ETZ 251 Casings won't split

[thomaskwscott]

Hi Guys,

I had a gearbox blow up on my ETZ 251 a couple of months ago and so bought another engine and am trying to make one good one out of the two. The spare engine i bought split fine and i have it in pieces already but after following the same procedure with the other engine i am unable to split the casings. I've checked for stupid stuff like peftover screws and there are none. Plus the back end seems to want to split ok. Where i am having problems is getting the cases around the crankshaft. It seems the shaft is caught on the bearings and will not release (at least this is my theory as on the other engine i could spin the inner race of the bearings without moving the crank and on this one i can't). Any suggestions?

[arry_b]

Have you drifted the brass bush out of the front of the cases where there's a normally a 13mm headed nut and bolt.

Otherwise - heat around the bearings will help. It doesn't sound normal that the inner races on the other engine could spin without the crank moving.

[thomaskwscott]

Ive drifted the bush all the way out. I remember thinking it was strange that the races spin but the casings separated easily whereas this one just doesn't want to go.

[therealche]

Get the cases nice and hot round the crankshaft bearings ( I use a hot air gun). The bearings should stay on the crank, not the cases.

[thomaskwscott]

Thanks to your advice the casings are now split (the heat gun helped no end). Now I'm hoping I can push my luck and get some advice on the next stage.

I should mention that I am splitting the casings Is to fix a gearbox issue. The front half of the engine has always been fine and I'm keen to re use it. My question is should I replace the main bearings and if yes what's the best way to get them off the crank shaft? I am worried that a couple of the "light" taps on the end of the crankshaft I made to free the casings may not have been too light and also that dirt may have got on whilst the engine has been sat in my shed. I lean towards replacement where possible but I've not got the best of set ups in my current house and want to be sure I can do the job before I get started.

Any help much appreciated.

[therealche]

MZ specify a nice little puller to get the crank bearings off. I always used a freshly ground cold chisel, slid across the crank to get under the edge of the bearing and few taps with a hammer, moving round the bearing to stop it tipping.Slowly work it up. Then use a puller once the feet will go under the bearing. Probably worth replacing them once the engine is apart because they will only fail 100 miles after you reassemble it if you dont! And make sure you get C3 bearings

[thomaskwscott]

Hmm, thus doesn't sound like the kind of thing I can do well on a workmate in my garden. There's an engineering shop down the road, I'll see how much they'll charge to do it for me.

Anyone know what the metal discs between the bearing and the crank seals are called? They got mangled when I removed the seals and I can't find replacements for sale.

[therealche]

http://www.themzshop.co.uk/product/oil- ... -bearings/

And I possibly made taking the bearings off sound harder than it is. I am a great believer in workmates , I have built many engines on mine! Ive done it with a couple of screwdrivers, and a couple of tyre levers.

[thomaskwscott]

Just wanted to say thanks for the vote of confidence. I decided to do it myself and despite a couple minor mishaps (selector fork shaft in backwards anyone?) The engine is now back together.

It feels much better knowing there's a bit more me in the bike (there's definitely a bit of my blood on some of those circlips...)

[MichaelTorre]

how would one know if they receive c3 bearings?
Do our friendly suppliers know about the specification?
Thank you.
M

[thomaskwscott]

Main had c3 written on the side. I got then from eBay but I think they originally came from Burwins in London. If you're in the UK Burwins are fantastic and have everything you could need for an MZ.

[therealche]

Your bearing supplier should know all about C3 bearings.. if they don't find a new supplier. As said they should be marked C3.

[thomaskwscott]

Slightly off topic but I'm having some issues wierd issues with the clutch adjustment after reassembling the bike. It seems now that the 3 bolts that hold the clutch adjustment plate in are now too long and are catching on the front of the clutch. Has anyone experienced this before? It's entirely possible that I'm using the wrong bolts (they were the only set of 3 left over after the rebuild) but they look right. I'm also pretty sure i did the clutch plate nuts up tight enough (the manual didn't specify but there are plenty of threads on there and the lever seems to operate correctly when it's all tightened up. I'm tempted just to shorten the bolts rather than drain all the oil out and take the cover off again. Any thoughts?