Stock Exhaust System Diameters for 1974 L18 620

[Cardinal Grammeter]

FINALLY successfully removed the brass nuts and put back with lots of Saf-T-Eze Nickel Anti-Seize (about 1/2 the price of Never Seez and Permatex and clearly a different formulation.)

 

I bot the 1800w Bolt Buster and was shocked that induction heated the brass nuts up just like a torch.  (Those induction cooktops say you have to have magnetic steel to use them.   So I don't understand that.)

 

I swear these nuts may have been removed for the first time.  They were definitely OE and VERY tall with 2x the thread engagement of a metric nut.  AND the tiny, thin lock washers under the nuts were there too.  Those would have been too easy to not notice them and lose them.

 

The lowest nut was a bitch maneuvering the BB - I had to use the one "wind your own" coil lead that was in the kit.  No other way to do it with the std coil.  Clearly the extended coil kit is a necessity.  I believe they are selling them for $60 from China - 2x here.

 

BB is a monster, I swear I could have melted them off with it.  Got to a bright orange - really getting close to brass meting, but not really, I could look at the "orange" and it is near impossible to braze w/o goggles.

 

I have everything including 304 clamps.

 

WELDS THAT DON'T RUST:

 

This separates the men from the boys.  I also learned stainless forms a Cr06 (hexavalent chrome oxide) on the surface which is what keeps it from rusting.  If the weld is done without contamination (very clean), the Cr06 layer "spreads" over the weld taking 24-48 hours to do so.  If it fails to cover the weld, the weld rusts.

 

Evidently "back purging" is related to non-rusting welds.  One welder used a mixture of Solar Flux and HEET, made a paste, coated the back sides and waited for it to dry being sure none was on the exterior surface being welded.

 

When it comes to corrosion resistant welds, the information is sketchy at best - people are more concerned about cracking.

 

I'd hate to ask a shop if they know how to weld stainless so the welds don't rust.  However, I loosened the exhaust pipe manifold stud nuts so they owe me!

 

Cr06 is nasty stuff and unfortunately is in the welding fumes, so ventilation is absolutely imperative welding stainless.

[Cardinal Grammeter]

LOL, this just never stops.....   ONE FINAL ISSUE:  The Stainless Flange:  Thicker and Larger Holes

 

THICKER:  3/8 vs 1/4

 

The new 304 flange is a fat 3/8"  however, the studs are just long enough to engage the nuts with the thin, OEM flange - in fact, the ends of the studs are machined back so that while a very tall nut, the thread engagement is less.  

 

If I lose 1/8" of thread engagement, the resulting engagement will be about 1/2 of what it was.

 

Datsun made a special effort that stud threads did NOT extend beyond the nuts.  And so i was able to get them off w/o having to deal with rusted end threads.

 

HOLES:  10mm vs 8mm

 

The SS flange has 10mm holes while the studs are M8.  The thin OE lock washers have an OD of about 10mm - they won't work with the 10mm holes.  Some kind of washer will be required further decreasing thread engagement.

 

SOLUTIONS:

 

1)  Spot face stud holes 1/8" deep (I actually have the correct s/f drill)

2)  Get flange milled down to 1/4"  (thinner flange easier weld - reduced thick to thin welding)

3)  Use the OE steel flange

4)  Replace with longer studs  (I won't do that - I assume the shop can replace the studs if the header pipe is off and they have good access to the OE studs.  I would let them borrow my Bolt Buster if they don't have one.

 

My thoughts:

 

BEST CHOICE:  is  2) since welding .065 tube to a thicker 3/8" flange has Thick to Thin issues.  However, I'm not sure if a thin flange might risk cracking welds when bolted down.

 

EASIEST CHOICE:  Spot Facing

[datzenmike]

Change the studs to longer stainless and be done with it.

[Cardinal Grammeter]

I don't want to spend at least $100 at the garage to change studs to stainless when I have good studs to begin with.

 

I can spot face myself for free and most likely get flange milled for free too.  Hard to complain about the price.  (I could even mill on my 9" SB lathe for which I have the milling tooling but that would take me a day to do - so that's not happening.)

 

....today, I feel like loafing.  620 still on stands, should spray down with CRC Marine Corrosion Protection and also swap out the rear drums (long story.)  

 

Edited October 6, 2021 by Cardinal Grammeter

[datzenmike]

You seem capable. You should be able to swap the studs your self. I wouldn't trust a garage to check tire pressure.

[Cardinal Grammeter]

On 10/6/2021 at 3:21 PM, datzenmike said:

You seem capable. You should be able to swap the studs your self. I wouldn't trust a garage to check tire pressure.

 

I could, I can, and I don't.  But I'm 69 and lazy af nowadays.

 

So I did counter bores:  Now you're gonna totally laugh at me:  What type of washers under the brass nuts?  Since the new flange has a 10mm hole & the stud is 8mm, I figure a washer is in order.  (The OE washer appears to have been a flat washer with a very small OD so it could have been a lock washer that rusted flat - it's so rusted should not be used but it does account for 2mm of stack height.   ....checking parts manual... 08915-13810 -> 08915-1381A  (!)  Check it Out, a split ring lock washer as I suspected!   EZ PZ

All right then, those lock washers will fit perfectly in the counter bore.

 

TOTALLY DONE AND READY FOR SHOP TRIP NEXT WEDNESDAY.  (well almost, have to peel the clear shipping tape off the tubes which actually is a PITA - 10 min w/o heat gun = TOTAL WASTE OF TIME)

 

 

Edited October 8, 2021 by Cardinal Grammeter

[Stoffregen Motorsports]

Nice.

 

And I totally agree about paper stickers on parts. The blinds I installed in our downstairs bathroom ten years ago still have the stickers on them, because it's such a pain in the ass. Depending on the part or where it's installed, I don't even bother removing the stickers anymore.

[Cardinal Grammeter]

Actually there is a nifty plastic label tag specifically made to slip over pipe - and it's reusable.  But that wasn't the problem, to protect the ends, they wrapped a couple yards of 2" clear packing tape over the ends.  Impossible to peel off.  Will have to use heat gun and scrape off then solvent the adhesive residue.  Don't want to potentially add to weld contamination.

[Cardinal Grammeter]

It just doesn't stop....

 

Shop called and said they don't have enough pipe.  I measured everything and the 8' and 5' should have done it.

 

So I told them finish to the muffler and I'll pay and pick up - I'll order pipe and bring back or have buddy bend.

 

Just saw today the Barnhart 500,000# OTR payload Transport System leave Elliott Co., Jeannette, PA

 

[datzenmike]

Obviously they screwed up a bend. Dicks.

[Cardinal Grammeter]

That exhaust pipe while not having large angle bends, has a bunch of little ones. 

 

I don't know how they bend up a long pipe with a bunch of bends in it. 

 

If you start at one end, you get to a bend where the free end hits the car - so what do you do?  maybe it's not unlike a good bulldozer operator must have a "eye for grade" otherwise he can't do anything.  

 

maybe you start with the up-bend and then mark the bend centers down the straight pipe - and then incrementally bend each until pipe fits????   I'm just guessing!  I have no idea how they do it.

_____________

Buddy had some SS exhaust weld repairs done that went sideways, but they corrected everything and stuck to the quoted price.

 

At this point I DON'T CARE - as long as it's done today, I'll be happy.  My buddy can bend the tailpipe if I want.

 

FYI, I actually got DR. to sign off on a CO blood test I took after a 30 min trip each way - I was sure I was suffering from exposure driving truck all over the place.  CO in blood has a 4 hr half life so I timed the test for what should be an exposure high point.  Very curious to see results.

[datzenmike]

This the '74 you're driving? Maybe wait till the new exhaust is on.

 

Buy a home CO detector. That should be sensitive enough to tell you yea or nay

[Cardinal Grammeter]

SCOREEEEEEE

 

Truck is done, they had enough pipe made the exhaust pipe in 2 pieces w/slip joint in center.

 

Cost was $432 for the labor.

 

Parts was $134 tube, 35 flange, 32 clamps so about $200 for just over $600 for the job.

 

I had told them to do what they could to keep exhaust away from transmission which I have to upgrade to the 5-spd and they went with my thought of going between the frame and torsion bar rather than between the bar and trans.

 

Truck is NINJA SILENT!   Found myself driving 70 mph home cuz I couldn't hear the engine.  EXACTLY what I wanted.

 

Welds look decent with no obvious blue overheating.  (I doubt if they back purged or fluxed but I just don't care at this point.)

______________

 

Next project choices:

 

*) Install 5-spd  (BONUS:  MAKES MORE ROOM so High on the Leader Board)

*) Weld A-pillar and install new windshield rubber - mine is as hard as a rock on the outside and has split apart at corners due to shrinkage (inside is still flexible rubber.)

[Stoffregen Motorsports]

After all that, you have to show us a pic or two.

[Cardinal Grammeter]

POST MORTEM:  Wonder if this was the Original header pipe?

 

 

[Cardinal Grammeter]

33 minutes ago, Stoffregen Motorsports said:

After all that, you have to show us a pic or two.

 

Yeah, My Bad - should have taken pics when they put it on the lift to show me.

 

I'll edit this reply with pics - the y-pipe will be the hardest to show - it really is tight up in there with the frame, torsion bar, and engine.  (In fact, with this new routing, getting the Bolt Buster on the middle stud nut will be a BEE-ATCH.)

[datzenmike]

There were several. I had one that was a single one piece down pipe with the second one, with slight bend, looking like it was shoved into the side of the first and welded up. It was stock and it looked terrible.

 

Actually, unlikely to be stock. More likely to be from a '70s off the shelf pipe from a muffler shop. 

 

 

[Cardinal Grammeter]

Better maintain the "timeline"  here are some laying on grass half-ass pics.

 

Regarding the saddle clamps, I told them to "not tighten so much that they crush the pipes" so they decided to really go not tight at all while putting a couple spot welds on the pipe and sealant.  The one pic looks like one of those spot welds broke.

I like to do saddle clamps this way:  Tighten until I cannot bull twist the muffler and then another 1/2 turn on the nut.  

 

Then went under the carrier bearing cross member instead of above, I don't see any real down side on that since I'm not rock climbing (LOL).  - and it does make for a nice straight length which is always a bonus.

 

Any those jerk wads at other muffler shops saying "...stainless wrinkles when you bend it..." are brain dead - they don't understand why it bends and how diameter and wall thickness effect that.  In fact, I might take it back to the local guy who said it won't bend and show him.

 

Edited October 15, 2021 by Cardinal Grammeter

[Cardinal Grammeter]

On 10/13/2021 at 3:16 PM, datzenmike said:

Obviously they screwed up a bend. Dicks.

Actually, they were working on the Y and tried to expand the ends to fit the larger flange openings and the tubing split.  So they lost about 1' of pipe.  (I only supplied and 8' and 5' which should have been about 2' extra.  I think the straight routing decision was based on getting the job done with what was available - which I agree with.)

 

20 hours ago, datzenmike said:

There were several. I had one that was a single one piece down pipe with the second one, with slight bend, looking like it was shoved into the side of the first and welded up. It was stock and it looked terrible.

 

Actually, unlikely to be stock. More likely to be from a '70s off the shelf pipe from a muffler shop. 

 

 

Mike, you are absolutely correct 

 

It's amazing how bad my memory is getting.  I had found an original head pipe that I was considering buying and the Y was a stamped piece.  Here are pics.  (I wonder if the flared ends are what hold the flange on?  EDIT:  actually looking closely at the flange pic again, it looks like those flared ends appear to be short rings - you can see the sharp shadow at the aft edge - I have no idea how they manufactured this.)

 

EDIT 2:  Further thoughts on manufacturing and the "rings."  It would be that there are not in fact rings, but a sharp stamped bend in the Y-form.  The flange would slide over the tube ends and rest of the sharp 90* corner that looks like the "end" of the "rings" in the pic.  Then the ends of the tube would be flared to capture the flange.  When made, it would seal.  It would not leak after a while because it would begin to rust and the rust scale would make the interference fit even tighter.

Still, how would you stamp metal to get 2 tube ends?  Perhaps the tubes were covered with the stamped sheet that is so apparent in the pic of the entire pipe.  

 

Would be interesting to see a "autopsy" of one that rotted out.

 

 

 

 

Edited October 16, 2021 by Cardinal Grammeter

[Cardinal Grammeter]

LATEST UPDATE:

 

Did they use steel wire - the welds are magnetic.  (I'm assuming 308 or 309 wire welds are not magnetic.)

 

Now knowing this, one look at the bluish tint of the welds and they sure don't look like the base material color - friends turbo manifold fabbed SS welds are the same color as the tubing.

 

EDIT:  If they used steel wire, I need to be sure because if they did, then I need to talk to them about the job.  The welds are strongly magnetic, just like steel.

Edited November 19, 2021 by Cardinal Grammeter

[datzenmike]

SS isn't very magnetic because of the high nickle content. SS will also color when heated...

 

 

[Cardinal Grammeter]

Thanks for the video.

 

There is a lot of discussion of "why are my SS welds magnetic" all over the place.  

 

I'm working from memory so don't quote me.  Has to do with the iron that is in the SS rod.  308 and 309 rod welds can vary from non-mag to mag.  it has to do with the phase of the iron.  310 rod has iron that is fully austenitic which is the key to getting non-mag welds (some applications required SS welds to be non-mag.)

 

Also, another key to corrosion resistance is to not over heat the metal during welding.  You do not want to end up with that blue purple color.  What is supposed to happen is after the weld, there is enough chromium present that a layer of chromium oxide forms within hours - this is the corrosion protection of SS.

 

My opinion of the exhaust job was it was terrible.  Bird shit welds.  Huge welds.  And they didn't even route the pipe over the aft crossmember.  The welds do not look like stainless - they look like steel welds where there wasn't enough shielding gas.  Who knows maybe they used flux core which wouldn't be horrifically bad if they used the proper wire.

 

I hope to jack truck up and inspect within a week to see where all the leaking is coming from.  My theory is that they didn't put the lock washers under the brass nuts and the pipe got loose at the gasket.

[Stoffregen Motorsports]

Unless they TIG welded the joints, they undoubtedly used regular ER70S steel wire. You would have had to supply the stainless MIG wire as almost zero muffler shops are going to be familiar with it.

 

For what it's worth, 304 stainless is non magnetic while 409 stainless is magnetic. 304 is what most "performance aftermarket" tubing and bends are made from, 409 is what most OEMs use on new car exhausts.

 

If you didn't spec stainless wire, you're probably SOL. And overthinking it. It will still last years with crappy welds.

[Cardinal Grammeter]

On 11/21/2021 at 1:18 PM, Stoffregen Motorsports said:

Unless they TIG welded the joints, they undoubtedly used regular ER70S steel wire. You would have had to supply the stainless MIG wire as almost zero muffler shops are going to be familiar with it.

 

For what it's worth, 304 stainless is non magnetic while 409 stainless is magnetic. 304 is what most "performance aftermarket" tubing and bends are made from, 409 is what most OEMs use on new car exhausts.

 

If you didn't spec stainless wire, you're probably SOL. And overthinking it. It will still last years with crappy welds.

Well I specifically asked if they had the right wire for the 304 and the owner said yes.  I had a list of wire & gas combinations and should have put them in the work order.  I even have a friend in the business that knows the owner and thought if he said "yes" it would be the right wire.

 

I'm more concerned about cracking.

 

"And now for something completely different:"

 

If you ever had to buy one of these, it's time to re-think the hobby: