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Discussion Starter · #1 ·
Hi,

Last week my 06 yfz stopped running while i was riding, it did fire back up only to stop after maybe 20sec of riding, after that i was only able to start it and let it run for 10-15sec max.

So i took down to engine and found out that my cylinder was damaged.
But this kind of damage looks weird to me, im wondering what caused this, i got a new cylinder and piston but dont want to put them on and damage them as well.

Also my cam chain guide was damaged i dont know if that had anything to do with it

Does someone have any idea what happend here?

Thanks
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Discussion Starter · #3 ·
Thanks for your response,

That's what i was thinking aswell, i have checked the rod play and there dident seem to be any, i will check later today to make sure.
Or do you mean the bearings inside the crankcase?
 

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Discussion Starter · #5 ·
I do not have the oil mod but since i'm from the netherlands its a lot harder to get parts, there is very few available and if i ship from the US its very expensive.
Also i only ride on mx track so oil will shake through the engine should be fine, i got it for over 7 years and this is my first engine problem (i dont drive very often).

I already got a athena cylinder, prox high compression piston, prox cam chain and new chain guide, i will inspect the chain tensor to see if it needs replacement

I just removed my flywheel cover and found alot of trash inside the flywheel, i think this is broken stuff from the chain guide, it is magnetic tho so idk maybe its something else? I will need to buy a flywheel puller now to inspect further.

I do have a spare wr450 crank at home but i dont really wanna take the whole engine apart if its not necessary.
 

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Discussion Starter · #7 ·
I think i might have found an issue with the crank, if im turning the engine over it looks all okay but then once in a while (10times around maybe sometimes less somtimes more) the connecting rod gets stuck, i cant move it left or right, then after some wiggling it moves normally again. If it gets stuck its pretty stuck i can really pull hard and it wont move.

This is not normal i guess? Maybe theres alot of trash from the chain guide thats getting into the rod bearing and stops it from moving?

I will try to flush the engine and maybe i can flush out the dirt in the bearing, or i will replace the crankshaft.

As you can see in the image im pulling the rod but it wont move.
 

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Discussion Starter · #10 ·
I removed the engine from the quad, waiting on flywheel puller to be delivered.
I will try to do the oil mod myself, i can get a OEM nozzle for 50 euro.

I will replace the crankshaft and bearings, i do have a used wr crank, i've seen people saying this crank is better than the yfz crank.
Is it okay to use this crank? it seems fine to me no play on bearings.
Can also get my hands on a cheap prox piston for the wr crank, but its the B 94,96mm instead of the A 94,95, this will work fine right? its cheaper by 60 euros for some reason.
 

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Discussion Starter · #12 ·
So i'm tearing the engine apart right now and i just removed the case where the oil squirter is supposed to go in, but i've seen the vids of people doing the oil mod drilling the hole etc. But mine doesnt even have the hole that needs to be drilled out... What the heck.

Probably you guys will know whats going on but i did a quick search dident find anything.

I thought it was a 06 yfz but maybe its a 04/05 then? Do these years have this case?
 

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Discussion Starter · #14 ·
well the oil squirter has nowhere to fall in place, theres just nothing there, its not level with the gasket surface.
this is what i just found on j&t website:
NOTE * Due to a mid-production casting change by Yamaha, a limited number of early 2004 YFZ450’s have a clutch side case cover that WILL NOT accept the new ’07 Yamaha oil nozzle. J&T Products has developed a high quality brass oil nozzle that will be used on these limited number of units. The nozzle will operate exactly as the Yamaha nozzle.

so i guess im the unlucky one here with an early 04 case....
 
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