DirtbikeBradley

Why is my bike overheating?

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I've got a TTR125. I change the oil after about 15 hours, (every month), but on occasion (like today), I can smell something burning, and the bottom end seems hotter than norm. I use the right oil, but I accidentally bought car oil last time. Is that my problem? Or am I missing something?

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On one occasion I took out a group of new guys. A lot of stopping, a lot of waiting. Didn't help that it was a hot socal summer day. Also didn't help that I was letting the bike idle longer than normal. The crazy thing about air cooled bikes is that they need air flow.

Anyway, the plastic oil fill plug melted and oil started blowing out the fill hole. I was unaware of this. As the oil level went down so did it's ability to help cool the engine. The clutch springs gave out and my day was over.

That's my experience with getting a TTR too hot. Now, you said you used car oil and I'd guess that cars get hotter than little dirt bikes, but at the same time cars are also water cooled and they have much more oil to help disperse heat. Maybe, just maybe it's possible that the clutch plates are worn. Not enough to where you can't ride, but maybe worn to where they slip more.

I say this because I had earned my mechanics badge on a little PW50 and an older KTM 50. They both have the drum type automatic clutches. A point I picked up in a thread was the amount of heat they create when they aren't engaged. An engaged clutch on those things fully grabs the drum and spins as one piece. When it's not engaged it just spins inside the drum and creates friction, which causes heat.

I'm not a master at this, never pretend to be. But maybe the wrong oil caused some clutch wear. Maybe a slightly worn clutch slips more. Maybe a clutch that slips more runs hotter.

That's all I got. Hoping someone comes along and either confirms or denies everything I've just told you.

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I doubt the oil is the problem, make sure the engine is clean of mud and if you do any mods ( air box , snorkel, or exhaust ) then you must rejet the carb. Running lean will make one run hot.

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Maybe, just maybe it's possible that the clutch plates are worn. Not enough to where you can't ride, but maybe worn to where they slip more.


My clutch is not slipping at all as far as I can tell. That just means That when I pull the clutch, it dosnt completely disengage the engine, right?

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My clutch is not slipping at all as far as I can tell. That just means That when I pull the clutch, it dosnt completely disengage the engine, right?

Well, my experience was with the springs. I noticed that the bike was revving but wasn't going anywhere. It was like constant neutral. Again, I'm not the professional. But if the clutch is slipping a little then the bike is working harder to transfer the power to the rear wheel. I'm not amazing at working on bikes, a lot of stuff I make up as I go.

Still hoping a factory Yamaha mechanic comes along and tells us what is what.
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On ‎9‎/‎25‎/‎2017 at 5:39 PM, DirtbikeBradley said:

 

I've got a TTR125. I change the oil after about 15 hours, (every month), but on occasion (like today), I can smell something burning, and the bottom end seems hotter than norm. I use the right oil, but I accidentally bought car oil last time. Is that my problem? Or am I missing something?

 

Make sure you don't have some grass or a twig up around your pipe... that will give you a burning smell for sure. Car oil has additives that are bad for motorcycle clutches, that's the main reason to use motorcycle specific oils. If your clutch is slipping it may cause a little more bottom end heat or darken the oil a bit. Slipping clutch is when you do not have the lever pulled in and you are accelerating under a load, like up a hill or a fast take-off, and you hear the engine rev up without moving you forward as much as it should be. I'd change the oil and see how it does.

Someone else mentioned running lean will heat up the engine a lot more than normal too. Make sure you don't have an air leak between the carb and motor... or if you put a different pipe or opened up the air box for more flow, then you would need to rejet the carb. 

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On 9/25/2017 at 7:31 PM, DirtbikeBradley said:

 


My clutch is not slipping at all as far as I can tell. That just means That when I pull the clutch, it dosnt completely disengage the engine, right?

 

No, that only means your cable isn't adjusted properly, your clutch plates are warped, or your basket is notched. Car oil with it's added friction modifiers can make your clutch slip due to the fact that it can actually over lubricate the system. Get moving, top gear, rev the motor and dump the clutch. If the motor immediately bogs, clutch is good. If it slows down slowly (or not really at all), your clutch is slipping. Meantime, get the car oil out of there..

Overheating can come from several factors. Clutch slipping, adding extra heat to the oil. Lean jetting. Clogged cooling fins in an air cooled motor. Bike like a TTR125 generally won't overheat from riding around slow or stopping a lot, needs some other input. Then, there's the scenario where trail junk thrown on a hot pipe can smell like the bike is melting down.

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No, that only means your cable isn't adjusted properly, your clutch plates are warped, or your basket is notched. Car oil with it's added friction modifiers can make your clutch slip due to the fact that it can actually over lubricate the system. Get moving, top gear, rev the motor and dump the clutch. If the motor immediately bogs, clutch is good. If it slows down slowly (or not really at all), your clutch is slipping.


Well, good news. I don't think my clutch is slipping (i did what you sugested).
I did recently take off my exhaust to paint the header... You think I reinstalled it not-quite-right?

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