Charlie,
1. Your torque wrench should be reading torque at the head. For 250
foot pounds with a 2.5 ft wrench you would need to apply 100 pounds of
force, 200 pounds of force would achieve 500 foot pounds but the torque
wrench would have already clicked or maxed out on the scale.
2. Check with the yard. I would not recommend overloading a torque
wrench by 50%.
3a. Yes, loosen the nuts prior to re-torquing.
3b. The values listed are for "clean and dry threads". If you
lubricate them, reduce the torque by 10%.
3c. If you are on the hard, I am not sure that it matters.
3d. Yes. Your progression is good.
I created the table on the list from a document that I had from the list
many, many, many years ago. We had a fairly long discussion a while
back on the proper torque and I went back and reviewed the numbers.
Based on 316/18-8 stainless numbers for a 1" diameter coarse thread
bolt, 350 foot pounds will leave an 11% margin on yield strength on a
"clean and dry" thread. Reducing the torque to 250 foot pounds will
leave a 9% margin on yield strength on a lubricated bolt.
This has never been an exact science and I have under torqued and over
torqued many bolts in my career with no detrimental effects. I have also
torqued bolts to the specified limit and had bolt failures (it is
interesting to sit in a vibration control room and listen to screw heads
bouncing off the window). I guess my point is that if it doesn't feel
right at 340 foot pounds, don't try for the last 10.
Neil Schiller
1983 C&C 35-3, #028, "Grace"
Whitehall, Michigan
WLYC
1. I used a tape measure and the keel/cb bolts look to be 1" in diameter
and the nuts require a 1.5" socket. Per the keel bolt specs from the
photo album, this requires 350 ft lbs of torque. The torque wrenches I
have located seem to either go to 150 ft-lbs or 250 ft-lbs so neither
works out of the box. What little I remember of freshman physics says I
need an extension on the 250 ft-lbs wrench to meet the 350 ft-lbs
specification. Depending on the length of the extension, I would need to
're-calibrate' the torque wrench values to include the additional
length. For instance, if I lengthened the wrench by twice is nominal
length, I should be able to reach 500 ft-lbs when the wrench gauge reads
250 ft-lbs, etc. Is this correct?
2. Most of the torque wrenches for 250 ft-lbs I have seen have a 1/2"
drive. My thought is to use a 1.5" socket with a 1/2" drive to tighten
the bolts. My concern is whether using a 1/2" drive on a 1.5" nut can
get to 250 ft-lbs without destroying the wrench or the socket. Bigger
torque wrenches come with 3/4" drives and a much higher price. Should I
be concerned? Since I will probably have to buy the wrench etc. (~
$200), I don't want to destroy it by trying to tighten something that
requires a larger wrench. (local wrench rentals top out at 150 ft-lbs
although the yard may have a larger one available--have not checked yet.).
3. I will need to remove all the floorboards for this job to reach all
the bolts--I am not sure any are under the mast. Either way, I need some
pointers on how to proceed. Once she is on the hard and appropriately
blocked so that the cb trunk/keel is supported what is the recommended
procedure?
a. Should I loosen all the bolts first?
b. Should I apply any lubricants to the bolts?
c. Which bolts should be tightened first--center then forward, then
aft, then forward, then aft, etc. or furtherest aft then furtherest
forward, then aft then forward, etc.
d. Should I do this incrementally in torque--say go to 250 with
all, then move to 300, then go to 350?
My hope is that this tightening will eliminate the small leak. However,
I want to be sure to do it correctly so I don't make it worse!
Dropping the keel/centerboard trunk would be a very big dollar item
which I hope to avoid!
Thanks,
Charlie Nelson
Water Phantom
1995 C&C XL/kcb
cenel...@aol.com
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_______________________________________________
Thanks everyone for supporting this list with your contributions. Each and
every one is greatly appreciated. If you want to support the list - use PayPal
to send contribution -- https://www.paypal.me/stumurray
