Blue smoke – oil from crank case vent

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September 14, 2009 at 6:04 am #97169

Trent
Member

I don’t believe my rings are gone because they only have 1500kms on them (CP rings not OEM ) but I dropped my bike on the weekend and I know that this can cause oil to leak out the vent and into the airbox and carby. I first noticed a problem when intermittently my bike wouldn’t idle but it was still running great. Then after a bit more riding it didn’t want to start easy and eventually wouldn’t start at all. I pulled the plug and it was filthy black so I put a fresh one in and it started first kick but was blowing a good dose of blue smoke the whole ride back. I pulled the air filter off when I got home and sure enough there’s a substantial puddle of oil in the box.

My thoughts are clean the air box of oil, drop the carb float bowl and clean, run the crank vent hose into a bottle and cap the carby where the hose normally enters then take it for a ride and confirm that its not consistently getting oil through due to bad rings. Once I’ve checked this is it as simple as cleaning both plugs (spare + fitted plug) then returning it back to normal?

I’ve read a little on re-routing the hose and capping it off but I think I may just get some longer clear hose and route it up then back down and into the carby so it’s easier to read what’s happening and harder to flow in therefore more likely to drain back into the engine.

Just after some thoughts from the peanut gallery.

Cheers,

p.s the ride with the trailmates guys was great and they’re a good bunch of bloke to ride with too Once they’ve put some pics up I’ll put some up here or link it.

September 14, 2009 at 6:57 am #152648

Bruce Curtis
Member

I think you have a problem that is really a problem Mr A Blue, sounds like you have lost ring tension or something has been swallowed up and given your bore a few issues…

I’m am sorry but it is the biggest and most likely cause of blowby, and all kidding aside it sounds sudden and dramatic.

BC

September 14, 2009 at 7:07 am #152664

Eric Smith
Member

My thoughts as well. Not any kind of expert, but it seems pretty much standard procedure for the 250EXCF’s. Oil in the airbox = rings.

September 14, 2009 at 7:19 am #152666

Greg
Member

Not sure here but a couple of things interest me.

It happened all of a sudden did it? Rings dont just lose tension like a light switch or wear out the same.

Does the crankcase breather go into the air box?

I have seen a KTM 525 at once cart wheel down a hill and blew smoke like a cold two stroke for the next hr back to the car.

He said he cleaned the oil out of the air box and it was fine all afternoon, someone on the ride said kato’s do that when dropped but I had seen that happen again and if you ride with Moto you will see one of them on their sides

That’s all I know on the subject, wouldn’t panic yet, but would get that option ready maybe :huh:

TB

September 14, 2009 at 8:41 am #152667

Paul
Member

I’m not a mechanic but I’m thinking if oil did run into the airbox and sortof coated the inside of the carb, then it could take a while for it all to get sucked through and stop smoking, like TB said about the KTM which smoked for an hour.

Can you get hold of a compression tester?

September 14, 2009 at 8:55 am #152675

alan
Member

when the rings went in my ktm 530 it pumped oil into the airbox but it was a gradual thing as TB said.seen a old ktm620 pull a real long mono than blue smoke came out of it evreywhere we thought it blew up but was just oil in the airbox from the angle of the moter

September 14, 2009 at 8:56 am #152668

Trent
Member

Yeah sorry I thought I made that clear but reading again I didn’t. KTMs breather hose runs back into the airbox and its a common issue that oil will get in there if you tip it up. It can also be caused by blow by but I check it after every ride and normally have none in there and I was sure to check that my air filter was on properly when I fitted it and when I took it off and its cleaned and oiled before every ride. Bike had no noises before or after and it ran strong all day with the exception of the starting and idling issue.

If I take a ride with a coke bottle catch can taped to the breather hose surely it would soon show up any oil if the rings were stuffed right?

I’m trying to be open minded and optimistic at the same time but I can assure you that prior to this issue I was already aware that oil in the airbox can either be rings, over filled oil or bike tipped up and the 250excf is known to have ring issues but this can be addressed by aftermarket ring and piston and that’s why I’m running a CP kit.

Since I put the new bore in about 10months ago it’s not used oil. Since I’ve had the drain plug re-drilled flushed it over and again and I’ve ridden about 15hours before saturday but I still have it in the back of my mind that there’s the slight possibility that something has made its way through. I’ll be dropping the oil and screens for a look anyway.

September 14, 2009 at 9:09 am #152676

Greg
Member

Austblue wrote:

Quote:

Since I put the new bore in about 10months ago it’s not used oil. Since I’ve had the drain plug re-drilled flushed it over and again and I’ve ridden about 15hours before saturday but I still have it in the back of my mind that there’s the slight possibility that something has made its way through. I’ll be dropping the oil and screens for a look anyway.

If something went through it and I dont think for a second it has, no chance is my thought but if something did it would be in the screen, the oil pump the filter but it would have nothing do to with the rings, trust you would fail a big end, main brg or some sort of lubrication failure before a ring related lubrication problem

TB

September 14, 2009 at 9:19 am #152677

Trent
Member

Compression tests are almost impossible with the new 4t bikes since they have auto decompression. You have to do a leak down but I’d just as soon put the new piston and ring in.

Is the catch can idea not a fool proof test for dud rings? I’m positive there wasn’t a loss in power and as I said, at the start of the day the bike was starting fine and even once there was an issue it was hard to kick as normal – no easy kicks.

September 15, 2009 at 12:33 am #152689

Bruce Curtis
Member

The catch can can be a really good indicator of a pressurised sump issue. And also knowing who you are and you previous issues, I jumped staright to the big one as you would have eliminated the obvious. The plug being fouled, the non-idling, all points to a sudden loss of compression. Now in other engines this can also be cracked liners, heads etc, but seeing as yours is a KTM ( I cannot believe I am saying this) not a little manufacturer from istanbul I would not go to those options first, although would not a cracked valved seat do this as well ( I don’t even know if yours has valve seat inserts or not) but the most common cause is the rings out to lunch.

TB in the ye olde days if you badly overheated your bike wouldn’t the Chromium rings loose tension quickly?

BC

September 15, 2009 at 2:02 am #152769

Trent
Member

What did you mean by “pressurised sump issue”? Is that just a different way of saying bad rings causing pressure in the case to be relieved with blow by?

Bike definitely didn’t o/heat – rads full with coolant and the day was hot but we were belting through s/t and dual + a transit section not long before the loss in idle ocurred.

September 15, 2009 at 2:13 am #152788

Greg
Member

I reckon the carby is also full of oil, the little XR70 did that once, went upside down and blew smoke for ages, wouldn’t idle etc, cleaned the air filter not better, removed the carby and blew it out, cleaned the oil out of all the air holes and happy days smoke went and it would idle etc

TB

September 15, 2009 at 2:26 am #152789

Bruce Curtis
Member

Yep pressurised sump is just lingo for compression getting past the rings and into the crankcase, it’s why old motors had foam breathers on tappet covers.
TBs suggestion has merit, has the bike been in any compromising situations recently?

BC

September 15, 2009 at 2:36 am #152793

Trent
Member

With me at the helm it’s constantly in a compromised position

Hopefully I’ll get a chance to pull the carby off and flush it this afternoon. Should I flush it with metho or just use fuel?

September 15, 2009 at 2:40 am #152797

Greg
Member

Just fuel, carby or brake clean in a pressurized can is real good, count the turns your jets are out if you are worried about setting it up again

TB
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