straightlinespeed
Sometimes I pretend to be normal
Very interesting read! Thanks for all the knowledge everyone.
How many times can rod and main bolts be torqued?
- Thread starter DartVadar
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Usually the rod cap bolts have a knurl on them which helps locate/align the cap and rod. If you replace the bolt, the new bolt may not locate exactly in the same location as the original one. This can cause a mis-match in the bore. Any mis'match in the bore, can cause a drag on the crank or even lock it up from turning altogether.
If you replace the bolts, it's best to re-machine the crank bore in the rod.
greymouser7
Vagrant Vagabond “Veni Vidi Vici”
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THis post has helped me out a lot, thanks guys.
I don't totally agree with their write up.
They recommend throwing away a bolt that has a .001" of permanent stretch. EVERY BOLT GETS .001" OF STRETCH WHEN TORQUED PROPERLY.
Their way of measuring bolt stretch is not accurate. They say to use a "bolt stretch" gauge when you tighten the bolt/nut. this method also gives elastic and plastic deformation. Elastic deformation will go back when the load is taken off. Plastic deformation is permanent stretch and can only be measured when the bolt is not tightened, before you tighten it, and then after it has been loosened. You can't determine the amount of plastic deformation by measuring the bolt length under load.
When I did my bolt stretch studies, I brought the rod bolts to the tool room to be ground and centered. This is where they GRIND the ends flat and parallel and drill center holes exactly in the center of the head and tip of the bolt. Then I would etch numbers in the bolts and measure them with ball micrometers. You have to use ball mic's as calipers are not accurate enough - ask M. Koppesser (he didn't listen to me and had to do his test over).
Then take them to the rod machining line and get them loaded in some rods and follow them to the end of the line. After they are finished, then I would loosen the nuts and re-measure the bolt length with ball micrometers (ball mic's). This will give you the accurate permanent deformation.
I would then have pistons pinned to the rods and then install the pistons in engines and send them through the dedicated torque multiples and record the data from the multiple for torque and angle. Then remove the pistons from the engine, and measure the bolts again with ball mic's.
I have done bolt stretch test, and worked with the industry experts to set up the equipment needed to torque the rod bolts properly. I am not just some "internet jockey" throwing bull ****.....
Bingo!
The knurl on the bolt shoulder will open up the hole every time a new one is pressed in. The new one may not go exactly to the same position/centered as the last one, and now the rod cap will locate in a slightly different position.
Minor cases, the mis-match will cause a drag on the crank. I've also seen "more serious" cases where it will keep the crank from turning altogether.
Any time you change the bolts in a connecting rod, you should have the crank bore re-machined.
69_340_GTS
Well-Known Member
Well, they are in business to sell you new bolts!
I just called ARP and then my engine shop. ARP said that there isnt really a maximum amount of times that they can be torqued, but after the 4th or fifth time it would be good to replace them. They said the way to tell is take a before and after measurement to make sure they go back to their original length. But I didn't do an initial measurement, but he said what I could do is measure them initially before I torque them for bearing clearances, and then measure once I loosen them to make sure they are the same. Because the bolt is essentially a spring like already mentioned, and as long as it isn't over-tightened then it will go back to its original length.
My engine shop said that it shouldn't be an issue either as the bolts aren't torque to yield (I just torqued them to the specified value), but just to use the ARP lube when I torque them.
And krazykuda did say that after 5 times they should be replaced, so I am within that. No cheaping out or anything but from what I am reading that as long as I dont have any obviously stretched bolts or something that doesn't torque properly I should be good to use them again. And about the fatigue that rusty was talking about they have only been torqued and ran once, so I should be good there too.
My engine shop said that it shouldn't be an issue either as the bolts aren't torque to yield (I just torqued them to the specified value), but just to use the ARP lube when I torque them.
And krazykuda did say that after 5 times they should be replaced, so I am within that. No cheaping out or anything but from what I am reading that as long as I dont have any obviously stretched bolts or something that doesn't torque properly I should be good to use them again. And about the fatigue that rusty was talking about they have only been torqued and ran once, so I should be good there too.
So the plastic deformation is what the concern would be, so if there is a measurable amount the bolts are no good from what I am understanding?
Mad Dart
Nothing to see Here!
May as well just buy some new Scat I Beams. You will be $ and miles ahead of the game.
65cuda360
Well-Known Member
I must be the luckiest person on the planet! Back in the "bad old days" we street raced and ran the hell out of mud trucks with "dirt road rebuilds" all the time. These were our daily drivers as well! My friends and I had piles of core engines and would rob a rod out of one if we needed to replace one that spun a bearing. One 360 (I called it lucky) that I ran in a nearly 4000lb. W100 had three #7 rods in it. My 72 challenger had a 340 that I built out of a pile of cores I bought off a retired bracket racer. That motor saw 8000 rpm on a regular basis at the hands of a rowdy 17 year old. The only thing we took a motor to the machine shop for was to get a block boiled.
I certainly cannot disagree with that logic.
I've build a LOAD of them the same way. But, it was always for me or for a friend just messin around and we never had trouble. I was speaking merely from the perspective of building engines for customers. No way would I use old rod bolts there.
Not really wanting to spend money on new rods...the budget isn't too much bigger considering I'm a full time student and still have to buy rockers and roller lifters still! lol But still dont want to cheap out, but when I originally torqued the rod bolts I did it properly with a recently calibrated torque wrench and used the lube.
Stock rod bolts I wouldn't use, especialyl since they would have seen thousands of miles, where mine only saw about 3k until I pulled the motor out.
Stock rod bolts I wouldn't use, especialyl since they would have seen thousands of miles, where mine only saw about 3k until I pulled the motor out.
In most cases, reconditioning the old rods with new rod bolts is just as much or more than an entry level set of new rods with good bolts, like the Scats MadDart recommended. I would check into it.
Well that would be if I do go with new rod bolts, but these ones if I don't replace them are ready to go back in. I guess ive just gotta decide, arp and my engine guy say they are fine, while you guys say to replace em lol. No replacing them is alot easier on the wallet anyways.
I don't see anywhere I have made a recommendation for your case either way. I will tell you this. If I were in your place, I would use the rod bolts again so quick, I wouldn't have time to think about it. How's that for a recommendation? lol
In the above, you are talking about ARP recommending replacing bolts with .001 plastic deformation. Then right after you talking about elastic deformation, which does not count towards plastic deformation.
Quality rod bolts have a smooth barrel, typically not a knurled shank, that is pressed into a bore of the rod which centers it in the bore. The cap is then installed centering itself, on the two rod bolts. This is as precise as you can produce a rod. Quality rod bolts have spherical "dimples" on both ends of the rod bolt which index the micrometer or stretch gage.
I'd have to agree. SBM rods are pretty beefy, have taken a set, and have had the big ends redone with quality rod bolts, then run for 3,000 miles. Just don't blame RRR or I if a rod scatters causing an expensive mess...
Nice disclaimer. lol
65cuda360
Well-Known Member
It wouldn't be a total loss.....scrap iron is selling for $200 a ton here.......
Mad Dart
Nothing to see Here!
:glasses7:
Wow, I used to get $20.
yes, when you tighten a bolt, you get both plastic and elastic deformation.
Elastic deformation is stretching that goes back when the load is released. (Like a spring, it goes back when unloaded).
Plastic deformation is when the bolt stretches PERMANENTLY and does not go back when unloaded.
You cannot measure plastic deformation with the bolt under clamp load.
It is difficult to get an accurate reading for bolt length unless the bolts are ground flat/parallel and with centers drilled in them. Otherwise the ridges that are made when they form the bolt can throw off the measurements.
Try to measure a bolt 10 times and see if you get the same exact reading every time. If you can't, then your measurement method is not good enough....
You have to use micrometers, not calipers. Calipers are not sensitive enough...
Thats good to know that you would do that, I am inclined to go that route lol
Okay that makes sense, now I didn't take an initial measurement when I got the bolts, but would it be worth it to measure the bolts with a micrometer before I do anything, then torque them to check the bearing clearances, and then measure again to make sure I get the same readings? Because if I notice they stretch then they are definitely not good to use, but If they stay the same then they would have only elastically stretched? Or are the current lengths not significant enough?
And using a micrometer for measuring the bearing clearances is more accurate than using plasti-gauge?
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