Bolt torque question

Replacing water pump on a 64 Ford 2000 tractor that started leaking. Figured I d go ahead and replace thermostat and hoses to. While replacing thermostat broke off bolt when I attempted to torque it to 30 ft lb. I assumed this was correct torque as my ford tractor shop manual FO-20 says “tighten the retaining cap screws to a torque of 25-35 ft-lbs” for water pump and both thermostat and water pump bolts are 5/16-18. I thought maybe it broke due to metal fatigue as I used the old bolts. Luckily I was able to get it out with vise grips and went and got new bolt for thermostat and water pump. Thermostat bolts are 5/16-18 1in and water pump are 5/16-18 1-1/4in long and all bolts are grade 5. However everything I find on general torque specs for 5/16-18 grade 5 bolts shows 157-209 in-lb (13-17 ft-lb).
So my question is do I need better grade bolts or is manual wrong for water pump screws torque specs?

This post was edited by perryjosh64 on 05/27/2023 at 12:21 pm.

(quoted from post at 14:08:12 05/27/23) Replacing water pump on a 64 Ford 2000 tractor that started leaking. Figured I d go ahead and replace thermostat and hoses to. While replacing thermostat broke off bolt when I attempted to torque it to 30 ft lb. I assumed this was correct torque as my ford tractor shop manual FO-20 says "tighten the retaining cap screws to a torque of 25-35 ft-lbs" for water pump and both thermostat and water pump bolts are 5/16-18. I thought maybe it broke due to metal fatigue as I used the old bolts. Luckily I was able to get it out with vise grips and went and got new bolt for thermostat and water pump. Thermostat bolts are 5/16-18 1in and water pump are 5/16-18 1-1/4in long and all bolts are grade 5. However everything I find on general torque specs for 5/16-18 grade 5 bolts shows 157-209 in-lb (13-17 ft-lb).
So my question is do I need better grade bolts or is manual wrong for water pump screws torque specs?

Click to expand...

I agree that 25-35 is correct for 5/16". Also, grade 5 should be just fine for that application. The old one must have been abused at some point in the past.



This post was edited by timcasbolt on 05/27/2023 at 01:02 pm.

I was just looking at a Caterpillar
engine manual when I saw this so I went
to their generic torque page. For 5/16''
Grade 5, 18 foot pounds give or take 5.
And CAT is known for GOOD bolts. That
would be 23 max. 25 to 35 is NUTZ!

Oh how a question on bolts vs torque can get confusing! So my I&T ford shop manual FO-20 says for water pump tighten the "retaining cap screws" to a torque of 25-35 ft-lbs. I just assumed "cap screws" was an old official name for bolts? However when I went looking up definition and torque specs for cap screws a few sites and charts had "cap screws" as another higher bolt grade (A574 socket head cap screw). So makes me wonder if I m using the wrong grade of bolt? Then in another manual (Ford Tractor shop manual 1955-1960) it says 10-15 ft-lb torque for water pump so now have different manuals saying different specs?!?
My head hurts.

The bolts AKA capscrews will be just fine
torqued in the low 20's. That's enough
for little bolts holding cooling system
parts together on an old tractor!

I also think that the manual has a misprinted value. The
YT chart shows 19 for a 5/16 grade 5, see link.
YT generic torque chart

(quoted from post at 16:49:06 05/27/23) Oh how a question on bolts vs torque can get confusing! So my I&T ford shop manual FO-20 says for water pump tighten the "retaining cap screws" to a torque of 25-35 ft-lbs. I just assumed "cap screws" was an old official name for bolts? However when I went looking up definition and torque specs for cap screws a few sites and charts had "cap screws" as another higher bolt grade (A574 socket head cap screw). So makes me wonder if I m using the wrong grade of bolt? Then in another manual (Ford Tractor shop manual 1955-1960) it says 10-15 ft-lb torque for water pump so now have different manuals saying different specs?!?
My head hurts.

Click to expand...

A bolt uses a nut to clamp unthreaded components. A screw makes threads of its own, or is used with threaded components. A hex head fastener, screwed into a threaded hole, like the ones retaining your water pump, are called hex head capscrews. Then there are socket (Allen type), Torx type and other capscrew head types.

For torque I agree with wore out and would add if you lubricated the threads (oil, grease, anti-seize, etc.) the torque should be even less. And CAT used grade 8 for most of their SAE bolts and capscrews. If you have to purchase new capscrews, I would get grade 8.

Be careful looking at torque charts. Some give a Nm (Newton meter) torque value right beside the ft.lb. torque and one might think it is an allowable range. It is not, it is the maximum torque for the respective torque measuring method.

Lots of good info. My favorite smart-alec answer is to stop one turn before it breaks...

Bolt vs caps capscrew is just an
argument waiting to happen. Doesn't
make a bit of difference what you
call it.

The manual is wrong. That's the
torque for a 3/8 bolt.

My rule of thumb is Torque it UNTIL it breaks, and then back off ten percent.

In critical applications, that's not far from correct. The torque wrench monitors torque vs strain. If
it goes a bit non-linear, it stops. The test department will sometimes test a sample of screws of the
length and diameter in fastening parts, properly lubricated, etc., until they begin to yield. Then they back off the torque a bit during assembly. Another method is to torque them slightly beyond yield as determined from testing. If ever disassembled, the screws should be scrapped. You might find this in
cylinder heads, or front suspension parts, etc. For more routine assemblies, it is not so necessary to take such precautions. If it comes down to a claim against the company, they would have computer records of each critical screw installation for their defense.
Back in the 80's some bad actors put out counterfeit screws which would fail in a matter of hours after being torqued into assembly. They should still be in prison..
Counterfeits

I just changed a thermostat in a Cat 936 loader with a 3304 Cat engine. I had a tough time getting the old 3/8-16 grade eight Cat bolts out. I was very careful not to break any. I put new grade 8 bolts back in and torqued to 32 foot lbs. My book said 30-35 ft lbs.

DWF

you dont need a torque wrench for that! ma1ke sure the bolts are well lubed with neversei and idze and tighten by feel. and if its a 5/16
inch bolt 30 lbs is way too much.3/8 rachet by feel!

35 would be a 3/8 grade 8 bolt. 18 for grade 5 5/16. I believe
24 if it was grade 8.

I rarely torque any bolt just tighten by feel yup some times I twist off one and more often than not never a problem with coming loose. If a bolt works loose it is not big enough for the job. Dad had a chopper tongue that had 3/4 bolts would always work loose drilled it out to 7/8 never came loose again. Just tighten to s good snug and you wil be fine just keep them even on the tighten.