Rust inside engine YZ250 05

[halfabee]

I almost cried. I seized the big end bearings about 4 months ago and had to have to top end,piston, crank rod and bearings replaced for a hefty price. I was changing my reed valves last night and had a look into the crank and to my shock i see there is rust on the crank rod and bearings again.
When i wash the bike i normally let it run for about 10 min afterwards to get rid of any water in there. I don't use premix older than 2 weeks and as far as i know there is no water in the premix i use.

Any sugestions of why i would be getting water in my engine and how i can prevent this happening?
I am using Motul 700 for premix, could it be the oil?

[Aus_Rider_22]

Never heard of Motul 700? Maybe your referring to Motul 800? I used to run it and never had any probs with this fully synthetic oil.

Do you do much mud riding or prolonged use in wet terrain?

Some other guys can probably offer better advice!

[halfabee]

Motul 800, finger problems

Do a bit of riding in rivers etc but not excesive and not in the last month or two.

[Aus_Rider_22]

Can you at all post some pictars of the surface rust? My rod used to have a very slight orangish colouration to it... Perhaps yours is the same?

[halfabee]

will take picture tonight and post them up. thanks

[Aus_Rider_22]

Sweet

Hopefully the photos can help us determine if it's a problem and what could be causing it

[Florida 393]

When you wash the scoot do you pull the filter and install an intake cover and put an exhaust bung plug in? If you use a pressure washer or even a hose with a spray nozzle you can push water past the filter and in the exhaust. I don't believe that Motul 800 is hydroscopic enough to pull in an adequate amount of moisture to rust a crank, but I haven't used their products.

Just a few thoughts, best of luck and post the pics so we can try and help.

Bill

[RallyImprezive]

Originally Posted by halfabee

I was changing my reed valves last night and had a look into the crank and to my shock i see there is rust on the crank rod and bearings again.

Again? Was rust the reason the rod bearing seized?

Is there any possibility you have a coolant leak?

[four26stroker]

As a rule if I cross rivers or hit a lot of mud puddles, I change the oil. Cheap investment parts (airbox cover/ rubber exh. plug) Fla.393 mentioned are a must for keeping the water out at wash time. Coolant level ok? Hows the plug look? Compression good? Are you sure its not just discolored from heat and your paranoid? Did you take a swab to the lab and examen it to be 100% rust? I'll wait for the photo, but rust is never a good sign. I can feel your stress take a few deep breaths.

[halfabee]

Thanks for the sugestions so far.
When i wash my scoot i put a plug in the exhaust and take the filter off and put a cover on. Run it for about 5-10 min after washing. I do use a high presure hose. I generally change my oil after every 2 rides. I don;t think i have a coolant leak as i check that regularly and the levels never go down.

Check the pictures below, maybe i am being paranoid and this is usual. Let me know what you think. Aren't the best pictures as i had to take it through the intake hole.

Yes, the last time it seized they said it was due to rust on the bearings.

http://i133.photobucket.com/albums/q...1/yzrust02.jpg
http://i133.photobucket.com/albums/q...1/YZrust01.jpg

[Florida 393]

halfabee,
Being it is a 2T bike I'd look at the gas you use for additives and see what the listings for Motul 800 is on its additives. My experience with coolant leaks is that the head gasket lets go and it causes the piston to burn or crack away a sliver or the crown edge.

If a pressure hose is forcing water in the base gasket try replacing the gaskets and using a low pressure stream and extra elbow grease. A complete gasket kit for the top end seems to be in order though.

Bill

[Faded]

Motul 800 uses a Group V ester base stock which is only slightly hygroscopic by nature and probably not the main cause of the problem. The oil however is combined with a dillutant in order to maximize its ability to mix with fuel. It could be the dillutant that is hygroscopic and causing the problems. Maybe a call to Motul is in order...

[Florida 393]

Okay that helps me and adds to my knowledge, thanks Faded!! I figured some type of slovent had to be present for the oil to go into suspension in the gasoline but never checked (it has been 20 years since I taught chemistry and did any organic chem research at all) I wonder if the gasoline formulation in South Africa is different from ours and something is reacting with the ester base to form a corrosive. The hygorscopic was a long shot anyway, just something to throw out. Nice work on this one, but we expect that now

Bill

[YZ125motoracer]

is ur bikes exhaust smoke white and sweet smelling? could be a head gasket, a cracked cylinder (i had this problem with an athena cyl) or even cases.

[Aus_Rider_22]

FWIW, I found the same sort of surface oxidation on my YZ's rod at one stage. It wasn't as pronounced as these photos but it was like it in a couple areas... I also used Motul 800.... Interesting??

[Florida 393]

Andrew,
Something another site had a post on that rings a bell here is the pH level of the Motul 800 and the gasoline formulation. If they are using some additives as well as the nature of hydrocarbons and the esters molecular structure, acidity is a possibility. Just a wild thought. The oxidation does not seem excessive in the pics but is worrisome. What do you think? I will be the first to admit this is out of my league now.

Bill

[halfabee]

shew, thanks for all the help so far. Some of it went way over my head. I have been chatting to a few other people and Motul seems to be comming up quick alot as the suspected problem. I think i will take it in and get the rod and bearings replaced and change the oil i use and see how it goes from there.
Great Forum, must say you guys know your stuff.

[ossagp1]

I have yet to see an oil in itself that will do that. Many of the fuels we get at the pump that contain various oxygenating compounds (viz methanol, ethanol etc) pick up moisture really fast. In times past, I know many of my south african correspondents were running on straight alcohol due to availibility.