While looking at equipment on Iron Planet like telehandlers they always have have a picture and states blow-by @ idle. What is this telling me about the the engine condition? Thanks. link to picture http://img12.imageshack.us/my.php?image=982161301.jpg
I know if you have excesive blow by, that indicated the engine has wear. More than likely worn rings alowing presure from the combustion chamber to enter the crank case. Then would be released through the oil fill cap as seen in the picture. Not sure if you would be able to see smoke in the picture or not? Hopefully someone with a little more noledge will help tune in on the subject
Blow By It really depends on the Engine Make. What's bad for a Caterpillar is normal for a Detroit etc. It's really a subjective thing. A Caterpillar is a very tight engine, if it is showing any blow by I usually stay away from it. Everything else I usually play by ear. If it's an engine that I don't know anything about I usually ask someone that has experiance with that brand or model. BTW if the picture looks like smoke comming out of a Freight Train thats a lot of blow by. I hope thats as clear as mud. IP has an inspecter in the North Carolina area that they need to run off. He is marking A lot of equipment as visible blow-by and taking the picture. I have a hard time believing every 330 Cat from 3000 hours up has visible blow by, especially when none of the pictures show it. That kind of defeats the purpose of an inspection IMO. Just my 2 Cents.
that was what I was supposing it was now I'll do it to my own machines I don't remember seeing a picture with smoke so I'll try my with a camera to see if it is visable. I have one Detroit which I know is a bit worn. Thanks guys!
Oil and pressure From the filler cap doesn't 100% mean blow by, This can be mistaken for crank case pressure, If the breather is blocked the pressure will find it's way up to the rocker cover. Perkins are prone for Breathing but doesn't mean a bad engine, I've worked on hyster Fork trucks with perkis that breath really bad but never stop. Steve F had problem's a while back and it turned out to be a blocked breather. (An extreme problem that was caused by ICE in the breather hose) 3406 CAT engine's breath heavy but this is normal (Older long stroker's) The fact you can use a gas flow gauge on the Breather Pipe and take a reading mean's this is a parameter that is normal within spec's.
Crankcase pressure means just what it says. The pressure can be caused from blowby, which is compression gas making it way past the pistons, rings and liners. Crankcase pressure is usually measured at the breather or the dipstick tube with a water tube manometer or a gauge reading in "Inches of Water". The Japanese engines used to make this a simple indicator. One inch of water meant it was time for you to look at your engine and find out why there was that much pressure. It usually was where you started considering a rebuild in the near future unless you found the breather was plugged. Cummins did the test a bit differently. For those engines you installed a plug in the breather that had a calibrated hole in it and a tee above the plug for the gauge. The hole was different for different sizes of engines. Generally the max pressure would be around 15 to 20 inches of water. However in my experience Cummins changed the spec several times over the years. Caterpillar used to put an extra large breather cap on their engines so the manometer almost never moved even with a worn out engine. In recent times the test method has been changed. Now a small turbine is installed into the breather tube and it measures the actual flow coming through the tube. I don't know it for a fact but I think this came about because of the emissions regulations instituted by government. Caterpillar and Komatsu both use this test for their engines. Reference has been made to "visible vapor" from the breather or the fill cap. Basically you will always be able to see some vapor from the breather and there will always be oil splashing from the filler cap hole. These characteristics don't mean anything and are of no use to the field mechanic or inspector. However there is one time when the vapor is important. Water vapor will collect on the bottom of the tube or emulsify on the bottom of the fill cap which tells you that an oil sample is probably necessary looking for coolant in the crankcase. What really shows up on engines with lots of blowby is that they will not start in cold weather without some kind of starting aid and they usually have lots of oil seeps from seals and covers. When I see this I usually will use my manometer to provide a specification, say 1.5 inches of crankcase pressure. The big clue is a can of starting fluid stored in a tool box or behind the seat. Now days the emissions regulations are doing away with crankcase pressure entirely because almost all the manufacturers have gone or are going to exhaust gas recirculation just like a gas engine in a car. With the electronic motors and EGR you are basically going to have to ask the computer what the condition of your engine is. It may sound funny but the computer systems installed on engines now have that capability. The manufacturers so far have decided that the end users can't have that capability.
Thanks you all for your time! :notworthy:notworthy
I forgot to mention that crankcase pressure is always measured at high idle under as much load as is possible to attain. The measurement on a wheel loader engine would be taken at converter stall or full stall. An excavator would show the highest reading at high idle running the stick out or in.