ETZ 250 Engine Re-build!

[ivor]

Ha ha, no you're both right, it works on plain bushes and probably not much at all on a roller bearing, put it down to a senior moment. Best just get a puller meant for the job, or see if you can make one yourself like I suggested from a heavy duty builder's fixing.

[AlanJ]

Hi Skyeport,
Did you melt the wax into the centre and then punch it while still soft? While writing this I have just thought in all my years of mucking about with bikes, I have never had to pull a blind hole bearing. There is always the first time for everything. Wish you well Alan.

[AlanJ]

Hi Ivor,
Good on you, mind you , at 80 yrs you can't have many more senior moments than me. Alan

[AlanJ]

Hi M,
You mentioned no gasket between crankcase halves. Have a look at my post Anaerobic Multi Gaskets it might be of interest. Alan.

[ivor]

Hi Ivor,
Good on you, mind you , at 80 yrs you can't have many more senior moments than me. Alan

[Skyeport]

Hi Skyeport,
Did you melt the wax into the centre and then punch it while still soft? While writing this I have just thought in all my years of mucking about with bikes, I have never had to pull a blind hole bearing. There is always the first time for everything. Wish you well Alan.

It was a while ago, but i think I just shaved the wax into the hole then tamped it down with a wooden drift made to fit into the bearing shaft hole. I found this technique somewhere on the web, can't remember where.
Bearing was starting to make it's way out when I over enthusiastically tapped the drift a bit too hard & popped the case behind the bearing. It's amazing what you can fix with devcon
In hind sight, once I got a bit more clearance under the bearing I should have then used the puller.........

[Blurredman]

Okay guys.

My bearings have arrived, and after a successful cleaning operation on the case halves I am soon prepared to install the new bearings.

However I have noticed that the replacement main crnak bearings (set purchased from Ost2rad) are open sided on both sides, when the original bearings had open side on teh oil seal only?


Even the official engine dismantling video on youtube uses bearings with one side closed. Also refering to it with "make sure the closed side of the bearing is facing the crank".


I have also posted this to the chaps on the MZ Facebook groups, they all seem to have a mixed response.

[AlanJ]

Hi M,
Just to put my pennoth in. Most companies will look at cost saving and as it will cost more to put that shield on a bearing if it wasn't necessary then I don't think it would be there, Just a thought if the shields are not on the crank bearings, what about the loss of pressure in the flywheel area. It's not my field so just a thought.
Wish you well Alan.

[AlanJ]

Hi M,
I meant to ask earlier, How did you get the blind hole bearing out? Alan.

[Blurredman]

Hi..

Well progress has been done.

My inner race type bearing puller came and it worked a treat.. One of these:



Thice I pulled on the weighted rod and on the third time it popped out completely! I've already got all the new bearings in, and I'm just trying to work out how to get the gearbox all in and then I'll get the crank in and the two halves together again.. Exciting! The gearbox is perplexing me a little. I don't enjoy gearboxes The only gearbox I like is the CX where it all comes out as a single unit on a fixed rear plate..

I will take a picture of the original bearing. It seems like the one side that is closed is actually a way to hold all the balls in place. It is made of plastic and the balls pop into it. I will take pictures and show, as the question I have posed seems like it has rather rocked the MZ community.


In reality.. I could have the engine back together in mere hours stretched over a couple of days (I work for a living.. )

[Blurredman]

Just posting an image of the original crank bearings. It isn't completely closed on the one side, it just seems to be a cheap and effective way of spacing the balls and giving support. They're still pretty good after 30k. But as you can see, they're not "completely closed".

[Blurredman]

Just an update.

The engine is back together and seems good. However the cylinder barrel will need a rebore as the 75.46mm 300cc piston is worn and, there is a 0.15-0.2mm clearance ALL around the piston. If I push the piston to one of the walls then I can almost fit a 0.5mm feeler guague into it. The clearance spec is around 0.03mm. So.. although this is an overbored 250 barrel with a 300 piston in, it is pretty much worn to the extent of allowing the introcution of a 76mm piston, which I think I will do. Otherwise the barrel is scrap.


Also: Does anybody have a spare 12v stator for the ETZ?