Crank bolt

[4bimmers]

Swaaping M20 engine from one car to another and got it on a stand doing a basic resealing, replacing gaskets, seals, etc. Got the cam belt and crank pulley off and realize I need to remove the crank bolt in order to replace front seal, intermediate seal. How do I hold the crank so I can loosen the bolt?

[nando]

jam the end of a hammer or something else hard in one of the crank counter weights.