Questions about exhaust manifold bolts and oil dipstick tube

[71CHEVYSHORTBED402]

71 C-10 402


Based on truck history, I'd have guessed these or most would be the original exhaust manifold bolts. Perhaps they are, but what a hodge podge. Some grade 5 & some grade 8. One is grade 2, which I bet we added when the A/C was pulled long ago.

Are the exhaust manifold bolts "supposed" to be grade 5 or 8? I'd guess 5.............................. On a side, Classic industry sells "original reproduction flange head bolts" for the exhaust. Not that I have much experience, but neither of my trucks have flange bolts. They're just a hex head and use lock washers.


The dip stick tube I pulled didn't have an O-ring, are they supposed to? From what I see there wasn't a leak.

Thank you.

[Steeveedee]

In the second row, second bolt in is one I recognize as an exhaust manifold bolt for one of our trucks. And no, you don't need grade 8 bolts for manifolds. Some people get all starry eyed when they see the Grade 8 designation, and want to put them everywhere, but it's pretty much a waste of money. If Grade 5 was good enough for GM, it's good enough for me. I just went and looked. I have a hodge-podge, just like yours.

The dipstick tube is a press fit, and has no O-ring or gasket.

[71CHEVYSHORTBED402]

Originally Posted by Steeveedee

In the second row, second bolt in is one I recognize as an exhaust manifold bolt for one of our trucks. And no, you don't need grade 8 bolts for manifolds. Some people get all starry eyed when they see the Grade 8 designation, and want to put them everywhere, but it's pretty much a waste of money. If Grade 5 was good enough for GM, it's good enough for me. I just went and looked. I have a hodge-podge, just like yours.

The dipstick tube is a press fit, and has no O-ring or gasket.

Interesting. That's the bolt I'd have thought was the grade 2 replacement. Doesn't have the common grade 5 or 8 indicator, which may not mean anything. Of the 15 bolts used, that and one grade 8 are pitted.

Ah, another hodge podge.....Go figure. Well, if we assume they're original, GM didn't care, and of course different vendors. Mine are two lengths as well, 1.1/4" & 1.3/16". Yours hex head and lock washers also?

Somehow I thought the bolts would be tight, but they came off easily. I agree, grade 8 is unnecessary, if not too much. It doesn't take a lot to break these manifolds. Perhaps an argument can be made grade 8 is too tough.

From what I've seen, and you eluded to it, there weren't many grade 8 fasteners on these trucks from factory. I haven't pulled the suspension yet, but I only recall seeing grade 8 cross member bolts. The 1/4 stainless screws were grade 8 as well.

After a glance of my heads, those bolts are cool. They're just stamped with a "+". Couldn't tell you what grade, but they're good enough for me too.


Thanks for the information.

Originally Posted by DeadheadNM

Love the makers marks on the bolts - it's been fun seeing all the different marks on the hardware I've replated.

My favorite is stamped with an anchor. I think I've seen a few, but one for sure, which mounted the brake booster arm bracket to the firewall.

Couple odd ducks are the bolts to mount the transmission vacuum module & brake distributor hose assembly to the a axle. Near as I can tell the symbol reads "MB". Two different sizes of course. They're a hex bolt with a slight recess. We better stop now , sounding like Mopar nerds

Speak of Mopar, I spent some time at Hot August nights. Once again I was most impressed by Mopar, for an original theme. While I haven't spent much time there over the last few years, I've yet to see one of our trucks that's high measure, less one that was modified. Disappointing. The coolest car was an old Plymouth or this VW. https://www.youtube.com/watch?v=QS8doRBygs8

[DeadheadNM]

Love the makers marks on the bolts - it's been fun seeing all the different marks on the hardware I've replated.

[DeadheadNM]

I like the anchor mark too. It's often on the 12 pt bolts for the hood latch. I'd like to start a thread just to show the varied makers marks. One mark that's cool is a leaning "F"

[randy500]

None of those bolts are correct. Big block has a washer head and rolled threads. The one on the right is correct for our years. One on the left is big block for later years I think.

[71CHEVYSHORTBED402]

Originally Posted by randy500

None of those bolts are correct. Big block has a washer head and rolled threads. The one on the right is correct for our years. One on the left is big block for later years I think.

Grade 8 you're saying. It's similar to many in the OP, only a flange head. What do you mean by "rolled threads"?

[randy500]

That marking in general is grade 8 but gm marks their bolts with many types of marks. Here is a pic of the threads, ours on top

[anew4961]

the original bolts were grade 8 which you can get at tractor supply cheap they also had washers which were thick and locks all of you can get at classic parts America . hope this helps

[71CHEVYSHORTBED402]

Originally Posted by anew4961

the original bolts were grade 8 which you can get at tractor supply cheap they also had washers which were thick and locks all of you can get at classic parts America . hope this helps

Are you saying they're hex head or flange head, they use washers and lock washers?


Just for clarification, the first image below shows the common hex head bolt. The second shows a flange head bolt. Both claim to be BBC manifold bolts for our BBC trucks.

[randy500]

I posted a picture of the exact bolts along with different year big block bolts, i have had dozens of big block trucks and vettes they all use bolts like I posted....if anybody says different then they are just plain wrong!

[71CHEVYSHORTBED402]

Originally Posted by randy500

I posted a picture of the exact bolts along with different year big block bolts, i have had dozens of big block trucks and vettes they all use bolts like I posted....if anybody says different then they are just plain wrong!

From what you've seen, do they use a washer of any kind or is it just a bolt?

[randy500]

No washers, just he shouldered bolt

[Steeveedee]

Interesting. My FIL had this rebuilt once about 25 years ago. That, and what appears to be a replacement exhaust manifold on the passenger's side, would explain the differences in the bolts. My truck is a Federal Emissions truck (no AIR pump), but has an AIR pump style exhaust manifold on the passenger's side.

[71CHEVYSHORTBED402]

Originally Posted by randy500

No washers, just he shouldered bolt

That makes sense for a flange bolt, just thought to double check........Thanks.

I found what I believe are your correct bolts. Wasn't going with grade 8, which I assume these are, but "if it's good enough for GM it's good enough for me"..............They're NOS, $24.50 Ebay. There's more if anyone is interested.

Personally, I feel there's a chance they were flange head bolts or a hex with lock washer, like both my Chevy's with the original manifolds. Course, the mess of bolts per the OP doesn't validate anything. Either way, I prefer the looks of a flange bolt, and they're uniform with the rest of the bolts on the block. On a side, the guy who sells the NOS exhaust bolts has the correct intake bolts as well.

[kwmech]

I am in the process of installing new manifolds on my truck using Gr8 flange bolts. They look a lot nicer than the hodge podge that I also found originally

[randy500]

Those bolts on ebay seem to be a good buy and have the same head marking as the one I posted. I wonder if they have rolled threads like the one I posted, they would in gm nos.

[71CHEVYSHORTBED402]

Originally Posted by randy500

Those bolts on ebay seem to be a good buy and have the same head marking as the one I posted. I wonder if they have rolled threads like the one I posted, they would in gm nos.

I see what you mean by rolled threads now. And yeah, there are worst things than $1.50 for an original bolt. I'll update when I receive the bolts.
http://www.portlandbolt.com/technica...threads-bolts/

[71CHEVYSHORTBED402]

OT: Here are the intake manifold bolts the guy is selling for the same price. They're like my intake bolts, only my "M" stamp is larger & not surrounded by a pentagon.

[71CHEVYSHORTBED402]

Received the Exhaust Manifold bolts. At this point I can't distinguish rolled from cut threads.

[71CHEVYSHORTBED402]

Originally Posted by 71CHEVYSHORTBED402

Received the Exhaust Manifold bolts. At this point I can't distinguish rolled from cut threads.

Oh, ha, now I see the difference. Those bolts are rolled. https://www.fastenal.com/en/78/screw-thread-design