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Frame rivets to bolts

Rex2nr

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What size bolts do you guys use when replacing riveted frame parts? I need to replace the crossmember above the fuel tank on my 99. I know grade 8, assuming somewhere between 3/8 and 1/2", 1-1/2" long? How tight should they be? 100ft/lb or 3/4" drive impact tight?
 


ratdude747

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What size bolts do you guys use when replacing riveted frame parts? I need to replace the crossmember above the fuel tank on my 99. I know grade 8, assuming somewhere between 3/8 and 1/2", 1-1/2" long? How tight should they be? 100ft/lb or 3/4" drive impact tight?
Size depends on the rivet. I've used a few different sizes... 5/16" IIRC was one of them.

Torque? I use the German spec of Gutentight (good 'n tight). They're grade 8 so unless you do something really dumb you'll be fine.
 

Rex2nr

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I was just wondering because the rivets allowed some flex, so I was wondering if they should be loose enough to allow the rails/crossmember to flex but obviously still tight.
 

ratdude747

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I was just wondering because the rivets allowed some flex, so I was wondering if they should be loose enough to allow the rails/crossmember to flex but obviously still tight.
Biggest size that fits. The rivets are form fitting so you you will want to match the size.
 

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I ground off the rivets on my spring supports and there was zero clearance on them...so I would find a bolt that is exactly the size of the hole...movement in support to me would be a bad thing...but, then again, I'm not a structural engineer...so I know zero about it other than I usually replace what I remove with something the same size because that's the way it was designed.
 

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On my current project I am finding that on 90% of the holes 7/16 bolts are not quite big enough, 1/2" don't quite fit. I have been punching the holes out to 1/2" because I am removing minimal material to make them fit, some of the holes are actually 1/2, and I only wanted to deal with buying one size of bolt.

Grade 5 is acceptable for frame repairs, but I am also using grade 8, with stover lock nuts. 100 ft/lb should be good enough, but I am going to 1/2" impact tight. I'm pretty sure a 3/4" impact will break the bolts.
 

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On my current project I am finding that on 90% of the holes 7/16 bolts are not quite big enough, 1/2" don't quite fit. I have been punching the holes out to 1/2" because I am removing minimal material to make them fit, some of the holes are actually 1/2, and I only wanted to deal with buying one size of bolt.

Grade 5 is acceptable for frame repairs, but I am also using grade 8, with stover lock nuts. 100 ft/lb should be good enough, but I am going to 1/2" impact tight. I'm pretty sure a 3/4" impact will break the bolts.
good info here. i believe they are probably 12mm from the factory. drill them out to 1/2" so a 1/2" bolt fits snug. they need to be tight. 100 ft/lb should be good for a 1/2" bolt.
 

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My 02.....

Torque? I use the German spec of Gutentight (good 'n tight). They're grade 8 so unless you do something really dumb you'll be fine.
==============
Use this QUITE FREQUENTLY myself on all my projects!


Grade 5 is acceptable for frame repairs, but I am also using grade 8, with stover lock nuts. 100 ft/lb should be good enough, but I am going to 1/2" impact tight. I'm pretty sure a 3/4" impact will break the bolts.
=============
I also use 1/2" impact & Grade 8 hardware .........if your worried bout them backing out, spot weld the bolt heads, then if the nuts loosen there is no way for it to come completely apart.

Have also heard of guys using carriage bolts & spot welded them to frame.
 

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good info here. i believe they are probably 12mm from the factory. drill them out to 1/2" so a 1/2" bolt fits snug. they need to be tight. 100 ft/lb should be good for a 1/2" bolt.
I agree, they were probably 12mm originally. 7/16" is 11mm, and as I said 1/2" didn't quite fit. As I said, the amount of material I was removing was minimal.

I also use 1/2" impact & Grade 8 hardware .........if your worried bout them backing out, spot weld the bolt heads, then if the nuts loosen there is no way for it to come completely apart.

Have also heard of guys using carriage bolts & spot welded them to frame.[/B]
That's a good idea. Here in PA steel lock nuts, not nylon and no lock washers, are required to be used when replacing frame rivets. I'd but using lock nuts anyway. I am probably going to be putting red thread locker on too.

I was actually using the drill bit one size under 1/2, 30/64 or 15/32, not sure, can't read the side anymore, because my 1/2" was MIA. It was enough that the bolts fit, but they were cutting threads in the hole, so I would make the bolts tight in the holes (and since the threads got cut through both pieces at the same time they match) and then run the nut down over the other side.
 

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I drill to 1/2" using a step drill bit because the step bit gives a round hole where a normal bit can give a triangular hole, and is much easier to drill with into a hole already close to the size you want. I use a Grade 8 bolt that has a shoulder that will touch throughout the hole. I then use hardened [grade 8] flat washers under the head and under the nut to build out enough that the steel lock nuts will not hit the shoulder [un-threaded portion of the shank]. I do this because you lose strength in shear where there are threads.

I've also used 7/16" bolts but they are harder to come by.
 

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The rivets expand to fill the holes as they are heated to the plastic range of the metal for installation...

I find that generally 7/16-20 fine thread bolts work well in most locations, but in those situations where I choose to use 1/2" bolts I do nor Drill or ream the holes...

I run a 1/2"-20 "fine thread" tap through the holes then run the bolt in snugly
then hold it in place while I tighten a self-locking nut onto the other side

I have replaced most of the rivets on my truck with bolts, and plan eventually to replace them all...

AD
 

alwaysFlOoReD

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I run a 1/2"-20 "fine thread" tap through the holes then run the bolt in snugly
then hold it in place while I tighten a self-locking nut onto the other side

AD
This is the only time that I have to dis-agree with AllenD. If the two pieces are not in contact with each other when tapping, there will be a vast amount of stress on the bolt and with no friction between the two pieces the hole could egg out over time. If you can clamp the two pieces together while tapping then it should be OK. Drilling and using the shank shoulder to fill the hole is easier and as strong, if not stronger IMO.
 

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General thread torque ratings and allowable loads for various sizes. 7/16-14 Gr 5 torqued to 50 ft-lbs and 7/16-20 torqued to 70 ft-lbs. Load on those with safety factor is 1580 lbs and 2255 lbs. 1/2-13 Gr 5 torqued to 75 ft-lbs and 1/2-20 Gr 8 torqued to 100 ft-lbs. Loads on those is 2060 lbs and 2950 lbs. Torque values for dry threads. Structural steel never uses lock nuts.
Dave - 45 years as mechanical designer
 

alwaysFlOoReD

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General thread torque ratings and allowable loads for various sizes. 7/16-14 Gr 5 torqued to 50 ft-lbs and 7/16-20 torqued to 70 ft-lbs. Load on those with safety factor is 1580 lbs and 2255 lbs. 1/2-13 Gr 5 torqued to 75 ft-lbs and 1/2-20 Gr 8 torqued to 100 ft-lbs. Loads on those is 2060 lbs and 2950 lbs. Torque values for dry threads. Structural steel never uses lock nuts.
Dave - 45 years as mechanical designer
Thanks for the input.

Structural steel never uses lock nuts.
Does structural steel have the same vibrations and torque put through the main beams? I've seen pics and I'm sure that anyone that drives over potholes has twisted the frame in their truck. I believe that's why everyone uses lock nuts. Do lock washers provide the same clamping force as lock nuts? Maybe better to use lock washers because of spring pressure? Or are you suggesting no lock system of any sort? Inquiring minds need to know....
TIA.
 

Mark_88

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General thread torque ratings and allowable loads for various sizes. 7/16-14 Gr 5 torqued to 50 ft-lbs and 7/16-20 torqued to 70 ft-lbs. Load on those with safety factor is 1580 lbs and 2255 lbs. 1/2-13 Gr 5 torqued to 75 ft-lbs and 1/2-20 Gr 8 torqued to 100 ft-lbs. Loads on those is 2060 lbs and 2950 lbs. Torque values for dry threads. Structural steel never uses lock nuts.
Dave - 45 years as mechanical designer
Good info...thanks...

What about lock washers? I've often used those instead of lock nuts and have found many on automotive applications...just can't remember where or when.
 

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