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Thomas
Manufacturer that specify stretch torque usually have a protractor adapter that fits between the socket and the wrench as well as a pointer that indicate's the number of degrees that the bolt or nut as travelled. ( they give you the number of degrees) as well you start with a basic torque wrench torque, usually around 15 ft lbs for head bolts.
I have done the same without degree specs, it's accuracy may be arbitrary but it comes close. I run a pap (tread chaser) through to make sure the threads are clean and a dye on the bolt to do same, I lightly oil the threads and the torque area on the bolt head, tighten to 15 ft lbs. Make a mark on the torqued surface that lines up with a point on the head of the bolt, mark a line from the center of the bolt head , through the point to the mark on the torqued surface, that becomes you '0' mark, torque the bolt to the specified torque + about 3lbs ( on a 50ft lb spec.) repeat the line through the existing mark on the head bolt, project it on the torqued surface & measure the angle with a protractor. I did this 3 times on different heads and torque , the results came out within a degree.
Do the thread cleaning on all the bolts & holes, us a light oil for lub. The the benefit other the torque wench method is that you will get an even STRECH on the bolts and you will not find loose bolts after heating & cooling cycles,
I know this will sound odd the you engineers out there but it works for me!
Georges B.
-------Original Message-------
Date: 02/05/06 18:14:12
Subject: [FlyRotary] Re: Torque and torque sequence
Hi George,
Question: Is there any chart/rule of thumb/etc. how to convert a torque-value into a rotation-degree value?
Rotation degree should be way more accurate than a regular torque-wrench....it's just not as simple as setting the value and listen for the click.
I dealt with 3 different ways to "torque" bolts/nuts ( except the usual torque-wrench way)
a) Ships diesel engine (8000hp, 7 cylinders), changing pistons:
Headboltnuts are tightened fingertight (no hex on the nut, just 1/4 holes radially to move the nut with a 6" long 1/4 rod - nut thread about 2" diameter, nut diameter about 5-6")
Then there is another nut on top of the lower one, which is engaged with a hydraulic ram, which will strech the stud. Then fingertight nut was "tightened" about 1-1/4 turn (or so - according to the manual) - hydraulics off and the devil wouldn't be able to move the nut...
b) Ships diesel engine: In this case the Headbolts/studs are hollow:
Head gets torqued down a relative low value, just to make sure it is seated right and then the nuts are backed off again. Then heating elements, some 1.5 meters long are getting inserted and heated up to somewhere around 240 ºC (not enough to cause any metallurgic changes). Then fingertight the same style nut as above (watch your fingers, it is hot!). remove the heaters - set. Call the devil again....
(Even if one forgot to back up the nuts they would come completely loose while the heat was on)
c) Rotorhead bolt and coning hinge bolts on Robinson Helicopters:
Measure the length of the bolts with a dial indicator (mounted to holding fixture), torque the nut in increments and check with the dial indicator often. About a 3/4 " bolt - stretch 0.021-0.022" ( I think....). Best is to lift the rotor blades to unload any shear from the bolt, otherwise it gets pretty hard to stretch....
I guess on the Rotary it is not necessary and/or practical to measure bolt-stretch, however there are fairly affordable "Rotation-degree" - wrenches out there. Just never came across any instructions that called for it.
One itchy issue with regular torque wrenches is, wether a given torque is "dry" or "wet" (lubricated).
What is dry? Just clean or "electrocleaner"-clean?
If you need/want to grease the nut/bolt how much do you have to reduce the torque? (There are values and lists in about every GA-maintenance manual, but how transferable are these values to the nonaviation materials in the Rotary?)
Also, how often do you have your wrench checked - you won't believe how much accuracy "bleeds" in a year....
Someone mentioned his "calibrated" arm - big no-no!! Whatever "feels" like a certain torque to you any given day will be off value!! Again what you feel in your arm may very well be the same "feel"-value, but how much force you actually apply is in the stars (.... and depends completely on your energylevel/physical state/psychological state/mood of the moment!!) -
Never replace the torque-wrench with your arm! Specially with smaller bolts and nuts!!
(Test yourself: "Feel up" some weight in a bucket covered with a towell, have someone add/subtract weight and feel it up again - note the numbers. Then run, weightlift, exhaust yourself and repeat the exercise - you will be surprised how much off your "feel" is!! It is something similar with speed perception: size, sound, distance will throw you off completely!!
FWIW,
Thomas Jakits
----- Original Message -----
Sent: Sunday, February 05, 2006 12:37 PM
Subject: [FlyRotary] Re: Torque and torque sequence
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FWIW backing off each bolt as you re-torque gives you a more accurate torque. Final torque is much more accurate when using the torque by rotation degree (bolt stretch). (never had to re-torque anything using the stretch system)
Georges B.
-------Original Message-------
Date: 02/05/06 09:19:12
Subject: [FlyRotary] Re: Torque and torque sequence
----- Original Message -----
Sent: Sunday, February 05, 2006 11:32 AM
Subject: [FlyRotary] Torque and torque sequence
----- Original Message -----
Sent: Saturday, February 04, 2006 6:28 PM
Subject: [FlyRotary] Re: Atkins errors
A couple of questions: Why are two of the bolts larger? What is the torque spec on these bolts for the 20B? I seem to recall 26-28 ft-lbs. I can’t get a torque wrench on the bolts without removing the re-drive, engine mount and flywheel, but I have a pretty well calibrated arm.
Al
When you add torque to those bolts, the bolts closest to them will go under torque.
So go through the whole torque sequence several times if at all possible. This has been the case on every engine I have built.
I don't havea Mazda Manual, but generally in a case like this there are 2 ways to tighten the bolts correctly:
a) Tighten 2 opposite bolts until seated - then torque each to spec. All other bolts are tigthtened spreading out from the 2 torqued:
e.g. Torque the 2 big bolts then: 1st bolt to left of one big b. - 1st bolt to the left of the other big b. - 1st bolt to the right of the one big b. - 1st bolt to the right of the other big b. - 2nd bolt to the left...... you get the idea.
This way you have the pieces flat together on a "centerline" and "lay" the rest down on each side of this centerline - spreading it out so that no "wrinkles" are created....
b) A stepped sequence is shown in a manual: mostly in cross pattern and something like 10 lb/18lb/26lb
Thomas;
I understand the niceties of torque sequence; but it would seem that is all out the window when the engine has been run about 6 hours, many cycles to full power, and a dozen or more temperature cycles to 200-210 F; all with the two large bolts loose. As far as I know nothing untoward has happened, but how can I be sure?
Al
Al,
didn't intend to step on your engineering prowess, you are waaaay ahead of me in that department!
Just was pointing out what (little) I remember from Engineering school.
In your case, the only acceptable (...for me) way to go is, to remove the redrive, loosen all bolts and tighten them according to the manual.
In a (race)car you might get away with an "emergency"-thighten-up, but it is your a** up in the air!!
Your engine was running well for a while now, so a complete tear-down seems excessive, but I believe wrong ( or none ...) torque-settings will show their ugly face in the long run. Better make sure everything is right and tight.
I understand that it is definitely NOT your fault, but your engine builders - you might believe these guys put a little more extra care into assembling an AC engine - manual on the job, step by step list to hook off items, after-assembly check list, etc.
In your case torques on bolts don't mean anything at this time. "Niceties of torque sequence" applies IF DONE (right) - obviously on your engine no one cared enough to check torque, let alone sequence.
Doesn't shine to well on a supposedly reputable shop....
Enough ranting, back lurking!
Thomas J.
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