Proper method for determining bearing clearances?

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gregsdart said:
I measure the journal for the bearing I want to check tolerance on, lock the mike to hold the reading, zero my Dial bore gauge to the mike, then check the bearing. If you do it all carefully, it is pretty much fool proof, because you are doing a direct measurement of the difference, and you are not depending on the mike being dead accurate and perfectly calibrated.
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That is going to be the first method I try. Thanks,

CE
 
BTW, on the re-use of the bolts..... I suspect a lot of failures in the past could be traced to inadvertent overtorquing. I bet there are a ton of guys who are sloppy in their work, and who don't clean and dry the threads on rod bolts before torquing them. It's pretty critical on SBM rod bolts, because the book torque of 45 ft lbs is right up near the limit of the bolt torque IF the threads are dry. If they are oily and you put 45 ft lbs on them, they are going to be well past the max load of the bolts and into the yield region.
 
nm9stheham said:
BTW, on the re-use of the bolts..... I suspect a lot of failures in the past could be traced to inadvertent overtorquing. I bet there are a ton of guys who are sloppy in their work, and who don't clean and dry the threads on rod bolts before torquing them. It's pretty critical on SBM rod bolts, because the book torque of 45 ft lbs is right up near the limit of the bolt torque IF the threads are dry. If they are oily and you put 45 ft lbs on them, they are going to be well past the max load of the bolts and into the yield region.
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Hmmm, this is totally contrary to what we always did at the dealership. We lubed the bolt threads with a grease (specifically for that purpose) before torquing. The reason given was that a dry bolt would drag or gall and not give you a fully torqued assembly.
 
nm9stheham said:
BTW, on the re-use of the bolts..... I suspect a lot of failures in the past could be traced to inadvertent overtorquing. I bet there are a ton of guys who are sloppy in their work, and who don't clean and dry the threads on rod bolts before torquing them. It's pretty critical on SBM rod bolts, because the book torque of 45 ft lbs is right up near the limit of the bolt torque IF the threads are dry. If they are oily and you put 45 ft lbs on them, they are going to be well past the max load of the bolts and into the yield region.
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You are correct...

The lube can make a HUGE difference in the clamp load for the given torque...

If you put too much or a different lube on the bolts, then you will affect the clamp load for that given torque...

If someone tried to re-oil the used connecting rod bolts in our factory, we would get many reject failures on the multiple nut runners that tightened them... we ended up having to save all the used ones and send them back to the manufacturer and they would re-coat the special oil/wax coating for us... Then we would batch run them at one time to keep track of them as they were more sensitive to fail in the torque station....

Fastener Engineering develops the torque specs based on how the parts come into the factory... The torque specs were set up to be on how the parts came in new with whatever coating was specified,so adding any extra oil/lube will throw off the torque specs...
 
ValiantOne said:
Hmmm, this is totally contrary to what we always did at the dealership. We lubed the bolt threads with a grease (specifically for that purpose) before torquing. The reason given was that a dry bolt would drag or gall and not give you a fully torqued assembly.
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BTW, what grease did you guys use at your dealership?

Torques are specific to the thread condition. Standard bolt/nut torques are for dry threads. There are some cases where the torque are spec'd for oil or other certain lubes. (ARP is a case in point.)

The real objective of bolt tightening is to reach a certain clamp load. Torque is an indirect method to reach a certain clamp load. There is a set relationship between torque and clamp load, and that relationship changes pretty drastically dry versus oiled versus plated, etc.; a certain torque with oiled threads will give somewhere in the range of 140% or higher clamp load (bolt tension) versus the same torque with dry threads.

A 3/8"-24 UNF grade 8 bolt is rated for a max torque of around 48-49 ft- lbs DRY. That torque level dry reaches the proof load and beyond that you enter the yield zone. If you oil those same threads, then put 45 ft lbs torque on it, then the clamp load will be around 45% higher, or the equivalent of 65 ft lbs of dry torque. That puts the bolt well into the yield zone...not good. It's not surprising that such bolts have failed when reused but IMHO it is not so much the re-use but the overtorquing of oily threads.

I don't know who put out that word at your dealership to grease the threads, but that is bad juju for rod bolts of this size and at this torque level. If you are greasing the threads on your SBM bolts, then IMHO it is time to worry and redo them. The rod bolts' designed clamp load is high and close to the yield zone, and so it does not take a lot of extra loading to push them past their elastic limits. If the SBM rods bolts were spec'd for oiled torquing, then the ft-lbs would be around 32 to get to the same clamp load. There ARE some specs set for oiled threads in certain applications; it is all up to the process, the clamp loads, and who specs the methods.

This all hangs with KK's info above: the factory bolts came in with specific coatings that gave a consistent and predictable relationship between torque and clamp load (bolt tension).

FWIW I have been pretty good at cleaning threads on head, main, and rod bolts forever, so I suspect that has helped me to not have failures when reusing bolts/nuts. I often use brake-kleen or paint prep on them to get them clean and dry, including the holes in the block for main and head bolts. (Dry threads are also important for Locktite to work properly on the rod nuts/bolts.) I also make sure that the faces where nut faces or bolt head ride on the caps are smooth and clean and free from burrs.
 
nm9stheham said:
This all hangs with KK's info above: the factory bolts came in with specific coatings that gave a consistent and predictable relationship between torque and clamp load (bolt tension).
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Yes, the process works like this:

the engineer schedules a torque test with fastener engineering... They get all parts and fasteners involved sent from the supplier or assembly plant that are off production tooling and processing... The engineer and fastener engineer meet one day and assemble the parts and twist the nuts and bolts until they break... (It's fun to break stuff - and get paid for it)... Lather, rinse, and repeat many times to get a good sample size to establish repeatability (capability)... Then the fastener engineer reviews the torque curves that were recorded during the testing and recommends the torque spec for that joint... That becomes the spec that the assembly plant will use and be held accountable to maintain...

There are also cases where they will also develop a spec for service to be published in the service manuals, realizing that most shops just use some form of torque wrench and not have special custom torque monitoring equipment like the factory uses...
 
nm9stheham said:
BTW, what grease did you guys use at your dealership?
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I wish I could remember, but that was 25 years ago. I do remember we only used it for torquing engine parts though. Was a Chrysler dealer as a matter of fact.

Well, I guess I'll torque them up dry!

Thanks,

CE
 
gregsdart said:
I measure the journal for the bearing I want to check tolerance on, lock the mike to hold the reading, zero my Dial bore gauge to the mike, then check the bearing. If you do it all carefully, it is pretty much fool proof, because you are doing a direct measurement of the difference, and you are not depending on the mike being dead accurate and perfectly calibrated.
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This is what I was trying to say, but work has my brain kinda fried lately. You pretty much can't go wrong with this method.
 
ValiantOne said:
I wish I could remember, but that was 25 years ago. I do remember we only used it for torquing engine parts though. Was a Chrysler dealer as a matter of fact.

Well, I guess I'll torque them up dry!

Thanks,

CE
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Nope. Torque specs are generally for clean, lightly oiled bolts. Use a tiny bit of 30 weight oil on threads and under the bolt head.
 
lilcuda said:
Nope. Torque specs are generally for clean, lightly oiled bolts. Use a tiny bit of 30 weight oil on threads and under the bolt head.
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Yeah, under the crank installation section of the 2000 factory service manual, step (8) is: Clean and oil all cap bolts, install caps and alternately tighten to 85 ft lbs.
 
ValiantOne said:
Yeah, under the crank installation section of the 2000 factory service manual, step (8) is: Clean and oil all cap bolts, install caps and alternately tighten to 85 ft lbs.
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OK, that sounds like it has a basis in actual engineering; I'd use the 2000 manual and accept that they spec'd the main bolts for oiled. My early LA manuals don't say.....

But I'd still advise the dry torque on the rod bolts; torque them oiled and you'll exceed the rated bolt tensions for grade 8 3/8"-24 UNF bolts. Tho' now I realize I am thinking of LA rod bolts, and have been assuming that Magnums have the same....
 
dial bore gauge,..that dang plasta gauge is old school,works ok when did right but in these modern times we've moved on!
 
nm9stheham said:
OK, that sounds like it has a basis in actual engineering; I'd use the 2000 manual and accept that they spec'd the main bolts for oiled. My early LA manuals don't say.....

But I'd still advise the dry torque on the rod bolts; torque them oiled and you'll exceed the rated bolt tensions for grade 8 3/8"-24 UNF bolts. Tho' now I realize I am thinking of LA rod bolts, and have been assuming that Magnums have the same....
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Yeah , 2000 fsm for rod bolts is exactly the same. Lightly oil and torque to......etc. glad I looked it up.

I was thinking about it today and the 273 engine in my 68 was put together (by me) with oiled bolts. So far no probs. Time will tell cause im not taking it back apart!
 
Well did the main clearances today they pretty much run from .0015 to .0025 clearance.

Almost all of them are out of round by .001 to .0015 as well. And all in the same direction/location
 
ValiantOne said:
Yeah , 2000 fsm for rod bolts is exactly the same. Lightly oil and torque to......etc. glad I looked it up.

I was thinking about it today and the 273 engine in my 68 was put together (by me) with oiled bolts. So far no probs. Time will tell cause im not taking it back apart!
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Someday the mysteries of why some re-used rod bolts fail and others do not will be revealed.....
 
Roger and thanks.

One still has to account for the increase in fastener tension when using any lubricant versus dry threads. The ARP fastener strength is well beyond that of normal rod bolts, and so can withstand the extra tension put on them. They and the lube are designed as a package to get to a certain tension. Using an ARP lube with fasteners designed to be torqued with dry or plain oiled threads will lead to over-tensioning the fasteners.

You and KK and others might find the following graph from ARP interesting; I sure do. It shows that the actual fastener tension goes up after several cycles of tensioning (presumably with the same nut and bolt and turning on the same surfaces). This could be one reason to say that going to the same torque repeatedly would over-tension a fastener. It does not show what happens with dry threads however, just with various lubes on the threads.

http://arp-bolts.com/i/t/PreloadGraph.gif
 
ValiantOne said:
Well did the main clearances today they pretty much run from .0015 to .0025 clearance.

Almost all of them are out of round by .001 to .0015 as well. And all in the same direction/location
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Out of round by .001 to .0015? I'd line hone it.
 
If a person has a bolt stretch gauge, tests could be performed on stock bolts to see just what will happen at what torque and lube. My idea is locate some factory virgin (once used) bolts, measure them, then remesure at 5 ft lb torque intervals till the bolt reforms at least .001 longer. I would measure using ARP assembly lube, to establish a consistent method. Then pick a percentage ( 75%?)of stretch or torque just shy of the failure point where the bolt failed to return to initial length. How does that sound? There have to be a few old used rods lying around to try this on.
This would also give you a stretch amount for that bolt, and a torque value that would be safe.
 
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dirty white boy said:
hole lot easyer to just use arp and there lube, im sure thay have tested this 9 ways from sunday already!
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This would be for factory rod bolts, since there is some disagreement on methods and torque amount. If I were unsure and had spare Stock bolts, I would do it just to learn, and then not have to worry about being too close to yield point.
 
I have 2 full rod sets laying about, one lighter, one heavier. No problem to use the bolts up. But, on the heavy ones at least, I have no idea how many times they have been torqued so those would be questionable. The small ones, probably were never torqued except at the factory. Now I just need TIME!
 
nm9stheham said:
I have 2 full rod sets laying about, one lighter, one heavier. No problem to use the bolts up. But, on the heavy ones at least, I have no idea how many times they have been torqued so those would be questionable. The small ones, probably were never torqued except at the factory. Now I just need TIME!
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How many times to you think they were torqued at the factory???
 
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