Thanks again guys! My brother came over this morning and helped me start putting things back together. We go the water pump removed, all surfaces cleaned up, and the new water pump installed. But I haven't been able to find torque specs for the bolts for the pulleys. The factory service manual has all the torques specs at the back of the manual, but I don't see anything for these pulley bolts. At the end of the torque specs listing there is a section called "Unless otherwise specified".



These bolts all have 10mm heads. Those in the water pump pulley are 6T, those in the eccentric shaft pulley are 8T. But when we try to torque the bolts into the front of the water pump to 30 ft-lb it seems like we are trying tighten them too much. Can someone verify what these torque specs should be?

Thanks,
Rich

 

The way I read it, 6T and 8T designate the grade (tensile strength) of the fastener. The heads are marked with a "6" or an "8".

A fasteners torque is in relationship to the diameter of the thread, not the size of the head. So the eccentric shaft pulley bolts may be marked with an "8" but the thread diameter is only 6mm. So the torque according to the chart would be 6-9 ft-lbs (.8-1.2 m-kg). The water pump pulley fasteners are softer at 6T but still 6mm diameter. Their torque would be 5-7 ft-lbs (.7-1.0 m-kg)

 

If I am not mistaken, thread pitch on a bolt will change the torque value as well. More threads, more max torque.

For most bolts that are available to us for our cars, the above explanation is perfect.

To get even deeper in the weeds, I looked up torque specs for bolts and some manufacturers have a separate torque values for nut/bolts that use lubrication and not.

 

Thanks again guys. That's obvious and I should have known that. They aren't going to specify torque based on head size. I'm glad we backed off. We'll hit it again tomorrow.

Just for documentation purposes, I think the water pump pulley bolts are 6T, 6mm, and the eccentric shaft pulley bolts are 8T, 8mm. I'll double-check tomorrow and correct if necessary.

Rich

 

Yes, its called "wet" torque vs. dry torque. Finer pitches (more threads per inch) do provide higher fastening strength of an assembly but the mechanical properties of the fastener material itself remain the same as a coarser pitch fastener of the same grade. They both will yield at the same maximum load.

I believe all the bolts that hold the pulleys and clutch fan are 6 X 1.0mm.