------------------------------ Date: Sun, 18 May 1997 13:42:49 -0700 From: Jim Larsen Subject: BMW: BMW Magnet Thread "Gray Paste" To whoever wonders about the metallic debris found on the magnets in your engine and transmission. I've been trying to read only and stay out of commenting but.... All engines and transmissions make (produce) a small amount of metal during the normal wear process. Depending on how the engine or transmission was assembled will determine the wear process. I've got five or more chip detectors hooked to warning lights on the helicopters that I own and/or fly. The only function of these chip detectors (magnetic) is to tell a pilot when he/she/it "MIGHT" have a problem that might deserve immediate attention considering that some small turbine engines are spinning upwards of 53,000 RPM and the failure of some engines/transmissions/gearboxes could ruin your whole day or at least get your immediate attention. Following are some of what you might find on your magnets on your BMW's: GRAY PASTE: Usually gear tooth wear. Set your backlash, gear contact patterns, total indicated run outs, and drag torques correctly, and use a quality lubricating oil and you will see minimum or no paste after initial run-in. I almost never see any on my equipment even during run-in. SLIVERS: Hair like metallic slivers or fuzz usually are found from spur tooth and bevel gear wear and are found during the initial run-in. This is the normal type of metallic waste that will produce a warning light in a helicopter and some airplanes. Some assemblies use a "Zapper" where you can push a button and electrically burn the hair or fuzz buildup from the detector and continue on your way. A chunk of gear, bearing, etc., will remain causing a landing ASAP. Slivers can also be a byproduct of assembly where a gear is improperly forced onto a shaft and a sliver is peeled in the process. Semi-ignore if you find only a hair or fuzz unless your magnet appears like a porcupine. SHINY CHIPS: Usually bearing race breakdown. On a motorcycle I wouldn't panic but would observe and collect the chips. Usually will produce problems as time progresses but bear in mind that a new bearing can fail as quick as a new one. This is not going to cause you to drop from the sky unless you go off a cliff while thinking about it. Semi-ignore chips smaller than 1/8" and observe. On many turbine (jet) engines the ball and roller type bearings are not replaced during overhaul but are replaced as an "on condition" item. Some of these bearings are serial numbered and cost many thousands of dollars! DULL GRAYISH CHIPS: Usually caused by spalling (flaking) of a gear tooth surface. Again observe and collect the chips. Semi-ignore dull grayish chips smaller than 1/8" unless your magnet appears like a porcupine. I've tried to keep the above a simple as possible. I could go into detail as to what every chip in an engine or transmission could be and how to identify each but it would not be interesting or easy reading for most. Like a doctor explaining DNA to me. I no longer overhaul engines and transmissions for others (liability) but continue to do so on my own equipment. I've been twisting wrenches my whole life and professionally since 1958. I could very easily flame my above comments but I've tried to answer the fears of some on this thread while keeping it simple. Enjoy! Jim Larsen K100RT & K100RS (and others in the back of my hangar) SF Bay Area ------------------------------