Interchangable years for "thru" bolts
 

Do the engine "through bolts" vary from year to year. For instance, will the engine "through bolts" on a '71 911T fit on a 2.4 case that has been converted to 2.7 specs? Or will 1966 "through bolts" fit in a 1977 2.7 or even a "78 SC 3.0. Where are the cut off years and varients. I'd appreciate the info. Thanks, R:confused:

I think I figured this out on my own. 911 / 914-6 Same '65-'89 according to Proformance Products newest cat. I just got. Thanks R ! You're welcome R !

That's why I use Pelican for new parts! ;)

65-77 through-bolts have a coarse thread
78- onwards have a finer thread pitch

If you want an upgrade, use the finer pitch versions (and associated fine pitch acorn nuts) - they are said to give more even torque readings.

Regards,
Andrew M

The fine thread through bolts are also larger in diameter. 8.4 mm vs 7.65 mm. The larger thread bolts add to case stability. Loctite 574 on the main webs and fine thread bolts are the next best thing to shuffle pins in a mag case engine.
There is also a difference in the washers that go on the through bolts.
The early 2.0-2.4 engines use a square edged washer and the 2.7, 3.0, 3.2, 3.3 engines use beveled washers for cylinder clearance.