Connecting rod bolts and stretch gauge?

I think this belongs to the "there are no stupid questions but..." category and I think I already know the answer but considering that the crank is surrounded with that cradle I assume that measuring connecting rod bolts with stretch gauge is out of question? i'm just preparing the project and I was reading connecting rod manufacturer's instructions and recommendations.... -- Mika

It can be done, according to YouTube. When I installed mine I used to torque to angle spec. I did not have the stretch gage and questioned my ability to accurately use it in the tight confines of the crank carrier. Instead, I bought an electronic torque wrench that reads angles. It has been a good investment in building this engine. Note that I used the K1 rods and the instructions that came with them have a bolt stretch value and the torque to angle value.

Well, I have Carrillo's connecting rods with their WMC bolts. I'm just wondering and preplanning how to measure first the clearances (main bearings + connecting rods) and then do the final assembly. Carrillo is of course strongly recommending to use stretch method instead of angle method, Those WMC bolts have max 15 torque cycles allowed and that's only valid when the stretch is within specs. Now when using angle method there's a theoretical risk of overstretching the bolts with that method but luckily the specs are quite broad as the max is 130Nm or so for those H6 spec bolts. I have also angle meter on my torque wrench so I can follow also torque so I should be on the safe side. But naturally it would be nice to use the preferred (stretch) method. ps. Do you have a link to that YoutTube video? AH, found this one -> You Tube

When I rebuilt mine, I used ARP bolts and they also recommend stretch gauge method. So I bought the ARP branded micrometer stretch gauge. i would have to say as a complete novice, trying to use this with confidence was challenging. These gauges measure relative measurements or changes not absolute. It's not a like a micrometer that measures from 0 to 2 inches and the measurement taken is always an absolute value and accurate value as long as the gauge is calibrated. The anxiety I had was not having a known reference point to go back to, to make sure that my dial gauge face or markers didn't move slightly. I'm not sure what it would cost, but one way around that would be to buy a precision reference block that is close to your bolt length to always go be able to reference back to. I only watched a little bit of that video but what happened to them early on was exactly what i faced. Taking a measurement that didn't seem right but then not having a known reference to go back to. Bolts like ARP can be reused as long as they don't reach a stretch limit to where they won't rebound to a close tolerance of their original length. But the bolts never go back to the exact value you started with. So like in the video, they stretched a bolt by using the torque and angle method and then measured the stretch. They decided one was too stretched so they backed them off and then went at it again. I didn't see in the video portion that I watched that they ever determined how much they changed the original length of the bolt. By itself, this gauge can't tell you if a bolt is 1.5650 inches long. it can only tell you the change from where you dialed the face plate to (and hoping you didn't move the faceplate slightly). My approach was to first find the shortest bolt in all of the connecting rod set of bolts and that's where I zeroed the dial at. So then my starting measurement of each bolt was the positive variance (because all of the other bolts were longer) that was my starting value for that bolt. i then also used the torque plus angle method to start. Then I measured the new length of the bolt and determined stretch by comparing to the original measurement for that bolt. Sounds really simple and straight forward until you get a measurement that doesn't meet spec and you are trying to then figure out why and how to start over. Its been several years since i did this so I don't remember but I would try to find a procedure or video that is done by someone who knows what they are doing. These guys seem very intelligent but they are clearly trying to figure it out as they went. Sorry if this explanation is confusing. As I started typing, i found it much more difficult to explain in words that I would have imagined.

@danielcooper9 Thanks for sharing your experience - being novice as well - at least what comes to installing bolts with stretch method - I've spent now about two days looking into this and it seems that at first it seems really complicated and daunting process but considering the theory behind this and then how it's done in practice it should not be actually that difficult.... although I'm prepared to face the fact that the reality might be different Esp. after reading real user experiences like yours Why I think that it's not that difficult is that the process itself is not that complicated in reality. Obviously there are multiple ways to do it and seems that there are small differences even within bolt manufacture's instructions but after reading a few stories, videos and contacting CP-Carrillo the process could (?) be done like this - simplified. 1) install that bolt on the stretch gauge and zero the dial indicator 2) apply lube and install bolts (both) and hand tight - not sure if there's a need to add some preload to both bolts - this seems to one area where there's a difference between instructions 3) from the manual check the stretch value where to aim + min/max torque specs if available and then using your torque wrench tighten the bolt using for example the lowest / min value of the torque value setting 4) measure the stretch - if it is within recommended values that bolt is done and repeat the process on the other bolt - if it is not then loosen the bolt, add more torque and measure again - remember to measure each bolt independently because they are not identical so this process requires some note taking. My plan is first to measure the clearances so I can use then those torque values - instead of measuring the stretch again when doing the final assembly. Of course I'll measure the stretch again but that's only for confirmation and not for the tightening process itself. Thinking.... this method should work if the first measurements are done on the rod vice. It's could be a bit more tricky if you go directly to final assembly. One way to overcome that issue with the lack of reference point in case there's a need to go back is that when you loosen the bolt install that back on the stretch gauge - it should read 0.000 or very close to that since the bolt stretch is still within elastic range.