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Old 05-02-2015, 09:40 AM   #1
Thomas B. OP
desert racer
 
Joined: Feb 2010
Location: Switzerland and around the globe
Oddometer: 234
I will probably regret this;another KTM 640 rebuild

Hi guys,
after finishing the TAT last year we rode down to LA and on the last km I suddenly had a ratteling noise in the engine. (see TAT Report in my signature). We brought the bikes back home and I was actually allready locking for new bikes, because we are planning a longer trip for next year. (And Im talking of months maybe years and alot of kms) After thinking about it alot we did decide to use our old 640s for the trip.
I know that I am going to regret this decision at some Point. But we still have These bikes and selling them is not really worth it. And we still can Mount a tank capacity of 45 l wich is impossible on any newer thumper.
My KTM has given us some Problems but Sandras was reliable up to now. The bikes both have around 60000km on the clock and have had to work quit hard at some Point. That is hours of digging in soft sand in second gear with almost full throttle in Mauretania for example. But they have allways been fun. So lets use them in the future as well.
Having the bikes back home I looked for the cause of the rattling and found this.


The big camshaft bearing was disintegrating.
Because of this and all the km we wanted to do I decided to tear the bike apart and have a look at everything to see what needed to be done to get the bike in a good shape.
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Old 05-02-2015, 09:51 AM   #2
Thomas B. OP
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So I got to work and took out the engine.





Parts that had to be taken off.



I then carried the engine into the basment and took it apart.









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Old 05-02-2015, 10:34 PM   #3
bmwktmbill
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Thomas,

That's impressive, must say you don't mess around.

Lots of screwing.
Oops, unscrewing....

Nice job.

bill
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The faster it goes the faster it breaks.
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Old 05-02-2015, 11:08 PM   #4
Night Falcon
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Good luck with the rebuild. If there is any bike worthy of a spruce up for continued service its the 640 - a proven performer and still one of the best adventure/dual sports ever made.
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Old 05-03-2015, 12:14 AM   #5
Thomas B. OP
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Location: Switzerland and around the globe
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After taking everything apart I started inspecting the parts and making a list of what I needed to order.
First all the seals went on the list.
The clutch is in a good state. All the plates Show very Little wear and are well in spec. The springs still have the right length.

Do you guys put in a new O-ring? The big one. The manuel doesnt say anything about it.

Then came the gears.
Looking at them closely I saw marks on many of the teeth. Putting the matching wheels into each other and rolling them I saw that the marks must be in the place where the top edge of the tooth touches the bottom of the next tooth

You can see the dark line at the bottom of the tooth. (by the way do you say tooth?)
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Old 05-03-2015, 12:32 AM   #6
Thomas B. OP
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I took a small screwdriver to see if I could feel any small Pittings. First i thought I could feel something but then saw that what I was Feeling was just a Little bit lower than the marks and was in every tooth on every wheel. That must be from fabrication. So I think Ill leave the gears with the marks in.
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Old 05-03-2015, 12:54 AM   #7
Thomas B. OP
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Location: Switzerland and around the globe
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But I will definitly Change the 5th gear. Both wheels looked more or less like this.





If anyone has any thoughts to what Im writing and my decisions feel free to make a comment.

All the bearings seem to be in good shape. There is very small Play, but almost not feelable, in the needle bearing of the shaft the sprocket sits on.
Asking about Play in the bearings in the Index thread Gunnerbuck made a comment about very Little being ok, but in his own rebuild thread remarked that he was concerned about exactly this bearing as it was turning faster than others.
Replace it or not? Im not sure. Since I have to watch the costs (I want to do Sandras KTM aswell) Ill look how much it is first.
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Old 05-03-2015, 01:40 AM   #8
Thomas B. OP
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Joined: Feb 2010
Location: Switzerland and around the globe
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Next came the heart: Piston, con rod, and crankshaft.
All bearings seem to run fine with no Play and no unnormal noise.
The Piston pin bearing in the con rod Shows no Play and the pin runs fine in it. But it does look used. What do you think? Is this a normal sight?



Piston and cylinder are 25000 km old. They do have scratches that might be a result of the debris of the camshaft bearing that was falling apart. In the cylinder you cannot really feel them and on the Piston you can feel them with your finger nail.












Apart from the scratches the wear seems to be minimal.
What do you think about this? What to do? Everything new is big Money.
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Old 05-03-2015, 02:03 AM   #9
Thomas B. OP
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Im not sure if I should take the head apart. The valves were done 25000 km ago. To do many more km would you have the head done again? Again that will cost, but if its necesary.

By the way sorry for the wierd capital letters on some words, but Im writing with a german Laptop and the Auto correction does that and I dont want to correct all of that. I think youll understand it anyway.

The canshaft has some marks aswell. Probably due to the debris running through the engine. I think Ill use it anyway as the marks are pretty small and dont look like normal Pittings to me. The rest of the cam is ok.





So thats it for the Moment.
Lets hear your comments on everything. Thanks
I might get to you later today.
Now Ill look at the spare parts catalog and see how many 100 Ill be spending allready.

Cheers Thomas
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Old 05-03-2015, 07:33 PM   #10
gunnerbuck
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Your piston and cylinder still look serviceable... I would push the piston rings up in the bore and measure the end gap, if close to max replacing them would not be a bad idea.. The cylinder would also benefit from a slight hone to restore the crosshatch marks ...

5th gear does look a little suspect...
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Old 05-03-2015, 08:23 PM   #11
clintnz
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Good advice from Gunner above.

I would replace that cam. Sometimes once pitting starts it can quickly get worse. Plus having a fresh auto decompressor is nice - they start to get worn at around your mileage.

You should be able to see if any of the valves are worn, have you had to adjust the valve clearances a lot? My bike has the slightly different high flow head, but it took 95K km to wear out the valves in that. Here's a pic of a brand new head & brand new valves for reference:



The big o-ring in the clutch - My 640 still has the original one at 135K km, so if it looks ok I'd use it again. Good luck with the rebuild.

Cheers
Clint
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Old 05-04-2015, 12:25 AM   #12
bmwktmbill
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Did you disassemble the oil pressure relief valve and find the lip seal in the clutch case?

Out of curiosity I'd like to see what the top of the piston looks like?

Do you know the carb jetting?

b
__________________
'02 KTM 640 Adventure-lowered
"On the road there are no special cases."
Cormack McCarthy-The Crossing

The faster it goes the faster it breaks.
And high performance=high maintenance.
Bill Shockley
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Old 05-04-2015, 01:16 AM   #13
Thomas B. OP
desert racer
 
Joined: Feb 2010
Location: Switzerland and around the globe
Oddometer: 234
Hi Bill,
I did disassemble the oil pressure relief valve, but what do you mean with the lip seal in the clutch case? I don't get that.
I can get you a picture of the top of the Piston, but I cleaned it a bit allready.
Don't know my jetting by heart, but I'll look it up (I'm at work at the Moment). It is bigger than it used to be and the air box has a bigger opening.
Why do you ask?
Cheers Thomas
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Old 05-04-2015, 01:18 AM   #14
Thomas B. OP
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Joined: Feb 2010
Location: Switzerland and around the globe
Oddometer: 234
Hi guys,
another question.
How do you measure the Play of the Rockers? Stick the screw into the hole and press the axle against it and then measure? Or how?
thanks for the help.
Cheers Thomas
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Old 05-04-2015, 02:55 AM   #15
hajoktejnSI
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I did it like this: put in both screws, screwed the M6 nuts on them a bit thight and measured the play.
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