Lot of questions.....
What bike did this pitting occur in? – KTM 300 EXC with about 70 hours on the rings, 140 on the piston and 240 hours on the rod and crank bearings (based of odometer and divided by 30mph ave.)
How did you realize it was that oils fault? – As soon as I saw the rust on the crank I googled “synthetic two stroke oil rust”
Can an engine be ran in that condition? – Sure. I just put 120 miles on it a few weeks ago. The red flag went up when I ran out of fuel after consuming over ¾ of a gallon more than the trip normally takes and ended up walking a ways. I monitor my mileage intensely and as soon as it starts slipping off I know I have a problem. If the air filter is good I pull the pipe and look for blow-by on the piston. If I have a dark ring and the rings have more than 1,500 miles on them its time. Each piston gets two sets of rings. Could go more, but then my cylinder will pay and that’s worth at least three sets of pistons and rings to re-plate.
Fix it to prevent a catastrophe later? – Absolutely. ANYTHING can happen with pitted ball bearings. Could luck out and run the thing for another 200 hours, or it could have packed up the next time I started it. I hit 85 MPH a couple times on this last trip. Can’t say I would have gone over 40 had I known what the bearings looked like.
Will a bearing just come apart shortly causing severe damage? – Could. Best case scenario the bearings start to chip apart and the crud starts to cause wear in other areas. I have some scratches on my piston skirt that likely came from particles getting on the sleeve and under the piston. Eventually the mains will get loose enough that the seals start to leak and that can cause a seizure. That is if the connecting rod bearing outlasts them, which in my case it probably would have. Hard to tell until the crank comes apart, but I can’t see any pitting on the pins at the moment.
What would likely happen to this engine, bearing seizure? – I think we already know. The bearing debris started to ruin the piston & rings and resulted in a 20% decrease in fuel economy. Next thing would likely have been a really loud rattling engine and a crankshaft seal leak, it could have also been an instantaneous bearing seizure. Ya never know until they blow!
Thinking run some regular non-synthetic mix before putting away for seasonal storage. Problem is the rm runs on 50/1 bel-ray and how in the world would i know how to mix a non-synthetic in the right ratio that would run long enough to ride it and warm up without getting it to lean and seizing the motor? Wouldn't be the same ratio, right? Wouldn't want to jet for the non-synthetic. – Don’t over think oil ratios. It’s listed on the can and in your manual. Anything between 20:1 and 32:1 would give you a nice coating and unless you’re doing tractor pulls with it to get it up to temp you can’t possibly damage it.
Got a headache yet? - Yes
Would fogging oil get into the whole crankcase covering all the places the synthetic oil has coated? Good question there huh boys! – No idea. I don’t even know that running a few ounces of non-synthetic oil would displace the synthetic oil from all the surfaces.
I know just start it and warm the oil every month........the answer. - Yep
Got to buy gas and keep fresh mix and drain carb and take out plug and.....fog it and....
I want to point out that there were previous signs that this was happening. I even posted some way back. First was that a brand new carb had a white fuzzy coating on the inside of the bowl above the fuel height and the zinc had corroded off one of the inner retaining screws. Another was that I parked another bike (same model, same fuel) for a couple months and when I went to use it the float bowl was full of water and the tank had water in it as well. It was as though there was alcohol in the fuel, be we don’t have ethanol down here. Instead it seems it’s the oil that is hygroscopic.
Humidity level is usually 20 to 40% here. It doesn’t rain much and my shop never feels humid. As well, The last time I pulled this engine apart there wasn’t a spec of rust in it, so I remain convinced that the pressure washing and not burning out the moisture from the cases is the main issue. If it was strictly a Motul oil issue it would be all over the Internet.
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Originally Posted by bkm
