2013 ybr 125 - seizes

[Ub7rm]

Hello, 

 

I bought a ybr125 with 29k miles.  On my first outing it conked out a few times and eventually just wouldn’t restart. Big fat clunk and that’s it. Fortunately I wasn’t too far from home and pushed it back. Battery voltage seemed ok so didn’t immediately think that was a problem. Though occasionally it would weakly try and turn the engine but mostly just a clunk. At the same time I read that I should be able to turn the rear wheel (and thus engine) in 4th - but I couldn’t. Became convinced the engine was seized and proper fubarred. 
 

I stuck a ratchet on the crankshaft and did manage to turn that, backwards and forwards. By now the battery was flat, lots of clicking from the relay but nothing else. So I stuck a new battery on it and she started up again no bother - but would cut out hot or cold periodically for no apparent reason.  
 

Cleaned out the throttle body and that seemed to help a lot.  Noticed with the engine running the battery wasn’t getting much voltage, around 12v.  Measured the resistance across the coils at the connector and all were very low, around 0.08 ohms. Clearly something dodge there, so ordered a new stator coil. By now I was starting to wonder if it really had been seized and all my problems were electrical and poor general maintenance. Feeling confident it was running reliably  - at least while the battery was charged - I changed the oil, ordered a new spark and air filter and took it for another spin.  This time I made it round the block with no mishap, switched it off in the drive feeling reasonably happy, went to do another lap, hit the starter and … clunk. Nada. 
 

into the garage, stuck the socket on the crankshaft and loads of resistance turning left, turned clockwise and it moved, tried left again and turned no problem.  Actually much easier than before, feeling a bit of resistance I guess at the top of travel but otherwise quite loose. Hit the starter button and away she went…

 

I can hear an occasional clatter. It doesn’t sound great to be honest but having listened to a few YouTube vids none of them do. 
 

at this point I don’t know what’s wrong with it. Valve clearance is ok. Seems to have compression, a little white smoke on startup but ok when warm. I have a nasty feeling there is something loose and occasionally jamming but I tend to jump to the worst case conclusion. If it’s bottom end I guess it’s f**ked? Would a new piston and barrel help? Doesn’t seem like that’s too difficult or expensive to try?  
 

sorry for the long post, grateful for and advice.  
 

 

[Blackholesun]

Try the electrics behind the headlight it’s what made mine do this 

[iangaryprice]

If it happens again. Try turning the crankshaft with the socket - but remove the spark plug first. Always turn it the same way the engien runs. Turning tii backwards acan cause problems.

There should be a lot less resistance, the only thing you should feel is the vlave springs. it will be slightly harder to turn the crank when the spring compresses, then it will pull around slightly as the spring expands. You should feel this twice in two full turnsof the crank.

Its only a small engine so the force to turn it should be low,

If this is all good then put the spark plug back in, now it should be noticibly harder to turn duet piston compression. IT shoud go harder to turn once in 2 full turns.

 

 

 

[Ub7rm]

2 hours ago, Blackholesun said:

Try the electrics behind the headlight it’s what made mine do this 

Cheers, what was your problem?  Not charging? 

[Ub7rm]

2 hours ago, iangaryprice said:

If it happens again. Try turning the crankshaft with the socket - but remove the spark plug first. Always turn it the same way the engien runs. Turning tii backwards acan cause problems.

There should be a lot less resistance, the only thing you should feel is the vlave springs. it will be slightly harder to turn the crank when the spring compresses, then it will pull around slightly as the spring expands. You should feel this twice in two full turnsof the crank.

Its only a small engine so the force to turn it should be low,

If this is all good then put the spark plug back in, now it should be noticibly harder to turn duet piston compression. IT shoud go harder to turn once in 2 full turns.

 

 

 

thanks, didn’t realise turning the engine the wrong way would cause damage. It feels like how you describe, very easy to turn then a bit of resistance and then a bit of a release. 
 

I think changing the oil made a lot of difference, first time even though it was turning there was a bit of drag but after oil change and run it was much easier. Don’t know why it would jam up though … or maybe it didn’t and it’s the starter itself that jammed up and turning the engine just freed something. 

[Blackholesun]

14 hours ago, Ub7rm said:

Cheers, what was your problem?  Not charging? 

One of the wires had burnt out and made the bike not turn over 

[Ub7rm]

Right sit rep, was all free and loose, took it out for a few laps, all going well for about 30 mins then there was a clunk and she stalled. Just a clunk when I hit the starter. Pushed it home and put a socket on the crank and it was well seized. Worked it back and forth and it broke loose.  Started up for about 10 seconds and died again. 
 

I suspect I can loosen it off and when cold it will be ok. Until it’s hot again…

 

I would have a go at changing the piston and barrel if I was confident that would solve the problem.  I put a bore scope down the spark plug hole but nothing jumped out as being damaged. No smoke when she’s running. There is some light cross scoring of the barrel mind you.  If it’s bottom end I’d rather just get a new engine. 

[Ub7rm]

Edit.  Put the bores ope in again with a different angle. This doesn’t look good … feeling more positive that a new barrel and cylinder might be the cure.  
 

cylinder is at the bottom of travel in the picture.

 

when stuck it was at the very top of travel. 
 

 

Edited October 27, 2022 by Ub7rm
Added information

[Ub7rm]

To bring some closure… the barrel and piston were fine, the bore scope just really magnified some minor scratches. The bearing between the connecting rod and crankshaft is very rough and sticks in some places. Sadly it’s new engine time as I don’t have the enthusiasm to swap out the crankshaft. 

[Yorky]

So the big end has gone??

[Ub7rm]

Yup, radial clearance seems fine and lateral play was within spec but it felt rough turning and totally jammed at certain points of travel. I suspect a previous owner was less than careful with oil change. It’s quite sad because other than that issue the rest of the engine and gearbox was actually in great nic for 30k miles. 
 

At least I’m getting a crash course in motorbike mechanics … 

[fastbob]

Go on give it a go . https://www.ebay.co.uk/itm/185625710021?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=9yaVSyO-Sly&sssrc=2349624&ssuid=9xhDzDPcSSK&var=&widget_ver=artemis&media=COPY

[fastbob]

On 30/10/2022 at 09:36, fastbob said:

Go on give it a go . https://www.ebay.co.uk/itm/185625710021?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=9yaVSyO-Sly&sssrc=2349624&ssuid=9xhDzDPcSSK&var=&widget_ver=artemis&media=COPY

Well that wasn't quite the reaction I was anticipating . Here you go , stick a big bore on it while you're at it . What's not to like ?  the bike's made in China anyway.

Edited October 31, 2022 by fastbob

[Ub7rm]

4 hours ago, fastbob said:

Well that wasn't quite the reaction I was anticipating . Here you go , stick a big bore on it while you're at it . What's not to like ?  the bike's made in China anyway.

 

Its a good suggestion, maybe I will try and replace the crank just for the craic - but I fear its beyond my patience at the moment.  Plus I think you need a press which I don't have.  They haynes manual suggests you can get by with a heat gun and a freezer but I dunno - maybe that worked with the nice brand new engine they took apart.  Throw in a little warpage on something and I'm not sure I would be so lucky.  

 

I have sourced an engine with 10k miles for £250 with effectively a months warranty on it.  If I tried repairing the engine there is a very good chance:

 

a) I would lose something important 

b) I would still be at it in a months time 

c) 'something else' would present itself as broken costing more time and money

 

New engine should be here this week and hopefully be back up and running by the weekend - just seems like a cleaner solution.  

 

Interestingly you can buy a brand new 'JSM' engine for ~£450.  Looks like a carbed version of the Yam.  I swithered about that.  I mean all that would be different would be the intake side (which I've got and works fine) and possibly the stator / crankshaft which is easily swapped?