Tips/Help on KTM SX125 top end Rebuild

Blaster528 · Feb 8, 2017

Alright so it's been a while since my last post..... here's a little update.
-carb off and cleaned
-air box off and cleaned
-subframe off and cleaned
- chain cleaned... will attempt to remove a link
-coolant drained and refilled with engine ice.
-compression tested cold at 125-130psi

Alright so I have a coolant question. So I put about half of the engine ice in it ran it and checked again. I couldn't see the level so I added a bit more. Still can't see the coolant level. I've put over half the bottle and I'm worried Ive just dumped $25 down into the bottom end. What should I do???

Blaster528 · Feb 8, 2017

Alright so it's been a while since my last post..... here's a little update.
-carb off and cleaned
-air box off and cleaned
-subframe off and cleaned
- chain cleaned... will attempt to remove a link
-coolant drained and refilled with engine ice.
-compression tested cold at 125-130psi

Alright so I have a coolant question. So I put about half of the engine ice in it ran it and checked again. I couldn't see the level so I added a bit more. Still can't see the coolant level. I've put over half the bottle and I'm worried Ive just dumped $25 down into the bottom end. What should I do???

best · Feb 8, 2017

Check the gearbox oil level. If it has gone up and looks milky, you have a problem.
That is why I like plain and simple Prestone concentrate. Cheap and effective.
And if you see green, you know where it came from.

It is hard to see the coolant level in the rad, only about cup (250ml) in the upper tanks.
Sometimes if you squeeze the hoses you can feel and see the coolant.

No real need for engine ice, KTM 125 rads are the same size as the 380 uses.
The 125 never overheats. even when crawling following my kids on their PW80.

These are quite sweet to work on, especially if you get used to pulling the subframe off.
I blew a crank during a Harescramble (it had been submerged 3 times!) and was able to swap the motor during the lunch break.

If you can pull a link off the rear sprocket like this:

If you can do this, it is time for a new chain. Don't bother trying to run it or take out a link.

Blaster528 · Feb 8, 2017

best said:
Check the gearbox oil level. If it has gone up and looks milky, you have a problem.
That is why I like plain and simple Prestone concentrate. Cheap and effective.
And if you see green, you know where it came from.

It is hard to see the coolant level in the rad, only about cup (250ml) in the upper tanks.
Sometimes if you squeeze the hoses you can feel and see the coolant.

No real need for engine ice, KTM 125 rads are the same size as the 380 uses.
The 125 never overheats. even when crawling following my kids on their PW80.

These are quite sweet to work on, especially if you get used to pulling the subframe off.
I blew a crank during a Harescramble (it had been submerged 3 times!) and was able to swap the motor during the lunch break.

If you can pull a link off the rear sprocket like this:

If you can do this, it is time for a new chain. Don't bother trying to run it or take out a link.

Ok so changing the gearbox oil is one thing I haven't gotten too on my list. It's next though once I get the damn bolt out of the subframe. I tried drilling it and then put an easy out to it with no luck. I've been soaking it with penetrating liquid. I just got done playing around with the chain and it's 10x better than I thought. The slack is only near the swingarm. I can barely pull it off the back teeth. I tried adjusting the rear axle but it looks like the Hulk put the lock nuts on

Blaster528 · Feb 8, 2017

best · Feb 8, 2017

You might as well change the gearbox oil while you are at it.
My favourite oil for it is Automatic Transmission Fluid (ATF or Dextron).
There are several types, any will do, especially for a 125.
The ATF-Type-F is a bit more grabby, and the others are just plain expensive.

There are special 2 stroke gearbox oils as well. I've used them.
Couldn't see an advantage.
I have been riding my KTMs with 2 oil changes a year for 15 years without a gear or clutch problem.

Do you have the KTM owner's or shop manual? Both are available on-line.
Be careful with the drain bolts. They will strip or crack the case if overtightened.
There is a "FULL" bolt that you remove to see when you have enough oil.
Damn I like the Blaster's little window. So simple.

Try heat and cold to remove the stuck subframe bolt.
Heat it red hot with a propane or MAPP gas torch, then splash with cold water.
Then do it again. And again. Then try the penetrating oil and easy-out. Patience.

Find a right sized wrench for the axle nuts.
Nothing says "Nimrod" like using a pipe wrench on them.
The KTM tool kit has a wrench for them. Short enough to not over torque them.
The next problem is the chain adjuster bolts. They usually seize and are a bear to get out.
Be careful to not break them. Heat and cold again.

Bell-Ray Waterproof Grease, nickle-antiseize and Locktite are your friends.
The weakest Locktite will act to exclude corrosion from the threads as well as hold bolts.

There are companies that sell the proper KTM bolts. You can buy a $20 kit that incudes most.
I prefer to use them as it looks better. On my Blaster I use socket head (Allen) bolts.
It pays to stick with one standard type bolt. You will need fewer tools and curse less.

This is something you might want to consider, relocating your CDI from the steering stem:

To underneath the gas tank so it doesn't get crushed when you turn:

Blaster528 · Feb 8, 2017

So about 5 minutes ago I got the bolt out. I upped the size of my drill bit and the bolt " gave up " and came out the other side. And I went threw my extra stash of blaster bolts and found the exact 1 I needed

. Talk about a plan working out.

I oiled the air filter then put some grease on the inside of the boot and around the rim. I haven't changed the oil yet because I wanted to put the subframe back on so I could get the oil warm. Yes I do have a manual however it's a 2004. I looked through and couldn't find anything different. Now referring to the manual the bike has 2 drain bolts and 1 check bolt?? How did you mount the cdi??

Blaster528 · Feb 9, 2017

the slight whining or ticking sound is the front sprocket freely spinning, i think. I was pretty happy after i got it all back together. I pulled the choke and it started up 3rd kick. I think thats pretty good for 12 degree weather. Also before I put the carb back on i checked the jets, the main was a 190 and the pilot was a 48. I looked in my manuel and I dont think thats stock. Thanks Best for all your help.

best · Feb 10, 2017

Here are the parts I made up to mount the CDI

Plate goes on

Then bolt the CDI and regulator on

Here was the turn angle before removing the CDI

And here it is after the CDI was relocated

More important than the small angle gain is protecting the CDI from crush damage.

Blaster528 · Feb 21, 2017

Sooooo, chain adjusters

. I was able to get the right one out perfectly but the left one still won't budge. I've soaked it in wd40/pb blaster heated up bolt red, then cooled it with ice water. The hex head bends but the threads don't. I've also tried heating up swing arm around the bolt with no luck. I don't know what else to try plus don't want to break the bolt. Suggestions??

best · Feb 22, 2017

Yup, that is a nasty one, I think I might have warned you about this. Here is the routine:
1) Take it to an expert, probably a machinist. It will cost. Oh well... Barring that:
2) Soak it in a good penetrating oil. WD40 is poor, PB-Blaster fair, Kroil is pretty darned good.
-- Soak it overnight, no longer. An alternate oil is 50/50 acetone and ATF. Heat the outer part up until oil smokes.
-- Work the bolt back and forth no more than the maximum rated torque. You don't want to break it.
-- You don't heat it up red hot because that ruins the temper and makes it prone to break off.
Red hot may burn the corrosion out, and a splash of cold water may shock and harden the bolt enough to remove.
Use this as a last a last resort. Experts often know just the sort of corrosion where this will work first time.
3) If that doesn't work, heat the outer part up until the oil smokes and dab the threads with paraffin wax. Try it.
4) If no-go, heat up until smokes, dab with wax, smack on bolt head with hammer to loosen corrosion. Try.
5) Repeated trys may eventually get it moving, work it slowly. The wax works better than oils in most cases.
6) If the hex head breaks off, put a nut over the stud and weld it in place. It is weaker than the original.
7) It it is into aluminum, you can use a strong alum in warm water mixture to dissolve the bolt and corrosion.
-- It has to soak for 12hrs and has to be kept warm and won't work with stainless steel.
8) If the head breaks off next to the surface, you are in trouble.
--a) Prick punch the EXACT center center of the broken bolt. Grind it flat if you have to.
--b) Drill a small hole in the EXACT center of the broken bolt. Drill it right through.
--c) this may be a good time to try the alum trick.
--d) The best extractors are the fine straight spline and nut type:

http://www.parts-recycling.com/Meta...r-/Blue-point-no-1020-screw-extractor-set.htm
9) if all else fails, drill the bolt until you touch the threads (tap drill size),
-- try the oil and heat and see if you can work the threads out.
10) If all else fails, drill it out for a helicoil, or the next size larger bolt (if there is room) and tap it.

Can be a nightmare eh?

The preventative measure is drilling a small drain hole in the lower corner of the swingarm and using antiseize compound on the bolt in the future.

Blaster528 · Feb 23, 2017

best said:
Yup, that is a nasty one, I think I might have warned you about this. Here is the routine:
1) Take it to an expert, probably a machinist. It will cost. Oh well... Barring that:
2) Soak it in a good penetrating oil. WD40 is poor, PB-Blaster fair, Kroil is pretty darned good.
-- Soak it overnight, no longer. An alternate oil is 50/50 acetone and ATF. Heat the outer part up until oil smokes.
-- Work the bolt back and forth no more than the maximum rated torque. You don't want to break it.
-- You don't heat it up red hot because that ruins the temper and makes it prone to break off.
Red hot may burn the corrosion out, and a splash of cold water may shock and harden the bolt enough to remove.
Use this as a last a last resort. Experts often know just the sort of corrosion where this will work first time.
3) If that doesn't work, heat the outer part up until the oil smokes and dab the threads with paraffin wax. Try it.
4) If no-go, heat up until smokes, dab with wax, smack on bolt head with hammer to loosen corrosion. Try.
5) Repeated trys may eventually get it moving, work it slowly. The wax works better than oils in most cases.
6) If the hex head breaks off, put a nut over the stud and weld it in place. It is weaker than the original.
7) It it is into aluminum, you can use a strong alum in warm water mixture to dissolve the bolt and corrosion.
-- It has to soak for 12hrs and has to be kept warm and won't work with stainless steel.
8) If the head breaks off next to the surface, you are in trouble.
--a) Prick punch the EXACT center center of the broken bolt. Grind it flat if you have to.
--b) Drill a small hole in the EXACT center of the broken bolt. Drill it right through.
--c) this may be a good time to try the alum trick.
--d) The best extractors are the fine straight spline and nut type:

http://www.parts-recycling.com/Meta...r-/Blue-point-no-1020-screw-extractor-set.htm
9) if all else fails, drill the bolt until you touch the threads (tap drill size),
-- try the oil and heat and see if you can work the threads out.
10) If all else fails, drill it out for a helicoil, or the next size larger bolt (if there is room) and tap it.

Can be a nightmare eh?

The preventative measure is drilling a small drain hole in the lower corner of the swingarm and using antiseize compound on the bolt in the future.

She ended up coming off pretty easy

Brought it to a friend who has quite the setup. He ended up re tapping the threads and walla. Now just got to pick up another bolt and nut

best · Feb 24, 2017

Sweet! Although a sad end for the Snap-on socket!
Those tensioner bolts and overtightening the gearbox drain bolt are the 2 worse "Gotcha"s on the KTM.

Blaster528 · Feb 24, 2017

best said:
Sweet! Although a sad end for the Snap-on socket!
Those tensioner bolts and overtightening the gearbox drain bolt are the 2 worse "Gotcha"s on the KTM.

Naw that snap on was already trash he keeps junk ones just for this purpose. I changed the gear box oil 3 times. It was grey ever time which would explain my low coolant. Going to order a water pump rebuild and another bolt soon. I only have to address the leaking forks and the black oil coming from exhaust and I'll be home free!!

best · Feb 24, 2017

Whew, good on the socket.

Black oil from the exhaust is commonly called "spooge" and is usually from 1) an overly rich oil mixture or 2) rich fuel jetting or 3) leaky flange seal. If the jetting is right and the you are running 50:1 no spooge will drip even with a leaky flange seal.

I've had problems with the waterpumps leaking over the years too. Setting around seems to be bad on them. Generally if I'm riding it weekly, no problems. Lay it up over winter and there is coolant in the oil. Using just water is hard on the seals as well. A 50/50 mix lubes the seals much better than water.

Front shock leaks, argh! I've never had one apart. I had a leaky set a few years ago and a local suspension guy convinced me to get all 3 shocks done at the same time. Wow, best money I've ever spent in shop work. He set the bike up for my weight and riding style and no more leaks.

I bought a 2000 Jeep Cherokee with a cracked head a few years ago. Owner had been pouring water into it and claimed it "just disappeared". Dip stick was filled with grey goo! Got about 3-4 gallons of grey mayonnaise out of it when I drained it. They had been driving the truck, just re-filling the rad with water every day. Replaced the head and did 4 oil changes (driving it between changes) with all the used oil I had in the shop, still came out grey. Filled with 15w40, oil pressure was low, but I got 2 years and 24,000 kms out of it before it finally rusted out. Always a bit worried if that motor would get me home but it never failed me...

Blaster528 · Feb 25, 2017

Trying to take off clutch cover and it appears the collar/ spacer on the kickstart shaft is preventing the cover from coming off. Should it just slide off the shaft?

Blaster528 · Feb 25, 2017

So I ended up getting that spacer off it was rusted on but nothing a quick wire wheel couldn't fix. The clutch and gear assembly look surprisingly excellent

. Water pump shaft could easily be slid in and out of oil seal so hopefully that is the problem. The bearing was fine but I'm still going to replace. I drained out coolant tanks and about a liter came out. Back a bit you said the upper tanks hold 250ml?? So next time I fill it up put 250ml in it??? 50:1 is the way to go? I thought yz125s and sx125s liked 32:1 similar to blasters. That's what I'm currently running, 93 octane with Ams oil Interceptor. Also no spooge is coming from cylinder it only drops from where the header meets silencer. I put a high temp radiator hose on it with 1 hose clamp but it still seeps out

best · Feb 25, 2017

Oil mix is a personal issue very close to a religion.
Try 32:1 and then 40:1 and finally 50:1 and see which works best for you.
I have run 50:1 (and occasional 40:1) for years in my KTM 125 with no bad effect.
I got no power boost from greater concentrations of oil as long as I was running high grade synthetic.
I do get power gains with heavier mixtures of Castor and cheap mineral oils.
I also get lots of spooge, fouled plugs and stuck rings and power-valves.
Therefore I have become a believer in Ipone or Motul or Amsoil synthetic at 50:1 in my KTMs.
Switch to at least 40:1 and get your jetting leaned out a bit and I think you will see your spooge disappear.

Your experience with the waterpump is the same as mine.
Bearing and seal are cheap, I've replaced often. The darned thing still leaks when it sits around.
Gets a bit of coolant in the gear oil. Has not hurt the gears or clutch.

That 250ml was an approximate. I just top the tank up every time I head out as an obsession compulsion.
Ride on! You are getting me excited to get the bikes out. When will this snow melt?

Blaster528 · Feb 26, 2017

best said:
Oil mix is a personal issue very close to a religion.
Try 32:1 and then 40:1 and finally 50:1 and see which works best for you.
I have run 50:1 (and occasional 40:1) for years in my KTM 125 with no bad effect.
I got no power boost from greater concentrations of oil as long as I was running high grade synthetic.
I do get power gains with heavier mixtures of Castor and cheap mineral oils.
I also get lots of spooge, fouled plugs and stuck rings and power-valves.
Therefore I have become a believer in Ipone or Motul or Amsoil synthetic at 50:1 in my KTMs.
Switch to at least 40:1 and get your jetting leaned out a bit and I think you will see your spooge disappear.

Your experience with the waterpump is the same as mine.
Bearing and seal are cheap, I've replaced often. The darned thing still leaks when it sits around.
Gets a bit of coolant in the gear oil. Has not hurt the gears or clutch.

That 250ml was an approximate. I just top the tank up every time I head out as an obsession compulsion.
Ride on! You are getting me excited to get the bikes out. When will this snow melt?

Alright I at least have to try riding it on 32:1 first. Then I'll switch. Snow?? Where are you located. I'm in Vermont with zero snow and 60 degree weather

Blaster528 · Mar 7, 2017

So I went to go get a tire tube. My tire is a 110/90-19 but the guy ended up giving me a 110/80-19. I just noticed this once I got back home. Will it work, or is it a big deal that it's not the same? I'm not too familiar with tires

Tips/Help on KTM SX125 top end Rebuild

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