Author Topic: Head bolts  (Read 869 times)

Offline KeithA

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Head bolts
« on: 07.09. 2017 14:17 »
Have found some misc 3/8 BSF bolts in my workshop that I want to use to make head bolts for my A7 52 project. Are these bolts normally high tensile??

Online JulianS

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Re: Head bolts
« Reply #1 on: 07.09. 2017 17:23 »
Yes with rolled, not cut, threads and reduced hex head.

Online rocker21

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Re: Head bolts
« Reply #2 on: 08.09. 2017 12:27 »
normal bsf bolts are not high tensile, you need to look at what is on the top of the bolt if they are high tensile they will be marked and you need them with rolled threads not cut with a die or turned on a lathe , so you need to buy the correct ones for either the iron head or the alloy one as they are different.
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Offline KeithA

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Re: Head bolts
« Reply #3 on: 09.09. 2017 13:40 »
Thanks for your answers gentleman, I didn't know about rolled threads, only for conrod bolts, and spoke nipples ect. I'm glad I asked.
Google says cut threads have minute tear marks that can crack into the centre of the bolt which is interesting.
Cheers KeithA

Offline KeithA

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Re: Head bolts
« Reply #4 on: 18.09. 2017 02:59 »
Yes These are the head bolts I have in another engine as I found it. Standard mild steel BSF.
I made a set like these ones, for my second engine, only to find out they are not suitable ie High tensile, rolled threads ect.
What could I do without this great forum. I will now have to order a couple of sets through Draganfly. Hope they are UK made not from the sub continent. Any recommendations.
Cheers KeithA

Offline coater87

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Re: Head bolts
« Reply #5 on: 18.09. 2017 03:24 »
 Kieth,

 I am going against the grain here.

 If the bolts you have are in good shape, I would use them.

 I am sure whatever Draganfly sells you will be substandard. What you have there is probably twice as good as what you will get from them, plus its the devil you know.

 If you cannot call SRM or a place with a reputation like they have, and that place tells you they do actually have high tensile with rolled threads on the shelf, ready to go head bolts for the bsa a10.....I would not waste my money.

 Lee

Central Wisconsin in the U.S.

Offline KeithA

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Re: Head bolts
« Reply #6 on: 18.09. 2017 04:41 »
Yes Thats reassuring to know, I should be able to use these.
The bolts in the picture are all nice condition with good threads ect, and not stretched.
I'm just building up a couple of standard engines, and wont be riding around everywhere at 90 MPH.
Thanks for the advise regarding suppliers.
Cheers KeithA

Online Black Sheep

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Re: Head bolts
« Reply #7 on: 18.09. 2017 06:41 »
If you have good original BSA bolts I would stick with them. Otherwise I would lash out on a set from C&D Autos or other reputable supplier. I would not use miscellaneous bolts. You would probably get away with it but it's your choice. Do avoid stainless head bolts which some suppliers offer. Nothing but trouble.
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Online JulianS

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Re: Head bolts
« Reply #8 on: 18.09. 2017 08:48 »
I agree re stainless - tried a set of the 4 outer visible ones. They stretched and would not hold a torque figure. You could see the necking on the threads.

Offline muskrat

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Re: Head bolts
« Reply #9 on: 18.09. 2017 13:37 »
Keith, don't get that box of beer this week. Instead buy a set of proper head bolts!
Cheers
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Offline KeithA

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Re: Head bolts
« Reply #10 on: 18.09. 2017 23:59 »
Yep Thanks for the advise. I'll buy a proper set then.
KeithA

Offline bl**dydrivers

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Offline Sluggo

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Re: Head bolts
« Reply #12 on: 16.10. 2017 19:17 »
Bolts can be anything you want,  Cheap and nasty, made with left overs from Chernobyl nuclear plant and meted down in a backyard smelter or Aerospace grade and everything in between.

A cut thread is okay in many applications but not for a cyl head that has a lot going on with thermal-heat issues as well as holding a torque, But a rolled thread is made by FORMING a thread and not cutting one so 2 different processes and the strength is different. But dont get too excited about reports of micro cracking.  It all depends on what material the bolt is made out of and heat treating.

Nothing wrong with stainless tho, stainless seems rather misunderstood.  No such thing as 1 type of stainless, there is a wide array of common stock stainless (17-4, Inconel and many others) all with specific properties.  Norton and Triumph owners have a wide variety of stainless fasteners readily availible on the market and other than some ill advised (IMHO) Stainless axles nobody every seems to have any issues with these other supplys.   But most decorative stainless hardware sold over the counter is rather soft material and typically only a grade 2 in strength.    In a pinch I  culled a large collection of bolts from auto engines in a wrecking yard or 2 and these make excellent donors provided you properly resize them and rethread them.

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