Most motorcycle problems are caused by the nut that connects the handlebars to the saddle.

Cb500 Engine investigation

Jameshambleton
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Post by Jameshambleton on Wed 10 Aug 2016, 12:25 pm

Just the header and a tease of what's to come, as I'm writing this I have no idea either I've just eaten a crunchy nut butty for lunch.

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Airbox side of the carb. 


Airbox 
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sullivj
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Post by sullivj on Wed 10 Aug 2016, 12:51 pm

Nasty....
mcalvert39
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Post by mcalvert39 on Sat 13 Aug 2016, 10:04 am

Oh dear! Don't normally see things like this between the filter and the carb. My guess its spat it out from inside the engine. :/
ANDYC
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Post by ANDYC on Sat 13 Aug 2016, 11:13 am

Is that the remains of your spark plug James?
Jameshambleton
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Post by Jameshambleton on Tue 16 Aug 2016, 10:08 pm

Well I don't need to annotate any of these photos but I might do some anyway. 

First thing out was the carbs and it wasn't looking well. This is metal hiding around my restrictor washer.
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Little bit more metal in the carb worrying but at this point it might just be the sparkplug 
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Now I removed the carb and found this on the airbox side and I was becoming a little more worried. 
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Then I rubbed my finger around it and got this. 
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Next up was the removal of all this stuff. so photo of where the hoses go would be useful for reassembly
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 With the carbs and airbox out of the way this is what I was left with. 
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I then had a look in the airbox and found this.
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and these. so they'll have come out of the engine, through the carbs and back into the airbox. 
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Next up was the engine removal. I didn't get many photos from this point onwards but as you can see all the engine bolts are out as are the lower part of the frame. 
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After disconnecting everything as much as I could me and my mum got the engine out. We had the bike dropped into one side and we wriggled the engine about a bit until it came out. Never the less it's out! 

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So after a uhh, crunchynut butty and 10w40 I was ready to go back to the bike. 
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Took the head off.
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And as checked before the cams were in the right position and the cam chain and tensioner was good.   

As I say I missed out a few steps so I lifted the engine up on my own and moved it about 12ft and 3ft in the air onto the work bench. 

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Next I slid off the bucket and found a cracked thing that the shim sits on. oh forgot I took the cams out too.  Rolling Eyes
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After removing them all I started to remove the head. 
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After fighting with the head bolts for ages with my trusty stanchion breaker bar I got the head off. 
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In the image on the left side you can see the remains of a valve. 
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After finding this I was a little annoyed putting it lightly... so I went up in my room and fiddled with the cb400's clocks.

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sullivj
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Post by sullivj on Tue 16 Aug 2016, 10:23 pm

Nice write up James of a VERY sad day.. I feel your pain with every photograph.

One question... Crunchy nut sandwich... WTF is THAT all about?!

Total respect to your Mum for helping lift the engine out!
Jameshambleton
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Post by Jameshambleton on Tue 16 Aug 2016, 10:24 pm

I had no breakfast and I needed some lunch but the fridge is literally empty so needs must.
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Post by Jameshambleton on Wed 17 Aug 2016, 8:17 am

I forgot the photo of the piston so here it is and the bore is damaged at the top too. 

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It's very likely that I'll get getting another engine within the next 7 days just in time for college starting.
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Post by eternally_troubled on Wed 24 Aug 2016, 3:34 pm

Wow. That is one cool sandwich. I might have to buy some crunchy nut cornflakes so I can try that out for myself.

That bit which had 'split' in half was a valve collet (spelling?) which stops the valves falling into the engine - it hadn't split in half, it usually comes in two pieces so you can assemble it around the valve stem while the spring is compressed, it is then held together once you release the spring back to its normal position by the metal bit on top of the spring (can't remember what that is called right now).

Are there any signs of why this happened? Did the one/both of the valve stems snap? Did the timing chain snap? Is it all so knackered you don't care? Smile Just wandering...
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Post by Beresford on Wed 24 Aug 2016, 8:16 pm

Looking at all that, and thinking about the normal unburstability of the CB500, it even seems to resist attempts to over rev it.  I would guess that the timing chain slipped/jumped a cog tooth or two and the piston hit the valves a few times until the heads snapped off stopping play for the day.
Jameshambleton
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Post by Jameshambleton on Thu 25 Aug 2016, 7:51 pm

Cam chain was the first suspect and it wasn't that, timings were spot on. It had indeed dropped a valve but I hadn't realised looking back, the only thing that I noticed a change in was that when it was idling it wouldn't fire on both pots, I gave it some revs and then it ran fine so I thought it was just some muck blocking the idle jet.

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