Removing MZ251 crankcase seals

[JSmellie]

Hi anybody,
an idiot question I am sure but I am about to try and replace the crankcase seals on my MZ251. I know to remove the wire circlips first (not done it yet so if there's a trick to make it easier, please let me know). Previous comments in this site suggest the seals should 'just pop out'. Can anybody explain how to make them pop out? I also note that some folks recommend screwing in some self-tapping wood screws and tugging on the screws with pliers. Is that recommended and what size wood screws? The new seals don't look terribly thick & I worry that the screws will simply tear out. Do I need to gently warm up the crankcase with an airgun beforehand to help 'loosen' up the seal in case it is a tight fit? Just looking for some practical advice so I don't end up ruining an otherwise good engine.
Thanks, John.

[Kruh]

They do pop out fairly easily.
If you are using the screw method, make sure you don't screw them too deep, or else you are going to damage the oil guide plate behind it. You can screw it in to about the seal width (7 mm).

You can also pop them out just by inserting a screwdriver or something similar, between the crank and seal lip and pry it out sideways. Just don't pry too much on the crank itself, so you don't damage the sealing surface. Using a softer metal, like aluminuim might be a good idea to prevent any damage or just put some tape on the screwdriver.

[Guesi]

I would order the oil guide plates, because most of the time you damage them when when you use the screw method.
And this method is the best method. The seals do not pop out easily....
And the left seal is installed with the flat side pointing to the oil guide plate, so there are no 7 mm between seal and oil guide plate.
The method with a screw driver often leads to a damage of the crankshaft or the crankcase.

[Puffs]

Removed

[Guesi]

These oil seal get harder by the years , so simply standing a long time unused can cause the failure of the seals.
And the material reacts with the additives of the fuel. This also limits their life time...

[Puffs]

Choices...

[JSmellie]

Thanks guys, all useful and welcome advice and much appreciated. For background, I was given (yes!) the bike back in 2009 and I ran it for 6 months. The owner said I either took it or it would be skipped as it was worthless to him. The exhaust system had rotted off but, once replaced it ran well & always started reliably but was rusty as hell (not much paint left) and had issues with jumping out of gear and some electrical problems. But it would sit at 65 all day, gave me 60 mpg and I got to love it. I took it on as a project then it sat unused for 10 years (I have other bike transport). Duh. In 2019 I stripped the bike, repainted it, fixed the known issues but, unlike any other bike I have worked with (admittedly all 4-strokes), it refused to start despite a good spark (jumps a 6 mm gap). Fresh fuel used too, though I am not 100% that it is getting through though I've stripped and checked the carb and it seems clean. My guess is that letting the bike lie for so long has not done the seals any good, hence my enquiry to you guys although if you think there's something else I should check/do, feel free to suggest it.
Thanks for all the tips. I'll try the self-tapping screw idea as I don't want to damage the crank prying the seals off with a screwdriver. Fingers crossed.
Regards,
John

[Guesi]

Hello

What gear jumped out ? Probably the 3rd ?

[Puffs]

Removed

[Blurredman]

Hi,

It is quite possible to take the seals out as others have mentioned.. I haven't done it myself, but would ber perfectly prepared to do so if I thought they was an issue. The seals themselves have metal sheilding in them, so that metal sheet is what the screw will grab hold of when you pull. And, the metal disc between seal and the bearing you can get replacements for. They're no issue to get if you do go too far. But if you are definitely going to do this- then just get new seals first, and make depth measurements by the ones in your hand..


But as Puffs says, why do you think they are an issue to you? Have you checked the other things first?

[JawasandMZs]

I'm actually pretty desperate to read "just bite the bullet and rebuild (or get rebuilt) the motor" ... having spent £650 in total for that very job in Oct 2020 it'd somehow make me feel a bit better! Seems to me that if you're looking at a barn find stroker, the default assumption should be that the crank seals have perished.
There are loads of tutorials on YouTube, not specifically for MZs but you might find them useful.
Good luck!

[DAVID THOMPSON]

its all about parts
here in the USA some times a 1974 model shows up
if its mz or bmw you can find parts
if its some other brand it may be hard to find the bit and pieces
even when its an HD that old you may find the part
but the price will kill your pocket book.
DAVE

[Puffs]

Removed