What would you do? Co byste dělali?

[StephanNLCZ]

Ahoj, pardon, nemluvim Cesky...

- I have taken apart an Ural 650 (IMZ 8.103 +/- 1992) for a friend. It used to run good (I've been told by my trusted friend) but has been idle for last 2 years.The engine was stuck.
- There was some water in Cylinders + Heads for some time so they are rusted and need to be replaced. That explained the fact that it was stuck.
- I have taken the cylinders+pistons and the transmission off and the main shaft turns without any problem.
- The rest is also in good condition (carbs, clutch, timing, gearbox, generator, bike itself).

However the crankshaft is also (superficially) rusted....see pics. The casing itself looks bright and shiny inside as far as I can see. As said: it turns without any problem.

So my dilemma:
- Option 1: Take off the clutch and timing gear, remove the crankshaft, have it replaced (expensive) or polished (difficult to organize). Costs time and money, is risky, and maybe I cannot even make the bike run....
- Option 2: Leave it in and first make the bike run. If really needed I can always take the thing apart again. I expect that the rust will "dissolve"/smoothed when the engine runs.

So my question is: is it wise to try to make the engine run with a crankshaft that is superficially rusted? Or will this rust surely create problems/damage? Does it (for example) need to be totally perfectly smooth/balanced?

I appreciate your well-informed advice!

Regards, Stephan.

[hipik634-750]

its easy, just put it together and let it run. if the rust is superficiall it will be gone soon. The iron usually can take a lot. Change all the bearings which were in contact with water just to be sure. the crankshaft will be ok and if not, you will hear it. I would recommend replacement/cleaning of the oil filter much sooner, there could be a lot of particles. Use a simple mineral oil and replace it on next 500 miles. Dont be scared

[Michal]

It all depends on connection rod lower bearing condition. It's either damaged by rust or not. The only suitable way to know it is to try it run and see how it works. If it is damaged then it will fail soon. There is no significant danger for the rest of engine. It will become very noisy long time before the bearing collapses.

[Michal]

In case of crankshaft failure I would suggest overhaul over purchasing new one from some Polish e-shop. Aftermarket crankshafts are of various quality, no one knows for sure which source is good. Ural crankshaft overhaul requires special skills that two-stroke crankshaft overhaul workshops does not possess. Only vintage BMW workshops can do it right. At least in your region. Ural dealers are probably not much of use. Ural 750 crankshafts are almost irreparable (unlike Ural 650) and Irbit factory does not provide 650 specific parts anymore.

[StephanNLCZ]

Update: I have put the bike back together and I'm running (driving) it with the old and a bit rusted crankshaft. Sounds are ok and all looks fine so far.