New Diamond Flex-Hone Used to Increase Engine Compression Ratio in “Hot Hatch” Automotive Restoration Project

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In high-performance automotive applications, valve guide clearance is crucial. Selecting the right cylinder hone for the job is critical.

In automotive restoration projects, it is often the small things that make a difference between an average and a performance engine. This applies to the new Diamond Flex-Hone® from Brush Research Manufacturing, a cylinder hone that can be used during a cylinder head build to ensure optimum valve guide clearance for “hot hatches” – high-performance versions of hatchback automobiles.

During the 1980s, the French carmaker Peugeot built what some automotive observers regard as the greatest “hot hatch” of all time: the 205 GTi 1.9L.

Early versions of this tunable supermini needed tuning, however. The in-line four-cylinder XU9J1/Z DFZ engine offered excellent throttle response, but the compression ratio was a mere 8.4:1. This often leaves car enthusiasts wanting for more power.

Forced induction is an option for increasing the compression ratio, but affects the sound and throttle response of a nicely tuned naturally aspirated engine. Another option is to bolt the cylinder head of the Series 3 Peugeot 205 GTi 1.9L, which features a higher-compression engine, to the bottom-end of a DFZ. This can boost the engine compression ratio to 10.5.1 because of the smaller dishes in the pistons of the DFZ.

This is the most economical way to extract power with the only investment being the costs in parts used. The first step of the process involves disassembling the Series 3 cylinder head, pressing out the valve guides, replacing them if necessary, and matching up the inlet and exhaust gaskets with the ports.

In high-performance automotive applications, valve guide clearance is crucial. Too much clearance between valve stem and valve guide can cause oil to slip into the combustion chamber, resulting in clogged spark plugs and loss of power. Too little clearance prevents the passage of oil between guide and stem, with friction-induced failure of piston, valve, and valve guide all possible.

Selecting the right tool for the job is critical, particularly because a ridge reamer can leave a rough finish inside the guide.

A better solution is the Diamond Flex-Hone from Brush Research Manufacturing, a cylinder hone used to achieve an exceptional surface finish with the ideal crosshatch on the inside diameter (ID) of cylindrical parts.

Using exclusive, self-sharpening diamond crystals laminated to the ends of flexible filaments, the Diamond Flex-Hone is a ball-style flexible hone designed for use in surface finishing of cylinders from 4mm to 20mm in diameter (custom sizes are also available).

The Diamond Flex-Hone can perform polishing, edge blending, cross-hole deburring, as well as deliver a beautiful ‘crosshatch’ finish much like that in a newly honed engine block.

Based on the widely recognized Flex-Hone technology, this diamond-laminated flexible hone uses diamond abrasives that “float” to the work-piece during operation, assuring that the tool is self-centering, self-aligning and self-compensating for wear.

The diamond cylinder hone is used to finish the exhaust guides to .0022-in. clearance and the inlets to .002-in. This allows the guide to hold oil while still having a relatively tight clearance.

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Heather Jones
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