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Engine Failure: Camshaft and Piston damage - Rebuild in progress

915 Views 24 Replies 6 Participants Last post by  Tamir
Hi all,
Hopefully Hello @Tamir as well, the one with the knowledge and kindness to reply the majority of threads!

My bike went in to mechanic for a new battery and fork seal maintenance as the right side was leaking.
Attached is the quote I got afterwards.

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.

  • Drove slowly home after the sound and there is a definite something gripping or slipping whilst the shaft is turning.
  • Got stuck in second gear, after a kilometer or so my gears came loose again and was able to shift up to third and then back to 2nd and 1st. Now able to shift through them whilst testing parked.
  • I parked the bike and left town for a week.
  • Returned back to bike shop and showed them the attached video, they said bike needs to be loaded on trailer and brought in to shop.
  • Removed the front sprocket guard and took video, all teeth seem fine no chips or breaks.

My Question:
1. Redacted*

2. What is the possible cause to this issue?

3. Is it possibly just a loose sprocket?

Thank you for the time you take to read and respond to my issue.
Exmoz greatly appreciates your input!


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Thank you for your response @Tamir

I've cleaned up the sprocket area, correctly placed the cable (thank you for that) and upload a new video:

Please let me know if you need a longer one and I'll ask the wife to take whilst I push.

Uploaded a few still images of sprocket as well.
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Chain and sprocket set ordered, thanks @Tamir

Got the DiD Xring which lasts longer I see, also went with stock 14T front and back stock 38T.

Cleaner up the area some more now, if you can't ride may as well clean her.
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Thanks for input Toby
Currently waiting for the mechanic to get back to me.
Seems to be internal issue as the new sprocket is doing the same thing.

Told them to open her up.
Mechanic says, "main bed on crankshaft root cause, bearing failed, it disintegrated, jammed the engine, jammed gears, Some gears got damaged."
Good news: A couple of the parts can be saved and reused in the engine.
- Awaiting a quote, hoping I do not need a whole new crankshaft as I see they are over 300usd.

@Tamir Have you ever had a bearing fail on the crankshaft causing similar issues?
Crankshaft and Piston rebuild kit is required.
With all the needed gaskets.
Local mechanic asking 1500usd to repair.

Sourcing parts from an alternative supplier to see if I can save costs.

It is a dark time, this cbr is costing me the same price as what I paid now.
But in all honesty, it's saves so much fuel and drives so **** good I have to restore it.

@Tamir unfortunately I did not notice any engine noise, but my hearing is not good.
The mechanic noted that the engine noise is odd on the picture of quote I attached about fork seals that were done.
Thanks for the condolences and advice.
Went with the risky route and ordered the parts from abroad and importing them Myself.

In South Africa there is a massive boom going on with motorcycles due to grocery delivery becoming a very big job market.
The odds of finding a 250cc engine is close to nothing, the delivery guys all buy them the second they are online.

Another point is this bike saves me roughly R2000 in fuel a month, so everyday I drive it, it saves me money.

Searched the bike market and could not find any other bikes below R70k.

I'm rebuilding her, and hoping to get another 60k km done on her.
Parts has been ordered from direct India Source, will share the details once parts arrive safely.
Seller is very responsive and quick, DHL waybill done this morning, parcel on the way.

Received some photos from the mechanic as well, hoping they can assist someone in the future!
Let me know what you think of the damage and what else may be good to replace.

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1. Could the damage caused to the black plastic be related to the issues I am facing?
(The mechanic claims he did not cause that damage, but I have photos of before I took in the bike in and after, as they damaged my front break fluid glass thing in December).
Hi there, this has been concluded to be completely unrelated.
The engine simply reached end of life due to excessive use, 66k km done, no idea how many owners the bike had.
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Thanks for the input @TheoR
The filter seems to have been installed correctly as seen in one of the images.
Also cross checked it the other day with Tamir's guide.

The left side of the bike got dropped that's for sure, there is a big round thing on the left side casing that's supposed to be silver, but it's black, so they resprayed for sure.

Previous owner messed up the wiring, had led strip inside and no working headlight!

The air filter cover was removed off the bike when I got it, that little black lid.
Ordered and installed one about 3000km ago, motorcycle also ran in cold dry climate it's whole life, then moved to the coastal area and used in 30-40degrees.
Parts Ordered and recieved so far:

DID Gold Xring chain with new sprockets OEM standard size.
Main Crankshaft Bearing - Blue
Piston Rebuild kit - with cylinder included
Bunch of gaskets and O rings
Crankshaft replacement kit
Spark Plug - Although current one only has 2000km done on it.


Second order (mechanic needed more-parts) :

Main Crankshaft Bearing - Blue
Night Eye LED
Handlebar ends
Handlebar grips
Oil filter and Gasket for service after engine is broken in (1000km)
Neck Steering Bearings - they are due for replacement, might as well do now.
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