"Knock" in LTD Stirling Engines

[stan.hornbaker]

My MM-6 LTD engine has a perceptible audible "knock" that comes and
goes in cycles. The engine runs continuously on top of an electronic
clock which provides the heat. Speed 150 to 200 rpm.

A second LTD similar to the one shown on Exergia's pages has excess
bearing noise, or so I think, but runs on top of the PC monitor at 150
to 200 rpm. Instructions said the ball bearing should run dry as oil
would introduce too much viscous drag (and also collect dust).

Any suggestions or insights?

[info74]

You are probably running it too fast. Most MM-6's will make some noise at 150 rpm or more. Back off on the heat. You also might want to try a tiny drop of very light oil like WD-40 (a light machine oil) at the place where the connecting rod attaches to the piston.


Make sure you don't get the oil on the contact surface between the graphite piston and the glass. If you do that the engine won't run.


Brent

[stan.hornbaker]

You are probalby correct. I'll try a bit of very light oil.
The LTT is sitting on a pretty warm electronic clock circa 70's or so.

I recently acquired a KYKO Stirling Fan. The party who passed it on to me advised NOT to use 3in1 mixed with kerosene 1:5 but "Marvel Mystery Oil" from auto supply stores to lube the piston and displacer shafts and wrist pins as it will not gum up as ordinary petroleum. A tiny drop of that should work wonders. Will advise.
s/Stan

[stan.hornbaker]

Marvel Mystery oil is a very light petroleum product which lubricates and apparently evaporates, over time or with heat, leaving little residue.

WD-4o was designed for displacing water, "WaterDisplacer - formula 40"
Neve use it for any purpose, other than to displace water. WD-40 is not a good lubricant as it becomes gummy with aging/drying.

In general the use of lubricants will introduce viscous drag, an impediment to engine operation.