Engine reving way too high --- Help please!

julien_d

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Oct 28, 2008
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You're meaning KDXRider I guess? Would be nice if you spoke in whole sentences sometimes........ Of course I will do what I can over there for Butterfly and the family, as well as for the site, if there is anything that I CAN do. Vince was a great guy and a good friend, may he rest in peace, and ride on forever.
 

_JOE_

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May 10, 2007
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gbruno21 said:
I will check the cylinder compression. Thanks for the help.


Compression won't tell you anything......that's why I linked you to a cost effective leak down test kit. :cool:
 

_JOE_

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May 10, 2007
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The leak down test will pressurize the engine, at about 10 or 15 psi, and watch for leakage. If the air leaks out you will probably hear it since it would take a pretty good leak to cause your symptoms. Make sure your air line coupler isn't leaking or you might not be able o hear it. Usually the crank seals or a gasket cause it to fail testing. I think you'll need to buy some caps for the intake/exhaust flanges as it doesn't look like you get any in the kit, you should be able to find them in the plumbing section at hour local hardware store.
 

gbruno21

Member
Jun 12, 2010
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Got it. I really appreciate the help guys and Boone is quite a bit closer than Atlanta especially since I work in Hickory, NC. I will do the leak test after I install the new head gasket, lower gasket, and piston rings.

I will post the results. If I can't figure it out I will drop the bike off in Boone then ski for the day!!!!
 

julien_d

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Oct 28, 2008
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Right. Compression test will tell you if you have good ring seal, leak down will tell you if head gasket, base gasket, or main seals are leaking.
 

_JOE_

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May 10, 2007
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You're much better off to do it before you install any new parts as the gaskets will be wasted if you find the crank seals to be bad. Unless you have it apart already, then you'll want to put it together with new gaskets.....
 

sr5bidder

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Oct 27, 2008
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julien_d said:
Right. Compression test will tell you if you have good ring seal, leak down will tell you if head gasket, base gasket, or main seals are leaking.


and new rings without proper break in will foul the leak down test completly... come on guys!!!
 

sr5bidder

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Oct 27, 2008
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julien_d said:
You're meaning KDXRider I guess? Would be nice if you spoke in whole sentences sometimes........ Of course I will do what I can over there for Butterfly and the family, as well as for the site, if there is anything that I CAN do. Vince was a great guy and a good friend, may he rest in peace, and ride on forever.



JC,
if you would email me the details...I am at a complete loss..really don't know what this is all about
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
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Merrillville,Indiana
4~6 psi is about all I would put in the motor. Some soapy water in a spray bottle will do the rest. I am feeling the cases are not sealed also, unusual? And Bruno never answered if the crank seals was ever removed, and put back in? I asked about leaving the temp on with the cases in the oven, them seals could have been damaged more. All the seals, do your self a favor and replace all now. Silly me, I would drop new bearings in. They can be cheaper in sets!
 

gbruno21

Member
Jun 12, 2010
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The crank seals were not replaced. I agree, I should have replaced the bearings while I was in there but they were still on the crankshaft and I could not get them off. I presume I need a special tool. I did not want to heat them up with a torch to remove them because I wasn't sure if that would screw anything else up. Again, ... I am an amatuer mechanic just trying to get the thing running again so that I can ride it with my sons. The bike ran great before the rotor magnets broke loose so I assumed it would run great again after I replaced the rotor. Little did I know that this repair would go on ... and on ... and on. The bike has been down for 6 months now and I am ready to have running again.

I agree ... I could replace everything in the engine and it would probably run great. But, how much money do I need to spend before I decide that I should have just bought another used bike. I am already into this repair at least $600 on a 1988 bike.

I really do appreciate all of the help you guys are giving and at this point I will probably just bite the bullet and buy new bearings, crank seals, etc. I was just thinking that a new head gasket, new lower gasket, and new piston rings might be enough to get me running again. I literally had this bike for 7 years and did nothing to it but change the oil. It was too good to be true ... and now it is coming back to bite me in the a$$.
 

sr5bidder

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Oct 27, 2008
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if you had it for 7 years and just changed oil then I believe you did indeed get your moneys worth out of her and if you are ready for a newer bike I could trade you for my 2003 kx 125 if you had a bit of your tax return to put with it... I always wanted an air cooled power valved and disk braked kdx.. it does have rear disk too right?

and are you in for $600 from the mechanic that did not know when to stop?... jeez
 

whenfoxforks-ruled

Old MX Racer
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You can not install the crank main bearings like that. They get installed first. I would be careful that they are holding in the case, some at least. A spun race in the case is not good! Pulling the bearings off the crank is no fun, the torch warming the bearing up will help. So would the special tools.
 

_JOE_

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May 10, 2007
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sr5bidder said:
and new rings without proper break in will foul the leak down test completly... come on guys!!!


? It wouldn't make a difference in a 2 smoker. You want the piston at BDC to pressurize the crankcase anyway. Crappy ring seal won't make a difference.........
 

gbruno21

Member
Jun 12, 2010
24
1
No, the back brake is a drum not disc. I have $200 in with the mechanic that went too far. The rest is in a new rotor, stator, rings, gaskets, etc. Thanks but I am not interested in a 125, it is too small. My son has a 2008 TTR 125. It is too small for me.

Should I split the case again and start from scratch with new crank bearings, new seals, etc. or should I try the inexpensive fix first which is replacing the head gasket, lower gasket, and piston rings? I was thinking that if I change out those 3 I could crank it up and see how it runs. If it is still bad I buy another top end gasket kit for about $30 and install it when I split the case and replace the bearings and seals.

What do you think, is it worth a try to change just the easy stuff first and see how it runs? I know there is a pressure leak because there was oil leaking out around the head gasket last time I cranked it up.
 

gbruno21

Member
Jun 12, 2010
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Ok. I do not have a case splitting tool. I will try to find one online. When I split the cases will the bearings stay in place in the case halves or will they stay on the crank shaft? Either way how will I remove the bearings without damaging either the case or the crank shaft?

I have heard that the proper way to install the new crank bearings is to put them in the freezer overnight, then drop them into the case halves. After that do I simply put the two case halves together with the liquid gasket sealer and screw them into place? Or is there another special tool to squeeze the case together?
 

julien_d

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Oct 28, 2008
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There is a "crank installer" tool, but I have never needed it. crank and bearings go in the freezer, cases in the oven (I use 200 - 225), then drop them in. Have an old bearing or socket the right size in case they need a little more persuasion. Then the case halves with bearings installed go in the oven. The cold crank will slip right through the heated bearings. It's all about the temp difference.

The bearings will likely stay on the crank. You can use a torch to heat the bearings and pull them off the crank. If they do stay in the case, you can heat the cases and pop them out.
 

whenfoxforks-ruled

Old MX Racer
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If you beat new bearings in, beat on both races at once. Some engines can be tapped apart with a dead blows persuasion, some not. It was just apart should make it easier. The separator tool rules, and making one is not difficult. If the bearings stick to the crank, make sure to use a locking agent to help hold the bearing into the case. It can wallow out the bearing race, and the case will be junk.
 

Dirtdame

Member
Apr 10, 2010
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Case splitting tool.
IMG_0204.jpg


I use a twenty ton press and brass hammer to put the cases back together. I put a solid one piece fork seal driver that is longer than the crank spindle over the spindle so that it rests on a strong spot on the case around the main bearing. The other crank spindle has to able to drop through the plate that the other crank half is resting on, on the press bed. I line up the cases, the fork driver and start to press. As I press, I pause and tap the back end of the crankcase where the axle goes through with the brass hammer till all the trans shafts have seated into the places they need to be and the knock pins are almost into the cases as well. By that point, the case halves should press all the way together quite smoothly. :cool:
 
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Dirtdame

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Apr 10, 2010
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whenfoxforks-ruled said:
I would never advise doing that with an air tool, but. By hand, and keep it even.
I agree that if you forgot to remove every last fastener in the center cases and you had a very powerful air tool and didn't know what splitting the cases should feel and look like, a disaster could possibly occur. Admittedly, I have split dozens upon dozens of different engines over the years.
 

sr5bidder

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Oct 27, 2008
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gbruno21 said:
No, the back brake is a drum not disc. I have $200 in with the mechanic that went too far. The rest is in a new rotor, stator, rings, gaskets, etc. Thanks but I am not interested in a 125, it is too small. My son has a 2008 TTR 125. It is too small for me.

Should I split the case again and start from scratch with new crank bearings, new seals, etc. or should I try the inexpensive fix first which is replacing the head gasket, lower gasket, and piston rings? I was thinking that if I change out those 3 I could crank it up and see how it runs. If it is still bad I buy another top end gasket kit for about $30 and install it when I split the case and replace the bearings and seals.

What do you think, is it worth a try to change just the easy stuff first and see how it runs? I know there is a pressure leak because there was oil leaking out around the head gasket last time I cranked it up.


I don't think it's too small, 4 stroke 125's are much different than the 2 stroke 125's

IMG_1813.jpg


see it it full sized with a 37 inch seat hieght :cool:
 

reepicheep

Member
Apr 3, 2009
670
2
The heater and freezer method worked great for me, they just slipped together. You have to work fast and deliberately though once you get going.
 
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