01-31-2012, 02:48 AM #1
OEM Cylinder Head Torque Values **Revealed**
I recently had to install new head bolts after replacing my valves. I decided to record the torque values after the 120 deg and the final 90 deg turns.
To begin with I decided to test the values of the bolts that felt funny when I was installing them the first time. All 3 bolts no matter how far you would turn them past the final 90 deg my torque wrench never went over 77lbs/ft. These bolts when I took them out were STILL under the manuals spec 5.846" before I stretched them out in the test.
Here is the setup I am using.
After the initial 30lbs/ft of torque I turned the bolt the first 120 deg.
Here is the torque values I was getting (+-2lbs/ft)
I then setup the wrench for the final 90 deg turn.
And here are the values I was getting. The highest torque recorder was 102.3lbs/ft.
I know in another thread that people were having trouble with Riva head studs leaking after they were torqued to 85lbs/ft and people had installed them at 95lbs/ft and had no problems. According to my test results the factory has these babies at over 100lbs/ft. Just an FYI...
01-31-2012, 09:16 AM #2
- Join Date
- May 2005
Love that torque wrench!
What were the torque values at 120 degrees?
Did all 8 new bolts torque the same?
01-31-2012, 10:43 AM #3
- Join Date
- Sep 2009
This info is interesting, thank you for putting it together and sharing it. However, I would like to caution everyone about drawing conclusions from it that might not be accurate. Basically, you cannot compare torque readings done during this exercise versus torque values used on ARP or Riva or any other stud systems.
The purpose of any bolt or stud is to provide clamping pressure. The challenge of all fasteners is that it is very difficult to translate torque values to clamping pressure. The problem with ordinary bolts or studs is that clamping pressure derived from a torque value can vary with lube on the fastener, heat or time, so many newer fastener systems employ stretch bolts. Stretch bolts have the advantage of keeping a very uniform clamping pressure with changes in temperature and over time. Once you get into the stretch region of the fastener, you are more certain of the applied clamping pressure, and you are more certain that the clamping pressure will stay constant over temp changes and over time. (This is the reason that you need to re-torque ordinary head studs like the ARP, but don't need to re-torque OEM bolts)
The best solution for our purpose would be a "higher clamping pressure" head stud system using stretch studs. But these do not exist in the market, so we are forced to use an old technology way of achieving higher clamping pressure (like ARP studs).
The bottom line of all this is you cannot compare the 102 ft/lb value seen on the OEM stretch head bolts vs 95 ft/lbs on the ARP studs. The actual clamping pressure might be much less on the OEM bolt even though the torque is greater.
However, there is an additional good data point about the 3 bolts he saw that had less torque during the final torque vs the others. I have seen this myself, as has Vern and others. This is important to watch for when using OEM head bolts.
01-31-2012, 12:45 PM #4
Thread pitch also needs to be taken into consideration. The finer the pitch the more clamping force is applied at the same torque reading. ARP uses a much finer thread pitch on the nut and stud.
Agreed that measuring stretch is a more accurate way of measuring clamping pressure given if the bolts are of high quality and consistancy, something that SD lacks from time to time.
01-31-2012, 08:22 PM #5
02-01-2012, 12:08 AM #6
It works awsome for checking sc clutch slip also. I have it calibrated for aircraft use so its dead on balls accurate...
Last edited by Alpheus; 02-03-2012 at 04:50 AM.
02-01-2012, 08:03 PM #7
so would it be better to use the manuals suggestion of torque and then angle or just plain torque to 100 ft lb?
02-01-2012, 08:24 PM #8
- Join Date
- Sep 2009
Please read my earlier comment. Using torque values will not work with stretch bolts.
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