange as carbon-fibre is known to be stronger size for size than steel.
To cut a long story short, a special jig was made to assess the strength of the standard and 5/16" carbon-fibre rods. We then made a one off push rod in 1/4" carbon-fibre. This was duly tested to be exactly what we wanted. It was one and a half times as strong and exactly half the weight of the standard item, yet would fit without ANY block or head modifications whatsoever. A far better product than standard, and a more sensibly dimensioned item than those previously available.
Extra benefits of a carbon-fibre push rod aside from its extra strength and super light weight, are its massively reduced expansion when hot AND almost total absence of resonance. The two latter benefits apply acutely to modern emission standards for modified road vehicles. Tighter valve clearances can be maintained to help reduce emissions. Carbon-fibre does not resonate, so valve train noise is reduced. In fact when in conjunction with our bushed, alloy, roller tip rockers and an alloy rocker cover - valve train noise is significantly reduced.
Carbon-fibre rods can also be supplied to customer required lengths.