Jeff Gilbert

N. Texas SP
LIFETIME SPONSOR
Oct 20, 2000
2,969
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125sx. Anyone ever replace top-end without taking the head off. Not being lazy but if it's not necessary why do it?
 

mopowa

Member
Dec 6, 2000
75
1
Hey Paul...I mean Jeff... I do it all the time. As for a sx, Ive read somewhere about checking the deck height(head off) and this being crucial. Personally I wouldnt worry about it as long as you use a stock KTM base gasket.
 

Jeff Gilbert

N. Texas SP
LIFETIME SPONSOR
Oct 20, 2000
2,969
2
Originally posted by mopowa
Hey Paul...I mean Jeff...

You're makin me laugh
 

Strick

LIFETIME SPONSOR
Nov 8, 1999
1,782
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Z-dimension, X-dimension - can not be set unless you remove the head.

Having said that, if you can mic the stock base gasket, and purchase the same thickness, then the X-dimension should be O.K. (assumption here). If your power valve is clean and not in need of servicing (and not hitting the piston), then I guess the Z-dimension doesn't need to be checked.

Two buddies of mine just pulled the jug and popped in new pistons and it worked fine on 380's, but I wouldn't (and don't), do it that way.
 

Strick

LIFETIME SPONSOR
Nov 8, 1999
1,782
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Just the jug. BUT, you HAVE to pop off the head to set the Z-dimension, which is mandatory when R&R the power valve.
 

Tiger

~SPONSOR~
Aug 21, 2000
235
0
Top End replacement...

You CAN do that, but be careful. The last time I tried it (on a YZ 125)...when I removed the cylinder, the extra suction (the head was still on) sucked coolant into the oddest places. I spent an entire Saturday with my bike upside down trying to get coolant out of it. I'll never do it that way again!
:mad:
 

Strick

LIFETIME SPONSOR
Nov 8, 1999
1,782
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Be careful Tiger. KTM power valve requires measurement when being set(with the head off). If you service that power valve. You MUST remove the head.
 

mcracer

Member
Jul 14, 2001
47
0
If you do not remove the head, be sure to measure the cylinder and inspect for plating coming off around the edges of the ports.
 

dstktmusa

Member
Jan 5, 2001
179
0
i would say that if your'e replacing the piston then you will have to re-check the deck height. to get 2 pistons the exact same height would sound to good to be true. the '02 125's have reusable o-rings like the 250/300/380's but the earlier 125's have an o-ring and a gasket.
 
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