Seized 2t - looking for cause

[XXX3]

My 2t has seized, but I can't figure out why...

Bike is a KTM 200EXC 2003 model. I had not used it in about a year other than every few months giving it a kick over (with some freshly mixed fuel) in the shed. It has been and was running perfectly right up to the point it seized. It's also in good nick - I am meticulous about servicing fresh coolant and gear oil etc. Air filter is kept clean.

Finally got an opportunity to use it midweek when in Kellerberrin. Everything worked fine on Tuesday but the weather was nasty so it was literally a 5 minute run. It was using KTM-endorsed 2T oil.

Went out on Wednesday but needed more fuel mixed. Now I'd run out of the KTM-endorsed oil, but had some other oil (different brand) lying about in the shed so brought that along. Note it was from my 250 days when I had an RS250, so it's literally 4-5 years old. The container had been opened (unsealed) but lid has been firmly screwed on in storage. Mixed up 4L of that and added it to the 1-2L of fuel in the bike.

Rode for about 10 minutes and then seized. Bugger.

Pulled it down today and got up to the stage of taking the head off. Top of piston was stuck about halfway up the topmost port. Application of liberal WD40 and some firm pressure on the kickstarter freed it up. There are no strange sticking or wear marks on the cylinder. Also the piston, now freed, moves quite easily when moving the kickstarter by hand (obviously no compression as head is still off). Piston has a lovely brown even burn.


Now I need to get on with some other work this evening so removal of exhaust and cylinder may have to wait for tomorrow to examine the piston skirts and piston rings, but at this stage I'm wondering what's caused the seize?

Surely if the piston rings were stuffed there'd be marking on the cylinder?

Has the mixture of 2T oil types caused some sort of oil mixing fail?

Has the usage of 4-5year old 2T oil caused some sort of fail? Is 2T oil very hygroscopic?

What else should I look for? Is it possible the engine has seized but there has been no damage caused?

[out_in_front]

My best guess - the oil left on the piston from the ride you had a year ago deteriorated / gummed up. Nothing to do with the new stuff.

I rebuilt a 2T engine that had seized due to the fuel oil / mixture drying up and and jamming everything up - I am suprised it ran for 10 min first though which is confusing me a bit...That being said, non-newtonian fluids can do some interesting things - including flocculation and shear thickening.

[Veefore]

We seized an engine some years ago using Bel Ray 2T oil. Apparently (unknown to us or the retailer) it had sat in a warehouse for a couple of years. At the time, we were told that ALL 2 stroke oils had limited shelf life. I don't know if that has changed with the modern oils but 4-5 years is a Looooonnnng time compared to the oil that seized my bike back then.

BTW, were you at the MX track at Kellerberrin? I used to race there once a year as a junior and still have family there.

[XXX3]

Thanks for the replies so far guys.

Yeah I am pretty suspicious about the oil - it ran for about one carbyload (the old but fresh oil) and then seized not long after the fuel in the tank got there.

Should I just empty the tank and drain the carb and carry on then? If I can avoid pulling the cylinder off it would be good cause I won't have to buy another Kosts Too Much gasket.

Veefore - I was not at the MX track, I was on a friend's farm. Seems like a nice tight-knit community though, everyone knows each other.

[filbert]

depends how much force it locked up with, you may want to get everything crack tested.

the damage could be in the bottom end, no damage in the bore could mean there's a torn up big end and cracked conrod to deal with.

[ninjaa]

Yeah I wouldn't carry on mate. How much is a new rod & full gasket kit or do katoom bend you over?

[XXX3]

Russ - KTM stands for Kosts Too Much

But yeah it'd be stupid to just stick the head back on and be all "she'll be right". I'll pull the cylinder off and check out the skirt and rings, check all the tolerances, give the conrod a good eyeball and make sure there's nothing odd floating around in the cases like bits of bearings.

Whatever caused the seizure, fact remains that it seized so there's got to be something that copped a bit of damage. It's pretty funny doing some research about seized engines and a lot of the "ask..." type websites typically just give a solution about how to unstick the piston, and then it's basically "great success, carry on!"

[HK31A]

i think you hit the nail on the head when you said you changed oils

you must be carefull when mixing oils as some just dont gell

you never said what brand the shed oil was

as for been hygroscopic it doesnt matter as its a total loss oil system

also a saleman told me once if you see an oil container on the shelf thats caving in its been on the shelf for a very long time- that was his spin

as for oil left in the engine for ages i would think every lawnmower shop would be full of stuffed 2t mowers

anyway goodluck

[XXX3]

Cheers HK31A.

I'd have to check the shed oil, but I'm pretty sure it's motul... the point is it's not servo oil, price tag on it is $60 for a 4L container so it's good stuff. But I agree, I think mixing the oil caused the seize. The KTM stuff is fully synthetic whereas the motul is semi synthetic.

[HK31A]

Cheers HK31A.

I'd have to check the shed oil, but I'm pretty sure it's motul... the point is it's not servo oil, price tag on it is $60 for a 4L container so it's good stuff. But I agree, I think mixing the oil caused the seize. The KTM stuff is fully synthetic whereas the motul is semi synthetic.

i understand what your saying

trouble is its an expensive exercise

[thro]

Russ - KTM stands for Kosts Too Much

I heard KTM stood for "Kick til monday", but then they started using electric start...

[96]

I heard KTM stood for "Kick til monday", but then they started using electric start...

and removed the kick starter and suggested that the electric start not be used when the bike was cold....

sucks to hear nigel. was the piston tight in the barrel? ie, did it rock side to side? if it had sideways movement maybe it was the bottom end.

[EEKNOWS]

Keep Taking Money

Had a lovely experience with some gearbox bearings that were convieniently 2mm under side on the ID and the other 2mm over size on the OD compared to stock bearing sizes. 1 was $50 and even the KTM dealer was ashamed to say $102 was the list price for the other grrrrr rant over

I think your oil was past it's use by date