What is meant by the term "valve lash" on a diesel engine?I am not sure where exactly the "valve lash" term originated, I am sure someone else will have some input on this, but it means the space, clearance, between the rocker arm or valve bridge and the valve's stem, exhaust or intake and sometimes even injectors. Usually this clearance is something like .025 of an inch or the likes, depending of what the manufacturer demands. This clearance is usually done with a cold engine, and is to allow for the thermal expansion of the valve stem when the engine is at operating temperature. Failure to set this probably, will result in a valve staying open, causing incomplete compression = bad running, or close meaning not enough scavenging being done = bad running.
Also, the compressor rears it's ugly head again. Here's a problem-causing exam question.
Air compressors are arranged to start up with the:
a) Compressor drains open slightly
b) Air relief valve on the receiver open
c) Air receiver drains opened
d) Compressor unloaded
Obviously, b) and c) are throw-aways, however, most condidates have been led to believe that opening the drains is the same thing as the compressor in an unloaded condition (because the machine will not compress air with the drains open). Is there an obvious correct answer, or does this question aslo need revision? I believe d) was supposed to be the correct answer.I understand where you could get confusion, but to me the question is very straight forward, I answered it with out reading your take on it without any second guessing. I am not sure how you would rephrase it to prevent the confusion you mentioned, I will maul it over and see if I can offer any further advice. Regarding your previous question on pressure gauges...
What is the difference between a Pressure and a Vacuum Gauge? The common logic seems to be...One measures pressure on the positve part of the scale while the other measures pressure on the negative part of the same basic scale. What's your take on this?My answer is that the markings on the gauge are the only difference, technically both measure pressure on the same scale. I am assuming your are talking about a round type (Bourdon type) gauge and not a u tube manometer. Zero pressure as we know is generally referred to as atmospheric (the most common reading), zero on this gauge (engine oil pressure gauge on your engine) is actually about 15 psi (14.69595 psi - or 101.325 kPa in SI units, or one atmosphere, or 1.01325 bar) above absolute pressure, which is 0 psi. Anything less than atmospheric pressure is considered a vacuum, so the markings on the gauge are marked as negative, but in fact just measure the actual 0-14 psi scale. I hope that is not too confusing, I write this with my two year old on my laps, so I will have to reread later and make sure I am not full of it. eheheh - you can read up for a more technical explanation of vacuum at wikipedia http://en.wikipedia.org/wiki/Vacuum