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Join Date: Dec 2001
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heads coming loose

This is my mildly modified 3.3 bus motor. The motor winds out so fast with the 5 speed I've never gotten past 1/2 throttle and .8 boost.
When I checked the head stud torque at 1,000 miles, the head stud nuts felt like they had about 10 lbs of torque. I re-torqued them down to 38 lbs. I recently re-checked them at 2,800 miles and again, the nuts feel like they have about 10 lbs of torque. I re-torqued them down to 30 lbs.
Not sure what's going on, or what to do. Are the studs being pulled out of the case?

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Harold
'79 930/DP935
'68 VW 3.3 Turbo Crewcab
Old 04-01-2018, 12:46 PM
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What kind/brand of head studs. Are you using any kind of wire ring or head gasket seal? Unlikely that the studs are pulling out.
Old 04-01-2018, 01:34 PM
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ARP, no head gasket seal. Heads 1,2, 4, 5, 6 were loose, 3 was fine.
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Harold
'79 930/DP935
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Old 04-01-2018, 01:39 PM
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There are a few conditions when the engine is assembled that can affect the torque retention. Simple stuff like the cylinder mounting flange not being clean, not being flat, too many base shims, stuff like that.

Same thing for the heads where the flat washers and barrel nuts for the head go.

I would just re-torque it and keep an eye on it, like you have been. Usually these things eventually stabilize.
Old 04-02-2018, 06:56 AM
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Should I re-torque to 38 lbs, or stay at 30 lbs.
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Harold
'79 930/DP935
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Old 04-02-2018, 07:01 AM
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I think the spec is for 38#. I know it was with Super Tec studs.
Bruce
Old 04-02-2018, 10:44 AM
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It’s a tough call. ARP specifies their assembly lubricant for 38 ft-lbs of torque. I suspect most of that has baked off by now. If you agree, then back off by 10% to around 34 ft-lbs.

I saw the comments in the other forum, and I agree with them, but there are plenty of steel stud engines running around. Go with 34 ft-lbs. I suppose it might be possible to scratch a line on the nut and washer to see if they are actually loosening, but I doubt they are.
Old 04-02-2018, 02:28 PM
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Thanks, I'll give that a try.
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Old 04-02-2018, 03:15 PM
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I did mine with arp studs a couple years back and haven't checked them since, I'll add it to my to do list and see if the numbers have changed.
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Old 04-02-2018, 04:18 PM
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Rather than scratching a line, a paint line on the nut/stud and stud/case works well. Known as torque stripe in the aircraft circles.
Good Luck
Old 04-02-2018, 08:49 PM
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I read on the other forum that the use of moly grease is the cause. Not to challenge this, but I have never seen this before. The moly grease or the ARP grease is there to reduce friction so the torque values or nut to thread engagement does not get affected by friction.

I think the std ARP studs are made from a chrome moly steel, 8740 I think. The steel gets some heat treatment to increase the tensile strength. The use of this material is based upon their most common fasteners. It was never meant as a replacement or straight conversion of the Porsche type. As "Rennsport Steve" suggests, the use of the factory studs is probably the better solution, unless you are prepared to do some checking prior to installation.

Whenever you decide to use something like an ARP stud, you should be pre checking its behavior when installed. Installed height, stretch etc., at different torque values. If you use torque values only, you really have to do some checking to see if you achieve the same stretch on each stud. Otherwise you could have different values at each stud. The clamping load is what you are after knowing to be the same on each stud and at an amount acceptable.

Best way is to tighten a stud with something in between the case and the nut. You can then measure the stretch verses the torque valve you wish to use. Just using 38 ft/lbs could net different clamping loads on each stud. Maybe 30 lbs is enough. maybe you need to increase the value. You can then make sure the stud is not pulling out of the case, the cylinder head isn't collapsing around the washer platform. Too much torque and not enough stud stretch could stretch the threads in the case or collapse the heads. Then the amount of torque applied will not go onto stretching the stud that puts the whole assembly under tension and hold everything together tight.

Make sure the heads are the same height, the case widths are the same from front to rear of each half. All the basic stuff should be checked also.

Seems like a simple thing but there are some important points that need checking and understood.

Old 04-03-2018, 04:07 PM
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