Differance between 1G & 2G 7 bolt cranks?

[JeanDSM]

Today a friend of mine who owns a machine shop called me cus a costumer left him a 7 bolt crank and he called me and gave it to me. The crank is in perfect condition and he told me it was from a 2g car.

I trust him but i want to know whats the differance between these two cranks? Are they compatible?

Also i do know 6 bolts crnaks dont works with 7 bolt blocks, i do know this, but for knowledge why? whats the difference?

 

[Zex4g63]

They are the same. I also have several that appear to be good but the thrust surface is bad. Make sure he checks that out.

 

[turboglenn]

And remember the 7 bolt motors have all different sizes in the main journals. You have to cross reference marks on the block along with measurements on the crank journals in order to get the correct bearings in them. However on 6 bolts (and it's one of my favorite things about 6 bolts ) is that they have ONE size bearing for all teh journals . Unless htey've been modified, and even then then they usually turn all the journals down the same amount. SO the bearings are easy to pick up a set and know you have the right ones. Just ahve the machinist you know use teh guide t and his measuring skills to get you the right bearings to install the new 7 bolt crank.

I've been told the reason this changes was when teh 7 bolts started being built in america, they were trying for tighter tolorances and that's what lead to having roughly 16 different size bearings for the 7 bolt crank journals. All this info was given to me by buschur racing when i was deciding to rebuild my old & bolt and just throw a 1g head on it or just do a straight 6 bolt swap. NOw i have a a couple 6 bolt motors and i won't come off them for anything