YFZ Central banner
1 - 14 of 14 Posts

·
Registered
Joined
·
7 Posts
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
Automotive tire Bicycle part Rim Composite material Circle
Wood Electric blue Metal Steel Fashion accessory
Tire Automotive tire Wheel Tread Synthetic rubber
Wood Rectangle Bumper Automotive exterior Natural material
Beige Auto part Cap Fashion accessory Metal
 

·
Premium Member
Joined
·
939 Posts
The most likely reason would be rod-bearing play. The reason I say that is the missing material at the top is typically from the piston rocking excessively at full extension. The guide can go from excessive timing chain wear or tensioner not keeping pressure correctly. Lack of proper oil or contaminates could or did contribute to this as well, especia;;y since 06 was originally missing the oil squirter.
 

·
Registered
Joined
·
7 Posts
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?
 

·
Premium Member
Joined
·
939 Posts
Definitely meant the bearing in the connecting rod on the crank side. If you dont have the oil mod I would not skip on doing that. If it was mine I would likely just do the top end, replace the cylinder, guide, timing chain, tensor, and do the oil mod if it doesn't have it. There is a few cheap kit you can buy without issues...just get an OEM or decent aftermarket piston since that's what is not good in those cheap kits. Then I would keep an eye on it and re-inspect it after break-in. If you hear chatter, plan on eventually doing a crank with bearings.
 

·
Registered
Joined
·
7 Posts
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.
 

Attachments

·
Premium Member
Joined
·
939 Posts
I wouldn't skip out on the oil mod as it is more than likely what caused the wear you see, especially on the track as it is under load where the issue exists. You can buy pre-done case sides for cheap on eBay once in a while or do it yourself if you are able to.. it's not too hard to do and way cheaper by far (seen parts for like $20 USD). Those are big chunks, defenilty see where that came from. Might not be a bad idea to repeatedly flush the full engine with diesel or a thin oil and then clean out the oil tank and lines really well.
 

·
Registered
Joined
·
7 Posts
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.
 

Attachments

·
Premium Member
Joined
·
939 Posts
That was the type of bad I was guessing. It's usually exactly how it feels when you turn it like you did. I have a cool link to videos that will make splitting the cases pretty painless and if you do it right you won't need to take out the tranny. The only bearings that usually go bad are what you had happen and the main crank bearings themselves. it's rare any both others go out.
 

·
Registered
Joined
·
15 Posts
The wear at the top of the cylinder is from "piston rock" as the crank goes around top dead center the piston rocks and wears right through the nikisil. I've done it with my motors and seen it on others. Totally normal on a high hour engine. Happens faster if you like to bounce your motors off the rev limiter.

You have excessive wear and scratches on the piston skirt and cylinder. Your air filter is not being cleaned enough or has poor fit and or quality. Dirt is getting through.

The timing chain guide I dont know.

No point rebuilding the motor if you are not going to do the oil mod. Could take as little as an hour to seize a new crank. Riding a track does nothing to help get oil onto the rod bearing.
 

·
Registered
Joined
·
7 Posts
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.
 

·
Premium Member
Joined
·
939 Posts
Personally, I wouldn't use a used crank because it's the rod bearings that pretend to be good. You are already tearing it down so why chance that part. Also, it needs to be an 04 WR450F and if I recall correctly you will need to reject it because you are going to be bumping up your compression some.
 

·
Registered
Joined
·
7 Posts
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?
 

Attachments

·
Premium Member
Joined
·
939 Posts
That does look different than what I have seen but the oil galley should still be in the same place and you likely won't need to do anything other than drill the hole.


The image below is where it needs to be placed so as long as you can line it up it should still be good.

 

·
Registered
Joined
·
7 Posts
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....
 
1 - 14 of 14 Posts
Top