Crankshaft worn

[Blurredman]

Hi guys,

Waiting for some equipment to carry on on one of my other vehicles, and not wanting to lose out on time when I have a little bit of it available I decided my interest in this problem had grabbed me.

So yesterday the engine came out and other than 1 screwhead that I had to drill out of the crankcase, the engine split went very well and quickly too.

Foremost, before the split occured I could inspect the little end bearing and you know- it was perfect, it wasn't all smashed up or had rollers missing etc. So onwards I went.

As expected, it went easier/quickly partly because there seems to be no interference fit between LHS inner race and crankshaft so it just came apart. The RHS of the crankshaft was very secure in the RHS bearing.....

But this is what I found....





What is this !? It feels like common green grease. It could be just an accumulation of oil residue left behind from petrol? It isn't gritty but it appears to be embedded in the bearing too as I expect it might be if it was in the crankcase, but oddly enough it is only on the LHS bearing. The RHS bearing is completely clear of this gunk and so is the RHS crankcase.. There seems to be little specs of rust on the crankshaft itself on the edge of the shoulder where it enters the bearing, and also a little bit on the inner race but also some possible witness marks of water being evident at the bottom of the crankcase (oil/water line)- Hmm..... But other than this gunk, I can't see any reason for failure per se (other than the slipping bearing inner race- but is this gunk a reason for that, or just coincidental? Or simply byproduct of use?). Engine was last apart @ 7k miles ago. Perhaps indeed, the clutch slipping has just overheated the crankshaft pinion maybe..

I suppose the metal I found behind the seal initially in this thread was the bearing cage/balls wearing? From the inner race seizing, or just failing to stay interference fit with the crankshaft so that the crankshaft produced this metal by simply spinning in the race? I offered up some old bearings to the crankshaft, some of them did just slip on, others needed force to get on and off. I measured the diameter (although with a basic vernier caliper and with restrictions of access) and found the bearing in the crankcase had inner diameter of 29.94-29.96mm and the crankshaft pinion had 29.88mm varying by 0.01mm depending on placement.


Additionally I found another issue however. I noticed on taking off the stator rotor that the seal seemed to be leaking:


It looks like the spring of the seal on the RHS has somehow come off (or inadvertantly incorrectly been installed which is most likely- and which therefore most of this wear probably occured in the first few thousand miles) and has not only therefore allowed a slighy weepage leak, but also worn a groove on the pinion. It isn't too obvious in the picture due to poor focus but it is actually quite pronounced.. I have however offered up a spare seal and it seems that with the seal facing in either direction it doesn't look like this will be in issue for the sealing surface that the seal actually rides upon...




So, basically... My plan, is buy a new bearing for LHS crankcase, I might need a replacement seal for RHS. Depending on how the new bearing fits on the crankcase I might go down the route of bearing retaining compound... It's likely I could install the RHS bearing with spring/lips facing towards the stator.


SNH bearings (https://www.snh-europe.com/en/): on the face of it, all the bearings that are installed (SNH) do not have any play that I can detect and all feel good.. So...





I have been in discussion with my friend RE plastic cage vs steel. He said the only manufacturer he could find was SKF with C4 clearance and plastic cage. Though with a price of £65 per bearing (?????) Seems a bit steep. Anyway, he mentioned that although the plastic cage is most ideal in regards to minimal wear and something to do with backpressure against crankcase (??) But, later Saxons apaprently just used metal cage so...... In all honesty, I don't think I need to read into this too much. Just get a new c4 bearing (although, i'd need 2x, seeing as the RHS bearing is also C3 currently).



I would like to know why Ost2Rad supplied C3 mains bearings https://www.ost2rad.com/MZ-Spare-Parts/ ... Z-250.html and actually seems to (maybe lost in translation) promote them over what is stated in the manual. Anyway, I can only imagine how hot that pinion got in order to let the race loose, because certainly it was a tight fit originally (I of course remember).


Given by some of the discolouration of the steel washer between crankshaft pinion and clutch carrier bearing, which was blue in places the temperature of that pinion could have been anywhere between 500-600f (250-315c). Definitely temperature at which the race could let go. But again... Why? As mentioned it wasn't long ago that I looked in the area very recently and found no evidence of issues. And clutch slip has constantly been a problem for me on this bike for the last few years.

[Puffs]

Following a moderator choice that is IMO biased and flawed (someone posting aggressive personal attacks is rewarded, while my technical posts are removed), I have withdrawn from this forum.

[Puffs]

Following a moderator choice that is IMO biased and flawed (someone posting aggressive personal attacks is rewarded, while my technical posts are removed), I have withdrawn from this forum.

[Blurredman]

Hi,

Yes a little progress here. I have some parts, but have yet to buy the main bearings. I can get a pair of Koyo C4 for a good price.

Interestingly I tried to save the seals if I could, esspecially the clutch side one as that had not long been installed. I used a pull-hammer from the inside and got the RHS one out okay. And was able to pull out the bearing, seperator plate and then simply pop the seal out. Unfortunately this one can't be re-used anyway as it has been leaking because of the mis-assembly on my part. The spring went back to it's proper position okay but all that time of the lip being a bit deformed I wouldn't want to put it back, at least not on the clutch side (because it's more of a pain to replace!).

The clutch side bearing just didn't want to come out. I don't have any source of heat (except the oven but then i'd end up potentially melting the seal rubber) so in the end I just punctured the seal anyway and then easily drifted the bearing out from that side. So, two new seals I have now got ready to go in (single lipped, and Nitrile).

I have Loctite 609 which if the spec sheet is to be believed that can withstand up to 150c so should hopefully be fine for this application.

I tested a bearing on the crankshaft and interestingly although the inner race was easily easily rotatable when the engine was assembled, it was actually a lot more difficult to do it when everything was disasembled. But was essentially easy enough to remove (it didn't fall off though)..


But, as it is my plan is:

Install 2x new bearings (koyo c4)
Install 2x new seals (nitrile, single lipped), both side to be installed with the spring facing outwards of the crankcase.
Loctite LHS inner race/lhs crankshaft shoulder.


One thing to note, whatever the preconceptions of SNH bearings, they felt really really good before removal. No descernable play, no noise etc... I'd trust to use the RHS one again actually but for the fact they were both removed with a pull-hammer (well, the LHS wasn't, but i certainly tried- and therefore damage probobly occured), and new bearing will be C4 instead of C3.. I couldn't see anything like a crack, or a broken cage etc in the bearing, and actually as mentioned before my spare old bearings which I had lying around also fitted onto the crankshaft in the same way- but I suppose they might indeed if metal has been removed from the crankshaft pinion.... I think the metal dust on the bearing is just from the same source as wherever the swarf behind the seal came from (crankshaft pin?).


The small needle bearing is good and conrod is not scored in that area. The large one is more difficult to see, but once again there's no play, what I can see looks shiney and perfect.

Piston: Looks the same as it was last time I checked it. A little scored but absolutely fine!


Still also a bit confused as to the metal swarf (it looked like a lot, but actually a lot of swarf can become of a small thing like this- It's all gone so I can't see if it's magnetic or not). And, yes there could have been scoring on the bearing race/crankshaft but they're smooth as they should be- but why wouldn't that be the case I wonder? If it was so close a fit then the wear might have been so circular that any witness marks that point to the obvious would only be apparent if the crankshaft was so loose in the bearing that there would be play and a hot spot I think. There's nothing decernable to see there at all..



I think using the same crankshaft but new bearing + retainer compound is worth a go! I'm not really losing much doing this. Who knows, the new bearing might not even need the retaining compound... - we'll see.

[Puffs]

Following a moderator choice that is IMO biased and flawed (someone posting aggressive personal attacks is rewarded, while my technical posts are removed), I have withdrawn from this forum.

[Blurredman]

Okay, it's been some time but that's because things have not gone to plan exactly.. plus all my other projects.. I only decided to investigate my problem now because i've stalled on my other projects.


So.. the engine went together fine with the new bearings. The crankshaft was put in place on the tight race side, and then green bearing retainer material was used on the other side of the crankshaft and a bit on the inner race of the bearing. Anyway, all went to plan and all very nicely too.

So about 15 or so hours later on that night I installed the bike in the frame and I got it started and it ran well. I thought, wahay we're all good to go. Great, about half an hour testing things all sounded good. It was however getting late so decided to call it a night and planned to go out the next morning.

The next morning arrived and I finalised some things (like attaching clutch cable and stuff like that) and I got ready to go, but soon after starting the bike, about 20 seconds or so I heard a metalic 'dink' sound and the cylinder sounded very wrong, I turned it off.

Cylinder is out as is the barrel and here is what has happened. The top piston ring on my 298cc piston has broken. Not sure what happened first whether the ring broke because it had twisted around and interfering with the exhust port, or whether the break occured first and that allowed the twist. However, looking at the piston ring retaining pin, it is quite deeply recessed. It is my opinion the ring was allowed to turn (because the pin has worn or managed to walk too far into the piston) and then that made the damage. Barrel is usable I think still. Piston however will need replacement.

[Puffs]

Following a moderator choice that is IMO biased and flawed (someone posting aggressive personal attacks is rewarded, while my technical posts are removed), I have withdrawn from this forum.

[Blurredman]

I have a new piston ready and waiting to be installed. Measurements seem to check out- just need to remove the small burrs that occured on the exhaust port, and to find the missing piston ring (probably in the exhaust but it could still be in the crankcase, you never know).

[Blurredman]

I finally had time to install the thing. All went well. Bike sounds good too (albeit sound on video isn't the same as real life). Also apologies for poor camera quality, you can see I tried wiping the camera a few times. But it was a hot and sweaty day, what with the other things I had already tasked before tackling this ETZ298.

video-1661102846.zip

(3.23 MiB) Downloaded 182 times

Started very easily after assembly and a quick timing adjustment/check. Now for careful running. Old random picture for fun.

The plan is to come back to it in 1,000 miles. I'm going to take the clutch off and inspect for any discernable issues like melting seals. I might even remove the seal and inspect the bearing (replacements can be just a couple of pounds). I will also be looking into a different issue concerning the kickstart at that time. Who knows, maybe i'll finally properly remove the oil pump too- It's been pumping the same little bit of oil in a loop system for years, and it's easier to install the clutch cover without the locating drive key in the way!).

[Puffs]

Following a moderator choice that is IMO biased and flawed (someone posting aggressive personal attacks is rewarded, while my technical posts are removed), I have withdrawn from this forum.

[Blurredman]

Finally had the opportunity to-day to wear in a bit that piston/rings. Unfortunately I didn't get far.

About 2 miles in I decided the idle was a bit high, and at the 5 mile mark I actually did something about it (no traffic/stopping you see). And well, an old problem came back, it was a bit missy, but ultimately it stalled at one point and the engine stopped momentarily and then it carried on going, but the rev counter was not going. I've been here before says I. I ride home.

The problem is that the engine is running backwards! Hence the rev counter not registering. I had this occur from '17-'18 and I did all sorts to try and rectify the problem, from re-building the engine (putting a different crankshaft in it), to putting electronic ignition on it, and lots of things in between but ultimately it was a desperate moment when I decided to ditch the electronic ignition at the time (I later sold it on) and put it back to points. And the problem never occured again. I must say though It ran backwards with points before back then, which is why after many part swapping and replacing I decided to try electronic ignition (the only reason I bought it at the time). So, to re-iterate, I still had the problem and reverted back to points and for years it never ever ran backwards ever again, until now!

Obviously I've timed it many times during the next process so I think I was spot on. But after I got back home from realising the above, I checked the timing (was fine). Changed points, changed condensor, and after each item was swapped I gave it a test. My test is basic but ultimately most useful. The test is to start the engine (so far has always started whilst rotating in the proper orientation-rev counter working). Then when it's idling just turn the key off and turn the key back on before the engine stops completely. about 2/5ths of the time the engine would come back to life but backwards.

Put the original points and condensor on. Taken rotor and alternator off and made sure surfaces were clean and clear.

The annoying thing is I don't even know what to look for, as in 2018 it seemed to just be a fluke!

For experimentation I decided to put the timing adjustment on it's furthest most advanced and it's furthest most retarded, but my test results are the same. A backwards running engine.

I unfortunately don't have another cam I can use, unless I temporarily steal it from my brother's MZ 30 miles away, but otherwise I'm not sure what else to do.

To be sure on timing, you get the lobe to actuate the points to their highest point (at TDC in my case, always has been) and gap to 3mm, then turn the engine backwards to 2.5-3mm BTDC, and then either by taking the spark plug out and keeping it in the cap, or using a timing lamp, or even just listening/watching for the spark you can with the ignition on move the timing plate. The points should not open at any other time then approaching TDC I'd say. The difference with this bike compared to other MZ's is that the points don't seem to stay open for very long, once the contacts start to close just beyond TDC they close immediately- is it possible my cam is not allowing enough dwell? Aren't points stay open for about half a rotation on a single cylinder? Or am I wrong in thinking that? I know obviously the longer they are closed before they open gives the ignition charge more time.


But here's the annoyance- I haven't changed any timing components on this engine in it's recent downtime! Gah! Help? The damn thing is fighting me all the way lately.

EDIT: checked my Trophy and the points opening/closing happens in the same way there so not sure that's an issue, now. Scratching my head!

[Puffs]

Following a moderator choice that is IMO biased and flawed (someone posting aggressive personal attacks is rewarded, while my technical posts are removed), I have withdrawn from this forum.

[Blurredman]

Yes, okay, interesting. Thank you for the document. Interesting reading.

As mentioned I'd already replaced the points and various ignition components including back timing adjuster plate etc and stuff when I got home yesterday after the quick test ride to see if I could locate/diagnose the problem, whilst I was still prepared to work on it. I myself also don't think it's a timing issue. The problem is, when this last occured in 17/18 I didn't really look into it other than replacing parts and getting myself into a bit of a rut as is what happens sometimes. We've all been there I am sure. I guess when I put the points back on in '18 I might have set the contact breaker gap a bit large, or maybe the cam or timing plate itself ended up seating in a slightly different position (perhaps from a slight bit of grit or something alike), or something stupid like that- and it simply eliminated the problem and made me lucky! And I carried on for almost 5 years with no more problems but ultimately without ever actually understanding WHY.


Yes after the recent rebuild I did set the contact breaker gap to 0.3mm (not 3mm!).


Now looking into it, it does seem very plausable that there is just points chatter, and it explains how it has come back despite no electrically mechanical item being changed in the bike's downtime, other than the fact that it has simply been disasembled and re-assembled.


What I'm going to try to do is put a low resistence in line bulb between the contact breaker + and earth. Spark plug out, put bike in 5th gear. And see if that light lights at any other time other than 2.5mm BTDC. And do the same in reverse. We'll see what we get. It might not be sufficient enough, vibration wise to do anything there, but it may or may not be caused by vibration, it could simply be an anomoly that could be adjusted out.
So yes we'll see what that gets me and then regardless of outcome I suppose I'll indeed put some greater gap on the contact breaker (0.4 maybe yes). And then do my further physical testing (ignition cut out/in) and gauge the results.

[Puffs]

Following a moderator choice that is IMO biased and flawed (someone posting aggressive personal attacks is rewarded, while my technical posts are removed), I have withdrawn from this forum.

[Blurredman]

Yes it's true, I was also considering an LED. Potentially, going very slowly might prove something, which is obviously much easier too with leverage rotation of 5th gear.


How would you polish the cam?

I'll have a think and ponder tonight.
Certainly there is a washer between my cam and the stator rotor- it's possible that removing the washer may provide a different riding surface for the shoe of the contact breaker, for the washer itself is roughly 1-1.5mm in thickness.


Interestingly as a side note, i've been looking through posts/PM's and it seems like I had already tried my brother's cam in 2018 when this occured and that didn't resolve the problem back then.