New ES250 Trophy Project!

[dirtsurfer]

Crikey
You're leaping ahead with this project
Are you still in lockdown?

[Blurredman]

Yes the progress for this initial mock up (we'll see) is going well.. I hope to get started on it again soon after i've had three or four days break.

No we don't really have a lock down- even if we did you wouldn't realise it when you saw the traffic and how people act now etc- restraunts are open, etc. Other than a visual representation (mask) it's pretty much all as it was in 2019... I myself have been going to work like nothing changed throughout all of this anyway.

[Blurredman]

Hey.

Well I had some time last night so decided to swish out that fuel tank (and once again unclog the tap). Stuck inside the tank was the gauze filter element.. Yuck!




I spent a few hours simply trying to start the bike again and to see if I could find a way to make it idle or just run without dying before too long, but I was unable to.. After a while I got so tired with the kickstarter. I could get it to fire, but not for long and the result was that it was a kindof boggy/fluffy mess and backfired/missed occasionally too. I tried to roughly time it up but the only real way I could do that was take the head off (no biggy) and use calipers to measure roughly 3mm BTDC, but it didn't seem to make a difference. Which is quite easy to do by the by. To take the head off an ES250.. The frame is nicely out of the way, and of course the engine is supported by the head.. Just take the tank off and you have plenty of room to get that head off!

The carb is still fairly clean the jets clear so I think the main cultrit would be unmetered air. I know there are a few air issues, mainly I don't have a few seals to fully seal up the airbox, and the air tube to the carb is split too- but I think now is the time to get the engine back out (i'll have to take picture of the wiring at the generator), and start to open it up properly. I think it's running lean. One or both main seals are broken I think. There may appear to be watery oil residue coming into the crankcase (unless it just hasn't cleared out which is extremely likely), but also with no oil in the gearbox it could also be sucking air from in there too (as well as the generator side).

I managed to at least assemble the throttle assembly.. It's quite interesting and but I don't have a picture at the minute. The design of it means that the throttle opens fully at about half a rotation as opposed to quarter of that with a typical 'modern' throttle assembly. So might take a bit of time getting used to that extra rotation to full throttle..

[Blurredman]

I decided to take the engine out tonight. It only took me about an hour I think to disconnect everything and get the engine on the bench again.. And you know the necessity for removing the head (in order to get it into the frame) of course makes it a little lighter too. I think in general that the engine does seem lighter than an etz250 motor... or maybe I'm getting stronger, despite my ailments ha.

One of the first things I did was to check that crank now that it has blown out a bit of steam, as it were.. and actually it looks pretty nice.. it's clean.. But rotating it, it doesn't feel particularly like there is nice green petroil. It seems a bit watery residue. Which is no surprise.





It took a lot of tapping and patience but I got the clutch cover off. And I am pleasantly surprised. There is some residue of course, but there's no chipped teeth, I can't see any metal shavings, all looks very nice other than the gunk. There is obviously some signs of water ingress, the clutch basket has some rust on it, but it's just superficial. Actually, I don't think the clutch has ever been apart. Infact, there is very little indication that that the engine has ever been apart...





Interestingly, if you were looking at the clutch gap indication, it looks like there is no clutch left... Maybe the assembly is slightly different than the etz's..



This one is for puffs: A clutch cover drain screw-






I rempoved the generator, and then had a go at the electronic rotor (not sure of it's name..).. I got out my handy bolt that I use on the etz250 motors to get that rotor off the taper. Thankfully it's the same thread here too and pretty much the same length. Infact, if the bolt was just 2 mm shorter, the head would have bottomed out on the end of the rotor- thankfully, it had that 2mm of space and a little bit of a twist with the ratchet and pop comes off the rotor- very nicely too. It's abit rusty, I suppose petrol, or maybe vinegar (?) might clean the contacts up. The inside of the generator is also a bit rusty. Hope that hasn't shorted out of anything.




With the rotor removed I could gain access to the plate that covers the main bearing. There's a shim, have to keep that safe, but the bearing isn't rusty- looks nice actually. The bearing on the clutch cover also ran nicely.. It's quite likely I can just wash them. They are all plastic caged, so original and easy to disasemble to individual components to clean out- the main bearinsg have a metal cage though. Will have to see about all this. Also don't worry about the rust in the end of the crank there- that's just crust and cleaned out.





Now it looks like I need to buy things again.. A clutch puller for one.. The 4 speed motors have a different puller than the 5 speed.....

Also.. It must be said... Looks like this bike has static timing as I cannot find at all an advance/retard mechanism....

[Puffs]

The book says it has. The pic I posted earlier was from the first generation bike, but the ES250/2 book shows very much the same, see Bild 93 from "Reparaturhandbuch MZ ES 250_2, ES 175_2":

93.jpg (9.84 KiB) Viewed 20509 times

It's the same pic as Fig.93 in your "MZ_ES175-250-1969_Official_Service_Manual.pdf", only slightly clearer. But of course they may have rigged something else in the 48 years since it was made...

Also, you may need (to make) a degree indicator to set the timing. Head difficult.

[Blurredman]

There is definately no advance system.. At the end of the rotor, is the points cam, and the bolt that keeps it all together- Exactly the same as our 251's, Puffs.



Seeing as I'm waiting on parts for the engine (engine disasembly), I thought i'd have another look at that headlamp.
First off- it's quite obvious why no bulbs would work through the connector (I should have actually looked at it more thoroughly, before taking the switchgear unit apart and checking continuity through the switches). The connections to the bulb teminals were broken! I thought the bulb fit a bit loosely in the socket.. hah! So I borrowed the one in my etz250. I swear I had a spare but I can't seem to find it.

Anyway, putting on a replacement connector and it works. Nice.

And actually, for a lamp with the lens not on the bowl anymore, the beam is quite nice. That's directional bulbs for you I suppose.. (?)





I cleaned up the surfaces of the glass and that of the bowl and used some clear silicone to glue them together-you know, the squirty bathroom stuff in a plunger, after the inside of the glass was cleaned anyway... Installed on the bike with the surround it looks nice..





I am pleasantly suprised with the output:




Small wins. Yes I know the bulb has seen better days, but we'll leave it there for now.

So far all the original bulbs that came with the bike (as I got it ayway) work.. At least, all but the brake light (it used to work, maybe the bulb has blown), and the speedo illumination lights. I do have plenty of 6v bulbs, but not a lot that fit this application so i'll have to stock up on that I guess..

[Blurredman]

My 4 speed clutch puller arrived.. So I couldn't wait to get out and try it.. I'm pretty pleased with the quality, it's pretty industrial (compared to the cheap 5 speed one I have), and what's more, unlike the cheap 5 speed puller I have, the bolt that came with this new clutch puller is strong and didn't require replacement out of the box.. Dirtsurfer knows what I mean.



As for the clutch. I've decided I'm not going to touch it, internally. I'm going to leave it be. If I need to replace parts from wear or whatever, I've decided I can do that later. The clutch thrust bearing is very interesting though, it's shielded but i;ve never seen one like this before.. Similar to how on most engines the main bearings (and some of the smaller ones) have plastic cages and not metal ones.

Got the piston out- I'm not actually sure what variation this small end is.. It looks like it could be an updated variant??



Someone's definately been here before too, at least in the barrel section..



The case is ready to split.. ALL screws came out extremely easily and pain free- didn't even need to use an impact or anything.. Now I am stuck though because I need to pick up my makeshift splitter (that I made for the etz engines) and try to adapt that if required, in order to pull these halfs apart.. It's going very well... I hate to say this but.. too well..

[Blurredman]

I got my splitter that I use on my etz motors. There was very little that needed to be adjusted. A few things of note: For one, there is no front bolt for the generator cover, so I used a long bolt going into the rhs bearing oil cover, but I did have to drill a new hole in the splitter for the different placement of the bolt that pushes against the crank end.

Don't worry about it looking crooked here, I took the picture after I had relaxed the tension after successfully splitting..



it all came apart very nicely, and the rhs main bearing came with the casing which is always my preference- I don't have the ability to remove bearing from the sides of crank.

With the gearbox out, and nicely put together in situe and put aside, The gears look all very nice.




You can see here this is the gear change mechanism.. The actual ratchet type item that acts with the gear change is still inside the rhs cover.





Now, there is gunk in there, but basically zero rust which is nice- I suppose there was still residual oil around the walls etc, but the bolt drains were not done up tight, actually- so a good deal seems to have escaped again since the flood in was in. There was residual but not bad. The bearings that support the gearbox are notchy despite not being rusty or seeming pitted at all. Interestingly, both mains bearings (before I punched them out, anyway) were very smooth. But in order to get the main seals out, It seemed easiest to get the bearings out first. As you can see, the ES250 bearing is quite a bit smaller than an old etz250 bearing... The gearbox bearings are all plastic caged- the main bearings have open metal cages. I can't actually see the condition of the mains seals themselves because they are encased in a metal cage themselves. Tearing them open is likely to break them anyway imo.





One thing I did notice is this score along almost the entire circumfrance of the RHS crankcase... Something serious happened here- I wonder what it was. I don't think this case has ever been apart so I suppose it just got pushed out the exhaust. There is a small indentation on the top of the piston, and it maybe the cause of why the piston has a few pretty deep score marks (on the outlet side).. I think it might be connected (maybe, who can say though), but interestingly the crank itself has no scoring on. I know it's a tougher metal and whatever caused this score in the case, was probably being pushed by the end of the crank weight but still an interesting sight.







Everything is apart.. It's time to start buying bearings at least...!
Now from memory, I've rebuilt both my etz250 motors with c3 items- i'll do the same again (unless anyone thinks it should be otherwise?), the official service manual says the 6305 (main) bearings should be "6305 c 003 f (silent)" so I guess that mens c3.

[Puffs]

basically zero rust

Well, that's good!

On the contact breaker cam: then they probably just installed one from the ETZ (or TS)... Maybe the hassle outweighs the benefit, seeing that MZ moved away from that mechanically advancing cam. I have no experience with mechanical advancers on 2T's, but on 4T's they are desirable.

Main bearing size: later engines are more powerful? Differences in lubrication?

Scoring: if it's that scratch I see a bit below the edge, that looks pretty serious. You would have noticed/heard it... That might be why they took the bike apart? Have a close look at the big end. Large sideways clearance? Could that fit? Did some spacer break? Time for Dirk Gently.

Edit:
Are you sure the conrod is straight? On these bikes there are procedures to centralise the piston path, by straightening the conrod (well, there are for the Jawa and I guess for the ES too - look in the book). You might see wear marks inside the piston, small end area, on the piston obviously (as you have), and I can imagine a bent conrod could give sideways load on the big end, causing failure of a shim & ultimately causing those marks inside the crankcase. Just shooting from the hip, but that might be an explanation.

[Blurredman]

Nothing much to report. Awaiting bearings, and just packaging up the crank to be posted for reconditioning.. I'll be making my purchase from Hungary very soon, as well.

I did sand down the burrs that were evident in the LHS crank though..




Maybe the advance/retart mechanism broke and it was just decided to use static timing?

I don't know about the size difference of the bearings- would petrol be more advantageous than transmission oil at lubricating bearings? I don't know- The engine power isn't all that much less than the etz really..
Well, that's good!

It's possible that a shim on the crank (both indeed) have come off and damaged the crank side wall? But I don't think this is the case (but who can say). I don't think it had any shims from the factory. And yes there is a noted proceedure in the book about rectifying conrod straightness, but there aren't any specific witness marks on the little end gudgen pin. Looks good.
The rebuilt conrod I believe will be shimmed.


EDIT:
Just for those interested. Here's a picture of the crank conrod and you can see how much side to side it has (out of the factory??) Anyway.. Just today it will be picked up for postage to be 'reconditioned'.

[Puffs]

Consider using a knife for burs like that (or maybe a file); that only takes out the high parts but leaves the surroundings intact. Sandpaper also sands around it, as you probably used your thumb.

I thought the ETZ bearings were the bigger ones? Lubrication with premix is always very thin, I would guess gearbox oil might give a better lubrication (particularly on the clutch side). Hence they figured they might get away with smaller bearings. But more likely these engines sometimes gave main bearing issues, so that in later models they just gave it bigger & stronger bearings.

Shims are quite common on either side of the big end bearing. See here the (original) big end of my ETZ251.

See the shims. I have not measured the sideways clearance, but it's not a lot. The big end is still fine, the crankshaft was replaced for small end issues (in the pre-webshop era, and I could not find a conrod where I lived).

I wouldn't know how shims like that would vanish. But eyeballing it, your burr could possibly be at the position of one of those shims, and btw, those witness marks would be inside the piston (where the small end of the conrod would rub against it). Yet a little search suggests that indeed the ES may not have had shims:

It's a picture of a 2nd hand crankshaft from https://www.ebay-kleinanzeigen.de/s-anz ... 9-306-2275 , and it appears to have no shims, yet still a normal sideways clearance. Anyway, water under the bridge. Yours will be new.

[Guesi]

ES/2 crankshaft don´t have shims.

On this crankshaft, the conrod is stabilized by the psiton, so the clearance on the bottom of the conrod is quite much.

The ETZ crankshaft has shims, because the conrod is stabilized and guided by the crankshaft pin.And so the clearance on the bottom is very low.

We call it top guided on the ES/2 and bottom guided on the ETZ models.

And about the bearings for the crankshaft:

The ES bearings were lubricated by the gearbox oil.

MZ changed it because of the danger of abrasive metal parts from the gearbox coming to the oil lubrication of the bearings.

And as a side effect, the oil seals of these bearings can be installed outside of the bearings, so they are changeable without taking apart the whole engine.

[Puffs]

Thanks for that evolutionary/technical perspective Guesi! Indeed, particularly the potential damage due to minute metal flakes makes sense. You sometimes see those in gearboxes, and I can imagine that would cause a main bearing to fail. Regular gearbox oil changes seem advisable.

Would you also have a view on why MZ abandoned the mechanical ignition advancer? Benefit, reliability,...?

[Guesi]

The mechanical ignition-advancer was meant to avoid the "kick back" of the kick-starter.
When the engine was running, even in idle speed, the advancer was fully advanced.
So it was not meant for changing the ingition timing over different revs.

And MZ abandoned this advancer because during maintainance by the user no one cared about this part and so many of them were not functioning and the benefit was not that important for the user.
And the normal contact breaker cam was simply cheaper than this complicated advancer....

Modern electronic ignitions have an electronical advancer who changes the ignition timing due to the revs of the engine.
But as I said, the mechanical advancer never was meant to do that.

[Puffs]

I see, thanks Guesi.

Yes, particularly for the early ones they prescribed quite an early timing (3.3mm bTDC), thus those might have a tendency to kick back. Poor fuel & a relatively low compression ratio will cause a lower velocity of the flame front after ignition (cause the mixture stays cooler after less compression), thus the engine requires a more advanced ignition timing for optimal performance. In later models the timing was a little less advanced (2.5 -3.0mm bTDC, say 2.75mm for the ETZ), thus those are less sensitive to kick-back.

Obviously with a fixed timing, the time difference between the moment of ignition and when the piston reaches TDC reduces with rising revs, so that the engine looses efficiency in the higher rev range. Increasing the ignition advance can help combat this, but this was apparently not the objective of the mechanical advancer.