Yamaha outboard, snapped off bolt, lowerunit stuck.

[jeroen1978]

Tried to remove the lower-unit, what a disaster.

4 bolts at both sides came loose but de bolt underneath the anode snapped off.
Lower-unit seems to be stuck at this bolt probably due of aluminium oxide.

Here's a picture of the snapped bolt:


Tried to pry with a big screwdriver but at the front side of the lower-unit there's a very tiny gap, at the backside where the snapped off bolt is, it doesn't give a gap.

I've heated up the bolt with a solder heat gun, spraying penetrating oil while heating, no result.

I've smacked the lower-unit with a rubber hammer, without any result.

Tried to drill a hole into the center of the bolt but I couldn't, the propshaft is in the way so I can't drill into the center.

I want to try again the heat and freeze method.
Can somebody tell me which part I have to heat and which part I have to freeze?
Heat the bolt and freeze the aluminium around the bolt or heat the aluminium around the bolt and freeze the bolt?

And can somebody tell me how to loosen this lower-unit from the snapped off bolt?

I expect when the lower-unit is off the snapped bolt will come loose easily from the exhaust tower.