Heat treatment of engine bolts

Nicolas_Arg · Jun 27, 2020

Hello board, this is my first post here although I've been reading the forums for years. I'm not a machinist, have a small general fab and proto shop in a tiny town in northern Patagonia.
A friend is rebuilding a truck from the 70s and asked me to machine a set of bolts for the block since the original ones are all (but one) stretched way beyond tolerances. Normally I'd send him to a job shop in a nearby town but decided to take on that job to help to pay some bills during the covid crisis and economy going down in flames.
The bolts came out okay but I can't seem to find a conclusive answer about the need for post machining heat treatment. I used 4140 steel that I bought as heat treated and tempered.
A couple of machinist books I have mention that for bolts, 4140 should be heat treated but I can work the original bolt with a file just ok. On the other hand, several articles on the web suggest that for blocks, the bolts should be more or less ductile to allow some expansion produced by heat.
My question is- how should I treat the bolts before delivering them?

DDoug · Jun 30, 2020

Nicolas_Arg said:
Hello board, this is my first post here although I've been reading the forums for years. I'm not a machinist, have a small general fab and proto shop in a tiny town in northern Patagonia.
A friend is rebuilding a truck from the 70s and asked me to machine a set of bolts for the block since the original ones are all (but one) stretched way beyond tolerances. Normally I'd send him to a job shop in a nearby town but decided to take on that job to help to pay some bills during the covid crisis and economy going down in flames.
The bolts came out okay but I can't seem to find a conclusive answer about the need for post machining heat treatment. I used 4140 steel that I bought as heat treated and tempered.
A couple of machinist books I have mention that for bolts, 4140 should be heat treated but I can work the original bolt with a file just ok. On the other hand, several articles on the web suggest that for blocks, the bolts should be more or less ductile to allow some expansion produced by heat.
My question is- how should I treat the bolts before delivering them?

Nicolas,
for not being a machinist, those look pretty darn good.
As for the 4140-ht material, I don't know if you need to heat treat them.

What I do know, is there are many people here that will know, please send some more details
of the particular engine (make & model).

BTW I would love to see some pix of your shop, and what town are you in ?

atex57 · Jun 30, 2020

What size and what torque on these fasteners?

I do a lot of special engine studs with rolled threads. If the torque is not too high you can get by with cut threads.

4140HT material is about 30Rc for hardness which is very similar to grade 8.8 metric or grade 5 US.

Ed.

Joe Miranda · Jun 30, 2020

Nicolas_Arg said:
Hello board, this is my first post here although I've been reading the forums for years. I'm not a machinist, have a small general fab and proto shop in a tiny town in northern Patagonia.
A friend is rebuilding a truck from the 70s and asked me to machine a set of bolts for the block since the original ones are all (but one) stretched way beyond tolerances. Normally I'd send him to a job shop in a nearby town but decided to take on that job to help to pay some bills during the covid crisis and economy going down in flames.
The bolts came out okay but I can't seem to find a conclusive answer about the need for post machining heat treatment. I used 4140 steel that I bought as heat treated and tempered.
A couple of machinist books I have mention that for bolts, 4140 should be heat treated but I can work the original bolt with a file just ok. On the other hand, several articles on the web suggest that for blocks, the bolts should be more or less ductile to allow some expansion produced by heat.
My question is- how should I treat the bolts before delivering them?

Nicolas - if you used 4140 pre-hard you will be fine (that will be 28-32 Rc). If you did not, I would heat treat them and temper to 40-45Rc. That will give you the equivalent of a grade 8.

Read through this thread: https://www.practicalmachinist.com/...ETD 175, produced to 175 ksi tensile strength.

Phil in Montana · Jun 30, 2020

I would use the bolts as is,4140 ht does not like sqr corners , like what a bolt has under the head to the shank. It would have been better to make a radius there and relieve the bolted part so there was no interference. If you heat treat the bolts you have made they will pop the heads off there...Phil

mmarquette · Jun 30, 2020

How do they compare to the originals in hardness. Could also intentionally sacrifice one to see what it will hold up to and see if it fails or deforms above what you both feel good with.

gbent · Jun 30, 2020

Your screws look good, but they need a radius under the head and at the transition from full to necked diameter. You would have a stronger screw if you were to neck the diameter just to get the proper radius. If torque values are used for grade 5 bolts or metric grade 8.8 you should be good. Since you started with heat treated stock, proper reheat treating should start with an anneal. The scale that would result from the heat treating cycles would ruin your dimensional accuracy unless you have oxygen limiting methods available.

ps123 · Jun 30, 2020

You might want to look at ARP Bolts and see if they make a fastener in the size you need. ARP are generally very high quality.

GregSY · Jun 30, 2020

Look like Chrysler bolts

DDoug · Jun 30, 2020

ps123 said:
You might want to look at ARP Bolts and see if they make a fastener in the size you need. ARP are generally very high quality.

Note Op's location....

Dave G. · Jun 30, 2020

Can we get a picture of the top of the original bolt? Head markings will show it's classification/strength range. Standard 4140 HT is about a grade 5 bolt in SAE or a 8.8 metric. As stated above Grade 8 bolts are higher strength and therefore harder.

gbent · Jun 30, 2020

A better quality threaded fastener that might be available locally would be Grade B7 threaded rod. Thread into the block and use a washer and nut on the other end.

muckalee · Jul 1, 2020

Your bolts have a couple of areas of concern that have been pointed out by other members. However the exact geometry and dimensions are not visible in the photographs.

Testing the bolts will give you confidence in their capabilities, if they pass. Failures will identify the areas for improvement. Fabricate a test fixture that accommodates your bolts. Try to duplicate the length of thread engagement, the length unsupported, and parrellism as original head/block configuration. Test three of your bolts. Use the original torque values, lubrication or sealant as prescribed by manufacturer. Mark each bolt, measure the total length of each bolt and document the length to three places, before the test and again after the test.
If any bolt yields, located the area that stretched and address that geometry and dimension. If all bolts measure the same length, retest, increasing the torque by about 10% or so, measure and test, increasing torque after each test until any bolt yields. This evaluation will give you confidence in your product and identify the torques value of original build is good. Please send a private message if you need further information.

Nicolas_Arg · Jul 2, 2020

digger doug said:
Nicolas,
for not being a machinist, those look pretty darn good.
As for the 4140-ht material, I don't know if you need to heat treat them.

What I do know, is there are many people here that will know, please send some more details
of the particular engine (make & model).

BTW I would love to see some pix of your shop, and what town are you in ?

Hello Doug, thank you for your kind words. The bolts are for a Dodge 100 truck from the 70s, they used to be made here in Argentina under US license.
I live in a very small area some 20 miles from the city of Bariloche, in northern Patagonia. It's mainly a tourist location.
In 2015 I lost my job and used the little money I got from there to buy a shipping container and try to set a tiny little shop for my ideas. In the meantime began a fab business with a friend (my day job) but never gave up with my tinkering. Began getting occasional reverse engineering jobs (I got a pretty good cad training in college) and slowly got some more tools and did a lot of little projects.
I'm 37 now, perhaps a bit late to start a new career but I'd love to patiently work my way up to a small machining shop.
Here are some photos, they are more adequate for the hobbyshop forum but nevertheless...

Shared album - Nicolas Belokurov - Google Photos
Shared album - Nicolas Belokurov - Google Photos
Shared album - Nicolas Belokurov - Google Photos

Nicolas_Arg · Jul 2, 2020

Hello gentlemen,
Thank you all for your kind help, I read carefully each and every one of the posts and will proceed as advised. I'll post a photo of the original bolt head tomorrow. Right now my friend told me that he was seeking the help of a professional mechanic and I gave him one of the bolts I made to inspect it.
Will update on the results.
Thanks again
(I'm kind of a slow poster due to some internet troubles we are having here as a consequence of heavy snow storms).

atex57 · Jul 3, 2020

muckalee said:
Your bolts have a couple of areas of concern that have been pointed out by other members. However the exact geometry and dimensions are not visible in the photographs.

Testing the bolts will give you confidence in their capabilities, if they pass. Failures will identify the areas for improvement. Fabricate a test fixture that accommodates your bolts. Try to duplicate the length of thread engagement, the length unsupported, and parrellism as original head/block configuration. Test three of your bolts. Use the original torque values, lubrication or sealant as prescribed by manufacturer. Mark each bolt, measure the total length of each bolt and document the length to three places, before the test and again after the test.
If any bolt yields, located the area that stretched and address that geometry and dimension. If all bolts measure the same length, retest, increasing the torque by about 10% or so, measure and test, increasing torque after each test until any bolt yields. This evaluation will give you confidence in your product and identify the torques value of original build is good. Please send a private message if you need further information.

Kind of like Muckalee has above ^^^^^.
ARP makes a lot of fasteners and has a good torque table for different sizes and grades of fasteners. Their chart says the recommended torque is 75% of the yield point which means if you take the required torque and divide by .75 it should be at the yield point. I made a tester to show this and several other points about fastener clamping force, comparing threads, breaking strength, yield, etc. Boiling it down, if your bolt yields (you feel it give way ) at the recommended torque divided by .75 or higher you should be OK. Example: recommended torque 120/.75=167 at yield point.

Make a couple extra and sacrifice them to science!!

Ed.

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