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Peregrinations Mexico and Central America on Motorcycle: Open road, open heart, open mind.

Excessive crankcase pressure

MEXICO | Monday, 30 May 2011 | Views [2188] | Comments [1]

After, front view

After, front view

Since this is a blog about motorcycle travel, I'll go ahead and post this little blurb on fixing a small (getting worse) problem my bike was having.

Back story on the bike: bought it from a guy in Colorado who only ever used it for commuting, changed its oil regularly, and otherwise didn't touch it. I did all the mods when I got it to New Mexico. Before the trip I gave it to a back-yard mechanic in Albuquerque to give it a pre-trip once-over and make sure all the bike's various parts were ready for the trip to Panama and back. Drove it to Tucson on my way to Baja. While in Tucson I visited the mechanics at ZMW Motorcycle Werks, and they helped me fix a few more things on the bike that the Albuquerque mechanic had missed. Then I was on the road.

Symptoms: It was in Tucson, when I topped off my oil for the first time, that I noticed how much pressure had built up inside the crankcase. When I took off the oil cap, hot air escaped and the cap nearly popped off into the air. I blamed it on the altitude change combined with the heat of summer...and ignored it mostly. From then on, every time I took off the cap to top off the oil, if the bike had been running at all, the pressure inside the case was noticeable. But nothing bad was happening to the bike, so I continued to ignore it.

The problem was, I kept having to top off the oil with greater and greater frequency. I knew the T225 was going to burn oil because 90% of my riding was at highway speeds, but it was getting ridiculous. By the time I reached Oaxaca, 4,700 miles into my trip, I'd used two full liters of oil to top off the bike. Considering that the entire capacity of the bike is 1L of oil...that was a lot. I'd burned through 200% of the capacity in under 5,000 miles. Additionally, the pressure build-up was getting worse. After just three minutes of idling in the morning, the build-up was bad enough to force the cap off as I removed it.

Diagnosis: I finally reached a hostel where I had both downtime and excellent computer/web access (Hostal Pochon in Oaxaca). So I got onto the xt225 forums, which is a wealth of knowledge for all things XT225. The guys were ready with suggestions, with the best bit of advice being check the crankcase breather tube. Excellent. Apparently there's a tube that goes from the crankcase to the airbox and allows excess pressure from the piston-action to escape. It's routed through the airbox so nothing can find its way back into the crankcase.

So I took off the side panels, seat, and airbox cover, and this is what I found:

Ew! Even I know that oil from the crankcase shouldn't be ending up on top of my airbox. Solved the mystery of where all my oil was going, though! Now I just had to find that damn breather tube...There were a few candidates, but I finally narrowed it down to this guy:

Except, it didn't look like that when I found it, it looked like this:

...with a whopping great 90 degree angle in it:

That must be it, right? And obviously the tube had been spliced. My best guess is that the mechanic in Albuquerque saw that the tube was damaged somewhere, spliced it with that extension, and the kink developed soon after since the splice was too long. That's just a guess, though I can't see how else it would have happened.

Solution: Solutions don't get much easier than this one. I pulled the tube down below the petcock so the kink was eliminated, cleaned all the oil off of the airbox, cleaned the air filter (which was unusually mucked up) and fired up the bike. After five minutes of idling, I shut the bike off, and took the oil cap off the crankcase. Absolutely zero pressure build-up. Success!

I'm truly in love with this little bike. She may not be the fastest or the most powerful, but she keeps on trucking through all this abuse, this combination of Mexican road conditions and her owner's utter lack of knowledge. Atta girl, Burrito!

Huge thanks to the other members of xt225.com, you've been amazing!



xt255.com should sponsor you! :)

  Esus Jun 22, 2011 8:36 AM

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