Valve Cover Bolts MY85
05-24-2019, 01:32 PM
#31
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Tangent:
Over the years I've enjoyed the benefits of bolts that have been too loose, while more frequently fasteners are stretched or stripped from over-tightening. Especially in expensive assemblies like aluminum Porsche parts, small industrial instruments and assemblies, the penalties for fastener failure can be $significant$. Enter torque wrenches and torque-limiting drivers. For most stuff on our cars, a click-type torque wrench is all that's needed. Access and some very small fasteners may demand a torque-limiting screwdriver or similar. I have a cool Japanese torque-limiting screwdriver that gets a lot of use, equipped with screwdriver tips or a 1/4" square drive adapter for sockets.
Even the bargain Harbor-Freight click-type wrenches are OK for most uses. At about $10 on sale, there's no excuse not to keep three sizes in your tool box. A decent torque-limiting screwdriver is less than $50 with bits on Amazon. The first bolt you don't stretch, strip or break off will pay you back handsomely for your whole torque-limiting tool investment.
At $10, a dedicated 1/2"-drive torque wrench and a few wheel nut sockets ride along in the Pilot DD. They've been used a few times during roadside events, fortunately never on my own vehicles.
Over the years I've enjoyed the benefits of bolts that have been too loose, while more frequently fasteners are stretched or stripped from over-tightening. Especially in expensive assemblies like aluminum Porsche parts, small industrial instruments and assemblies, the penalties for fastener failure can be $significant$. Enter torque wrenches and torque-limiting drivers. For most stuff on our cars, a click-type torque wrench is all that's needed. Access and some very small fasteners may demand a torque-limiting screwdriver or similar. I have a cool Japanese torque-limiting screwdriver that gets a lot of use, equipped with screwdriver tips or a 1/4" square drive adapter for sockets.
Even the bargain Harbor-Freight click-type wrenches are OK for most uses. At about $10 on sale, there's no excuse not to keep three sizes in your tool box. A decent torque-limiting screwdriver is less than $50 with bits on Amazon. The first bolt you don't stretch, strip or break off will pay you back handsomely for your whole torque-limiting tool investment.
At $10, a dedicated 1/2"-drive torque wrench and a few wheel nut sockets ride along in the Pilot DD. They've been used a few times during roadside events, fortunately never on my own vehicles.
05-24-2019, 02:06 PM
#32
Racer
Besides losing the tension on that particular section of the cover, you'll have a hole where the bolt passes through the cover, where said bolt normally maintains pressure on the rubber seal.
To say that the system is torque-sensitive is an understatement. Regardless of bolts used, the max torque that should be applied is around 6 lbs/ft. Requires the use of a 1/4"-drive torque wrench or "torque driver", set to limit at less than 48 lbs/inch. Relating to Stan's guidance in post 2 above, that's two very gentle fingers on the Allen wrench.
The sealing is all managed by the cam cover "gasket", a close to round cross-section seal that indexes in a groove in the cover. The compression on that gasket is complete as soon as the bolts are drawn snug. Increased torque on the bolts beyond guidance does not increase compression on the gasket, but does stretch the bolts towards or past failure. If you see a little seepage from the gasket, waste no time or effort tightening the bolts more. Instead, --loosen-- and remove all of them, remove the old gasket, clean the groove in the cover, and correctly replace the cover and gasket. A thin film of your favorite non-hardening sealer on the gasket is appropriate, as is the two dabs of silicone gasket maker as called out in the WSM instruction. I like Hylomar for the non-hardening sealer, while others recommend Hondabond or the WSM-recommended Dreibond sealants. Any will get this job done.
There's a TSB that recommends adding thin washers to all the cam cover bolts to add a little to the compression on the gasket. Prior recommendation was to use these washers only on the lower bolt locations. Our Favorite 928 Parts Vendors have these recommended washers available.
Lesson: Regardless of how tempting it might be to just snug the bolts a tad to try and stop the seepage, you must resist. If you can't help yourself, at least pull out your trusty tiny torque limiter and use it to stay south of 6 lbs/ft or 48 lbs/inch. Stop when it clicks. Stop when it clicks. Stop when it clicks.
To say that the system is torque-sensitive is an understatement. Regardless of bolts used, the max torque that should be applied is around 6 lbs/ft. Requires the use of a 1/4"-drive torque wrench or "torque driver", set to limit at less than 48 lbs/inch. Relating to Stan's guidance in post 2 above, that's two very gentle fingers on the Allen wrench.
The sealing is all managed by the cam cover "gasket", a close to round cross-section seal that indexes in a groove in the cover. The compression on that gasket is complete as soon as the bolts are drawn snug. Increased torque on the bolts beyond guidance does not increase compression on the gasket, but does stretch the bolts towards or past failure. If you see a little seepage from the gasket, waste no time or effort tightening the bolts more. Instead, --loosen-- and remove all of them, remove the old gasket, clean the groove in the cover, and correctly replace the cover and gasket. A thin film of your favorite non-hardening sealer on the gasket is appropriate, as is the two dabs of silicone gasket maker as called out in the WSM instruction. I like Hylomar for the non-hardening sealer, while others recommend Hondabond or the WSM-recommended Dreibond sealants. Any will get this job done.
There's a TSB that recommends adding thin washers to all the cam cover bolts to add a little to the compression on the gasket. Prior recommendation was to use these washers only on the lower bolt locations. Our Favorite 928 Parts Vendors have these recommended washers available.
Lesson: Regardless of how tempting it might be to just snug the bolts a tad to try and stop the seepage, you must resist. If you can't help yourself, at least pull out your trusty tiny torque limiter and use it to stay south of 6 lbs/ft or 48 lbs/inch. Stop when it clicks. Stop when it clicks. Stop when it clicks.
In this case, I'm hoping that the PO OVER tightened the bolts a little toooo tight to give me a little (and temporary) advantage in the short run against leaks... My first attempt at living with this problem a while is to dremmel off the bracket on the PS (LHD car) that holds the gizmo attached to the aux air appliance at the back PS area of the cover near the fire wall.... Attempting to remove the bolts holding the gizmo attached to the aux air system is how i got into this mess in the first place...
The bolt I sheared still has the lower end of the two part design attached. I cannot get it out of the hole. After the bracket is removed and I have better access, I intend (don't hate me) to seal the bolt back to the cover over the hole with JBweld and or epoxy to prevent leaking. I'll start her and see what happens with the seal surface, gasket and,,,,. If it leaks immediately,,, I'll go from there. If not leaking immediately, will check the site compulsively... Leaking alarms might be the small of burning oil leaking onto the manifold - thats good for me (strange to say). I hope for that. It's also good to know the gasket lies in a grove and won't just be blown out - thank you Bob for that insight. I've never handled a 928 cam/valve cover and didn't know what was going in under there... I can see the gasket (maybe the PO had a modified version? It looks to have a square edge sticking out. I've had the car a short time mind you. Wonderfully, the gasket looks very fresh.
Down the line I will be powering the intake and covers... I will be forced into this situation soon enough.
I am open to ANY second guessing about my directions. I am not thin skinned as long as it's constructive criticism... jus sayn
Last edited by JayPoorJay; 05-24-2019 at 02:23 PM.
05-25-2019, 11:54 AM
#33
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Dave K
05-25-2019, 01:22 PM
#34
Chronic Tool Dropper
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So this is where my opinion skews. When you draw the bolt down to the correct torque the first time, there are no flexible pieces between bolt metal and head metal. So long as you have the rubber seals between the bolt and the cam cover, and the bolt is installed correctly, there should never be another 1/2 turn available. The bolt tightens to the adapter and that to the head, and ends up at exactly the same installed height whether there's a cam cover there or not.
The "squish" on the gasket is a function of the total height of the gasket/cover/bolt seals & washers, vs the height of the bolt. The bolt height is constant once the shoulder meets the adapter and is torqued correctly. Additional torque on the bolt tries to stretch the threaded part of the bolt without reducing the installed height. If you feel the need for more squish, add a shim washer under the bolt head to reduce the effective stack height of the bolt. The rubber bolt seal and the gasket will share the additional compression as they both fit in the smaller space.
Again, this is my opinion.
The "squish" on the gasket is a function of the total height of the gasket/cover/bolt seals & washers, vs the height of the bolt. The bolt height is constant once the shoulder meets the adapter and is torqued correctly. Additional torque on the bolt tries to stretch the threaded part of the bolt without reducing the installed height. If you feel the need for more squish, add a shim washer under the bolt head to reduce the effective stack height of the bolt. The rubber bolt seal and the gasket will share the additional compression as they both fit in the smaller space.
Again, this is my opinion.
