KTM 450 motor issue

[joeyvb]

Hey guys.

I just rebuilt a 450 motor changed rings but not piston... Put all back together and adjusted valve clearances and cams and i am only showing 60lbs of compression on my compression tester. It has spark and shoots fire out the pipe when i hold throttle open but will not fire. Any ideas what could be causing this low compression issue?

[flooringit]

id guess you didnt do the cam timing right or valve adjustment right, but im betting cam, put it at top deaed center and do a leak dow test youll know if its piston or not, your cam lobes should be facing down not pushing open valves and piston has to be up so your not pumping air threw exhaust or intake.

[Fast64ranchero]

You use the cam bridge when you put it back together?

[joeyvb]

I don't have a leak down tester here at the moment... I did not use the bridge I put cam lobes facing out and the holes at seal level as it said and made sure the flats on the cams were even with each other... If I don't have the bridge is there a method to use to make something that would work as an alternative?

[flooringit]

I missed this I'd a sx motor.

[joeyvb]

I missed this I'd a sx motor.

It is a 450 sxf motor... 2009

[flooringit]

i wouldnt know how to time one ive never done it. Sorry i cant be more help.

[ktmbill]

The compression is right it has a decompression valve so you it will read 50 60 lbs
Did you lock your crank in at top dead center did you turn your motor over to find top dead center on the cam chain gear if not then your cam timing is off

[joeyvb]

Steps I did was :

Disassembled the motor and removed and cleaned vortex piston, replaced the rings.
Re assembled everything however I did forget to premark cams and so on before dissassembling. So I locked the crank at TDC where the bolt threads into crank to lock it. I then positioned the upper timing gear so the dot is centered between the two bolts on the cam carrier. I then put the cams in place the flats would not even out the way it explained so I loosened cam gears and rotated cams till the flat surfaces were at the same spot on the cam carrier. I have all the valve clearances inline but bike will not fire. It will backfire once in a while and consistently when holding throttle wide open. I don't have the cam bridge tool but the eyes of the cams are lined up at seal height and the flats are both sitting in up position at relatively same position to make a straight line.

[ktmbill]

Are you using the stock cam chain adjuster if so recheck your cams and make sure the adjust do not slip and let the cam chain skip a tooth I hope you used assemble lube on the cams
If every thing is in line and right spray some wd 40 in the carb and see if it fires

[ktmbill]

All so you can find a false TDC on the crank so I put a long screw driver in the sprock plug hole to make sure I am at TDC to be safe

[joeyvb]

I did use lube for cams and all parts. I have built many bikes but this is the first KTM... And the last at this rate lol... When putting motor back together I put piston at tdc and locked it and rechecked by looking at top of cylinder. Then aligned the upper cam gear with dot straightup. Put cams in and it wouldn't fire so I then popped the cam gears off and aligned the flat spots straight up and the same location as the other one and retightened. The hydraulic tensioner has not skipped a tooth the dot is still ligning up in same place as it was originally when motor was built.

[ktmbill]

Ok I would try the wd 40 I had one do the same thing the carb float was stuck. If it starts with the wd 40 check the carb all so just had one the orings in the carb inlet was bad put in new one fired right up.
You can open the drain screw on the carb to see how much fuel is getting to the carb bowl.

[joeyvb]

Okay just checked fuel out carb hole it is getting fuel in bowl it comes out nice and fast when fuel is turned on. The other weird thing is it is rolling over normal then speeds up really fast then goes slow again then speeds up... The guy who owns the bike said he had it fired it ran then he went and washed it before he went to the track and the bike would not start again... I changed out rings and stuff as there was 50hrs on them but still have the same problem it rolls over normal then it is like the starter has a turbo and starts rolling over way faster and makes a higher sound...

[flooringit]

battery? just a thought

[ktmbill]

Ok check the big nut behind the mag they are noted to come loose tighten the shit out of it and red locktie it. It will spin loose then spin tight then loose. All so check the wiring under the tank on the right side its bundled up and tie straped to the they will break their and make contact some time

[joeyvb]

I have not done to much work on electric start does the battery cause issues with starting? I know I have to put a battery charger on it to charge it and start it everytime...

[joeyvb]

Okay perfect I will try that also... Thanks again... You are talking about the torque limiter gear that goes inline with the starter gear?

[ktmbill]

Its the gear behind that they is a big nut that holds the gear that turns the cam chain gears the it loosen up it pushs against the back of the limiter gear then trys to lock the motor up

[joeyvb]

Okay... So the one that is in the top left of the side case it is a gear that pulls out by hand but has a big nut on it?