Over torqueing pressure plate bolts

[Forest Gump]

I have seen posts on here recommending a little more torque on the pressure plate, specifically from maTT.

I also saw that ACT recommends installing grade 8 fasteners and torqueing to 30 lbs.

The stock fasteners appear to be approx metric grade 8.8 which is about grade 5 in sae terms.

When I installed my pressure plate last night I was targeting about 16 ft/lbs which is at the upper limit of factory recommendations. I noticed that I had snugged them down to about 18 lbs before I even got the torque wrench out.

I set the torque wrench to 20 ft/lbs and all of the bolts torqued just fine with no signs of the bolts yielding.

From what I have read around 18-20 is about the max for an 8mm grade 5 fasteners.

Does anyone see any harm in this or has anyone had experience with this before? The only thing I am worried about is that possible the bolts have lost some strength, although they felt perfectly fine.

I have not had pressure plate bolts walk out and I always use loctite, but the idea behind running more torque is that the heavier pressure plates could use more clamping force at the bolts and some people have had their pressure plate bolts walk out torquing them to the factory low end of 13 ft/lbs.

I'm considering buying grade 8 fasteners and torquing back to 20 ft/lbs, but if others have run the stock bolts this tight I'm not going to worry about it.



Edit: Here is an exceprt from ACT:

ACT PRESSURE PLATE INSTALLATION INSTRUCTIONS

Once the inspection is complete and you have determined that there are no issues or problems with the existing clutch or operating system, installation of the new clutch can be accomplished as follows (note: every vehicle and clutch design is different and may vary):

1. Lightly grease the splines of the disc and slide the new disc on the input shaft to insure fit and smooth travel, and wipe off any excess grease. Replace Pilot bearing/bushing, and apply a light coat of motor oil to bushings, or high temperature bearing grease to needle-type bearings.

2. Use an alignment tool to center the disc against the flywheel. Manually tighten pressure plate bolts using a star or diagonal pattern. ACT recommends using metric grade 10.9 (SAE grade 8) or stronger fasteners. The use of high temperature thread locking compound is recommended for performance applications. Tightening torque specifications will vary with bolt size and grade. The following torque specifications are recommended by ACT for new pressure plate bolts with the corresponding sizes using metric grade 10.9 or SAE grade 8 bolts:

7mm x 1.0 15 ftlbs / 20Nm
8mm x 1.0 25 ftlbs / 34Nm
8mm x 1.25 26 ftlbs / 35Nm
10mm x 1.25 50 ftlbs / 68Nm
10mm x 1.5 50 ftlbs / 68Nm

5/16 x 18 29 ftlbs / 39Nm
5/16 x 24 29 ftlbs / 39Nm
3/8 x 16 45 ftlbs / 61Nm
3/8 x 24 48 ftlbs / 65Nm

If you choose factory standard bolts and are unsure of the grade of fastener, use the factory recommended torque values.

3. Lightly lubricate the release bearing inside diameter and the mating surfaces between the fork and releaser. Lubricate the clutch linkage as recommended by the vehicle manufacturer.

4. Make sure all bellhousing dowels are in correct position and tighten bellhousing bolts. Any misalignment will result in premature clutch failure. Correctly support the transmission during installation. Neglecting to do so may cause clutch damage and premature failure.

5. Adjust the clutch release system by following the vehicle manufacturer’s procedures and specifications. Recommended break in for ACT Street Discs is 200-300 miles of mild street driving. Avoid driving habits that would allow excessive slipping or overheating of the clutch. Failure to properly break in the ACT Street Discs may result in clutch damage and premature failure.

[Boost4VR4]

Originally Posted by Forest Gump

I have seen posts on here recommending a little more torque on the pressure plate, specifically from maTT.

I also saw that ACT recommends installing grade 8 fasteners and torqueing to 30 lbs.

The stock fasteners appear to be approx metric grade 8.8 which is about grade 5 in sae terms.

When I installed my pressure plate last night I was targeting about 16 ft/lbs which is at the upper limit of factory recommendations. I noticed that I had snugged them down to about 18 lbs before I even got the torque wrench out.

I set the torque wrench to 20 ft/lbs and all of the bolts torqued just fine with no signs of the bolts yielding.

From what I have read around 18-20 is about the max for an 8mm grade 5 fasteners.

Does anyone see any harm in this or has anyone had experience with this before? The only thing I am worried about is that possible the bolts have lost some strength, although they felt perfectly fine.

I have not had pressure plate bolts walk out and I always use loctite, but the idea behind running more torque is that the heavier pressure plates could use more clamping force at the bolts and some people have had their pressure plate bolts walk out torquing them to the factory low end of 13 ft/lbs.

I'm considering buying grade 8 fasteners and torquing back to 20 ft/lbs, but if others have run the stock bolts this tight I'm not going to worry about it.

I torqued mine to spec. If you have torqued them to spec, why worry? Your pressure plate sits on the flywheel dowels anyway, those are usually quite snug and requires a lot of effort to push the PP on. I think that overtorquing the bolts could cause other issues. What about those locking washers as seen on the caliper bolts? Do you think those would help?

[AdamVR4]

The potential problem with over-torquing the bolts is that they're going to be exposed to cyclic stresses (heat) in addition to the normal cyclic stress of clutch use... By over-torquing, you've increased the stress in the bolt, increasing the maximum and minimum stresses of the cyclic stress. Since these are ferrous, it's no guarantee that fatigue failure will occur, but if it is going to, you've ensured that it will occur sooner. They may yield and ultimately fracture.

They may also be just fine. It's a pretty involved problem to solve... If you feel like you need the additional torque, I would go with stronger bolts... Just for the peace of mind. They're cheap and it will cost you less to buy bolts than it will to solve the problem and determine if it's safe

I've always torqued factory bolts to spec I've never needed anything more.

[Forest Gump]

eh, to be safe I think I'll just back them down to 15 lbs.

hey does anyone know the exact thread pitch and length on these? I'm going to replace them with grade 8 hardware in case I stretched them.

[keithmac]

Stock torque with Locktite blue for me everytime, never had a problem.