Timing of valve clearance adjustment


(big4) #1

invarious topics it has been stated that valve clearances shoul be done when engine is hot then the mk5 manal states the opposite shoulbe done cold is this because of the slight differences in cam shafts can any body answer intrested a suggestion re cooling i have deen done with sucess is running a mk7 fan yes it can be fitted peter


(Roger McWilliams) #2

In the temperature range experienced in valve trains, metals expand when heated. Such expansion alters valve clearances, typically reducing the gap. Clearances when hot matter for engine operation. But setting clearances while engine is hot can be problematic. Having the correct hot temperature can be hard to achieve and maintain during adjustment process since the clearance setting process takes time. Setting several valve clearances when hot would likely result in a series of clearances each set at different temperatures of the metals and would not give desired hot temperature uniformity on the clearances when engine is operating at normal temperature. And handling hot engine parts is hard.

Setting clearances with cold engine puts the temperature variation within a range of about 40 degrees F depending on local weather. This puts all the clearances done at pretty much the same temperature, and no length-changing cooling of hot parts while adjusting the whole lot. And the clearance reduction when the engine warms up from cold is predictable and repeatable, so cold clearance setting has its benefits.