CASE STUDIES · PART TYPE
Covers and structural parts: large flat faces, oil-tight joints and sound ribs
Crankcase side covers, cylinder head covers and valve covers are large and thin: joint-face flatness decides whether they weep oil, and rib intersections decide whether they are sound. Below: what makes them hard, how we handle them, and every case we have published.
What makes these parts hard
Large thin covers warp on ejection and cooling, and a joint face out of flatness weeps oil once fitted. Rib intersections and mounting bosses are where shrinkage collects, sometimes showing as sink marks outside, and since most covers are coated, those defects only become more visible after finishing.
How we handle them
We spread the ejector pins evenly, hold rib thickness in proportion and radius the intersections; joint faces and bearing seats are rough- and finish-machined in separate operations, with flatness re-measured after the part has rested. As-cast flatness is generally 0.15–0.3 mm, so tighter joint faces are milled. In the cases published here, a 230 × 190 mm crankcase side cover holds 0.08 mm flatness with oil-weep complaints under 0.1%, and over 99% of cylinder head covers pass X-ray for shrinkage.
Covers & structural parts · Production cases3
Motorcycle Crankcase Side Cover
The 230 mm cover came off the die 0.15 mm out of flat. Even ejection, stress relief and gentle fixturing now hold 0.08 mm; oil-weep complaints are under 0.1%.
ADC12 (JIS H5302) · 约 780 g
Motorcycle Cylinder Head Cover
Where honeycomb ribs meet, the metal freezes last and shrinks. Ribs near 0.6× wall, thinned intersections and added venting now pass X-ray at over 99%.
ADC12 (JIS H5302) · 约 460 g
Motorcycle Engine Valve Cover
A 6 mm land and a porous breather root caused sporadic leaks. A larger root radius, an overflow and single-pass milling now give 99% first-pass leak yield.
ADC12 (JIS H5302) · 约 130 gQuestions
How flat can a large cover be held?+
As cast, flatness is generally 0.15–0.3 mm; where the joint face needs better, it is CNC milled to 0.05 mm per 100 mm.
What finishes can a cover have?+
In-house we offer powder coating, bead blasting, shot blasting, vibratory finishing, anodizing and PVD; plating can be arranged through a partner plater, with quality still owned by us.
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