I am replacing the idler/tensioner pulley on my 1995 3.8 LeSabre. The bolt that holds on the pulley has a left-hand thread.

I managed to mess up the head of the bolt before I realized that it is a reverse thread.

Does anyone know where I can get a new one?

Thanks,

Neal Lewis

 

The idler/tensioner pulley bolt on a normally aspirated (non-supercharged), 3.8 L L27 engine, is a metric flange bolt, grade 10.9, 12 mm x 1.75 threads per millimeter (tpmm) x 35 mm long. It is a left-hand thread. It takes a 15 mm socket.

The bolt is not available from GM. I would like to know the part number so I can see what might cross reference.

It is not available from the auto parts places. It is not available from Fastenal®. It is not available from any of the other large or specialty bolt and fastener manufacturers except as a special order in large quantity.

One company does offer a 12 mm hex head cap screw 12 mm x 1.75 tpmm x 70 mm long, left-hand thread, grade 10.9, for $26 and shipping (for one bolt). You should buy the appropriate nut, thread it on before cutting and then use the nut to chase the threads.

A washer would be needed with the cap screw to simulate a flange bolt (spread the load more evenly into the cupped washer that goes on the bearing).

It appears that 37 ft. lbf (50 Nm) is the correct tightening value.

The spring will let the arm start to move a little at that force, but it will stop when the force in the spring equals 37 ft. lbs and your wrench will click or indicate that 37 ft. lbs. has been reached.