xr250 binding

After top end rebuild.

Thought I was care full valve timing on the chain, went around a couple times on then crank nut I thought, but think maybe off a tooth on timing, caused valve to bind w piston?

Any suggestions r welcome to make sure timing right. Marks seem to alighn.

Thanks

Chuckster

I'm thinking the decomp may have jammed the exhaust valve open. Will check first

Nobody knows where to start........................do you understand your post??????

Check TDC by feeling the piston with a piece of wire through the spark plug hole.  Is that a high compression piston?

Hmm...

Rebuilt top with 280 kit. Put the cam chain on sprocket, aligned the top mark up, sides horizontal with the head, crank case mark on the notch just before the T. Cam lobes pointing down, moving away from intakes. Everything looked good.

Cranked it over a few times with the wrench and crank nut. OK, but no real test until cover on.Put cover on, assembled. Checked valve clearance.

Kicked it over slowly. Worked fine. Squeezed decomp. Let air out at top. Kicked again slowly. Squeezed again, decomp very loose. Binding.

Hope more clear..

Slightly hi comp 10.5. Have valve cover off, still binding.

Slightly hi comp 10.5. Have valve cover off, still binding.

Timing looks spot on. Wouldn't turn counterclockwise. Very slight movement clockwise and turns counterclockwise fine. My guess is something yo do with decomp going in too far for hi comp je piston?

Are you using the oem steel rocker cover gasket?

Cometic 3 layer steel came with the kit. My plunger and spring r in the right spot, didn't fall in. Will put cover back on, see if decomp is issue. I was gentile moving it so I'm not sure I need take head off and look.

Exhaust valves were tight at bind.

Curious, how does the cdi know its at?

As far as I know your meant to use the T mark for cam timing and not the one just before..

Edited by w00dzy

Got it figured out. Timing spot on. Bad lower oil retaining ring looks not to spec. Folded up as bike was starting. Next kick it seized up.

Got it figured out. Timing spot on. Bad lower oil retaining ring looks not to spec. Folded up as bike was starting. Next kick it seized up.

Glad you gotnit sorted. Did you do the timing off the t mark?

Timing was correct.

Issue seems to be whether the right rings were sold with the piston or not. I followed the chart putting them on, and the machinist gapped them. First piston sold me was deformed ...had a bigger crown than skirt, not the usual other way around. I'm wondering if this snafu was part of that glitch. Last piston was 77 mm on crown, 76 mm skirt. Vendor and machinist are two different entities, proving what happened may be an issue...I think I gotta eat this one...

Man that sucks. Sorry to hear that. Not sure you undertand what im getting at with the timing? I understood it had to be on the t.. you mentioned you timed it on the mark just before? Want to make sure mine is right as I did mine on the t.

The machinist needs to have the piston in hand to create the bore for that particular piston.

 

If he found a problem when measuring the piston, he has the option to reject the piston or proceed with boring. 

 

If he didn't check the piston to make sure it would work in the bore he was creating for it,  It would be his fault.

 

But, what's the whole story.

I'd like to see a picture of the lower oil ring. Is there a chance it was not installed on the piston correctly, and/or when the piston was installed the ring damaged?

Ring was not damaged when installed. The scraping started after then. There's a deep gouge in the stroke length the a small scratch when I pulled the cylinder off.

A new machinist and I looked at it last night. His thoughts were incorrect ring or gap.

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