Don Terrill’s Speed-Talk

Can I use a vernier micrometer to measure rod bolt stretch?

I haven't compared it to my stretch gauge yet, but I will when I get a chance. I know it would be a different measuring point, but do you think it will be accurate?

To me, there is nothing more aggravating than fighting that dang stretch gauge when trying to measure rod bolt stretch.

Even before talking about that lets talk about what material the bolts are made of and once torqued up this time how many torque up rounds will that be on these bolts?

I assume they have atleast 3 torque up sessions on them now, and with most bolts once you get to 5 of those rounds your really playing with Fire in regards to a bolt failure!!

1 What are you doing up at 3:15 am
2 Yes just be careful
3 Good idea I will try it my self

Nova,
Which stretch gauge do you have ? I have ARP one and I cant imagine using a micrometer instead ? I would think it would be hard to be consistent with a micrometer as the top and bottom of the bolts usually are not machined flat.

mag2555 wrote: ↑Wed Dec 18, 2019 6:10 am Even before talking about that lets talk about what material the bolts are made of and once torqued up this time how many torque up rounds will that be on these bolts?

I assume they have atleast 3 torque up sessions on them now, and with most bolts once you get to 5 of those rounds your really playing with Fire in regards to a bolt failure!!

I have full respect for your knowledge Mag, but I struggle with the 5 rounds of torque.
Last set of rod bolts I installed I torqued to about 75% stretch of what arp said, checked big end for round, backed them off a bit, torqued a bit tighter and checked again, decided the big ends needed a hone, got that done, got them home, torqued them up, checked the machinists work, then went through about 3 combinations of bearing shell to get the clearance I wanted, then finally torqued them in engine.
About 7 torque cycles in total.
Are my bolts worn out before I start the engine?

BillK wrote: ↑Wed Dec 18, 2019 11:46 am Nova,
Which stretch gauge do you have ? I have ARP one and I cant imagine using a micrometer instead ? I would think it would be hard to be consistent with a micrometer as the top and bottom of the bolts usually are not machined flat.

good answer here,
i complete most of my conrod work in a rod vise on the workbench.
rod bolt stretch and free length and rod and bearing clearances.after a few cycles you can get close with a torque wrench,and checking with stretch gauge.
when bolts are snugged down i stretch in one full motion to spec i require.
if i dont get to spec i back bolt off and go again.

Biteme wrote: ↑Wed Dec 18, 2019 4:07 pm

mag2555 wrote: ↑Wed Dec 18, 2019 6:10 am Even before talking about that lets talk about what material the bolts are made of and once torqued up this time how many torque up rounds will that be on these bolts?

I assume they have atleast 3 torque up sessions on them now, and with most bolts once you get to 5 of those rounds your really playing with Fire in regards to a bolt failure!!

I have full respect for your knowledge Mag, but I struggle with the 5 rounds of torque.
Last set of rod bolts I installed I torqued to about 75% stretch of what arp said, checked big end for round, backed them off a bit, torqued a bit tighter and checked again, decided the big ends needed a hone, got that done, got them home, torqued them up, checked the machinists work, then went through about 3 combinations of bearing shell to get the clearance I wanted, then finally torqued them in engine.
About 7 torque cycles in total.
Are my bolts worn out before I start the engine?

100% agree,
rod bolt life is dependent on engine cycles not how many times you torque the bolt as long as it is not stretched beyond yield and free length(relaxed) is where you started.
but i have been wrong plenty times before

You can torque and retorque to you’re hearts content as long as you don’t exceed the design limits and enter permanent distortion. The 3 torques before installing the final time is for when using a torque wrench. You want the threads/nut burnished/polished to get rid of the friction the torque wrench has to overcome that can give false readings. This also applies to using the correct lubricant the manufacturer recommends to achieve the correct torque.

Now using a stretch gauge you could theoretically install on the first go around and as long as it meets the stretch requirement you’re good to go. No burnishing. No matter what the lube. Personally I like to go a few rounds with a torque wrench to say 50%-75% torque spec to get a feel for everything and make sure nothing feels wired. Then the final install I use a stretch gauge. It’s cycles on the bolt that matter, not how many times it’s been tightened and loosened. To a point. I mean I wouldn’t do that 50 times before final install on a un-run bolt but I supposed you could.

I’ve used a mic with a small ball bearing epoxied to one end that registered in the small dimple in the bolt head...very slow but accurate for sure

408 Nova wrote: ↑Wed Dec 18, 2019 3:15 am Can I use a vernier micrometer to measure rod bolt stretch?

I haven't compared it to my stretch gauge yet, but I will when I get a chance. I know it would be a different measuring point, but do you think it will be accurate?

To me, there is nothing more aggravating than fighting that dang stretch gauge when trying to measure rod bolt stretch.

Yes but you can only do one bolt at a time. Put the rod in the rod vise, lets say its .0045" stretch or 63 torque, torque the bolt and I always start on the tang side of the rod. Torque it to 63, pull the rod out of the rod vise, set the stretch gauge to read lets say .0055" on that bolt torqued, put the rod back in the vise and loosen the bolt and let relax, take rod out and put stretch gauge back on that bolt. If 63 stretched it to .0045", that bolt is gonna read .001", if it reads anything over .001" it did not stretch it properly. Write down tang side rod bolt, and bolt #2 torque specs on a clean note pad with the bolts length to check at rebuild. I use the billet ARP stretch gauge (CLEAN YOUR HANDS BEFORE USING MICS, STRETCH GAUGE ETC) and longer bolts will take more torque. The Scat 1.400" UHL 8740 bolt is 63/.0045" and it takes 65-68 foot pounds on all of them, I also take the stretch gauge on and off when its tight & loose a few times to be sure it repeats before moving forward

jed wrote: ↑Wed Dec 18, 2019 10:20 am 1 What are you doing up at 3:15 am
2 Yes just be careful
3 Good idea I will try it my self

Thank you. I work nights and was thinking about rod bolts on an engine I'm building so I posted my question up, on break of course. Lol.

BillK wrote: ↑Wed Dec 18, 2019 11:46 am Nova,
Which stretch gauge do you have ? I have ARP one and I cant imagine using a micrometer instead ? I would think it would be hard to be consistent with a micrometer as the top and bottom of the bolts usually are not machined flat.

I have an el cheapo Powerhouse Products rig. I had a Summit but it fell off and broke when torqueing rod bolts one time, so I bought this one. I would love to get myself an ARP though, because it looks like a well built unit. And I never thought about the ends of the bolts not being flat.

steve cowan wrote: ↑Wed Dec 18, 2019 4:12 pm

BillK wrote: ↑Wed Dec 18, 2019 11:46 am Nova,
Which stretch gauge do you have ? I have ARP one and I cant imagine using a micrometer instead ? I would think it would be hard to be consistent with a micrometer as the top and bottom of the bolts usually are not machined flat.

good answer here,
i complete most of my conrod work in a rod vise on the workbench.
rod bolt stretch and free length and rod and bearing clearances.after a few cycles you can get close with a torque wrench,and checking with stretch gauge.
when bolts are snugged down i stretch in one full motion to spec i require.
if i dont get to spec i back bolt off and go again.

You torque them in your rod vise, then measure stretch, note the value, then torque them in the engine to that value?




Thanks everybody for your help.

408,
early days i tried ring spanner on bolt trick with stretch gauge etc to hard.
i dont stretch the bolt in stages as i think the stop/start can mess you up.
buy a conrod vise and ARP stretch gauge,if you are doing motors at home even only once a year or so you have these tools for life.
like everything you have to find what works for you

Sorry, but the way he is intending to do it without the proper tools IS playing with Fire!

In my experience there is the need to torque the bolt in stages so the load is distributed even it does not matter if it's a con rod big end or Cylinder head then loosen the bolt or screw completely one at the time and only this you torque to the specified torque on one stage.

fellers, think of the bolt as a rubber band.

if you don't reach the required stretch, back it off an 1/8 or 1/4 turn after marking with paint, orient your torque wrench at a true 90 degrees, and go again.

ya'll need to read more engine blueprinting books, food for thought anyway.