Questions page 2

The following information is the sole property of P B Blackman Sportcars Ltd. T/A formerly Abbey SportCars Ltd. The information is not to be copied for use elsewhere without prior permission or reference. The pages are written for guidance only, the information contained therein is the view of the writer and should not be taken as the definitive recommendation.

What do I need to check on pushrods?

This operation is relatively simple. Once the pushrods have been cleaned, they can be rolled on a level surface. Any visible oscillation as the pushrod rolls is indicative of a bent pushrod. It is also worth checking the pushrods for scratches/dents or similar marks as this can lead to premature failure

How do I identify worn rockers?

The standard cast alloy rockers are equipped with steel pads to prevent premature wear to valve stem tips and the rocker arm. On high mileage engines the steel pillar can become severely worn which may cause incorrect operating clearances and noisy operation.

Roller Rockers on competition engines - what are they for?

On racing engines (engines that live at 7000RPM for a great deal of their operating lives) it is important to minimize frictional losses. Roller Rockers are also used as they provide greater reliability than stock items. The valve gear is heavily loaded at high RPM, especially with wild cam profiles and dual or triple valve springs using a standard rocker arm in a race application has resulted in costly failures. When rockers fail they have a tendency to fracture causing ingress of aluminum/metallic particles within the oil/lubrication system, as well as possible irreparable engine damage.
On a fast road engine the standard rockers provide adequate service. They can however be upgraded to steel items at a cost roughly equal to that of the standard alloy items. The only minor snag however, is increased mass which tends to give the valve spring greater inertia and less precise valve opening and closing at high engine rpm (float). The benefit of the steel items outweigh the additional mass and aids reliability.

Do I need to worry about the Timing Chain?

We find that although adequate, the standard timing gear and chain set-up shows wear even in low mileage circa. 35,000 Miles units. Once a chain has begun to wear, the rate of wear accelerates at an increased rate often being all but useless before 70,000 miles often much earlier.
The easiest way to check your cam/timing chain in situ is to place a straight edge on the external run of the chain between cam and crankshaft sprockets. Chain deflection mid way between the sprockets greater than 20mm or ¾“ imperial inches means that your chain has stretched and or gears worn. This will result in inaccurate valve/cam timing. To remedy this a replacement chain and gear set is required.
Budget. As well as more efficient performance chain sets are available. Roller type duplex chains feature pre-stretched chains with hardened and balanced sprocket gears. They enable more accurate cam timing, reduced friction, subsequently greater power, as well as substantially increased engine longevity. Vernier Timing chain sets allow very accurate cam timing. Where a couple of degrees inaccuracy would not be noticed on a 4 cylinder motor, 1-2 degrees on a V8 would. A Vernier Timing set allows timing accuracy to within one quarter of a degree……depending on the installer.

Paul Blackman 2019

Kit car.jpg