Labyrinth seals?

[Toki]

I have been discussing labyrinth seals with some Yamaha owners.
These are designed as a non-contact solution to sealing, used at crankshaft partitions of multi-cylinder two strokes.
Some say that they can wear and lose some abliltiy to seal.
Does anyone have experience or knowledge of this?
I'm interested to learn how this could come about.

I can only find that Yamaha used this type of seal in their motorbikes, like at the centre of the 100cc twin.

[jato]

if there is no failure of adjacent bearings or alignment and no ingress of dirt/water/corrosion then these seals will last thousands of hours . Jet engine and some industrial applications do so routinely although a racing engine should be more highly strung

[Toki]

Thanks.
Contaminants and/or bearing damage or wear sound likely causes of lab seal failure.
Is it common to see these worn?
Do we know what the clearance is between rotating shaft and the seal?
Wear limit?

New old stock seals are selling for silly money, but the seals look like they would not be too difficult to make on a lathe.

[jato]

i've got some tz ones that once unearthed can be measured - i'd expect a size for size fit in the cases and a radial clearance of .03/.04mm per side on a 25mm diameter shaft. i'll report back soon. i understand the width and depth of the grooves is important to effectively generate the eddys that do the "sealing" i vaguely recall some were split outers and others one piece outers ...

[husaberg]

this (http://www.t20suzuki.com/racing.htm#TZcrank) i think gave the specs for crush and case clearence as far as i know a lab seal needs to have a line bored case. as they run very close clearances to work any bearing rock and they will be shot.
some special ones have outer o-rings like the ones BTK build.

[jato]

Looks like TZ cleararance is around .05/06mm per side on a 40mm diameter shaft (sleeve in actual fact).

[husaberg]

BDK makes these
https://bdkraceeng.co.uk/tc/images/products/originals/556_1741_552_1719_img_20210624_102312.jpg


https://qph.cf2.quoracdn.net/main-qimg-807727199e0a054868c5ed278687645d-lq
Never heard of doing this with the oil?

https://www.youtube.com/watch?v=FPI6oQPN06A

oh look the XS650 has one on the camshaft
351694

i have just found that one of the contributors to KB has made some and used some in small engines
i will let him explain.


Labyrinth type sealing has been extensively used in model IC engines. It takes carefully fitted piston and liners made from materials with similar thermal expansion. Piston rings are easier to get a good seal under less exacting conditions. Larger bore (over 1" or 25 mm) applications have not been successful, especially where gasoline is the fuel.


My simple minded porting templates for small, industrial type race engines is described below. Those engines have one piece cylinders with included heads so it's difficult to use port to head measurements otherwise. Maybe something similar would be helpful in larger engines.

Lohring Miller

351643

paging Lohring

[jato]

Looks like the youtuber is building up a H2 crank - very nice but surely the labyrinth runs more than five ten-thousands clearance (0.013 mm) as the bearings will have more clearance than that then add in a whisker of run out and 2 whiskers of flex...

[Toki]

Looks like TZ cleararance is around .05/06mm per side on a 40mm diameter shaft (sleeve in actual fact).

Thanks. How did you measure it?

[jato]

Measured with a telescopic gauge and micrometer across the internal lands and compared with the same micrometer on the sleeve. the hardened sleeve measures 39.99mm and the lands measured 40.10/40.11. this is a used seal i've been measuring but looks to have never been traumatised...

[Toki]

Great. Thanks for the numbers, jato.
What is the capacity of the TZ engine?

[jato]

TZ 350 i believe - i 've been thinking about the guy that floods his seal with oil , while it is no doubt fine for a road bike, it would slightly detract from the performance of a race engine with the drag at high speed compared with labyrinth seals running clear. my 5 cents ...

[Toki]

Flooding with oil is another mysterious aspect of two stroke lab seals.