Labyrinth

[hdavy]

See references to this in discussion on oil leak. What is this labyrinth? Somewhere to get lost in the engine?

[SteveClem]

I'm always lost when it comes to engines!

[mike.perry]

It is the scroll on the back of the crankshaft which should throw the oil back into the sump, provided that the engine ventilation system is working correctly

[bmcecosse]

It's not a scroll - it's a labyrinth.....

[mike.perry]

I was describing the end of the crankshaft which has a scroll.

[123]

It is the scroll on the back of the crankshaft which should throw the oil back into the sump, provided that the engine ventilation system is working correctly

Please will you explain that a bit more?
Especially exactly where this roll of papyrus can be found?
And how one can tell the back of a crankshaft from the front.
.

[bmcecosse]

It doesn't have a scroll - 'scroll' suggests a screw thread - it is just a series of raised edges which intermesh with the cavities formed in the rear main cap and the matching half-moon top section, These form a labyrinth through which it is hoped the oil will be reluctant to escape - provided there is no crankcase pressure pushing it out........

[philthehill]

And to cause even more confusion:-
In the MM Wksp Manual - Section AA.34 it mentions the 'oil return thread'

[bmcecosse]

[philthehill]

Technically it can be called a return thread, a labyrinth and a/the scroll.
The return thread has a start and a finish so it is a thread, it is a square cut thread which causes the oil to be baffled and the scroll/thread winds the oil back into the rear main cap/upper half cap where it then drains back into the sump through a drilling(s) in the rear main cap.
Hopefully before the oil gets to the return thread/labyrinth/scroll it is thrown off the throw ring on the rear of the crankshaft which is located between the rear main bearing and the return thread/labyrinth/scroll.[frame][/frame]

[123]

Technically it can be called a return thread, a labyrinth and a/the scroll.
The return thread has a start and a finish so it is a thread, it is a square cut thread which causes the oil to be baffled and the scroll/thread winds the oil back into the rear main cap/upper half cap where it then drains back into the sump through a drilling(s) in the rear main cap.
Hopefully before the oil gets to the return thread/labyrinth/scroll it is thrown off the throw ring on the rear of the crankshaft which is located between the rear main bearing and the return thread/labyrinth/scroll.[frame][/frame]

Yes, thanks, now we know what we are talking about

Is that tape around the journal please?
.

[Declan_Burns]

Very well explained Phil and a very good photo!
Regards
Declan

[philthehill]

Thank you Declan.

123.
The insulation tape is holding a pair of main bearings shells onto the crankshaft main bearing journal to help protect the journal and keep the shell bearings relative to the journal they have been used on. All of the crankshaft journals are so protected/covered.
Phil

[mike.perry]

Just to add a bit more info, the ex WD version of the side valve does not have a scroll/labyrinth/return thread on the rear of the crankshaft, it has a plain journal with an oil seal