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Help Valves ttr125

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my dirtbike i put a hi comp. piston in and it idled good but when i cracked open the throttle i started hearing a ticking sound and shut down immedently and looked at the timing fine but when i took the head of and sure enought a bent valve now i believe that the cam sprocket bolt was not tight enough causing the sprocket to come off because the bolt was really loose when i looked at the timing but i am get a shop to put in valve and a hot cam and i will put the rest back together but i want to know what you think was wrong?

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my dirtbike i put a hi comp. piston in and it idled good but when i cracked open the throttle i started hearing a ticking sound and shut down immedently and looked at the timing fine but when i took the head of and sure enought a bent valve now i believe that the cam sprocket bolt was not tight enough causing the sprocket to come off because the bolt was really loose when i looked at the timing but i am get a shop to put in valve and a hot cam and i will put the rest back together but i want to know what you think was wrong?

Is it a kickstart or an estart. It sounds like you bent a countershaft and the bent shaft is causing the idler gear to hit the primary.

You may be in for a complete teardown.

The cause, increased compression, causing it to put more stress on the kick shaft which in turn causes the kick gear to ream out the idler bushing. When the idler gear gets mushed, it can randomly catch the primary gear and then you bend or break the countershaft.

DO you also have the bbr rev box as well?

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its a kick start and i do not have a rev box so ill get valve and hot cam and locktite it and if it doesnt work then ill sell parts off on ebay

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If I was you I'd do a compleat tear down may be because the # 1 problem is the main drive shaft is weak metal as are the gears.You put a hi comp piston in a kick start which puts more stress on it and it often is ready to snap at any time any ways.I know I have documented the problem on 5 motors just to see for myself.

I have one motor that has any mods and it's a electricstart.I had the same thing happenen to one of my motors even though I often tear it down to check it. The main shaft snaped it then whiped out the gears two bearings the timeing chain and gear a valve and the cam + the crank bearing when piston smaked the valve.

It happens even to compleatly stock motors I now have several motors and they don't get ridden but 1 - 3 times before a compleat tear down. I ride put a compleatly new motor in and do a compleat tear down on the one that was in it so I know there is no wear to any parts and has good bearings ect.

Just to let everyone know it still happens often I do a tear down and the shaft is broken or has wear or the two gears or first gear have a tooth or teeth gone even on compleatly stock motor that was a hundred percent .The funny thing is often you don't know till a compleat tear down because it's still running fine.

All my motors are perfect all the time with less than 3 rides on them.

I now use rotella oil 15 w 40 1 qt + 1/2 qt -a lil more mobil one 15 w 50 which helps a lot .I don't knotice as much wear useing this combo of oil.

But it is still possible to snap the shaft it has a break put in at the factory and a oil hole which is where it breaks. The gears are soft metal allso.I can not stress enoughf how serious a problem this is .The motor can't handle what most people dish out on it because of it.

Im very aware of the problem so I ride knowing it and don't jump am easy on the throttle don't slam the breaks on in gear ect. The shaft still breaks easily and most don't even know it's broke.

I could assemble a motor that has a lil more mods then what someone is rideing now . Say the head done a stroker crank big piston ect so on and on .With every bearing bad with slight play a broken shaft a tooth missing from just about every gear and most would be wow this is awsome its better than mine lol.So those of you who say I have had no problem I laughf to myself because I know there is a problem .

I have done the work it takes to see for myself and over the years I have fixed hundreds of ttr 125 motors with the problem .Just about every motor I bought off E-bay for parts the person said low miles runs great no problems lol .Most everyone had problems when I tore it down as soon I recieved it .

So those of you who swear you don't never had a problem all I can say is tear it down it's easy motor to tear down most of time I don't even need any gaskets ect .See for yourself it is a problem.

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Funny you say this is such a "common problem" with the TTR motors, you're the first one to ever say this is so prevalent, much less a problem.

More often, it's the carb that gives folks headaches.

Why tear a motor down if there is no symptom of internal problems? Mine runs and rides just fine, no wierd noises or feel on the shifter.

Mine got well over 100 hours last summer, and all I did was check the valves and continue to abuse it. No problems.

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Funny you say this is such a "common problem" with the TTR motors, you're the first one to ever say this is so prevalent, much less a problem.

More often, it's the carb that gives folks headaches.

Why tear a motor down if there is no symptom of internal problems? Mine runs and rides just fine, no wierd noises or feel on the shifter.

Mine got well over 100 hours last summer, and all I did was check the valves and continue to abuse it. No problems.

I agree. After having the kid beat the crap out of ours for a year doing MX, the fact we didn't have a full blown chain guide finally caught up with us. Our fault, we recognized the potential, but dared fate anyway. The only damage found after doing the complete tear down was the shreaded gears, both 1st and 2nd due to the catastrophic chain pile up against the case. No cracked shafts.

How about people doing whatever work on the clutch side, not orienting the idler and kick shaft gear in the right orientation? That would make things come to a stop in a hurry. What if the kick shaft spring wasn't completely tight? Again. The two would be more likely to come together and make for a broken shaft.

Anyway, the initial problem was more than likely the loose cam bolt. It allowed the timing chain to jump teeth and a valve was bent.

-Kerry

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thanks every one i dicided to continue to use the stock cam and save up for a frame cradle and olalla o thought it was what u said to

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thanks every one i dicided to continue to use the stock cam and save up for a frame cradle and olalla o thought it was what u said to
If you plan on being rough with it, the cradle is the smarter choice.

The cam will help with performance a small degree. The cam doesn't help you, if the bike is trashed. It is completely up to you and what you want to do with the bike. We are here to provide advice. I just noticed that the piston was not going to make much of a difference without something to help the engine breath. That's where the cam comes in. Then you keep going from there, that's the problem I discovered. The prices also tend to be cheaper if you buy things as a setup. Procycle offered a deal with the hi comp and cam, I jumped on it. I found that trying to make things interesting for a teenager ended up making the two-stroke a better choice in the long run. Now I have a little play bike.:)

I appreciate that you want to keep learning, though. That's good.:banghead:

Just make sure you are torquing things down to the right settings and take things easy. If it's worth doing, then take your time, do it correctly.

-Kerry

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also i seem to have lost.......misplaced my service manual can someone tell me the valve clearances and help tell me how pics would be best i have everything i need just need a valve spring compressor and to do valve clearances but i dont know how to set them and adjust them up

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The valve clearence specs are (cold ) IN 0.08 - 0.12mm

EX 0.10-0.14 mm

If your going to put new valves in you'll have to lap them in make sure all specs are correct and set the clearence on them .

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When you put new valve in you have to lap them in the seat to ensure they are seated and seal right.

You use a valve lapping compound that is like a past with gritty sand in it and a tool (a handle with a suction cup ) that spins the valve to grind it in the seat .

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What do u mean by lap them in???
You're having the shop install the valve, right? The shop will lap them... I hope.

-Kerry

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no i dicided the shop would charge 40 dollars labor and 35 dollars for valves that 75 dollar i dont have will i spend 20 for a compressor and 30 dollar for valves off the tt store its 50 thats 25 dollars i could save and plus i will learn how to install valve so not bad save money and learn :)

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i have read that you dont have to lap valve on newer engines do i have to??and what grit should i use

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i have read that you dont have to lap valve on newer engines do i have to??and what grit should i use

Some engines use titanium valves that are specially coated that should NOT be lapped-the lapping compound will remove the coating.

IDK if the TTR125 is one of these engines....many of the high perf thumpers are.

Either way, the seats should be cut if they are in any way worn or damaged to get a proper seal.

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Since the bike was built on a simple principle, the head, valves, and seats aren't going to be something exotic. Check the web for some videos on how to lap. They are pretty useful. This is a rough breakdown of how it goes... I realize you are on a budget, so I'm writing this basic guide with that in mind.

The premise is that you make the valve have the same contour as the seat so the valve seals tight. By the way... there are other parts you haven't mentioned that I'm hoping you either have or won't need. The seals and guides are replacement items since you are tearing this apart. I know the seals are included in a full blown gasket/seal kit. I would think they are in a top end kit, as well. In my opinion, the guides are better installed by a shop... but we will get to that.

When you get the head tore down (locks & retainers removed, springs off, seals out, valves out), flip it over so you see the combustion chamber. Inspect the seats (where the valve sits against the head on the combustion chamber side) for any gouges or scratches. You need a way to measure the seat width where it meets the valve. The largest they can be, per the book, is 1.6mm. If they are damaged or too big you'll need new ones before you can lap.

If the seats look good, temporarily install the new valves(no springs, etc). Clean the combustion chamber to remove the carbon build up. A wire wheel and a slow speed drill work pretty good. Be careful not to scratch your gasket seating surface and just get the head clean in the areas around the valves. By the way, it's ok to touch the valve on the flat section with the dimple in the center with the wheel, just make sure the valves are seated good, don't spend too much time in one area, this is to prevent scratches to the seat that will make lapping take longer and wind up putting you closer to having to re-cut the seats (machine work=$$). The areas on the combustion chamber do not have to be too clean, just clean enough that the head is exposed from the carbon around the valve.

Once most of the carbon is gone, push the valves out and clean the combustion chamber and valves. If you have access to some precision measuring tools (really small bore gauge and an outside mic/caliper) I can give you the measurements to make sure your guides are good, you don't want to have to replace those - you need a specialty tools with an oven, or a machine shop= $$ - By the way Yamaha recommends replacing those with the valves, so they are a matched set.

If all looks good, seat the new valve in the guide.

At this point, if you can't see any visable damage, you can start the lapping process.

Once you clean off the new valve and the seat, you'll need to see if you have any high spots and if the valve is centered. A cheap way to do that is with a permanent marker. Mark the stem side of the valve and the seat where the two meet when the valve is closed. Then lap until the the valve and seat are back to being the bare metal you started with. Check to see if the valve is centered by looking at the pattern all the way around the valve on the stem side. You should have a small bit of marker showing near the outside edge. If it's not... guess what? machine shop =$$ you'll need the seat recut.

I've never used paper, not even sure how that would work, just lapping compound - which is a paste with the grit in it... kinda like a gritty toothpaste:smirk: . My preference is a grit between 240 and 320. The higher the number, the smoother the finish - which isn't good, necessarily. If you have a rod/dowel and an old nerf dart you can make a cheap lapping tool that will grab the valve and allow you to turn it in the seat. Use a light pressure, and feel. When the grit kind of gives, the seat is polished. Pick the valve up, rotate it 90 degrees and see if the resistance picks back up. If it does, then begin to lap again until it gives out.

Remove the valves again and clean all the parts. At this point you can look at you marks and check your seat measurements. If it's good, then reassemble the head with your new valves.

Once completed you do a "leak" check by pouring a "solvent" into the runner of the valve that was just assembed. If that liquid leaks around the valve into the combustion side, it's not sealing and the valve needs lapped again.

Hope I didn't confuse ya too much...:thumbsup:

-Kerry

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