Manufacturing custom bolts and studs

I'm rebuilding my engine and I had problems with the differents bolts that are inside my engine. Several of them have to be renewed however I can't get them locally in Hungary (same with some decent wires but that is another story). Plus it is an older car (nearly 30 years old).

I thought a lot and I think I will have a machinist manufacture it using a lathe machine. I talked to one he said it is absolutely doable. These bolt are M9 and M11 which are not standard (the thread pitchs neither) so we will start from thicker bolts and he will make my bolts out of them. I suggested using 12.9 grade bolt, those are the strongest I can get here.

I also thought about manufacturing studs instead of bolts for example for the main bearing caps and cylinder head. However I wouldn't know what torque specs to use since I only have torque specs for bolts. Can I use for example ARP recommendations even though I have custom made studs?

I would appreciate any insights for my approach! Thank you!

Bolts of the same size, pitch, material, used in the same location for the same purpose, may require similar torque spec.

How they are machined can impact material properties, whether they're annealed or a metal treatment process is performed can also be a factor.

Then ARP specs often assume use of their lubricant, and using engine oil instead for example, does change the torque level required.

Did you by chance ask ARP if they have something suitable?

In theory, it can certainly be done, as can the studs option - but there will be potential issues with micro-tearing by the tool tip, and micro-tempering from the heat produced by the cut - even with a brand new insert.

For a steady state, it shouldn't be a problem, but with cyclic (repeating) stresses (loads) it can quickly lead to failure.

If you would post the engine details, and the specifics of the bolts/studs - what they were used for, length, diameter, thread pitch(s), etc - we may be able to find something that will be a direct replacement?

ARP did do a 9x1.25 - 9x1.0 stud that was, IIRC, 4.060" long, which might do as a head stud, if still available?

Thank you Guys for the insights!

I was able to find the M9 bolts for the conrods which are not exactly for my engine however they have the exact same specs.

As for the head studs. ARP is out of the question because of the price here in Hungary is definitely a no from me. However I decided to go with new bolts since I can get them here.

So I guess I call this solved.

OK, but if you would specify the engine, and it's details, might be able to help otherwise?

Turning down larger bolts to make smaller ones is not recommended, especially if they have high loads on them, as you will damage the heat treatment of the material, and weaken it in places. Depending on the Quenching and Tempering processes used, along with the size of the bolt, it may be that only the outside 10%~15% of the material thickness has actually been fully heat treated, with the core of the bolt not having the same treatment. If you machine off some or all of this treated outer layer, then the bolts is only as strong as the core remaining.

You will probably find there are local specially fastener manufacturers servicing manufacturing industry if you wish to go further. Rolled, heat treated threads made to your specification are generally regarded as best strength and toughness for size.