Running rich or blown rightside crankcase seal?

[andre111]

I'm looking at buying a used 07 YZ250, but there is black oil (and plenty of it) seeping out from the cylinder / exhaust pipe join. The guy says its because theres a bad seal, and yes it does leak smoke from there. I'm just not sure if its caused by just rich jetting or worse, a blown crank seal. I've never had a blown crank seal on any of my past bikes so I dont know what to look for. The bike starts second kick from cold.

[RCannon]

I know a seal is possible, but I think it would be a stretch to diagnose one from that symptom. Try leaning you jetting and see what happens.

[andre111]

Problem is I havent bought the bike yet or if i will because of this issue. I dont want to think the worst but I'm guessing the guy who's selling it isnt going to admit it even if it was a blown crank seal, so that one symptom is all i have to go off. Its just that I've owned 2 strokes in the past and ive never seen one leak so much oil out of the cylinder exhaust port / pipe join even with a bad seal. I was hoping there would be someone out there who has seen or had a blown crank case seal and could shed some light as to how much oil will leak from the exhaust. ie is this a typical symptom? My understanding is that gearbox oil makes it into the combustion chamber where it is then spat out of the exhaust as black goo.

Also, are right side crank seal leaks common on YZ's or are they very rare?

[Aido_DRZ]

Agree with RCannon, sounds like a case of rich jetting and a leaking expansion chamber O-ring at the exhaust port.

[yathump]

At least find out if he's played with the jetting, if he hasn't and only trail rides it he is probably way rich on the jetting side of things

[bryawn]

I would see if you could get a really good deal. If the bike runs OK, it's most likely a jetting issue, or could be something like a partially clogged exhaust. Could be a straightforward fix.

I've only seen one bike with a blown seal, and it would start but then not run right after that. Seems like a blown seal would allow is extra air causing a lean condition and less spooge.

[yathump]

I would see if you could get a really good deal. If the bike runs OK, it's most likely a jetting issue, or could be something like a partially clogged exhaust. Could be a straightforward fix.

I've only seen one bike with a blown seal, and it would start but then not run right after that. Seems like a blown seal would allow is extra air causing a lean condition and less spooge.

If the clutch side seal goes out it will pull tranny fluid into the motor

[halffastrider]

I find it hard to believe a seal went bad on an '07, unless the bike was totally abused and ridden a TON. The only way i can see the seal going bad is no oil, or a large amount of contamination in the oil (water?) to allow the seal to be abused enough to leak. I know you have not purchased the bike, but can you check the oil? The YZ's like all 2st's are very rich from the factory, even after leaning mine out I would still get spooge at the power valve and the rubber seal were the muffler/pipe come together after a few years. If he did not rejet the bike, trail rode a few times a month, and maintained it normally (at least changed the oil yearly, used a decent premix blend) it's only spooge. One of the reasons your probably looking at a YZ is because it's a "Timex" 2st, will take a lick'n and keep on tick'n with very little wrench time. Good Luck!!!

[shrubitup]

It it very likely exhaust O rings or that the pipe is bent and won't seal properly on the cylinder or that the exhaust flange itself is bent causing it to not seal properly despite a fresh pipe. At worst you'd have to buy a whole new cylinder.

Black drippy oil is spooge and most frequently is not created by a blown crankshaft seal.

[watermoccasin]

I had a leaky right crank seal on my 03 YZ250 a few years ago. There was an unbelievable amount of spooge running all the way down the silencer and splattered all over the swingarm. Doesn't sound like what you're seeing.

The two o-rings that seal the expansion chamber to the cylinder wear out really quickly and are cheap to replace. And there's a good chance the pipe is bent and not sitting square on the exhaust flange. And stock jetting is a bit rich, especially if the bike was not run hard.

[bryawn]

I had a leaky right crank seal on my 03 YZ250 a few years ago. There was an unbelievable amount of spooge running all the way down the silencer and splattered all over the swingarm. Doesn't sound like what you're seeing.

The two o-rings that seal the expansion chamber to the cylinder wear out really quickly and are cheap to replace. And there's a good chance the pipe is bent and not sitting square on the exhaust flange. And stock jetting is a bit rich, especially if the bike was not run hard.

How did your 2003 run with all that spooge going on? Were there any other symptoms? I'm assuming the tranny fluid disappeared pretty quickly.

[mdkcrf250r]

my 06 runs absolutely phenomenal and was jetted perfectly but after a day of riding I had alot of spooge coming out of the silencer..I did a pressure test aka leakdown test and found a leak and assumed it was my right side crank seal...after replacement spooge went away completely..its not hard to replace and is a common failure..you dont have to split the cases or remove the motor...

[ride5150]

try jetting first, but even if its the seal they are RIDICULOUSLY easy to change, all u have to do is remove the side cover and crank gears, yank the old 1 out and put the new one in.

[harjp1959]

Could someone please point out this seal on a part fiche? Thanks.

[mdkcrf250r]

Could someone please point out this seal on a part fiche? Thanks.

[mdkcrf250r]

number 17 is the clutch side crank seal and a leak would cause excessive spooge or fouling of plugs...Number 14 is the flywheel side and a leak would cause erratic or high idle etc. and a lean condition...

[harjp1959]

http://fiche.ronayers.com/Index.cfm/Module/Main/TypeID/26/Type/Motorcycle/MakeID/4/Make/Yamaha/YearID/44/Year/2003/ModelID/1977/Model/YZ250R_YZ250/GroupID/346955/Group/CRANKSHAFT_PISTON_

Thanks.

[cvest788]

A crank seal doesnt sound plausible. Of course, just like everyone else has said, check jetting. But as well the exhaust chamber seals could just be gone and its a simple fix. Either way the bike can easy be fixed if its either of those problems. Its common for those exhaust seals to wear out. ?

[watermoccasin]

How did your 2003 run with all that spooge going on? Were there any other symptoms? I'm assuming the tranny fluid disappeared pretty quickly.

The bike ran great - no bog, no plug loading/fouling, tons of snappy power. So I started measuring how much tranny oil came out - 750 mL in, about 500 mL out after 1-2 rides.

[moab39]

If you have a bad seal ,does this mean that your bearing might be going bad? In other words what caused the seal to start leaking? thanks John