axial vibration of camshaft

[ivymike]

Thought problem -

What could cause significant axial vibration of the drive end of a camshaft (measured only at the cam nose), which worsens with increased engine load?

Application:
inline six-cylinder diesel engine
cam-in-head with roller followers
spur gear timing drive

Frequency of excitation not currently known. The motion is not believed to be related to dyno coupling problems, and has only been observed in a lab setting, but has never looked for in other settings.

Some things that I came up with
- axial vibration of the engine assy (due to coupling problem?)
- thrust loads from (spur) geartrain due to small misalignments, deflections of gears, crown offsets, etc
- torsional and/or bending strain of the cam somehow giving an axial displacement at the nose

 

[bklauba]

Both the frequency and the amplitude might well supply direction for your investigation and fixes. I have seen several drive trains where your #2 was the culprit, but let's not jump on that yet.

BK

 

[GregLocock]

I'm a bit puzzled that it is load dependent, on a diesel. Do camshaft drive torques vary with load? well I suppose the exhaust valve opening force is somewhat load dependent.

So I'd be looking at the tappet/cam interface.

That'd come through at firing frequency.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Warpspeed]

I have read about "roller cam walk" in an Iskenderian Camshaft publication, but have never experienced it myself.

http://www.iskycams.com/pdfcatalog/2004-05/page192.pdf

It could happen if either the cam lobes are not ground exactly square, or the lifter bores are not machined exactly normal to the camshaft axis. A side thrust will be generated that tries to screw the cam out of it's bearing bores.

The way Ed Iskenderian described it, you remove the cam drive gear, and rotate the cam by hand with a socket brace, and it will be seen to move sideways after several turns. Reverse the direction and the cam will move in the opposite direction.

I could imagine if the machining were particularly bad on several lobes/bores, some sort of nasty axial vibration could be set up. I really don't know about any of this, it is just speculation.

 

[ivymike]

no lifter bores in this case, but I suppose there could be some kind of problem with the crown on the lobes.