Laser-clad valve seats

Motor Trend - - First Drive - FM

The UX en­gines fea­ture a rel­a­tively rare in­no­va­tion that Toy­ota pi­o­neered on a World Rally Cham­pi­onship Cel­ica race car in the ’80s. The alu­minum in a cylin­der head isn’t strong enough to with­stand the pound­ing that oc­curs ev­ery time the valves slam shut, so valve seats of a much harder ma­te­rial (typ­i­cally a cobalt-chromium al­loy called stel­lite) are pressed into the alu­minum head.

That piece and the alu­minum re­quired to sup­port it tend to force the in­take air run­ner to make a slight turn as it en­ters the cylin­der. The WRC ad­vance was to use in­tense laser light to melt a layer of steel onto the alu­minum in the valve seat area. This al­lows the in­take run­ner to straighten out con­sid­er­ably, per­mit­ting greater tum­ble and faster, more com­plete com­bus­tion.

It also means the coolant pas­sages can be re­lo­cated closer to the valve, drop­ping the valve tem­per­a­tures by a sig­nif­i­cant 68 de­grees. This al­lows for greater spark ad­vance be­fore knock oc­curs.

In the ’80s, do­ing this re­quired mov­ing the head around on a turntable while a laser wag­gled back and forth on con­trol springs as metal shav­ings were dropped onto the seat. It was so dif­fi­cult and ex­pen­sive that they dropped it af­ter that pro­gram. But mod­ern com­puter nu­mer­i­cal con­trols and laser wire-arc de­po­si­tion of the metal per­mit eco­nom­i­cal ap­pli­ca­tion of the tech­nol­ogy in the new UX en­gines, in the LS 500’s twin­turbo V-6, and soon in the ES.

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