The technical data shows for 8T bolts use 27-40 ft/lbs.
That seems high.
I broke 3 of the 4 with the wrench set at 30 ft/lbs. It could be the torque wrench had failure. I have two inch-pound ones I can set to 360 for comparison. I tried one and kept moving up from 120 in/lb by 20 in/lb increments. All seemed good up to 160, but at 180 I had that feeling it was not going to click.

I tried to drill one of the broken bolts but only eneded up drilling into the flange.

Plan B:
I marked 4 new holes on the flange 45 degrees offset from the original holes. I will drill and tap the holes and then use new metric flange bolts, full thread, Class 10.9 steel plain finish, 6mm x 1.0mm x 16mm (Bolt Depot). Before I thighen the new ones down, I can test the 30 ft/lb setting on the last remaining original bolt.

And yes the timing notches on the pulley will be correct. My flange has a bit "T" marked on it for aligning the proper original bolt hole.

 

The title of your thread mentions (4) 10mm pulley bolts. Which pulley are you attaching? If I'm interpreting things correctly, the pulley fasteners are actually a 6mm X 1.0P thread. 10mm is just the head size, torque is based off the actual thread size and pitch. Another factor is the type of material the fasteners are actually threading into? If its aluminum, which is softer than the steel alloy the bolts are made from, then all things being equal, the threads in the aluminum flange should fail before the bolt.

12 ft/lbs is a more acceptable amount of torque for a 6mm thread.

 

Are you sure it is not in INCH pounds?

 

Exactly what I was thinking.

 

Oh #$&@!!!
You are correct. I was looking at the head size not the thread size.
The specs for a 8T 6mm are listed as 6-9 ft/lb

Now I have to pay.
Thanks for the info the flange is aluminum. That will make this a little easier and feasible.

 

Success!

I had 1 good bolt left. I attempted the dril and bolt-remover but could not get the drill bit started properly. Plan B: Drill and tap 4 new holes in the flange 45 degrees offset. I put blue tape between each opposing pair of holes on the small pulley. Used a piece of paper to measure the distance between two bolt holes on the pulley, folded the paper in half and used that to fine a near midpoint between the two holes. Repeated this for the other 3 pairs of holes. Then drew 2 lines across the center of the pulley connecting the opposite midpoints. With the double AC/PS pulley positioned center-hole to center-hole with the small pulley, I aligned the bolt holes in the doulble pulley with the 2 lines across the center of the small pulley. Then marked the approximate center of each of the large pulley polt holes onto the blue tape. Center punched and drilled a small hole in each. With the one remaining good bolt I secured the pulley on the flange, being careful to alighn the timing notches with the big "T" on the flange. Using the pulley as a template I drilled 4 small pilot holes into the flange, removed the pulley and drilled each using a 13/64 drill bit. Then tapped each of the 4 holes using M6 -1 tap. Drilled out my 4 small holes in the pulley to 1/4" and attched the pulley to the flange with new bolts, again matching the timing notches to the big "T." After completing the assembly, I warmed up the engine to idle, with a timing light I re-confirmed the timing notches were in the correct position. Not wanting to upset the balance, I slightly cut the shaft the last good bolt a little below the flange, tightened it into position and kept going till the head snapped off.



How did I get to this point?
The alternator belt was peeling off on the outside so I decided to replace it and the air pump belt. The AC stopped working about 15 years ago so I just removed it's belt. I was curious about taking out the compressor so I searched and the forum did not disappoint. Good posts going back to 2005. So I took out everything under the hood and capped off the two lines to the evaporator by plugging up the connectors. After doing that I had no need to keep the double AC/PS pulley.





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Improvise, adapt, and overcome, great job!

 

7-8ft/lbs is about the max for any 10mm head bolt, the threads are only 6mm. the heads on those things would be popping off in the 15ft/lb range. honestly most folks don't even torque them, it takes some serious effort holding the pulley to even get near the point of breaking them so something should have seemed very wrong. in fact there's very few bolts that have critical torque on an engine assembly, mostly those are only like tension bolts, exhaust manifold fasteners, oil pan bolts and stationary gears, i don't even torque the oil pump because that requires unnecessary disassembly.

the issue folks have is the bolt size specified is the thread size, not the size of socket a bolt uses.


edit: oops, noticed you found the error of your ways. what i'm trying to say is sometimes torque specs get you into more trouble than they should, as an auto tech one of our lessons was to learn how tight in general a bolt should "feel" and just use our hand strength to torque bolts, if something seems off double check it with specs.

 

I have a history of overtightening bolts. When rebuilding the 12a in 2014, I broke the head off one of the bolts on the oil pump. Luckily it was easy to remove after lifting off the part I was trying to attach. Ray Green came to my rescue and mailed me a replacement. This is when I purchased an inch/pound tourque wrench with the desired range. I don't do this often enough to muscle learn so assistance is necessary.

I don't know where my head was at. I grew up on 1/4-20 bolts. All good now and earlier today at a stop light in the Rx7 at guy pulls up besides me, compliments the car and states he had an '85.

 

yeah i get that, rule of thumb for me is any 10mm or smaller bolt head gets an inch lb torque wrench, foot pounds can get you in trouble real quick with small bolts.

 

Congrats for using a torque spec (many people don't) and recovering after your issue.

There are some good "Table Torque" charts available online, such as this one --> https://www.metric-bolt-torque.com/m...-torque-table/
If you combine this with a thread gauge to make sure you have the correct fastener size, you should be in the right window.

I have 3 torque wrenches -- 1/4", 3/8", and 1/2". I started using them religiously after I disassembled my rear suspension and discovered "brinelled" bolts (image). What I found is that I had severely under-torqued my rear suspension bolts. Those marks are the result of the control arm beating on the bolt. When properly designed and torqued, there shouldn't be relative movement in the joint (which causes brinelling).

The extra time to check the chart and break out the torque wrench is worth it.

 

I have a 1/4", 3/8", 1/2" to 150 ft/lb, and a 1/2" to 250 ft/lb. I bought the 250 only because I needed a left-hand torque wrench for the left-rear axel nut on a Ford Transit.
And I still have a 140 ft/lb right/left beam torque wrech I used to replace the clutch on my 1974 Rx3, that I don't use anymore.

Thanks for the link. Very useful information.