Hello,
I'm looking for clarification on correct functional exhaust manifold bolts.
I have a late build 68 BB. I'm retaining the orig cast exhaust manifolds.
It has AC and PS.
I have an orig. exhaust manifold for replacement for the passenger side as current one has two cracks at the opposite furthest mounting points.
I looked on various vendor sites and there is so much differing info my eyes went crossed.
Some offered flanged bolt sets, some said only use flanged on outer four mounting points. Others said use flanged instead of French locks.
Still some offered stainless steel washer required under the four outer most mounting bolts so they don't bottom out and fail to provide a tight sealing point.
Some kits have no flanged bolts and claim authentic head stamping.
I'm probably never going to have the car judged, but my goal is to accurately replace what I take off even if casting dates are not correct.
I know I could just go out and look at what's on there now but I think the outer mounting points broke because someone reinstalled improperly over the past years and it cracked.
I would like to do it right and figured start new with mounting hardware as I am sure they will be rough if not broken when I go to remove.
Thanks for the help in advance.
Marshal

 

What do you have on the left side? Any reason to believe the lefts have been replaced?

 

1967 was the last year the big block used the French locks. Starting in 1968, they went to a special prevailing-torque self-locking exhaust manifold bolt (also called shouldered torque bolts) for the front two bolts and rear two bolts on each side. (A stud was used on the front number one exhaust port if you have N40 power steering and two studs were used on the front of number two and number 4 exhaust ports if you have C60 A/C). None of the bolts will have washers, but some cars have been observed having bolts with captured washers in the non-shoulder bolt positions.

Ed

 

Mike,
Left side same bolts with a split lock washer underneath.
Unsure if all were changed out when heads were reinstalled several owners ago?
Restoman,
Thanks for explaining. Washers are not needed but special shoulder bolt is.
I saw in a Chevy BB vendor site the 16 shouldered flanged bolts.
The corvette vendors just have the shoulder bolts.
Do I buy the flanged set off the Chevy site and get the studs from our corvette vendors as needed. I'm going to have all new hardware in hand for the passenger side at disassembly because no telling what condition the bolts will be in when I get them out.
Thank you again,
Marshal

 

Marshal, the special prevailing-torque self-locking exhaust manifold bolts (P/N 3909821) are still available from your local GM dealer! You can also get them from AMK (PAGE 26 in their online catalog). The other bolts (P/N 3736035) should be available from any of the vendors.

The C60 studs (P/N 3928906) aren't available from GM any longer, but AMK has them on PAGE 134.

The N40 stud (P/N 3928905) isn't available from GM or AMK, so that one you'll have to get from one of the vendors.

I don't know if any of the vendors have the "correct" stuff in kit form, but you might try Paragon or Doc Rebuild. Or give Ernie (WILLCOX CORVETTE) a call and see what he says.

Ed

 

Restoman.
I see why they call you that!
Thanks, thats about as close as it comes.
I never heard of AMK but sure glad you did.
Love this forum, Yeah!!
Marshal

 

Ed,
AMK sells the special bolts in batches of 8 for 10 bucks.
Do I just use these in every hole minus the holes for the studs for AC and PS?
I could purchase two batches(16) of special bolts and two single c-60 studs.
I'm not disturbing the drivers side so I have time to hunt down the PS brkt stud should I need it.
Thanks and sorry for so many questions
Marshal

 

From the factory, the torque bolts were used in the #1, #2, #7 and #8 exhaust ports, but I guess you could use them in all the holes if you wanted. The only thing different between these bolts and regular bolts is that they are made so that the threads distort a bit when you tighten them up (which is why you're not supposed to re-use them).

The 3736035 bolts used in all the other holes were originally 3/8-16 x 1-5/16" long. AMK sells 3 styles that are 1-1/4" long, so just a hair shorter than originals. These are on the top of PAGE 27 (B-10082, B-10083 and B-10084). You might want to check those out.

Ed

 

Ed,
Thank you again!
I'll use the other bolts in between the special ones.
I guess they had a tendancy to lossen up on the extreme ends?
Maybe that's why my P/S exhaust manifold is cracked on both oppopsite ends only
I hope this discussion will be beneficial to others as well
Marshal