Main shaft seals

[AlanJ]

Hi All,
On the other MZ Riders web site the subject of main shaft oil seals came up, and I answered it saying on my 3 Z's
I fitted double lip seals on all 3. It was mentioned that in the Haynes manual it suggested a no to that. Now I don't particularly like Haynes myself (like many ) but coming from an engineering background it seemed ok to me that double lip would be the right way to go but as most of the offered sales are for single lip, it has got me wondering, single, double or doesn't matter?
Stay safe Alan.

[nice2day]

Hi Alan...I have the Haynes manual but never seen any mention of a" No No" against double lip seals....What page is that on please? I have already bought my double lip seals awaiting the engine rebuild....can't see why they aren't any good....Les

[AlanJ]

Hi Les,
Sorry I can't enlighten you about the Haynes, it came up in the forum and as I said double lip seems the way to go to me if you have the choice, mind you
I doubt whether there are any problems with single lip or people would not sell them. As I have one more engine to do I was wondering what you guys thought.
Alan.

[nice2day]

Not to worry Alan, but doing a search here many others have used double lip seals.

One way to obtain the longest life from a lip seal I reckon, is to make sure the shaft is as smooth as possible at the contact point area. I even polish the surface making sure that there are absolutely no marks whatsoever in the longitudinal plain. I burnish with grade 2000 wet and dry abrasive paper and finish with Solvol-Autosol on a thin length of strong rag so you can use both hands in an oscillating manor as used by "shoe shine boys" and work equally around the shaft to get the shaft polished brightly. The main objective is that any microscopic marks on the steel are purely circumferential. This will reduce the cutting effect on the seal as it spins so they should last longer....Les

[Kruh]

That second lip is just a protector. Specifically, on the ignition side, that lip keeps dust and debry away from the main lip (the one with the spring).
The main lip gets lubricated by the premix or on the clutch side - gearbox oil or premix (depending on how you install it)

The way I see it, a second lip can only help.

[DAVID THOMPSON]

when i was a kid my dad had a Harley 2 smoker 165cc a poor copy of a dkw 125
it was bad about blowing oil out the seal all over the points
it did not oil the bearings very well and wore out the seals very quick
every winter dad put new bearings in it and new seals
what a piece of junk it was
my ride was a bicycle with a 1.5 hp Briggs and Stratton 4cycle
and two different size pulleys but not rideable at nite because it had only a brake lamp
and it was faster about 1954to 59

[Puffs]

Removed

[Kruh]

Exactly. Thats why most 2 strokes have seals fitted with spring facing the crank.
So I find it quite odd that MZ recommends the opposite - spring facing clutch.

[dave47]

Of the 4 possible ways to insert the oil seals, MZ may have used 3 of them for the MZ250 alone.
Springs facing out - 4 speeds
Facing right - Supa5 (according to MZ engine drawings)
Facing left - ETZs
I don;t know if they have ever made an engine with the 4th method but other manufacturers certainly have.
Obviously the seals have to seal in both directions and I imagine its just a case of which the designer decides to prioritise. Air leaks, oil leaks or fuel air mixture. I don't suppose the MZ seals have a hard life compared to some, and can probably cope whichever way they go in.
Some years ago I realised after assembling an ETZ engine that I had put both seals in the 'wrong' way round. I decided to leave it, and it has made no difference that I am aware of.

[Kruh]

From what I can tell, they used the spring facing away from the crank orientation on all the 250s. Atleast for the clutch side.

I suppose it doesn't matter much for road going MZs. Since both ways are proven to work just fine.

But obviously the pressure is in the crankcase. Therefore the spring side should face the crankcase because that pressure puts a bit of additional force on the lip. Which helps it seal.

But thats more relevant for higher performance engines. Such as racing MZs. Where the increased fuel/air mixture and rpm create a higher pressure.

[nice2day]

Hi Kruh...I was convinced you were wrong about the clutch side seal facing outwards but no....you are correct...I'm so pleased you mentioned this as I would have automatically assumed both seals should face inwards...Many thanks...Les

PS: As it is possible to make double lip seals the ideal version would have a spring loaded seal facing both ways...I wonder if one was ever designed?...There must be occasions this would be useful on other types of machinery...

[dave47]

springs facing out

springs facing right

It isn't clear whether Supa5 seals were ever actually fitted this way.
I have no picture available of the ETZ engine but seal fitting instructions can be found on pp 34-35 of the ETZ250 Workshop Manual. It says both springs are to face left.

[Puffs]

Removed

[nice2day]

For the ETZ engines: The Factory videos clearly show the correct way.

"MZ MAINTENANCE" No 3 (Montage des Motors)................. Right side seal: 10 mins 01 sec
"MZ MAINTENANCE " No 4 (Montage des Motors, continued)...Left side seal: 1 min 16 secs

Les

[nice2day]

Hi Puffs. Your last message appeared as I was entering my last one above....Yes it's strange that the seals are orientated differently in basically similar engines. I really cannot remember now how I installed them in a TS 125 and Saxon 301 engine. With my luck, they are almost certainly in the wrong way round. They run OK though.

I checked my ETZ 250 just now and sure enough the clutch side does face outwards.

If you think about it, the bearing steel shim creates quite a barrier in its own way against gas flow and although we picture the engine in a static way pressure wise, we have to remember the crankcase pressure is oscillating (positively and negatively) very rapidly up to 50x times a second with, say, an average of 25x a second! Air has mass and inertia (yes inertia again ) so the "resultant" gas flow is likely to be a zero nett gas movement when the engine is running.
With the tight restriction of the steel shim and the natural strength of the lip seal spring, which ever way round, there is very little chance of gas leakage occurring.

Leaking seals are most likely to have their effect in the ability to start an engine where the crankcase seal is likely to let in air if badly worn as the slow turning engine does not create the high frequency "inertial air block" that I describe earlier.

Just some thoughts hopefully to calm our worries......

Les