Who makes high grade 26 tpi allen head bolts?

mdt-son said:
Jim, I wouldn't use a 3/8" cap head Allen bolt for cylinder heads if I were you. Depth of the hexagon hole is less than 5mm, unsuitable for a high-torque bolt in standard form.
I've never seen standard cap head Allen bolts used on cylinder heads. Application of high torque requires a large head for safe tool interaction.
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The bolts I use are 12.9 grade, (top) and can be torqued up to 103 nm , more than twice the required value for a Norton head.
hole depth 5 mm.
(some) Mercedes cyl. head bolts are 12x1.75 , also 12.9 grade, and are torqued to 100 nm.
Hole depth is 6 mm.
If you use a coarser thread for Norton head bolts, the specified torque values no longer apply.

Who makes high grade 26 tpi allen head bolts?
 
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mdt-son said:
Jim, I wouldn't use a 3/8" cap head Allen bolt for cylinder heads if I were you. Depth of the hexagon hole is less than 5mm, unsuitable for a high-torque bolt in standard form.
I've never seen standard cap head Allen bolts used on cylinder heads. Application of high torque requires a large head for safe tool interaction.
I'd stick to hex head (BS, DIN 931, ISO 898-1, SAE J1199) or flanged 12-point head (SAE J58_201502) if I were you.
For cylinder head bolts, I recommend metric class 10.9 or a corresponding imperial class of high tensile strength (150 000 psi).

- Knut
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What kind of bolt are you going to use for the cylinder through bolts then? What was the basis of you making this statement 'unsuitable for a high torque bolt' ? What evidence have you got to back it up? Or is this just your opinion?
I personally must have tightened 1,000s of 3/8" cap bolts in my working career, to far higher torque settings than we are talking about here. Never had the cap bolt head fail, the screw broke or the thread failed or the hex key tool broke.
 
ludwig said:
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The bolts I use are 12.9 grade, (top) and can be torqued up to 103 nm , more than twice the required value for a Norton head.
hole depth 5 mm.
(some) Mercedes cyl. head bolts are 12x1.75 , also 12.9 grade, and are torqued to 100 nm.
Hole depth is 6 mm.
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I don't know which core you used for your head bolts, but Mercedes and VAG uses cap head bolts, M12x1,75 for their diesel engines (maybe for their petrol engines as well).
Grade 12.9 is necessary for a diesel engine, because of the high combustion pressure. It's overkill for a rather low compression Otto engine.
As you say, the specified torque for a Norton is much lower.

What's not shown in your picture is the head form. The cap head is more robust than on a standard cap head Allen bolt, and beyond all, the tool form is internal polygon, not internal hex.
For this reason, they can be torqued to much higher values than a standard Allen head bolt. Please note my wording, "in standard form". These bolts are non-standard.
I thought hole depth was more than 6mm for M12, but I take your word for it.

It needs to be pointed out that these bolts are not to be re-used. Also, tooling used in the factory workshop provides a much gentler torquing process than is possible with a manual ratchet.

Picture shows internal polygon shape of cap head (the example shows head bolt for a VW engine).

- Knut

Cap head cylinder head bolt.jpg
 
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mdt-son said:
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I don't know which core you used for your head bolts, but Mercedes and VAG uses cap head bolts, M12x1,75 for their diesel engines (maybe for their petrol engines as well).
Grade 12.9 is necessary for a diesel engine, because of the high combustion pressure. It's overkill for a rather low compression Otto engine. So a cap head bolt is suitable for our Nortons then.
As you say, the specified torque for a Norton is much lower.

What's not shown in your picture is the head form. The cap head is more robust than on a standard cap head Allen bolt, and beyond all, the tool form is internal polygon, not internal hex. This is for speed of production purposes, instead of six positions that the tool can fit, it has 12 or more, nothing to do with how much torque is applied.
For this reason, they can be torqued to much higher values than a standard Allen head bolt. Please note my wording, "in standard form". These bolts are non-standard.
I thought hole depth was more than 6mm for M12, but I take your word for it.

It needs to be pointed out that these bolts are not to be re-used. Also, tooling used in the factory workshop provides a much gentler torquing process than is possible with a manual ratchet. Wrong. The torque tooling in the factory will tighten the bolts to the set figure, nothing to do with how gentle it is.

Picture shows internal polygon shape of cap head (the example shows head bolt for a VW engine).

- Knut
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You still need to tell us what type of through bolt you are going to use




 
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Steve Maney cylinders and hardware used regular medium strength stainless steel socket head allen bolts which were OK unless you bumped up to a high compression Alky burning 920 and then they could break and wipe outthe cases - hence the need for ARP, grade 8 or similar high strength fasteners. Its also important to reduce the shank so they can stretch and retain consistant tension through heat expansion etc.

Who makes high grade 26 tpi allen head bolts?
 
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dobba99 said:
You still need to tell us what type of through bolt you are going to use
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Enclosed calculation sheet for a 3/8 UNC cap head Allen bolt used for holding down the Norton iron barrel is based on some approximations (friction is hard to grasp accurately),
but the calculation is still enlightening.
Without discussing every formula here, you will see that only a small fraction of the applied torque goes into bolt stretching. Most is spent on friction work (while applying the torque).
Secondly, I have estimated the dynamic tensile and total tensile force in a bolt, assuming perfect load distribution in the barrel. This is a valid assumption for a cast iron barrel,
but load distribution in an alloy barrel will probably differ.
The total tensile load calculates to 24 kN while the permissible elastic load is 36 kN at the proportional limit. This gives a utilization of 67% for this tensile class 10.9 bolt.

My calculation is not meant to be a bullet-proof evidence of validity, but I hope it's still convincing.

(Numbers used are for an 850 engine running at a moderate compression ratio. The calculation scheme LRFD is according to Eurocode for steel construction. The automotive trade uses the WSD scheme, but the results will probably not differ much.)

- Knut
 

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The purpose of bolts having reduced shanks and being able to stretch is to help maintain constant tension, keep the head/cylinders from loosening/leaking or the alum threads from pulling out when the alum swells and contracts repeatedly from cold to hot. They should also help absorb the explosive impacts from combustion and vibration.
 
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mdt-son said:
Enclosed calculation sheet for a 3/8 UNC cap head Allen bolt used for holding down the Norton iron barrel is based on some approximations (friction is hard to grasp accurately),
but the calculation is still enlightening.
Without discussing every formula here, you will see that only a small fraction of the applied torque goes into bolt stretching. Most is spent on friction work (while applying the torque).
Secondly, I have estimated the dynamic tensile and total tensile force in a bolt, assuming perfect load distribution in the barrel. This is a valid assumption for a cast iron barrel,
but load distribution in an alloy barrel will probably differ.
The total tensile load calculates to 24 kN while the permissible elastic load is 36 kN at the proportional limit. This gives a utilization of 67% for this tensile class 10.9 bolt.

My calculation is not meant to be a bullet-proof evidence of validity, but I hope it's still convincing.

(Numbers used are for an 850 engine running at a moderate compression ratio. The calculation scheme LRFD is according to Eurocode for steel construction. The automotive trade uses the WSD scheme, but the results will probably not differ much.)

- Knut
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You still haven't said what through bolt you are going to use, or should i say what bolt head form you are going to use as clearly the cap head form in your first quote isn't suitable. The through bolts Norton used for the barrel are standard socket cap headed bolts, holding down a iron barrel so the coefficient of expansion is similar between the two. Problems arise with the Alloy barrel (see jims photo) using s/steel bolts. Notice the bolts broke at the thread, Not head of the bolt. This proves your statement 'Depth of the hexagon hole is less than 5mm, unsuitable for a high-torque bolt in standard form'. Is false. The thread is always the weakest part of a bolt (unless designed otherwise)
 
jseng1 said:
The purpose of bolts having reduced shanks and being able to stretch is to help maintain constant tension, keep the head/cylinders from loosening/leaking or the alum threads from pulling out when the alum swells and contracts repeatedly from cold to hot. They should also help absorb the explosive impacts from combustion and vibration.
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Morning Jim
If you manage to find a supplier of 26 T.P.I. socket head bolts, will you be wanting them to have reduced shanks?
 
dobba99 said:
You still haven't said what through bolt you are going to use, or should i say what bolt head form you are going to use as clearly the cap head form in your first quote isn't suitable. The through bolts Norton used for the barrel are standard socket cap headed bolts, holding down a iron barrel so the coefficient of expansion is similar between the two. Problems arise with the Alloy barrel (see jims photo) using s/steel bolts. Notice the bolts broke at the thread, Not head of the bolt. This proves your statement 'Depth of the hexagon hole is less than 5mm, unsuitable for a high-torque bolt in standard form'. Is false. The thread is always the weakest part of a bolt (unless designed otherwise)
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Of course it is, and I never said the cap head Allen bolt as such would fail at or below the head under in-place tensile loads. My comment related to high-torque pre-tensioning. Read me again!

Another argument for not using cap-head Allen bolts at the cylinder head is corrosion. Unlike car engines where bolts are protected under a valve cover, our bikes have exposed bolts.

- Knut
 
mdt-son said:
Of course it is, and I never said the cap head Allen bolt as such would fail at or below the head under in-place tensile loads. My comment related to high-torque pre-tensioning. Read me again!

Another argument for not using cap-head Allen bolts at the cylinder head is corrosion. Unlike car engines where bolts are protected under a valve cover, our bikes have exposed bolts.

- Knut
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I have read your first comment again, you mentioned nothing of high-torque pre-tensioning. (what ever that is) You haven't provided any evidence to say the cap head form of bolt head design is no good for high torque applications. One of the reasons automakers use the spline drive, 12 point socket design, or torx head etc design for there engine bolts is because of the production tooling that they use to speed up production.
Cap head bolts can be obtained in plated finish so your corrosion argument is false as well.
 
Dobba, please stop. If you think the cap head form of bolt head design is good for high torque applications, you may demonstrate it. Otherwise, you have made clear to us all that you disagree with me.

Reason for automakers to use the polygon shape and the strengthened head rather than a standard head is not due to production tooling, but most likely a design/strength consideration. In most cases, tooling is chosen according to design requirements, rarely the opposite.

Because of the tool's higher contact pressure vz. hex head bolts, any plating applied within the cap head Allen bolt (if plating is possible at all) would wear off quickly, so the internal hex will start corroding. This may or may not become a tool interaction problem. Why select a cap head Allen bolt if the hex head bolt is clearly better suited in this application, and there is no space constraint?

I rest my case.

- Knut
 
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VW use thick hardened head bolt washers as due to the torque and the head being aluminium the bolt Torx head is too small for the application.

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If needed they could be used under allen headed bolts depending on the head material and the torque applied, all depends on the application.
 
mdt-son said:
Dobba, please stop. If you think the cap head form of bolt head design is good for high torque applications, you may demonstrate it. Every single time i, and yourself! Tighten the through bolts in the barrel.....Otherwise, you have made clear to us all that you disagree with me.

Reason for automakers to use the polygon shape and the strengthened head rather than a standard head is not due to production tooling, but most likely a design/strength consideration. In most cases, tooling is chosen according to design requirements, rarely the opposite.

Because of the tool's higher contact pressure vz. hex head bolts, any plating applied within the cap head Allen bolt (if plating is possible at all) would wear off quickly, so the internal hex will start corroding. This may or may not become a tool interaction problem. Why select a cap head Allen bolt if the hex head bolt is clearly better suited in this application, and there is no space constraint?

I rest my case.

- Knut
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QED = Quite easily demonstrated
 
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kommando said:
VW use thick hardened head bolt washers as due to the torque and the head being aluminium the bolt Torx head is too small for the application.

If needed they could be used under Allen headed bolts depending on the head material and the torque applied, all depends on the application.
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Apart from spreading the load, there is another reason for using a hardened steel washer between bolt head and alloy head.
Without it, the sliding friction between head and alloy easily doubles, so in order not to erode bolt pretension completely, hardened steel washers are prescribed,
at least for bolts of tensile class 10.9 and 12.9 . They are required at the Norton cylinder head as well. Standard washers 016213 - I don't know if they are hardened - are too small IMO.

A small remark regarding torque values. VW diesel engines are torqued to 60 Nm plus another half turn. That's considerably more than Norton's 40.7 Nm figure.
Yes, the former are M12 while Norton's bolts are 3/8". VW's bolts are restrained by a cast iron block. Scaled against bolt area, Norton's bolts are actually torqued more (40.7 vs. 37.8 Nm).
Hmm, interesting, and surprising, given the fact the cylinder through bolts are screwed into Helicoil thread inserts.

- Knut
 
jseng1 said:
I'll be reducing the shanks myself.
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If you are going to reduce the ID of the shanks why not buy in 3/8 bolts with a long enough shank to accommodate the length of the bolt you require. Cut the unwanted threads off the end and then cut the 26tpi BSC threads required at the same time. I'm pretty sure 3/8 BSC split dies are still available.
 
mdt-son said:
Apart from spreading the load, there is another reason for using a hardened steel washer between bolt head and alloy head.
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Yes!

I've had a couple of heads where the stainless hex heads were smaller than usual, and the dummy didn't use washers. This caused the aluminum to collapse in on the bolt. They were hard to get out and I had to re-open them to the right size before assembling. There's no doubt in my mind that Allen cap screws must have tight-fitting washers to prevent this as their heads have even less bearing surface normally.

Even the 850 through bolts into cast iron can have that trouble. I recently took a set off where the prior guy apparently got confused and had 1 bolt with two washers, 1 with none, and 2 with one. Again, very tough to get the one with no washer out due to the top edge of the cast iron collapsing in on the bolt.

I'm sure Jim knows this, but worth mentioning.
 
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