Service time!

[Blurredman]

So it comes the time to do some large service to my '90 251 @ 45k.

Quick warning- you migt have to right click and open in a new tab/window unless you have a widescreen/large monitor as i'm not sure how to downsize within the forum, or even if it is a capability.




I thought it'd be nice to implement a thread for this on the forum as I think we may be lacking picture threads at the minute and I always enjoy pictures ! It's not a re-build, but standard maintenance that should be at least checked often..! Mine coincides to have a lot of things to do at one time.

Some of the items are hit and miss, and just preference for me- other are overlooked items of service.




My list was thus:


-CHANGE CHAIN + SPROCKETS (?)
-CHANGE REAR TYRE
-DEBLOCK EXHAUST
-EXTEND FUEL PIPE BEFORE RESERVE
-REMOVE OIL TANK ON NEXT AIR FILTER CHANGE
-CHECK REAR BRAKE DRUM ON NEXT TYRE CHANGE
-INSTALL BRAKE CALIPER DUST SHEILD
-CHANGE FRONT INDICATOR FOR 251 TYPE
-CHANGE AIR FILTER
-CHANGE SPARK PLUG
-CHANGE FORK OIL
-GREASE REAR BRAKE PIVOT
-LUBRICATE SPEEDO AND TACHO CABLES
-GREASE WHEEL BEARINGS
-GREASE HEAD BEARINGS
-CHANGE ENGINE OIL?

For a start, As far as I know the front and rear chain sprockets were original. I had previously changed the chain 13,000 miles ago with a 2nd hand one down from my brother which had only 10,000 miles on it. I was replacing one which I had no history on, so I thought it best to be safe with a 10k mile rather than potentially 30k at the time. So that 2nd hand chain is time to go!.

Before that however I started on my rear tyre. It was now at the end of it's life. A Heidenau K33, which I got 7,000 miles from. Not toooooo bad, but I suppose good for a Heidenau.



Out with the old and onto the pile..!



I have to replace that old tyre with a tyre I have had before and had 8,000 miles before I got rid of it (only because it got square and not because end of tread life). This is the Duro HF319! It has a nice tread pattern too I think.



Whilst I was replacing the tyre I thought I had punctured the tube, as I could hear a hiss- the tube came out and I pumped it up and it held air, at least visually- I put the tyre tube under-water and saw bubbles coming from through the valve.. I then put the dust cap on and no more bubbles..
I would have changed the tube but I didn't have a spare so tried tightening up on the valve core and that worked. It was older type of valve as the tube had Pneumant symbol on it. So the tube was re-installed, and I just put a bit of thread tape on the valve and put the cap on. Seems fine still as of this morning. I also cleaned up and lubricated the rear brake assembly- including using that grease fitting for a squeeze!

Whilst the wheel was off however, let's go back to that chain! Let's check that rear sprocket.. It is worn, true- but it seems to have a fair amount of life left. If both front and rear sprockets are original- the rear has turned a lot less than the front!



And so to the front sprocket- what does that look like? Well.. Like this:



I would have continued to use it, potentially for another 5,000 miles maybe, but I know I have a NOS same tooth sprocket that I purchased in Hungary some years back. But, upon proper inspection there was a crack in one of the tooth, and so- I decided to use my replacement. I must mention that I did purchase an ETZ250 chain, so had to remove a link of the new chain before installation!



And now- time to replace the air filter. My old one was very dirty



and as luck would have it, just the day before my package from MZ-B arrived..! BUT... I have something to do before I install the new filter. I have to remove the air box, this is to remove the oil reservoir. I've never used the oil pump- indeed It's not even installed- so thus off it came. And interesting too.. It seems to have been touching the frame for many years. I should clean that up.



This has two advantages, one is weight, and easy clean of the frame. Second is foremost to me, and that is to EASILY remove and implement the carburettor. With the reservoir installed it can be a little bit of a hassle. Not a hassle anymore.

An extra thing to mention- When the airbox was off I had a good look inside as it looked dirty, and it WAS. I didn't bother to take pictures as my camera is pretty poor.. But the lower inside was covered in a layer of dirt and debree- slightly oily from presumably carb blow back. The airbox was therefore given a good clean.. It's worth a look if you ever take one off!

Now for the fork oil! I haven't done it for 4 years-which is when I got the bike. Now the seals weren't leaking, so I didn't bother to replace them- I merely took the forks off..


Emptied them out!



For those thinking "nah, i'll do the fork oil next time". This is only after four years and 15,000 miles. That isn't a lot of mileage, and that isn't really a long time either..!

On re-assembly, I cleaned up the fork stansions, and tree so that crap doesn't fall into the stansion upon re-assembly. I like to assemble the forks into the bike, and then put the springs in, and THEN put the oil in. This way the fork oil doesn't go everywhere when you try to push the forks in!

One thing to note is that the full amount of each tube was only about 190- they were both equal in oil measure so I suppose that was me who used that figure, but I'm not sure why because the book calls for 230ml...But anyway.. I used ATF myself for the oil. I have a lot of it...

Some small things more I did, is change the spark plug (Denso W22FSU) and change one of the front indicators- I had previously some years back put a round type on because that was all that I had spare. But these days it bugs me- so it was changed out. And I also put on a replacement front pad dust cover.
Some things I didn't do but I had intended to:

-Grease the wheel bearings: They aren't original- and have actually been replaced by metal dust caged type, so I couldn't really grease them. They were a little grumbly and one was a little loose. But I didn't have any to hand so I will just mark them down as required maybe at 50k interval.

-Grease headstock bearings: An often overlooked item. And this time it was overlooked again.. I didn't have a socket or adjustable spanner large enough to get the tree off the headstock. Maybe next fork oil change..


So it's been a busy day, and there are a few things I didn't have time for..

DEBLOCK EXHAUST
EXTEND FUEL PIPE BEFORE RESERVE
LUBRICATE SPEEDO AND TACHO CABLES
CHANGE ENGINE OIL?

I have already lubricated the clutch, choke and throttle cables about a month ago- but in the want of longevity- I decided I should also add the tacho and speed cable. Next time.
Also next time is to deblock the exhaust.. I intend to do this with caustic soda! I have an issue that I cannot seem to easily get to touch 5k which equates to about 75mph.

Also- I seem to have a bit of clutch slip around 4 to 5k, so intend to change oil to 20w50 mineral(advise me?). Currently in the bike is Semi Synth 10w40.

I also intend to increase the length of the fuel pipe in the tap. Currently reserve is 6 miles and that is NOT ENOUGH. I have run out of fuel many times whilst touring, and a few times run off the last drops of fuel coasting into the petrol station. The Neutral light seems not to work anymore either- I have checked the switch connection itself but I suppose it could be the bulb- it may have taken a knock when the front assembly was removed. Will look into that when I lub the tacho cable!

One major thing I do need to do is to take the barrel off and piston out. The piston is only 5k miles old, but is one of the cheap RAM items and i intend to look for wear... There is a distinctive sound to this bike that doesn't sound too healthy, but despite being on 2nd piston (the old one had a crack in the skirt after 30,000 miles..), and a total rebuild at 40,000 miles.. there isn't anything discernable to be worried about - but I would like the check that piston!


Finished product so far: I must admit that it looks a little naked without the oil tank- but so did my 250 when I removed the one off that. It just takes a little getting used to! Don't mind the puddle. That is my oil, but from months ago..




Watch this space

[Puffs]

Thanks for this overview. Still working on the Zen (?), but the art of MZ maintenance you're practising!

Some comments:
- The rear sprockets are good quality & last a long time. The one on my 251, at 35k mi, is also definitely original. That front sprocket too seems original. Yes, it has some wear on the sides, but still, after such a distance (+ several worn chains) it could have more wear inside the teeth. For comparison mine, which I replaced (for a smaller one, rather than for wear) after 30k mi:

- Yes, front sprockets rotate more often than the rear (by that gear ratio), but normally front sprockets are harder steel. Low power, good shielding from dust, finer sprockets and good quality help longevity!
- Yes, that tire is worn a bit, and I like the looks of that Duro. You get and admirable mileage out of your tires...
- Pneumant became Heidenau, right?
- If you add oil when the forks are still out, it might be easier to compare their damping function. Anyway, that's what I do. Also, after this distance it is not inconceivable that the internals would benefit from maintenance.
- Oil: why not just use the advised gear oil, rather than engine oil? If you use engine oil, best use an oil of MA classification, which is compatible with a wet clutch. Higher viscosity will cause drag when the oil is still cold, yet not necessarily prevent slipping.
- Consider adding 'service shocks & replace oil' to your programme.

Please keep us posted!

[Blurredman]

The art of motorcycle maintenance.. And the Morality of doing so!


I do actually have a rear sprocket hub/carrier assembly. A never been used, but slightly damaged (but wouldn't effect anything) for £10 inc. delivery years ago... And it looks like it could be years still before I need to use it.. My etz 250/300 has an aftermarket rear hub assembly which is made of aluminium, including the sprocket part. Last time I looked at that it was still holding up very well despite being fitted 10k miles ago. But the NOS rear hub might be going on that bike as opposed to the 251.

Your front sprocket looks good, still life left in that- more than mine at least. Like I mentioned, I might have continued to use mine if it wasn't for the chip. I was considering still using it anyway because the chip was on the rear of the driving tooth so would get less contact anyway. But.. I have a NOS sprocket that can potentially last 50,000 miles... what is 5k more on the old one? Let's just replace it now I thought.

What interests me is that I fully intended to replace the chains every 10,000 miles mainly because the chains are so cheap to buy £10. But I think it's likely a chain could last maybe 30,000 miles in an MZ if properly adjusted and lubricated often enough (would using Moly grease be better than generic green grease?).. But I woudn't like to stretch to 30,000 miles- even in an MZ it seems it could potentially be pushing it a bit? The downside of the fully enclosed chain on an MZ is that if the chain breaks, there is 100% chance it will snag something up, whether it gets caught in the back wheel or the front sprocket - unlike an open system where there is a fair liklihood that the chain can simply be thrown onto the road..

The tyre is indeed worn a bit, and although fairly square still nice to lean on.. But alas at the end of life.
From what I gleam, Heidanu became Pneumant became Heidenau. The tube itself can't have been all that old because it didn't have 'Deutsche Demokratische Republik' anywhere.. But the bike is a 1990. The bike had almost 30,000 miles on it when I bought it and had Pneumants on both front and rear and those were obviously not the first set of tyres on the vehicle.


Oil: Maybe? But the official service manual states can use motor oil if gear oil 80 is unavailable. This works perfectly well on my etz300 - The reason I resorted to motor oil is because I get different results with varying gear oils. Sometimes the gear change is rock solid when cold, sometimes the clutches slip or drag (even warm) or even both! But maybe I will? I have heard good things about Silkoline? But I might try conclusively 20w50 mineral on the oil change and if that doesn't work- focus full time on finding a gear oil.
That said. I do have 10w40 Semi, that is MA2 class... Would this be appropriate for the old type plates in the bike? Maybe.. I have never tried MA class oil in an MZ before..


As for the rear suspension.... my oil seals arrived in the UK on the 24th.. So they should soon be with me! I have a fourth that I haven't actually taken apart, so that would be the main focus on a thread..

[Puffs]

I can't see that chip in your sprocket. What happens (can happen/has happened to me) is that a tooth breaks off. Then, when the engine pulls on the chain, because of the extra play caused by the missing tooth, you get jerking & much higher loads, causing rollers to break, and potentially the chain to break. And then it gets more expensive. Yes, on the ETZ with it's enclosed chain, the rear cover is likely to explode, on other engines with less room around the front sprocket, the chain may wrap around the front sprocket & ruin the engine casing (if it breaks @ the rear end). Even more expensive.

But normally teeth breaking off would only happen after much more wear, and will probably require more torque than a 251 can give - unless there's a crack or material flaw. Anyway, it's an incentive for sensible maintenance on the journey to achieving Zen.

There is definitely a difference in quality of chains - some last much longer than others. Grease: I wouldn't know. I used to use old engine oil, nowadays any dedicated chain spray.

I was told the wall came down in '89, and the DDR was absorbed into Germany during the course of '90. So when your 251 was made, Zschopau may not actually have been in the DDR anymore...

Gear oil: I just use EP80 gear oil. For engine oil classification, for instance see https://www.oilspecifications.org/artic ... ASO_MB.php. Companies like Silkolene, Motul, Motorex, ... doubtlessly produce excellent oils, but someone has to pay for their advertising. And I'm not sure the ETZ requires very expensive or exotic oils, it was designed for democratic oils.

Yes, my shocks required service too, after just 30k mi (including Scottish salt winters). Maybe I'll take 'em apart again.

[dave47]

Here are my thoughts on some of the above:

Wheel bearings. Is it really worth messing about with these any more? When they are worn out just replace them with the fully sealed type. They are maintenance free and will probably outlast the rest of the bike.

Rear Shocks: The MZ schedule only states that the preload adjuster should be greased. I move them whenever I remember to stop them seizing up. It makes no mention of changing the oil. Are they not meant to be maintenance free? The damper is well shrouded.

Speedo and tacho cables: Again, no mention of lubing these in the schedule. Are they not permanently lubed ex factory?

Front forks: Well gaitered, so do you really need to change the fork oil, except when the seals go?

Gear oil: I tend to agree with Puffs. EP80 is my choice. It is'nt a horrendous expense every 20,000 Km.

I have a different attitude towards maintenance than both of you. Part of the MZ250s appeal for many of its original owners was its ability to tolerate neglect.
Did either of you finish Zen etc. I started it several times but never got beyond page 100. Sent my copy to the charity shop only last year.

[Puffs]

Yep, agreed on wheel bearings. But it is something to look at when you change the tires.

Shocks contain a piston with rings which wear, and then the oil gets dirty (if it doesn't start leaking). After sufficient miles they require service. That is why the (original) shock can be taken apart. Similarly, any cable requires lubrication after sufficient use, IMO, even those with a layer of nylon around the inner (which were probably not common in the DDR). And again, similarly forks wear with use, again pistons & ring, but also the stanchions & outer tubes. All that stuff ends up in the oil & changes its viscosity and/or plugs holes.

Of course they keep on going, even without maintenance, just not so good. And only until something fails.

Yes, I did finish Zen - but lost the book many years ago...

Edit: see one of my stanchions which I replaced a few years ago, after having done some 30k miles:

It's a bit difficult to see, but there is wear, particularly on those places where it carries the torque when you brake. At the lower edge it is clearest, you can see the wear patch just above the tapered section.
I replaced them primarily for corrosion between the triple clamps (not shown), but it also reduced the play in the forks. And made them better.

[Blurredman]

Chains: Even the cheapest standard chain should last 10,000 miles - esspecially when within the MZ enclosed system I should think. Esspecially with regular greasing and adjustment.


Of course, it could be a later tube. Pneumant were around a lot longer after the wall came down..



Dave:

Wheel bearings.. If the bike had original wheel bearings (which I thought it did- maybe that was my other MZ), then obviously a good feel for wear would be required. But if they were open, and if they still felt fine- Why wouldn't you just work a bit of grease in them every time the wheel came off? As it happens though, all four wheel bearings have been replaced already with metal caged type. Which I think can be counter productive- yes they may be closed, but after a certain amount of wear can occur, the elements can actually ingress behind the cage and then just sit.

What's more, without the ability to pack a bit of grease in every now and then, there's nothing you can do to sustain them. As mentioned, these are obviously not original bearings and maybe might have just 20-25 k miles. In which case, they haven't done as you say and outlasted the bike...

That said, one thing I did miss is the bearings in the rear hub assembly- there are two in there and I forgot to have a look. Now, they COULD be original- as often overlooked. They may be requiring replacement considering they have been neglected in my own maintenance except 5k miles ago where I took it out. If they were open, I would have greased them, but I can honestly not remember what they felt like.


As for rear shocks, I have four to re-build (if I can), two of them started leaking, so decided to rebuild in pairs. The ones without any more oil in them may not be re-buildable, but the ones which had oil in had a really bad colour to them. Mixed with rust and water and whatever.. The shocks can be re-built and I suppose the oil should be replaced as often as the forks. And I will make a thread of it.

Speedo and Tacho cables. I'm not a fan of the replacements, they're okay- but this 251 has really cool white/cream colour sheeth. Why this bike has them I don't know, But I like them, and what's more the gagues are completely stable and do not flutter. Half of this could be because the clocks themselves are running well, the other half is because the cables are in good condition or quality. I intend to keep these cable for as long as possible because they are cool looking (and odd at the same time), but also because the clocks are stable within a hair, and there's 50% chance the reason for that is because the cables are good.


Front forks: Yes Gaitors mean protection from the elements on THE OUTSIDE of the fork. Without fork oil changes you'd get the same outcome as with the rear shocks. Besides which, I just use ATF and when 230ml of a few gallons of ATF is used up it's nothing. The only thing I use my ATF for is the transmission, and power steering of my Buick, but also for the fork oil (i've done all four of my bikes now within the last year).

Gear oil: i'm sure within 20k km the oil is definately going to get water ingress. I change my oils fairly regularly and it always interests me how often the oil in an MZ turns from a nice gold to a coffee late colour in not necessarily a long time!


It is true.. Some maintenance is just pro-active, other maintenance is re-active.. You might argue that the price of oil in the gearbox might outweigh the costs of the 5 or so bearings.. So.. why bother putting new oil in it- I could just re-build the gearbox with new bearings when the time came... ??

With my bike.. It may look neglected.. But it is almost 100% mechanically viable and reliable.. I'm not sure I would like the feeling in the back of my mind that says "something could break at any minute.." or "tonight I push you home"


As for Zen.. Yes I read and finished it- and also read and finished Lila... Like most people, I picked up Zen thinking it was all about bikes... At least with Lila I had no preminintions regarding what may be contained within- except someone elses middle aged depression..

[dave47]

Well done both for finishing Zen. It defeated me. Lila?

Blurredman,

I take your point about the need to renovate your faulty shocks and your perfectly valid reasons for wanting to prolong the life of your instrument cables. And I do change my gear oil long before 20k. It becomes toffee coloured by the time you have put the cap back on the oil can. None of these things are going to fail suddenly and involve a long walk home. I would not fail to lubricate control cables for example.
By "messing about" with wheel bearings I meant the whole business of knocking them out of their housings (which does them no good) cleaning them, drying them, spinning them and packing them with new grease. I was recommending fully sealed bearings, not metal cage bearings. You don't need to pack in a bit of grease now and again, its not a problem.
I fixed a loose wheel bearing in its worn housing with Loctite Stud and Bearing Fit.

Is picture 2 of the Heidenau? I had not heard of Dura tyres before. I see that the HF319 is belt biased which is rather unusual for the old school tube tyres we use - mostly crossply. What is your front tyre in the last pic. It looks even more chunky than a Mitas H03.

I needed a front tyre in a hurry for an MOT and dragged this 35 year old Pneumant out of a dark place. It has no obvious sign of deterioration, and I have just done 20 miles on it. Don't worry, I will replace it before doing too much mileage

.

[dave47]

Puffs.
I've just noticed your edit. I'm sure these components do wear as you say. Its just strange that the MZ maintenance chart makes no mention of changing the fork oil let alone the shock oil, even though it is quite comprehensive in other respects. It seems quite lax in other ways too. Not just oil changes at 20,000km. It suggests you might like to "apply 3 drops of Hypoid oil to the lubricating felt pad of the contact breaker cam" every 5000km and change the brake fluid every 2 years.

[Blurredman]

Dave,

Lila is the 2nd book that Robert Persig wrote (and the only other one after Zen) and released in 91/92ish.



I end up changing the oil every few thousand miles. Not because of being over-enthusiastic about oil changes, but more so because I have 4 bikes, and although I have only covered 600 miles on one of them since 2015, the other three remain in constant use but albeit in a sort of 'cycle'. The cycle being, that I ride one until some sort of unexpected work needs to be done on it- I hop on the other bike and repair the old one and maybe the one I am riding at that time breaks down.. the cycle continues. As a result, I amass fair mileages in a year, but distributed between three.
If I take all three bikes into consideration since February 2018- I have done 17,000 miles. 5,000 of that being a tour in europe however so that maybe shouldn't count.

Anyway, the sort of breakages that can be deal breakers for a while. Take for example my Honda which most recently I had to repair. One day when I put it on the centre stand at work, the exhaust note got suddenly louder and I heard a 'ping'. One of the exhaust studs had snapped clean off and unfortunately flush with the head. I tried all I could in my garage to get the stud out whilst the head was still on the bike, but in the end had to take it off and put a spare head that I happened to have.

I then thought that opportune time to get the miles in and 'shake down' the 251 for another european tour on it. But that won't happen now with the virus....

Anyway..
How fortuitous you mention Loctite bearing fit... I recently had to use the same compound on the rear wheel of my Honda.. It wasn't a terribly loose fit, infact smaller than my feeler guages went down to- but the bearing fell out when the wheel was facing down. I was worried a little about using it and wondered the difficulty in removing said bearing if I ever had to replace that one.. Have you ever removed a bearing that had been fitted with bearing fit?? Apparently the sheer sideways force is quite weak so shouldn't be too much of an issue to hit out.. I'm semi-tempted to buy a bearing just to see...

Yes picture 2 is of the Hidenau K33. A fair tyre to be honest... 3.5x16. I've had Duro tyres before and I feel they are quite nice.. As a coincidence, the front is also a (front wheel specified) Duro HF319. I say coincidence, because I don't purposely pair tyres, it just ended up that way. I really like the front tyre too, and as someone who has just fitted a Mitas H-03 to the front of my etz250 (but I don't like it- might take it off and keep for a rear), the duro hf319 front tyre form factor is great, it has held it's shape, it has loads of tread left (that's 5k miles it has on it in the last picture)...


The 251 I have in this thread had a pair of Pneumant's on it when I got the bike. The rear was at end of tread life so was replaced, but the front was still within tread wear. It was probably 20 years old. But I continued to use it for about 3,000 miles until the wear lines....And.. well, I didn't feel any issue with using the tyre- there were no occasions where I felt unsafe.


As for brake fluid. I last changed it in July 2018... I do have brake fluid to spare.. and it's always good to crack open the bleed nipple every now and then... I may do that too..
My 251 is now contactless (been contactless for 14,000 miles- but that was only because I had no choice...) - but my 250 is as original as I can make it- so it is on points still there.. I normally just put a drop of old motor oil on that felt pad..

[dave47]

I would say a 5000 mile tour of Europe definitely counts. I was planning a European tour myself but as you say, the virus has put paid to such plans, probably.
By coincidence, I also some years ago bought a bike with a Mitas H03 on the front, and quickly replaced it. Fortunately I also have a TS150 and it went on the back wheel where its fine. I am reassured by your experience with the old pneumant and might leave it on a little longer. I will certainly consider fitting Dura tyres when the time comes. The HF319 seems like a good choice, especially for the 16 inch wheels.
Loctite: they claim bearings can be removed when required with hand tools, but I have never tried it.

When I originally googled Lila I just found references to Hinduism etc, but have now found the Pirsig book. It seems there are no motorbikes in it and probably an even more challenging read than Zen judging by wikipedia. Free downloads are available so I might take a look. But would that be moral?

[Blurredman]

Yes, I agree. Infact I have already set my mind to put my Heidenau K39 (which wasn't completely dead yet) on my other MZ... I will take the Mitas off and keep it as a spare for the future- even if it is a 3*18, rather than a 3.5*18. As odd as it sounds, I am 'excited' to wonder how many miles I can get from the Duro HF319 on the front of my 251. It has 5k on it already and looks still very meaty.. But I have had 11k from the Heidenau K39... I wonder which tyre will win the longevity test... Oh.. The small things in life ....
As for books. I myself buy 2nd hand from e-Bay a lot.. for just £3 for a 'real' copy.. it can be nice to see print on paper than on a screen.. It doesn't strain the eyes so much..





So.. Onwards to to-day's progress. I have oiled the speedo and tacho cables... I like to cut the corner off a plastic bag (the flat type that you might buy washers/nuts etc in), then a small hole.. fit the cable through and zip tie the end... Or I suppose you could use elastic bands.. Sometimes it can take a full day, soemtimes just 30 minutes... When it comes through the other end it's finished.. I just use 2t oil- because I have lots of it.. At the same time I found out why my neutral light didn't work- it was a blown bulb.




So. Exhaust off. Here is an example of the only original MZ tool I have that serves as the exhaust nut c-spanner at one end, and a tyre iron on the other. I religiously use this item for both requirements and I urge anyone to pick one up if it comes at a fair price..




And with the horn out of the way, the rear mount removed, the whole barrel and assembly can come off. This is more difficult to do with the 250's - the tank has to come off. But with the 251's and the weird banana shaped tank, it means there is fair clearance to get even the barrel up and out.. Interesting to think that all you have to do is take a few bolts/nuts off and you're topless..




So.. I found it difficult to get specs of the caustic soda to water ratio, but I came up with 150grams of caustic soda to a litre of water. I stood the exhaust up straight, put a potato in the end. I measured the soda out, then put water in the pouring jug and just poured it in. It did burp a bit and I even plugged both ends to wash the mix through a bit more to get through to some areas that proved difficult to 'burp'. As of this moment (2 hours after putting the stuff in), the water level does still go down a bit and burps a little so I am just topping up with water now. I will keep it like this for a week and then rinse it out and check what crap comes out.. Give it a good bang... I will decide then whether I put it on the bike and test it, or give it another treatment..





And so the engine top end assembly is on the bench..



First thing to do is blast through the blocked water drain on the head..... I noticed quite a bit of collection of water/oil up there.




And lets have a look at the head first. It looks fine- there is a witness mark of foreign object though- and this is also evidenced on the piston (a few pics down...)




The barrel. It looks okay, but there is that line mid way down (just above the ports) where the engine had been sitting for, well, 13 years.. I bought the replacement piston and got the barrel machined hoping in naivity that the rust corrosion would just be machined out, a lot of it was- but not all of it! Maybe a 71.5mm piston...(?)




The piston itself looks pretty good in my opinion. Very little wear on the side wall- no cracks, no big gauges, you can however see the witness mark of the forign object. It's not too important to me, because it's on the head. I wonder if, whatever it is, came from either the dirty air box (you didn't see how bad it really was), or perhaps something might have fallen in from the top with spark plug replacement/checking..You may also notice a small chunk missing from the cylinder wall in the previous picture of the top of the barrel.. It may be a piece of that.. Cleaning up the head a bit can tell me which direction to re-install it. Also confirms this is a '71mm' piston. The only good thing so far is it looks like there isn't too much blow-by.








So- I checked clearances-- And it isn't very good.. First piston ring gap..
I took the top ring off the piston and placed it half way down the barrel as perpendicular and square as possible. I measured 0.70mm(0.0027in). Specs in the Haynes book is 0.2mm(0.008in) but service limit of 1.6mm(0.063in). That's okay.

The piston was also pushed about half way down the wall- however I can fit a 0.08mm(0.0031in) feeler gauge between the piston and cylinder wall.. That's not so good- esspecially when I had the barrel bored to 2 thou (0.05mm).

This is however somewhat to be expected- This is a cheap RAM piston that I bought for 15 Euros all in (gudgeon pin, circlips, piston rings). I installed this piston 5,000 miles ago. For now it will all go back together. The purpose for this exercise was to check how quickly a cheap piston wears.. The answer = very!



PS: Have also hosted original post's pictures on my own source and re-sized appropriately.
PPS: Have also realised my server cannot hold so many consequtive links .... so have uploaded to a different website for now.
PPPS: What I am going to do for curiosity's sake, is take my 30k mile original size piston and barrel and compare the gap on that. I stopped using that pison because a crack appeared in one of the skirts- but I never actually did measure the clearances. I am also intrigued as to the wear of my other MZ. That has a 76mm piston and also has almost 5k miles of use.. But it is significantly a quieter engine.

[Puffs]

Ta for the update!

0.08mm clearance for a RAM is about right, but are you really sure it was actually bored to 0.05mm at the time? Some wear on the piston is seen above the top ring, where there are no carbon deposits, due to piston tilting (obviously that is not where you measure piston wear). Tilting might have caused the loud running, assuming small end, big end & bearings are OK.
I can not see any of the original machining marks on the skirt, and that would be an indication of wear.

Nevertheless, 0.08mm clearance is no real reason to walk away from the RAM, or do a re-bore. But corrosion pitting in the liner may be the cause of faster wear, on particularly the rings. Did you measure their clearance/end gap after the re-bore? It was probably not 0.2mm.
It might be the picture, but to me that liner does not look very healthy, with all that deep corrosion. That could be improved, but indeed, if it ran fine, you'd wonder: why do another re-bore. Also, piston choice in 71.5mm is limited.

The FOD (learned that one recently!) might be caused by part of that ridge coming off, but from a shard like that I'd expect more damage. And an elongated imprint. Something coming through the plug hole seems more plausible.
Make sure your rings (particularly the top one) still has a proper clearance near that impact zone.

I'm interested to learn if the trick with the caustic soda will work!

[Blurredman]

Well yes. It's a good point, and considering the problems you have had in the past yourself Puffs, It's no surprise you should raise the question. It is true that I didn't measure the barrel/piston clearance when I got them from the re-borers some 2 years ago.. The shop however was quite adament that they were to use 2 thou.
Which gives me an idea I can possibly do in the future to determine their thruthfulness. I have also had a Suzuki TS185 barrel bored at the same place with a 2 thou clearance- The piston is higher quality, but even if it wasn't- I've have done no more than 600 miles.. Measuring that barrel and piston would be a good indication of what the garage would have done at the time...


I must admit that I did measure in the wrong place looking back, so I measured in every place and I could fit nothing more than a 0.08mm feeler in. So it seems the figures I got still stand. The bearings all seem perfectly fine.
Whilst I was at it, I also took my 30k mile original 68.95mm piston and 69mm barrel and that also had a 0.08 clearance..

So I decided there was not much more I could do other than keep a record of my results and put everything back on the bike. Just for reference, it's an early barrel of June '89.




You're right- I always wondered about that deep corrosion.. I say it all the time- but this particular bike has had a hard life.. case in point being a third oversized piston at only 30k! But, if I really thought it an issue it can still be re-bored again (probably not for a long time however) and a search for a much nicer quality piston. At this junciton however, the bike ran, and I suppose just made a bit of noise. I still like to keep this bike going for as cheap as possible. Not affecting safety or mechanical ability (within reason). At least the noise correlates with what the bike actually looks like I suppose. You're also right about the ring end gap. I never measured them new so the only reason to do it was not to check for wear new vs now, but to see if it was still within tolerance in general. And that's fine.


The honing marks can actually be seen throughout the barrel- it's just my poor camera doesn't bring them out very well. Here is a different angle with better lighting.



I inspected the exhaust last night, and other than the fact that the water mix seems to go somewhere... (maybe relaxing itself into channels previously blocked before pouring it in), it seems like it is holding the mix. I can see a white substance come through the join of the two pipes, it looks like ground chalk. It is interesting to note that I personally think the majority of the carbon will be at the front of the pipe. If you look at MZ's you will often find that the exhaust rear ward of the rear mount is often corrosion free on the outside- this is because it's a lot hotter than the mid section.

[Puffs]

On measuring the TS185 barrel: no, after just 600 mi, that gives a fair indication of how he bored the TS185 barrel. Indeed, Suzuki pistons are of good quality, better than the RAM (in fact, my CZ has a Suzuki piston, RM I think). Professional boring technicians may take a view on the piston provided and give it a clearance depending on that view, rather than what is said. So he might have drilled the TS185 barrel indeed @ 2 thou, and still the MZ/RAM @ 3 thou. (Also, the other thing is that the TS185 has a smaller bore, so should get less clearance - I don't know what Suzuki prescribes.)

On the markings on the foot of the barrel: are we really sure this is how those numbers should be interpreted? That would mean my barrel was produced in September '89:

Apologies for the shadow, but it does say either 9 89 (if read upside-down), or 68 6. Problem is, the V5 says "Date of first registration: 14/08/1989". It is possible, but then it had a new (original) barrel before I got it, in '98, with 8500 mi. That is possible, but it seems improbable.

Btw, see the 1mm plate at the foot, w/ silicone gasket at both sides, to increase Maß A from 13 to 14mm. See an older thread on barrel differences 250/251; did you measure yours?

On the end gap in the rings, I think I looked at it, and that it was more than it was supposed to be, but it looks like I didn't write it down. Mine was bored to 3 thou, but actually it runs & sounds reasonably OK, mixed @ 1:32.

Yes, but I didn't mean honing marks in the barrel, but marks from the lathe on the piston.