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Dirbikes Blowing Up

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I've seen and heard a lot about motors blowing up on youtube. It's making me a bit nervous as I ride my 250r a lot and ride it fairly hard. I couldn't find anything really explaining why it happens so I decided to ask here. Is it different on 2 strokes and 4 strokes? If you can please leave as in depth of an answer as possible especially if it has to do with maintenance so I know what to do to prevent it from happening to me.

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It has everything to do with maintenance, get yourself an OEM service manual for your bike and it will tell you how to maintain it.

The manual will tell you intervals to change oil, clean air cleaner, lube, tire pressures, time to replace parts......

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As for 2 strokes, other than having a large vacuum (air) leak, or jetting being so far off, that they burned a hole in the piston, the main thing I've seen for failures are from running cast pistons too long. Cast piston will fatigue after a period of time and break a piece out of the skirt, which falls into the bottom end causing carnage. You used to hear about them seizing a lot, but modern oils and manufacturing processes have all but eliminated it. They still can seize, but when the truth comes out, it was somebody running a 125 wide open down the highway for several miles, forgot to mix their gas, or was flogging a wore out top end. Rarely you can have piston ring failures or piston pin keepers come out and mess up the cylinder.

4 strokes can let go from a lot of different reasons. Dropped valve keepers, valves floating or sticking open from over revving or excessive carbon build up, broken rods, oil pump failures, etc.., from a general 12,000+ rpm lifestyle, many times coupled with overall poor maintenance.

Edited by OLHILLBILLY
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+1 on previous posts,

 

people buy high tech race bikes and treat them like toys,

they add gas and ride, only repair things when the toy stops working.

 

They are also surprised at the actual cost of operating a race bike even for recreational use,

cheap out on maintenance, replace only the 'broken' parts and re-assemble the engine

leaving many more wear items untouched until they are next parts to fail.

Edited by mlatour
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For most engines it 85% maintenance, 10% riding habits (abuse) and 5% bad luck.

Modern 4t engines with short skirt pistons and light weight construction can fail spectacularly when when run hard on out of spec parts.

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I've seen and heard a lot about motors blowing up on youtube. It's making me a bit nervous as I ride my 250r a lot and ride it fairly hard. I couldn't find anything really explaining why it happens so I decided to ask here. Is it different on 2 strokes and 4 strokes? If you can please leave as in depth of an answer as possible especially if it has to do with maintenance so I know what to do to prevent it from happening to me.

On my cr250 the intake skirt broke off, not sure how many hours were on the bike, but it actually was still running when I tore it down. Made quite a bit of noise for a few seconds, but passed it out the exhaust. 

Honestly, so far my bikes that have shattered pistons have been cheaper to fix than the ones that seize.

 

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The term "blown up" sometimes get used to describe aby motor problem. I've seen posts about tight valves being described as blown up. Bikes get taken to dealers who want to replace everything so very expensive.    If you don't know how many hours on your R throw a new piston at it and check the crank, or if lots of hours rebuild the crank too. 

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Two strokes and four strokes blow up at the same rate, almost never. Just go ride. I have been riding since 1977 and broke a ring one day and another guy around 1980 or so grenaded a piston riding a kx 250.

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People get clapped out bike and dont maintain them because they know nothing about dirt bike maintainance. They think that if they clean the air filter and change the oil once a year their good

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I've seen and heard a lot about motors blowing up on youtube. It's making me a bit nervous as I ride my 250r a lot and ride it fairly hard. I couldn't find anything really explaining why it happens so I decided to ask here. Is it different on 2 strokes and 4 strokes? If you can please leave as in depth of an answer as possible especially if it has to do with maintenance so I know what to do to prevent it from happening to me.

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maintenance is a big one. I bought an 08 rmz250 that blew up with in 4hrs of riding it and the problem was engine maintenance. what happened was the needle barring come apart which broke my conrod in two places broke a fare chunk out of my cylinder and piston. all that metal made it through my sump casings. So my engine was a complete right off. After alot of money spent and time finding parts I always change my oil every 5-6 hrs depending on what riding I do and always check over my bike for any broken or worn parts

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In general:  Keep the air filter clean and tight(making a good seal). 

 

Run the best 2-stroke oil you can afford.

 

For a 2-stroke make sure you are mixing the correct ratio oil for what you do:  Ride Trials 80:1,  Enduro/single track 50:1, mX: 32:1 .  Then Jet accordingly.  After reading just about every oil and jetting thread my understanding is that you should mix for how you ride, then jet for minimal spooge and/or the performance you want.  It's not the oil that makes the spooge, it's running too rich (often at part throttle).  more oil = less fuel = you need to jet richer. 

 

Doing regular top-end overhauls and keeping on top of leaky seals is a good way to keep out of trouble.  If you don't care about absolute HP you can use an extra base gasket for a little less compression and a little less power. 

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