Engine Failure: Camshaft and Piston damage - Rebuild in progress

Exmoz said:

I noticed the black plastic (Can be seen on video, it's the black plastic round thing) is damaged, drove the bike home (5km) and there was a hard "klunk" sound on the front sprocket.

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• There is no connection between the battery treatment area, and the areas related to the treatment of the front forks. The front sprocket area is also a separate area and independent of the other two areas. That's why I don't see a connection between the repairs that was recently carried out in the garage and the problem you claim appeared after that repairs. The front sprocket problem It seems to me not related to the last mechanic's work.
• As it can be seen in the video, your chain is very rusty, the front sprocket is already quite worn, I understand that both require replacement, and then it is customary to replace everything as a set, meaning also the rear sprocket.
  
  
  
• I'm not sure I understand what the round black plastic part is. The electric wire that reaches the neutral gear sensor passes in front or the front sprocket, this wire should sit inside his rail/slot. Maybe the front sprocket cover was tightened over the wire when the wire was not in his slot, so it damaged the wire?
  

Exmoz said:

bike needs to be loaded on trailer and brought in to shop.

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Yes

Exmoz said:

Removed the front sprocket guard and took video, all teeth seem fine no chips or breaks.

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In the video it was hard to see because the camera was constantly moving, but you can download a stills image here, zoom in on the front sprocket and I'll try to see again. From the video I got the impression that the sprocket and the chain both look damaged to me.

If I understood correctly. your problem is that the chain jumps on the front sprocket.
If so, in the first video you can't see it well, you can see that there is a kind of jump.
In the second video you hardly turn the chain so you can't see the problem.

You have to be really careful when you are turning the chain, you can catch hairs and fingers and then it ends in really serious injuries💀☠

In my opinion, and this is how I get the impression(Rust + worn + jumping), go to a mechanic to change the set: two sprocket + chain.

For routine maintenance, I lubricate the chain with SAE90 transmission oil every 500 kilometers or les.

Yes, if you know that the motorcycle is going to stay with you for a long time, it is worth investing in a quality chain. If you keep the lubrication on time, it lasts at least 30,000 km.

Pay attention to the link, today you have a Spring Link that can be assembled and disassembled easily, if you do not have a special device(WEMOTO) for assembling a chain, then check that your order is for a Spring Link like the one you have now.

If you intend to do the replacement yourself, then my tips are:
1. Be careful not to get seriously injured by catching fingers or hair in the sprockets.
2. Replacing the rear sprocket requires disassembling the rear wheel axle, pay close attention to the order of the parts, who is on the right or left and in terms of rotation what is up or down, and before you put them back in place look at the parts diagram and you will see that everything is back in its place - link to Partzilla.
3. When you clean, in the motor-shaft-seal area work really gently, because otherwise you can destroy that seal(link).
4. Finally, adjust the chain tension, and repeat the test after 200-500 km.

TrueFaith said:

A rebuilt engine will never be as reliable as stock.

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YES Of course it doesn't have to be that way,
but at the level of practice you are unfortunately completely right.

I have repaired engines two times, and it wasn't a perfect repairs.
All the faults I have was from one type: Spare parts availability problem.

You see that there is a part that needs to be replaced, but you didn't order it in advance, because you didn't know it was needed, and you already want to return the motorcycle to active service, and the problem you were running away from appears after a relatively short time.

From time to time I improve, part of the payment for the DIY hobby is the cost of your mistakes.
The sad part in that story is that even in "professional" workshops they take similar decisions, give a warranty of barely six months, and hope that the repair will last at least six months.

I hope my next big repair should be at the "Honda factory" level.
Maybe next winter I will open the top engine to improve my compression(Which is probably the problem that is causing my cold engine starting issue.

Thanks for the photos

It's hard to see from the pictures, I can say what I would considering to do:

• I would inspect the parts closely and looking for cracks or unusual wear, then replace them.
• For axles and other precise parts, you will find minimum dimensions in the manual, and if necessary, replace them as well.
• I would replace all the seals, O-Rings &' gaskets, and all the bearings, also those of the coolant pump.
• What is the condition of the timing chain, so maybe it is worth replacing it and the components related to it?
• What is the condition of the valves? So maybe it's worth polishing?
• What is the condition of the piston? Maybe it's worth replacing, including rings, and polishing the cylinder?

Bottom line, if you're already doing the big job, then it's worth not saving on spare parts, use compatible work tools, and try to do it as good as possible.

TheoR said:

66k km is not that high a mileage on these bikes. I suspect something was done to the bike, resulting in your engine seizing. The fact that the external component, although unrelated to the engine, was damaged leads me to further think that something happened.

From the pictures you posted, the cylinder wall looks to be scored. Perhaps, the bike was serviced and the oil filter installed in a reversed manner. Or, perhaps, the engine was run dry accidentally?

Obviously, it's all conjecture at this time.

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Your hypothesis makes sense. I bought a motorcycle that was neglected. When I bought it, it looked good, it drove well, but I knew I was buying a motorcycle that had been neglected.

Several years have passed since then, and since the
I'm still chasing a fault, I started with what was easy and cheap to fix, and today the problem still exists.

My problem: The engine has difficulty starting when cold. Below 25 degrees I starting it with a rotation of one degree in the throttle. I bought the motorcycle in the summer and I could feel this problem, then winter came...
Now I only have the major treatment left, apparently (because this measurement is not accurate), I have a compression drop when the engine is cold, and when the metals expand from the heat, everything works normally. There is no smoke from the exhaust and no other evidence of oil leaking into the engine, but that is currently the main suspicion I still have: a compression drop.

My motorcycle has already traveled over 70,000 km, and the engine works smoothly and beautifully, except for the problem I mentioned.

I think I received the motorcycle after an event of overheating as a result of an oil leak from the coolant pump oil seal. A 250 engine that working at high rpm doesn't have much to do to destroy it, 70,000 km is very respectable. Maybe I did treatment to the upper engine, to improve the compression? But maybe not! Why to touch it as long as there is no oil leakage. Nothing will happen if at low temperatures my engine is starting with the addition of a tiny turn in the throttle