Head Bolts

goxu1

goxu1

Well-known member
I know it’s been discussed a 1000 times , but I’d just like to know if the head bolts I bought from TM (grade 8 I believe) are up to the job?
I don’t want to get half way thru the job and end up with another broken bolt. Past threads have said grade 8 are rated at less than the required head boot torque. Do I need to get grade 9 and cut them to length , or are they available in correct sizes ?
 
They are fine. It is important to use a new gasket, use the copper gasket spray on the gasket, place the gasket the correct side up, and use thread seal on the bolts and to torque in sequence per the manual and retorque after some run time.

I think I read somewhere on this site that the dot bolts from the early cubs would be rated at or below a grade 5 by today's standards. SO a grade 8 is an upgrade. The two reasons for the torque spec on a head bolt is clamping force. The second and main reason is to stress the bolt above what it sees in the field to reduce high cycle fatigue. There are torque charts available for bolts. https://www.fastenal.com/content/feds/pdf/Torque-Tension Chart for A307 Gr5 Gr8 Gr9.pdf

Remember to use the spec for "lubricated" as the thread sealant is also a lube.
 
goxu1 said:
I know it’s been discussed a 1000 times , but I’d just like to know if the head bolts I bought from TM (grade 8 I believe) are up to the job?
I don’t want to get half way thru the job and end up with another broken bolt. Past threads have said grade 8 are rated at less than the required head boot torque. Do I need to get grade 9 and cut them to length , or are they available in correct sizes ?
Click to expand...
 
In addition to what’s been advised, I would also run a thread tap through all the holes to clean them up.
 
Google says the max torque for a 3/8 grade 8 is 58 , so the setting of 45 should be fine I guess
From the chart above , 3/8 lubricated = 33. Does the sealant make it “lubricated” ?
 
I don’t know where Dr google got its number, but the gm bolt torque tables for a grade 8 3/8 bolt is 38 ft lb. When they talk lube, think arp bolt lube, threads and under the bolt head.
When I did the ‘65 a few years back, I used grade 8, with grade 8 washers, thread sealant, light lube, no gasket spray, torqued in sequence to 40 ft-lb, no retorque after running…and it’s still running almost 10 years later.
 
As I understand it bolts that are marketed as engine head bolts are made differently than a standard application bolt. The bolt material and torque ratings, among other things, are different.
 
Ok , the more I look the more it seems to be the max torque for a 3/8-16 is 45
The torque spec for the cub head bolts is 45 too.
So , like ntrenn said, should I just go to 40 with the sealant and be on the safe side ?
 
Definitely use grade 8 bolts…..your future mechanic in 20+ years will thank you!

No one like to remove broken head bolts!

NJ Farmer
 
Hi,
Below is the bolt torque chart from the Cub and LoBoy service manual, telling what IH said about bolt torques. This chart is in their 1976 manual.
It has info about the bolt markings lower on the page. IH started using modern bolt head markings with lines on Cubs in about the mid 1950's, from what I have seen.
Before that they had just the dot in the middle of the heads.
They were putting WP on the heads in the 1970's, like the pictures show.
 
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goxu1 said:
Ok , the more I look the more it seems to be the max torque for a 3/8-16 is 45
The torque spec for the cub head bolts is 45 too.
So , like ntrenn said, should I just go to 40 with the sealant and be on the safe side ?
Click to expand...
I sent an email to Ron at TM Tractor asking if he knew the maximum torque value for the head bolts that he sells. And if he doesn't know the value, could he provide the material specs for his head bolts. His response: "my head bolts are grade 8 and can be torqued to more than the head torque for the Farmall Cub. I have used them many times with no issues". While not answering my specific question, it does support my understanding that:
  1. Head bolts are usually higher alloy compared to standard application Gr 8 bolts
  2. They achieve the grade 8 levels of yield and tensile strength without being brittle
  3. They are manufactured with a shoulder (as confirmed on TM Tractor website) and higher class threads
If you wish to reduce the torque for thread sealant applied to the head bolts, that is your decision. The primary thing you are trying to achieve with the manufacturer's recommended torque values is the clamping force. The clamping force that is provided should be the same when comparing the dry torque values with the suggested, torque values for a lubricated bolt. I will tell you that I used the TM Tractor head bolts when I rebuilt my '48 Cub engine and torqued them to 45 ft-lbs with the thread sealant. That was over twenty years ago with no detectable issues to date. Hope this gives you a little comfort going ahead with your installation.
 
Bill V in Md said:
I sent an email to Ron at TM Tractor asking if he knew the maximum torque value for the head bolts that he sells. And if he doesn't know the value, could he provide the material specs for his head bolts. His response: "my head bolts are grade 8 and can be torqued to more than the head torque for the Farmall Cub. I have used them many times with no issues". While not answering my specific question, it does support my understanding that:
  1. Head bolts are usually higher alloy compared to standard application Gr 8 bolts
  2. They achieve the grade 8 levels of yield and tensile strength without being brittle
  3. They are manufactured with a shoulder (as confirmed on TM Tractor website) and higher class threads
If you wish to reduce the torque for thread sealant applied to the head bolts, that is your decision. The primary thing you are trying to achieve with the manufacturer's recommended torque values is the clamping force. The clamping force that is provided should be the same when comparing the dry torque values with the suggested, torque values for a lubricated bolt. I will tell you that I used the TM Tractor head bolts when I rebuilt my '48 Cub engine and torqued them to 45 ft-lbs with the thread sealant. That was over twenty years ago with no detectable issues to date. Hope this gives you a little comfort going ahead with your instal
Click to expand...
Hi Bill , thanks for doing that. It gives me more confidence to know you used them with no dramas torqued to 45.
Thanks again
 
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