Take the bolt out and (if you can) put the bolt in the opposite way with a 2 pence in the gap and slowly do the bolt up - this should spread the stem apart enough.
This is assuming they are the correct size.
@DaveH started
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Take the bolt out and (if you can) put the bolt in the opposite way with a 2 pence in the gap and slowly do the bolt up - this should spread the stem apart enough.
This is assuming they are the correct size.