2 Stroke big end

[Gazdaman]

Well, turns out the big end's seized on the MZ.

I suspect this is due to me not having plugged a few holes properly that I should have done.

Anyway, is it repairable? What are the chances the crank's wrecked?

Not a huge deal cuz a new engine is cheap, I would like to salvage this one as a spare though.

New big end bearings? Just trying to think what would seize the big end, yet not seize the bore..

Gaz

[Guest]

Dunno about MZ's, but for most Jap strokers you can get a rod/bearing/crankpin set and just have the crankshaft re-built.

[lee125]

[Barry_M2]

You might just get away with bearings, but you should measure the crank thickness to see if its within the service limit. I'm not sure, but you might be able to grind the crank and fit a smaller bearing?

[Barry_M2]

[finpos]

Bottom end seizure probably due to lack of lubrication - not enough oil in the pre-mix or oil pump borked. Can be helped along by general overheating (i.e. the top end was partially siezed), but if the engines done enough miles it may just have been brought on due to wear. Or some idiot (me) has fitted a pattern bearing supplied with a dust-shield and not removed it.

Re-building the crank with new bearings and seals (old ones may be heat damaged) should be pretty straightforward. It's not like a plain bearing setup in a 4 stroke where you need to worry about the actual crank being worn out - unless you really knackered it!

finpos.

[cagiva gezzer]

Big ends go as they get a hell of a lot of stress. When you rebuild stroker cranks you get a whole new rob with crank pin and bearing, so it's unlikey the crank webs are unuseable.


John Robinson Wrote

[Gazdaman]

Never been stripped before, and yes it may have been low on gearbox oil, but that shouldn't be lubricating the big end, so not an issue.

I think my mixture was ok, slightly too rich with 2t oil, but that shouldn't have caused a seizure.

I'll phone burwin tomorrow, see what light he can shed on it, I suspect cost of repair will be more than the cost of a new engine though.

Might just be usefull to salvage parts from.

Gaz

[Guest]

[NSR Mick]

too much oil means it's actually too weak

(a whole 20 minutes )

Depends whether you are running premix or pump though. A weak mixture (fuel) wont sieze a big end, wear and tear or a lack of oil will.
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