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Hello,
I was trying to finis the reassembly of my bike following a change of piston and timing chain on my 250 crf 2013.
But I can not put the timing chain back on the camshaft sprocket, chain is way too tight.
Or if I get there (on the sprocket), I can not push back the bearing into its housing to put the camshaft in his normal position ...

I counted the number of links, 106 and compare the length with the old chain it's ok. \
I've also opened the lower carter to ensure the chain was properly set around the crakshaft sprocket and yes

The chain tensioner is at the moment unmounted.

Help me please, Do you have a trick, is it normal ?
Sorry for my english.

Welcome to the site !!

First , you posted in the "Jetting" Forum , this should be in the "General" forum , OR in the "CRF250R" forum , but i will try to help you with this if i can....

Questions:
Is the engine at Top Dead Center ?? , and is the cam being inserted with the cam lobes facing UP ?? (the lobes should be facing 2-O Clock position , facing rearwards with the sprocket "notches" staying level with the head) *like this* _ _

Are the shims properly seated in the valve stem and the bucket seated down all the way ?? , and did you confirm the shims did not get mixed up or left stuck in a bucket and some buckets have 2 shims instead of 1 ?? , this would hold the cam up and not allow it to seat properly

When installing the chain , did you make sure the Chain Guide is seated properly and not putting tension on the chain ??

When you install the chain on the cam sprocket you should be able to tilt the cam into position and it should go right into place if everything above is done correctly

If any of these items are missed that could be the issue , hopefully one of these things is your issue ...... Check and reply back ......

Jim, shouldn't he have the cam tensioner removed not just backed off ? Could be still pushing on the chain ?

First thanks guys !

the cam chain tensioner is totaly removed, not just backed off.

>Is the engine at Top Dead Center ??
Yes it is, ont the mark below, and I see the close piston through the spark hole.
>and is the cam being inserted with the cam lobes facing UP
Yes As suggested by the manual.

>Are the shims properly seated in the valve stem and the bucket seated down all the way ??
Yes checked and anyway the bucket dont event touch the camshaft at the moment

>did you confirm the shims did not get mixed up or left stuck in a bucket and some buckets have 2 shims instead of 1 ?? , this would hold the cam up and not allow it to seat properly
so yes

When installing the chain , did you make sure the Chain Guide is seated properly and not putting tension on the chain ??
I think so this is the only part I'm not sure in your propositions, This is why I join 2 photos:
https://data.anons.fr/index.php/s/hHC6mvlQ8syMUFc
https://data.anons.fr/index.php/s/hHC6mvlQ8syMUFc

I'm starting to freaking out.. No one knows.
I will dump more pics in couple of minutes

Other photos:

https://data.anons.fr/index.php/s/2lbpTCOaCTDGXs5

https://data.anons.fr/index.php/s/3qlkQFRI3OC0ILY

https://data.anons.fr/index.php/s/6QAWnzh6yAI51zt

Finally it appeared that the chain sent by the supplier was too short by 2 links, 104 instead of 106 simply. They sent me a chain of crf250x ...

Finally it appeared that the chain sent by the supplier was too short by 2 links, 104 instead of 106 simply. They sent me a chain of crf250x ...

Well that would be that last thing that i would have thought would have been the issue ..... Glad you got it figured out , good job !!

Could have been the other way around with a 106 link chain on a bike meant for a 104. That would have caused some carnage if there was enough adjustment in the tensioner initally.

There is one to put in the memory banks for future issues.
Thanks for sharing what you found and good deal on getting to the root of the problem.