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On 16 May 2006 at 10:26, Keith Park wrote: > I don't think the FI engines are any harder on valves than a carbbed one > would be, that doenst make sense but a valve job on ANY AC engine at about > 60K (miles) is recommended, even the T4 engines. I agree that the FI is probably no harder on engines than carbs. The FI engines I've had have had very good life, and I let most of my valve jobs go at least 100 kmiles. > I think another important factor is how well the valve train geometry is set > up, Im not sure how much that would have varied from engine to engine from > the factory but in rebuilds it probably does. That has a HUGE effect on > guide wear. I tried to model this a few years ago and worked thru a math problem to let me try to optimize the valve train geometry. It turned out to the be quite a difficult problem, but the geometry I finally came up with was within my ability to measure the stock geometry. As valve seats are ground, however, the valves recede into the head and this changes the geometry, so shimming the rocker stands is necessary to compensate for this. Adding swivel-foot rocker adjusters changes this a bit more and requires more shims. In the end I have to shim the heads a bit and shorten the pushrods to make everything work out right, but the end result has worked well for me so far. Note that changing the valve springs or the valve lift would require a new calculation and a different optimum geometry. I've only done this for stock components. Note also that the intake and exhaust valves are different lengths. This is important, because it allows the optimum position for the rocker shaft to be the same for all the valves, even though the lifts are different. -- Jim Adney jadney@vwtype3.org Madison, WI 53711-3054 USA ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~