Yamaha YZF450 Scored Cylinder Liner

[boozewz]

So I had to have my 450 cylinder head pulled out as the bike was not cranking. Its a 2004 model, and its had regular oil changes as part of its service, but nothing else has been done. When the mechanic took it apart, we found that the liner was scored and needs to be replaced, as well as the piston, and the rings. Everything else is ok otherwise.

I asked the mechanic what would cause the liner to score, and his response straight off the bat with no hesitation was "your timing chain is fecked"...and did not manage to give me a convincing answer as to what caused it. My only concern is when we put it back together, I dont want it to occur again.

Anyone know what would cause the piston to score the liner? or put another way, how can a bad/loose timing chain affect the motor?

Timing chain according to mechanic was loose



The head and valves seem ok.



The scoring marks



The piston/con rod pin has to be replaced.

[SkiFly01]

Real answer would be to get a bore gauge and measure it. The piston may be reusable and even the sleeve. I have seen pretty severe detonation markings in a cylinder wall which caused no adverse affects to the engine performing, however I wouldn't run with marks like that. Your sleeve I would probably run again, but take the sleeve and piston to a machine shop and get them measured. As far as the chain, you can check how much stretch has occurred, but from first thoughts I would doubt a chain would cause cylinder wall scoring. If your timing was that far off to cause wear like that you have bigger issues. If the engine ingested debris it would cause wear on the walls and piston.

[tntmo]

Seems more likely that dirt or something else got into the cylinder and caused those marks. The YZF has a nikasil cylinder, not much can be done for damge done to it except for replating the cylinder or getting a new one if the damage is beyond limits.

A timing chain will not cause that damage. If your timing change was loose enough to cause damage, it would have skipped time and you would have bent valves.

[Kjharn]

Could be cold seuizure, if it hasn't been allowed to warm up properly. Is the piston scored similarly?

Could be, as noted earlier, dirt/sand getting in to the engine, but that usually makes everything look very smooth.

Could have been overheated.

There are a lot of things that could cause it; timing chain is not one of them. If you can, post pictures of the cylinder.

[boozewz]

Really appreciate the comments and help fellas.

Dust entry is a major possibilty as I'm based in Saudi and all our riding is in the desert.

I just inspected the pistons, and lo and behold, there is a crack on the bottom side.





Could the impact from the piston scoring the liner be such that it would cause the piston head to crack? That seems like a serious failure, regardless of the dust entry or not.

[motomike14]

What kind of riding do you do? The YZ450s of that era produce a TON of heat, and have small oil capacity/radiators. If you do a lot of trail plonking, they still build up quite a bit of heat. Check your oil often and make sure you allow it kind of "air out" from time to time. They don't like sitting idling.

[boozewz]

Originally Posted by motomike14

What kind of riding do you do? The YZ450s of that era produce a TON of heat, and have small oil capacity/radiators. If you do a lot of trail plonking, they still build up quite a bit of heat. Check your oil often and make sure you allow it kind of "air out" from time to time. They don't like sitting idling.

Thanks motomike....most of the riding we do is trail/desert riding. ie no MX tracks etc.

Its also worth noting that I had this bike for 3 years then sold it to a co worker, who then sold it to someone else, and then I recently bought it back (5 year gap), so in all honesty I dont know how they rode it, or if the bike was parked up. I did an oil and filter change when I bought it back, as well as checked the air filter, which was brand new so clearly the PO serviced it.

[Kawidad]

Possibility:

Revving the piss out of it when first starting up before the engine has a chance to properly warm up and the oil to circulate. It has nothing to do with cam chain wear. As was stated, if it were related to the cam chain, you would have bent valves.

If I were you. I would pull the cams and check them for scoring or wear along the bearing surfaces. I would also pull the clutch cover and take apart the oil pump and check the lobes for wear. And, when you do that, pull the oil pump screen and look for debris. You might be surprised at what you find.

[trailrider383]

Originally Posted by boozewz

Really appreciate the comments and help fellas.

Dust entry is a major possibilty as I'm based in Saudi and all our riding is in the desert.

I just inspected the pistons, and lo and behold, there is a crack on the bottom side.

Could the impact from the piston scoring the liner be such that it would cause the piston head to crack? That seems like a serious failure, regardless of the dust entry or not.

Google "yzf450 sucking sand through breather hose". It's a well known issue with those bikes. If you are high centered/stuck on a sand dune or in deep water it sucks stuff up through the hose into the engine.