Head bolts 8n

[used red MN]

I have been running my 9n and today torqued the head bolts to make sure they weren't loosening up and they were still tight, so the washers worked!

The purpose of a retorque it to reintroduce the proper compression on a gasket that has been compressed and taken form to the surfaces that are sandwiching it relaxing the tension on the fasteners. The heat cycle is a major attributer to gasket compression.

 

[Non-farmer]

used red is spot on. The bolts need to be retorqued on occasion due to the gasket being compressed with use as compared to brand new, leading to less torque. The washers have nothing to do with stabilizing the torque. Their only function here is to prevent you from doing further damage to the head by using the wrong fastener, namely, bolts with 5/8" heads. If yo had used bolts with 11/16" heads, as intended, you would still need to recheck the torque. You just wouldn't be breaking off chunks of the head.

 

[TheOldHokie]

used red is spot on. The bolts need to be retorqued on occasion due to the gasket being compressed with use as compared to brand new, leading to less torque. The washers have nothing to do with stabilizing the torque. Their only function here is to prevent you from doing further damage to the head by using the wrong fastener, namely, bolts with 5/8" heads. If yo had used bolts with 11/16" heads, as intended, you would still need to recheck the torque. You just wouldn't be breaking off chunks of the head.

Possibly the "wrong bolts" were exactly that - bolts and not cap screws and head size has nothing to do with it.

TOH

 

[Dave G9N]

Possibly the "wrong bolts" were exactly that - bolts and not cap screws and head size has nothing to do with it.

TOH

What is the difference between a screw and a bolt? The first thought that came to mind here was that this is one of the few times that something said by TOH was wrong. Not very important, but it is a common misconception. Not worth posting, but it got me thinking. As far as I know, the only distinction is in the usage, not the screw itself. After many go rounds on that question on one job, we settled on an answer. A bolt is a screw with a nut, and a screw is the same bolt used in a threaded hole. If there is some difference between bolts and screws, we are not looking at ASME B18.2.1.

So why waste time posting? Everything else about bolted joints throughout this thread makes perfect sense, as usual. Right until you said that head size has nothing to do with it, which I initially agreed with.

I have done some torque tension testing over the years. While a generic torque table is not ideal, anyone without access to load washers, a huge budget, lots of time and material, the generic table is all that is available. At best, you can get some refinement along the lines of bolt and thread materials, plating and lubrication. So bear with me, I have done this kind of testing myself. I have a spreadsheet left over from those days, and for some reason I had included the pressure immediately under the head.

I think that head size had everything to do with it. I only say this after running the numbers, because I did not see just how much a small difference in head size would affect the pressure between the underside of the bolt head and the cylinder head until I saw the numbers pop up, and then I thought that there was an error in my spreadsheet. Having looked at the numbers, I would absolutely want to use a washer under with the smaller head here. A washer spreads the load under the head. the stress fans out at a 45 degree angle, so the effective washer diameter is increased by twice the thickness of the washer. That's why bridge washers are so thick to spread the load on the relatively soft wood.

The washer diameter difference between 5/8 and 11/16 across the flats make for a difference of about 2 ft-lb torque to reach 75% of yield strength. The pressure under the head of the bolt in the washer area was surprisingly different though. when I changed the head size from 11/16 to 5/8 the pressure went up from 49 to 69 ksi. That should be enough of an increase to cause problems with the cast iron here. The contact area is just a narrow ring under the head, so small differences in contact area width can make a big difference.

Bolt heads! I agree some lube on the bolt to head surfaces probably would have helped.

If I plug in the difference between the coefficient of friction between a generic dry steel on steel (0.3) and lubricated (0.15) joint, and separate oiled threads from oiled head I get the following tension for 75 ft lb of torque on a 7/16-14 grade 8 screw with the standard 5/8 distance between the flats:
Both oiled: 10449 lb.
Just threads oiled: 7140 lb.
Both dry: 5594 lb.
These numbers, as stated several times in this thread, would be different if measured on the tractor due to a lot of variables, but the difference between them would follow the same pattern and be pretty much just as big.

I have an 8n that I am rebuilding when I torqued the head down this happened at two spots!!....... What do you guys think? I didn't over torque it.

I think the question that remains to be answered is what are you going to do with the head? The uneven surface under the screw heads is bad for both the head and the bolts.

I would be tempted to look at drilling/spot facing or whatever you should call it to get a flat surface, but that surface may wind up in a bad place. Welding is not an easy task in cast iron. The third thought that comes to mind is to drill the hole larger and insert a threaded cylinder to spread the load better and give you a flat place under the screw head. At this point, I have to stop criticizing TOH knowing that his answer will be better than mine.

 

[TheOldHokie]

What is the difference between a screw and a bolt? The first thought that came to mind here was that this is one of the few times that something said by TOH was wrong. Not very important, but it is a common misconception. Not worth posting, but it got me thinking. As far as I know, the only distinction is in the usage, not the screw itself. After many go rounds on that question on one job, we settled on an answer. A bolt is a screw with a nut, and a screw is the same bolt used in a threaded hole. If there is some difference between bolts and screws, we are not looking at ASME B18.2.1.

So why waste time posting? Everything else about bolted joints throughout this thread makes perfect sense, as usual. Right until you said that head size has nothing to do with it, which I initially agreed with.

I have done some torque tension testing over the years. While a generic torque table is not ideal, anyone without access to load washers, a huge budget, lots of time and material, the generic table is all that is available. At best, you can get some refinement along the lines of bolt and thread materials, plating and lubrication. So bear with me, I have done this kind of testing myself. I have a spreadsheet left over from those days, and for some reason I had included the pressure immediately under the head.

I think that head size had everything to do with it. I only say this after running the numbers, because I did not see just how much a small difference in head size would affect the pressure between the underside of the bolt head and the cylinder head until I saw the numbers pop up, and then I thought that there was an error in my spreadsheet. Having looked at the numbers, I would absolutely want to use a washer under with the smaller head here. A washer spreads the load under the head. the stress fans out at a 45 degree angle, so the effective washer diameter is increased by twice the thickness of the washer. That's why bridge washers are so thick to spread the load on the relatively soft wood.

The washer diameter difference between 5/8 and 11/16 across the flats make for a difference of about 2 ft-lb torque to reach 75% of yield strength. The pressure under the head of the bolt in the washer area was surprisingly different though. when I changed the head size from 11/16 to 5/8 the pressure went up from 49 to 69 ksi. That should be enough of an increase to cause problems with the cast iron here. The contact area is just a narrow ring under the head, so small differences in contact area width can make a big difference.

If I plug in the difference between the coefficient of friction between a generic dry steel on steel (0.3) and lubricated (0.15) joint, and separate oiled threads from oiled head I get the following tension for 75 ft lb of torque on a 7/16-14 grade 8 screw with the standard 5/8 distance between the flats:
Both oiled: 10449 lb.
Just threads oiled: 7140 lb.
Both dry: 5594 lb.
These numbers, as stated several times in this thread, would be different if measured on the tractor due to a lot of variables, but the difference between them would follow the same pattern and be pretty much just as big.


I think the question that remains to be answered is what are you going to do with the head? The uneven surface under the screw heads is bad for both the head and the bolts.

I would be tempted to look at drilling/spot facing or whatever you should call it to get a flat surface, but that surface may wind up in a bad place. Welding is not an easy task in cast iron. The third thought that comes to mind is to drill the hole larger and insert a threaded cylinder to spread the load better and give you a flat place under the screw head. At this point, I have to stop criticizing TOH knowing that his answer will be better than mine.

Any fastener with screw threads is a screw.

The differrence between a hex head cap screw and a hex head bolt is the underside of the head.

A hex head cap screw is designed to be tightened by turnimg the head against a fixed surface and it has an integral washer like surface under the head which acts as a friction washer and reduces gouging of the fixed surface by the corners of the hex head. See picture below. The fixed surface is also typically spot faced to make it flat for the same reason.

A hex head bolt is designed for applications that are tensioned by turning a nut, usually with washer. It lacks the underhead washer like feature of a cap screw and has a larger base radius for added strength.

The SAE automotive fastener standard is a 5/8" head cap screw and it works fine on millions of similar applications. I have used them without issues on N-series heads.

The failure shown in this thread occurred on just two of the fasteners and appears to be gouging.around the peripehery of the head on the fastener as the fastener is rotated against the cylinder head. Three possible causes that come to mind are the corners of the head biting into the surface of the head, Inadequate spot facing, and/or degradation of the cast iron surface itself.

TOH

 

[TheOldHokie]

What is the difference between a screw and a bolt? The first thought that came to mind here was that this is one of the few times that something said by TOH was wrong. Not very important, but it is a common misconception. Not worth posting, but it got me thinking. As far as I know, the only distinction is in the usage, not the screw itself. After many go rounds on that question on one job, we settled on an answer. A bolt is a screw with a nut, and a screw is the same bolt used in a threaded hole. If there is some difference between bolts and screws, we are not looking at ASME B18.2.1.

So why waste time posting? Everything else about bolted joints throughout this thread makes perfect sense, as usual. Right until you said that head size has nothing to do with it, which I initially agreed with.

I have done some torque tension testing over the years. While a generic torque table is not ideal, anyone without access to load washers, a huge budget, lots of time and material, the generic table is all that is available. At best, you can get some refinement along the lines of bolt and thread materials, plating and lubrication. So bear with me, I have done this kind of testing myself. I have a spreadsheet left over from those days, and for some reason I had included the pressure immediately under the head.

I think that head size had everything to do with it. I only say this after running the numbers, because I did not see just how much a small difference in head size would affect the pressure between the underside of the bolt head and the cylinder head until I saw the numbers pop up, and then I thought that there was an error in my spreadsheet. Having looked at the numbers, I would absolutely want to use a washer under with the smaller head here. A washer spreads the load under the head. the stress fans out at a 45 degree angle, so the effective washer diameter is increased by twice the thickness of the washer. That's why bridge washers are so thick to spread the load on the relatively soft wood.

The washer diameter difference between 5/8 and 11/16 across the flats make for a difference of about 2 ft-lb torque to reach 75% of yield strength. The pressure under the head of the bolt in the washer area was surprisingly different though. when I changed the head size from 11/16 to 5/8 the pressure went up from 49 to 69 ksi. That should be enough of an increase to cause problems with the cast iron here. The contact area is just a narrow ring under the head, so small differences in contact area width can make a big difference.

If I plug in the difference between the coefficient of friction between a generic dry steel on steel (0.3) and lubricated (0.15) joint, and separate oiled threads from oiled head I get the following tension for 75 ft lb of torque on a 7/16-14 grade 8 screw with the standard 5/8 distance between the flats:
Both oiled: 10449 lb.
Just threads oiled: 7140 lb.
Both dry: 5594 lb.
These numbers, as stated several times in this thread, would be different if measured on the tractor due to a lot of variables, but the difference between them would follow the same pattern and be pretty much just as big.


I think the question that remains to be answered is what are you going to do with the head? The uneven surface under the screw heads is bad for both the head and the bolts.

I would be tempted to look at drilling/spot facing or whatever you should call it to get a flat surface, but that surface may wind up in a bad place. Welding is not an easy task in cast iron. The third thought that comes to mind is to drill the hole larger and insert a threaded cylinder to spread the load better and give you a flat place under the screw head. At this point, I have to stop criticizing TOH knowing that his answer will be better than mine.

I know the numbers. Grey cast iron is perfectly capable of carrying the higher load. Period.

This damage is dynamic and most likely caused by deterioration of the cast iron over time or possibly missing/inadequate spot face surface allowing the corners of the bolt to dig into the head.

I would spot face the damaged area and move on with a fastener of choice. This would be my choice - 12pt flange bolt. Just make sure it has a smooth not ribbed flange. Better than OEM

Dan

 

[Dave G9N]

TOH:
As I expected, you do have a better idea than I do of what to do here. I thought that spot facing would be the way to go, but the damage looks pretty deep to me and I don't know enough to say if it is too much. I figured that you know a lot more about the heads and would have a much better idea as to how much material you can safely remove. You know how to do it. I know that for me to get the job done, I would have to find someone like you to do it for me. I had not thought of the 12 point flange heads, but I agree that they would be the best choice.

The OEM screws are Grade 8. Grade 8 chemical and mechanical properties are defined by SAE-J29 and the dimensions by ASME B18.2, so the OEM screws did have washer heads. As you explained, it would not be a good idea to use a fastener without the washer area. I agree with you about the 12 point flange heads. The 12 pt flange heads would meet IFI 151 the mechanical properties of ASTM A574 which is around 15% higher than Grade 8.

While the pressure under the head was calculated based on nominal dimensions and a higher than specified torque, the spreadsheet was based on ISO standards my numbers are not entirely accurate, but do indicate fairly high pressures at the torque level I used. Without knowing the grade of gray iron used, it is hard to say how strong the head material is. However, I doubt that Ford didn't apply a fairly generous safety factor knowing that some shade tree mechanics measure torque in number of white knuckles, and have little use for calibrated torque wrenches. As for idiot proofing; it can't be done. That still leaves us with the age and condition of the gray cast iron, which you did address. I would still consider the larger head size and or a washer to minimize the pressure.

 

[TheOldHokie]

TOH:
As I expected, you do have a better idea than I do of what to do here. I thought that spot facing would be the way to go, but the damage looks pretty deep to me and I don't know enough to say if it is too much. I figured that you know a lot more about the heads and would have a much better idea as to how much material you can safely remove. You know how to do it. I know that for me to get the job done, I would have to find someone like you to do it for me. I had not thought of the 12 point flange heads, but I agree that they would be the best choice.

The OEM screws are Grade 8. Grade 8 chemical and mechanical properties are defined by SAE-J29 and the dimensions by ASME B18.2, so the OEM screws did have washer heads. As you explained, it would not be a good idea to use a fastener without the washer area. I agree with you about the 12 point flange heads. The 12 pt flange heads would meet IFI 151 the mechanical properties of ASTM A574 which is around 15% higher than Grade 8.

While the pressure under the head was calculated based on nominal dimensions and a higher than specified torque, the spreadsheet was based on ISO standards my numbers are not entirely accurate, but do indicate fairly high pressures at the torque level I used. Without knowing the grade of gray iron used, it is hard to say how strong the head material is. However, I doubt that Ford didn't apply a fairly generous safety factor knowing that some shade tree mechanics measure torque in number of white knuckles, and have little use for calibrated torque wrenches. As for idiot proofing; it can't be done. That still leaves us with the age and condition of the gray cast iron, which you did address. I would still consider the larger head size and or a washer to minimize the pressure.

The OEM screws were made before the SAE grade standards were established. The Ford torque specification indicates a tension on the lower end of your numbers so I doubt the OEM bolts would meet Grade 8 standards. If you really want to know you can buy a copy of the original prints for $50. I am sure they specify the material properties for both the head and fasteners.

The failures pictured do not look like compression failures to me. They look like tearing and galling caused by surface interference during tightening.

The fastener I pictured is a cheap ($1.20 each) and effective substitute for an OEM cap screw. It is a Grade 8 fastener and the flange has an OD of 21/64. It also requires a flat spotface on the cylinder head if you want to avoid tearing and galling at the flange/head interface. Any reasonably skilled mechanic can spotface the head with a hand drll and piloted counterbore.

TOH

 

[soaked]

Hi Dan,
Hope you get well soon.

Think I'm seeing 16 of 18 holes with countersink, or counterbore damage. Looks like the 2 undamaged ones have a bracket the bolts go into ( post 38)

We all know cast iron cuts like butter

If his 5/8 cap screws, with the small bearing surface, are also too resistant to stretching, wont they just have to start cutting till the 6 points get a purchase?

 

[TheOldHokie]

Hi Dan,
Hope you get well soon.

Think I'm seeing 16 of 18 holes with countersink, or counterbore damage. Looks like the 2 undamaged ones have a bracket the bolts go into ( post 38)

We all know cast iron cuts like butter

If his 5/8 cap screws, with the small bearing surface, are also too resistant to stretching, wont they just have to start cutting till the 6 points get a purchase?

View attachment 117853

Why are the other ones OK?

I had a better look st the damage on a full size monitor and its more extensive than it appeared on my phone. The sides of both bosses have disentegrated. I suspect 80 years of heat cycling has created internal stress risers and weakened the cast iron itself. Thats pretty common.

Cast iron cuts easily with HSS but that damage is beyond a spot face repair and a washer is not going to fix it either.

TOH

 

[soaked]

Dont know why others did not break.
If used the updated torque diagram, holes 3 and 17 crumbled.

5/8 on left, 11/16 8n head bolt on the right

Looks like his 9n with 8n engine now has an aftermarket head from a parts tractor, so not using the crumbled one.

John