Exhaust port issue

[Bristol Daz]

Hi guys, just finishing an enforced rebuild due a casing issue and whilst setting up the top end I've noticed the exhaust port is open at tdc. Is this a problem? (the piston had to be shortened previously to stop it hitting the crankcase due to long rod/stroke crank)

[dickie]

Some of your charge will go straight out of the exhaust port rather than into your chamber via the transfers. Also crankcase compression will be reduced.

Also depends how long it's open. It might not run at all.