68 thru 72 BB Indented Flange Exhaust Manifold Bolts

[Mark D.]

In the past, I know several of you have had to endure the pain of some tyrannical Mechanical judge deducting points for lack of these 'shouldered' bolts at the L and R outer attaching points on your big block Corvette. They are fairly difficult to locate and I have been on the hunt for quite a while.

I stumbled across a set of aftermarket ones recently on Ebay and wanted to let folks know what I discovered. I purchased these and was pleased with the configuration including the head marking. They are painted black, however, most would expect them to be black phosphate, but, that can be remedied.

I have no affiliation with the seller, The Parts Place, Inc., but wanted to let the membership know, IMO, these are a viable alternative if originals cannot be procured.

[Terry M.]

Re: 68 thru 72 BB Indented Flange Exhaust Manifold Bolts

Mark are those the tri-lobe locking bolts?

[Mark D.]

Re: 68 thru 72 BB Indented Flange Exhaust Manifold Bolts

I'm not sure what you are asking, T Mac.

Are you asking if they are a design that combines the excellent chemical, thermal and plasma resistance of perfluoroelastomer parts with a unique cross-sectional shape that eliminates many of the problems associated with semi-dynamic seal applications using a dovetail groove? :-)

[Terry M.]

Re: 68 thru 72 BB Indented Flange Exhaust Manifold Bolts

The exhaust manifold end bolts, beginning in 1968 or 1969 have a threaded portion that is not round. It is shaped like three lobes. Somewhat like a three leaf clover. The purpose is to jamb the threads into the round tapped hole so no lock washer is needed. Thus the term: tri-lobe locking fastener.

Joe Lucia has described this unique fastener in the past, and it along with the flanged head identifies these bolts. Of course once installed all that is visible is the flanged head.

[Mark D.]

Re: 68 thru 72 BB Indented Flange Exhaust Manifold Bolts

Terry,

You have remined me that I am but a grasshopper...trying to ****** (now that's funny, I don't care who you are) the pebble from your hand.

These are NOT tri-lobe but, once installed, could not be distinguished from.

Mark

[Bill C.]

Re: 68 thru 72 BB Indented Flange Exhaust Manifold Bolts

Mark,

I have 8 NOS bolts. I grabbed about 16 of them 3 years ago. They are black oxide (I think - kind of have the same feel/finish as the spash sheilds dark gray parkerizing).

How many you want?
I have eight left....

I may also have the originals from my car in a baggy downstairs. I did not realize they were a special configuration on the shaft -
I can look for them. If I find them, you can have them too if you want.


You are welcome to them - I used what I needed for my 72, these are left over.

Just pay the shipping to your house.
Let me know.

[Mark D.]

Re: 68 thru 72 BB Indented Flange Exhaust Manifold Bolts

U Da Man!

Mark

[Joe L.]

Re: 68 thru 72 BB Indented Flange Exhaust Manifold Bolts

All------


This is the bolt I believe was used. However, I don't think this manufacturer's headmarking is among those originally used. However, notice the unusual "6 point" indention. I think this is an identifier for the locking bolt configuration.

These bolts do not have a "tri lobe" locking feature. They use some sort of "distorted thread" locking feature which is not readily apparent but I can guarantee you these are locking thread bolts. Just try running one down by hand and see how far you get!

These bolts are why the french locks were eliminated after 1967. Very late 1967's may have used them, too.

[Bill C.]

Re: 68 thru 72 BB Indented Flange Exhaust Manifold Bolts

Mark,

The ones I am sending look exactly like the pictures that Joe posted.

[Dennis S.]

Re: 68 thru 72 BB Indented Flange Exhaust Manifold Bolts

In case anyone is interested, here are some pictures of my March '69 L36 original exhaust manifold bolts. That was about the best picture I could get of the head markings.