18.125X (21750 CPM) SPIKE ON CAT G398 ENGINE
18.125X (21750 CPM) SPIKE ON CAT G398 ENGINE
(OP)
Routine vibraton readings were taken on a caterpillar G398 engine generator set. This unit runs at a constant speed of 1200 rpm. An increase of over 100% in the overall amplitude of vibration was detected for a reading on the outboard axial (non drive end radiator/fan side) of the engine. Normally the overall amplitude is 0.11 ips. Our last measurement is .25 ips. A mild increasing trend was observed. Analysis of the spectrum indicated a spike at 18.125X at o.14 ips. Also 1X spike at 0.17 ips was detected. Sidebands at 16.625X, 18.625X, 19.125X and 20.375X were detected also. The 18X spikes first appeared in Jan 2003. Two other similar engines do not show this behaviour in the spectrum. The outboard axial reading is taken at crankshaft level. The probe is positioned axially in the area of the water pump.The spectrum for a horizontal reading taken at this point show the 18.125X spike present. The spike is not evident on the inboard. I have no doubt a problem has developed at the front of the engine but I would like to know some possible sources of the 18.125X spike and its sidebands. Can anyone help?





RE: 18.125X (21750 CPM) SPIKE ON CAT G398 ENGINE
Are there any rolling element bearings at this end of the engine? It may be a bearing defect frequency (or harmonic of a fundamental bearing defect frequency) with the typical sidebands that typically surround the defect frequencies when they appear. However, the sidebands seem to be spaced at 0.5X RPM rather than 1X RPM so could the bearing be on an accessory drive that runs at 1/2 the crankshaft RPM (or camshaft?)?
I am unfamiliar with this particular engine so you may have already eliminated these possibilities.
Skip Hartman
http://www.machinerywatch.com
RE: 18.125X (21750 CPM) SPIKE ON CAT G398 ENGINE
RE: 18.125X (21750 CPM) SPIKE ON CAT G398 ENGINE
Cheers
Greg Locock
RE: 18.125X (21750 CPM) SPIKE ON CAT G398 ENGINE
RE: 18.125X (21750 CPM) SPIKE ON CAT G398 ENGINE
RE: 18.125X (21750 CPM) SPIKE ON CAT G398 ENGINE
Is the engine generator assembly attached to a skid? If it is a frame work such as what the radiator and the fan assembly is mounted to. Then it may be some sympathetic vibration harmonic due to something like a mounting (weld) comming loose. It may not be the engine at all.
You mentioned that this is an axial frequency.
How many hours are on this engine?
Have you eliminated a chance that it could be something to do with the generator? Like thrust bearings, how does that vibration compair with what ever frequency the generator is putting out? Have you tried varying the engine speed? What happens?
RE: 18.125X (21750 CPM) SPIKE ON CAT G398 ENGINE