engine cross member question

[bb400ho]

hello new guy here.what a great site this is. i am hoping for a little help. is it possible to have the engine cross member in backwards? i bought an abandoned project with the frame already finished. after looking at pics on here im thinking it is possible that it is in backwards. does anyone have a pic of the bare frame so i can see the cross member? it is a 68 gmc 2 wd short bed
thanks bryan

[Jeff's72C10*]

Post a pic, sure someone will chime in as to if it's correct or not

[zicc1835]

pictures...of mine I think it would be real hard to get this backwards....but anything is possible show us a picture

[mike16]

what was the question again......? my mind drew a blank when I saw Zicc's framework.That is NNNNIIICCCEEE!

[zicc1835]

Originally Posted by mike16

what was the question again......? my mind drew a blank when I saw Zicc's framework.That is NNNNIIICCCEEE!

... ah shucks... thanks for saying

[Knight72]

Originally Posted by zicc1835

pictures...of mine I think it would be real hard to get this backwards....but anything is possible show us a picture

Did you knock out all the rivets for the frame cross supports? How are you putting them back in? Bolts and nuts or replacement rivets?

[zicc1835]

Originally Posted by Knight72

Did you knock out all the rivets for the frame cross supports? How are you putting them back in? Bolts and nuts or replacement rivets?

check out post #100 in my Doc & Kim build 7/16 Pan Head alan keyed stainless little pricey but i like them ...

[Steeveedee]

I'm curious about people's experience with the lifetime of bolts used in place of rivets. Rivets place thousands of pounds of clamping force, and are smooth (and fit quite closely in the holes, as well). Bolts are put in with hundreds of pounds of clamping force, and usually are installed in holes that are oversize. One might end up with the frame racking to some degree because of the hole slop, at a minimum.

[kwmech]

X-member correct orientation for oil pan clearance

[zicc1835]

Originally Posted by Steeveedee

I'm curious about people's experience with the lifetime of bolts used in place of rivets. Rivets place thousands of pounds of clamping force, and are smooth (and fit quite closely in the holes, as well). Bolts are put in with hundreds of pounds of clamping force, and usually are installed in holes that are oversize. One might end up with the frame racking to some degree because of the hole slop, at a minimum.

I thought about that ...7/16 is pretty tight and in some cases i had to hone a bit... I also replaced all grade 5 with grade 8 ....I will be driving this truck and report back in a few years if I see any slopGod Willing

[SeanB242]

Originally Posted by zicc1835

check out post #100 in my Doc & Kim build 7/16 Pan Head alan keyed stainless little pricey but i like them ...

What length? Or are they all different?

[bb400ho]

wow thanks for the help. i will try to post a couple of pics. it looks like my cross member is in right but the engine mounts are not. my engine perches are hanging off the cab side of the cross member.from the pics it looks like they should be hanging off the front side. i have a 5.3 from an 02 silverado and a 200r4 in it. with the engine slid all the way forward it is tight to the cab
(dirty dingo mounts).

[bb400ho]

here is an attempt at pics you can see the mount is hanging over the cab side of the cross member. is this backwards?
thanks bryan

[kwmech]

Correct for a small block mount. The factory ran the brake line across the rear of the x-member though..........if it that matters to you

[bb400ho]

Originally Posted by kwmech

Correct for a small block mount. The factory ran the brake line across the rear of the x-member though..........if it that matters to you

so the mounts are in the proper location? is it possible to move them to the front of the cross member? would i have to drill the lower holes? i think i bought brake lines for a 70 with disc brakes. i thought it should go along the back but this is the on way it would fit.

[zicc1835]

Originally Posted by SeanB242

What length? Or are they all different?

If my memory is right mostly 1’’ few 3/4 some 1 1/4 on the pan hard c member and nylock nuts and flats

[Steeveedee]

Originally Posted by zicc1835

I thought about that ...7/16 is pretty tight and in some cases i had to hone a bit... I also replaced all grade 5 with grade 8 ....I will be driving this truck and report back in a few years if I see any slopGod Willing

Also make sure that there are no threads on the bolt where it goes through the frame. Any movement will end up hogging the holes.

[bb400ho]

Originally Posted by zicc1835

pictures...of mine I think it would be real hard to get this backwards....but anything is possible show us a picture

wow that is very nice. is yous a v8? my crossmember is in the same as your but my motor mount perches hang over the back edge instead of the front edge like yours
thanks bryan

[Rufas]

zicc1835 Nice work on the frame!!!

[MQUnlimited]

Originally Posted by Steeveedee

I'm curious about people's experience with the lifetime of bolts used in place of rivets. Rivets place thousands of pounds of clamping force, and are smooth (and fit quite closely in the holes, as well). Bolts are put in with hundreds of pounds of clamping force, and usually are installed in holes that are oversize. One might end up with the frame racking to some degree because of the hole slop, at a minimum.

Would be true, but grade 8 bolts are strong enough so long the proper shank length is used. Meaning the section of the bolt with no threads is inserted the full length of the frame and nylock nuts are used with washers and torqued to spec. One should always periodically inspect their hardware security though and rivets do fatigue over time.

This is a good rule of thumb.

T = K x D x P

• T
Target tighten torque (the result of this formula is in inch pounds dividing by 12 yields foot pounds
• K
Coefficient of friction (nut factor), always an estimation in this formula
• D
Bolts nominal diameter in inches
• P
Bolt's desired tensile load in pounds (generally 75% of yield strength)

[kwmech]

If you want a little more strength, use grade 8 fine thread hardware and stay away from the grade 5 ny-locks and lockwashers. Use a crimp nut and torque them down to the rated spec. I think (off the top of my head) that a Gr8 7/16-20 torques to 70lbs. I did a conversion from 2wd to 4wd about 25 years ago on a 71 with a front x-member for the spring hangars. I bolted the member to front of the frame rails and did that very thing. Never had to touch the bolts again. They never came loose or moved. Sold the truck to somebody in Washington state.

[zicc1835]

Good info hear for all thank you

[MikeandCheryl]

It's good to discuss bolt strength for the replacement of factory rivets, but remember that Grade 8 bolts while stronger in tension, are definitely more brittle in shear. The Grade 5 smooth shank portion of a longer, slightly oversized 7/16"UNC or UNF bolt might be a better choice. torqued to spec, they will be stronger than 3/8" bolts, and may better handle the side loads a shifting, driving frame may impose on them.
Since my truck will become a Sunday driver, i don't think bolt choice is an issue, and certainly crawling under from time to time to put a wrench on anything you can reach would be an add.