250sxf 2008 not starting after top en rebuild???

Related:
Create New Tag

9/22/2018 2:43 AM

Hello,
ive just done a top end rebuild on my ktm 250sxf and what a process it was and is. ive put it back in the bike with a new piston and rings / gasket now it wont even attempt to start, i can feel alot of compression in the cylinder, it has fuel and air and spark but wont even attempt to start. very frustrating the bike was put in tdc and locked in place with the locking nut my bike has, mind you it was a absolute pain in the ass to start before as well, i havnt checked valve clearences since i lost my feeler gauge and cant check them untill tommorow. whats everyones opinion.

(PHOTO IS TDC ON THE BIKE AND YES THE piston is 100% TDC ASWELL) ~ also the starter is pretty hard to kick over now is that normal for the 4 stroker assuming that its just alot of compression. (2 stroke guy over here) Photo

|

9/22/2018 2:44 AM

is it possible for the cams to be 180 out somehow?

|

9/22/2018 5:51 AM
Edited Date/Time: 9/22/2018 5:56 AM

If you locked it in place it cant be 180 out, which i dont think is possible anyway since i think it fires every 360 degrees regardless of what stroke its on. The manual should tell you how many pins in the chain need to be in between the cams sprockets. The lines or dots arnt always 100% accurate. Does it have the hydraulic timing chain tensioner? Of those are set right the chain could jump a tooth. First off i wouldnt be rebuilding a bike unless i had feeler gauges. Did you replace the valves or atleast have them re cut?

|

9/22/2018 5:57 AM

i agree with you, not checking if i had a feeler gauge before the build was a pretty stupid thing to do.
didnt do anything with the valves as of yet, the plan of attack was just to swap the piston and rings and redo the gaskets and do the valves when i can afford to.
with the valves would of anything have changed i cant find a reason why it wont even spurt, i didnt change them at all so it should still atleast backfire if the teeth were off?

|

9/22/2018 6:21 AM

If they were still in spec it should but if they are out then probably not. I would check the timing mark on the flywheel and confirm that the cams are in time. Once you are sure its timed correctly then check that valve clearence.

|

9/22/2018 6:22 AM

How many hours are on the bike since last rebuild?

|

9/22/2018 6:28 AM

rebuild history is completely unknown its about time ready for a bottom end rebuild aswell when i changed the piston the con rod had abit of movement aswell :/
such a pain in the ass, also it genuinely really hard to kick the bike over, could that mean the piston didnt seet correctly or is it normal for a fresh rebuild?
sorry for the stupid questions just trying to wrap my head around this

|

9/22/2018 6:36 AM

Check your auto decompression device. If not working correctly it will be very hard to kick over.
How long did the bike set while the rebuild was being done?

Paw Paw

|

9/22/2018 6:37 AM
Edited Date/Time: 9/22/2018 6:41 AM

Gohard wrote:

rebuild history is completely unknown its about time ready for a bottom end rebuild aswell when i changed the piston the con ...more

If its hard to kick that tells me the timing isnt correct or the added compression from new piston combined with valves out of spec is causing to much compression. Did you measure the play in the rod? By piston seating you mean the piston rings seating..? The rings wont seat until after you start the bike and do a break in procedure.

|

9/22/2018 6:40 AM

Paw Paw 271 wrote:

Check your auto decompression device. If not working correctly it will be very hard to kick over.
How long did the bike set ...more

I didnt even think of that. Good call.

|

9/22/2018 6:48 AM

the engine was out of the bike being worked on for about 12 hours give or take, the con rod didnt have enough play in it to make a difference or replacing straight away, but it will need to be done relatively soon, ill go over everything tomorrow when i get a chance and located the decompression device tommorow and check whats going on there, also is there another way to find top dead center more accurate then using the cam gears, so i can tell if it has skipped a tooth, thankyou for everyone's help so far hopefully i can smash this out relatively soon

|

9/22/2018 7:02 AM

Gohard wrote:

the engine was out of the bike being worked on for about 12 hours give or take, the con rod didnt have enough play in it to ...more

Take spark plug out and get a wooden dowel or something that wont damage the piston. Stick it in the plug hole and rotate it until it reaches a the top.

|

9/22/2018 7:06 AM

ah ok the old school method yeah ill give it a go, thanks for your time, i think ive figured out what i need to do now thankyou so much ill keep everyone updated

|

9/23/2018 7:29 AM

Back up. If your rod has up and down movement it must be replaced. Lateral movement has a spec too. Feeler gauges are used to check the lateral play. If your valve clearance is off by even .003, it can be the difference between the bike running or not.

|