74 454 EGR Bracket Bolt Question

[Victor S.]

Help! Is the EGR bracket mounting bolt for a 454 the same as the one that was used on the 350 motor? I do know that it is a hex head bolt with a french lock. I just haven't had any luck in finding information about the correct bolt size and head mark that was used for the 454.

Thanks in advance for your help and support. Happy New Year!

[Joe L.]

Re: 74 454 EGR Bracket Bolt Question

Help! Is the EGR bracket mounting bolt for a 454 the same as the one that was used on the 350 motor? I do know that it is a hex head bolt with a french lock. I just haven't had any luck in finding information about the correct bolt size and head mark that was used for the 454.

Thanks in advance for your help and support. Happy New Year!

Victor-------

The bolt is a standard hex head bolt. I think it's the same as small block and about 1-1/2" in length and 3/8-16 thread. The big block and small block EGR valve clamps were different but very similar in size and configuration. However, all you need is a bolt which retains the clamp and does not bottom out in the manifold. Whatever the length, if it meets those two criteria it will be fine. As far as headmarking goes, since this is just a standard bolt, I would think that any period-correct headmarking should do (e.g. "C", "M", "TR", etc.).

As far as the french lock goes, that's another story. I can't find a GM part number for it and I have no idea where to obtain one.

[Tom R.]

Re: 74 454 EGR Bracket Bolt Question

Hey Vic

See if this helps! Page from the revised 73-74 TIMJG manual and shows the 74 LS4 EGR french lock. Don't have a good picture of the headbolt but it shows the TR headmark. I've included the photo as well that is shown in the PDF page.



1973-74_TIMJG_EGR_LS4_03Dec18.pdf

[Jimmy P.]

Re: 74 454 EGR Bracket Bolt Question

Hi Vic,
Yes as Joe and Tom both point out the 73-74 EGR mounting bracket/ bolt Assembly are exactly the same. The 73-74 Revision Team found that TR head marking might have been the most common, but again as Joe stated above other head markings were also found. Below are two that I have, one is on my 73 L48 and the other is an extra I have. The one on the car is in original Condition. The other one has been repainted. Note the different head markings used. The toughest item to find when searching for these is the special French lock washer. These brackets show up on eBay every once in a while. Sent you a PM!
Hope these photos help.

[Victor S.]

Re: 74 454 EGR Bracket Bolt Question

Thanks Joe, Tom and Jimmy - I appreciate the information very much - best -
Vic

[Robert R.]

Re: 74 454 EGR Bracket Bolt Question

Vic,
Here are shots of my '74 L48 and LS4 EGR valve clamps and bolts.

The first picture shows the LS4 clamp. The distance between the arrows is 5 1/2". Note the crack in the clamp.



The second picture shows the L48 clamp. The distance between the arrows is 4 1/2"



The next two pictures show the bolts. I'm not sure about the length of the bolts, but the L48 is the "TR" bolt and the LS4 is the "SB" bolts. Both bolts are grade 5 (3 radials).



Jimmy's photos above are from his '73 L48 and is identical to my '74 L48. I would assume that the L82 clamp is similar to the L48, but it is obvious that the LS4 clamp is different than the L48 clamp.

Hope this helps,

Bob

[Robert R.]

Re: 74 454 EGR Bracket Bolt Question

In reference to my above post, it is difficult to measure the length of the LS4 EGR clamp when installed. After moving some of the hoses, I was able to get a more accurate measurement. I can confirm that it is 5 1/4" and not 5 1/2 as I indicated above. I also believe the the correct part number for the LS4 clamp is 353087.

[Steve L.]

Re: 74 454 EGR Bracket Bolt Question

It's impossible to find the french lock. I got an original on loan from one of the NCRS members and made a 3D CAD copy. I got a handful laser cut. I still have a few kicking around. I'm in FL for the winter but anyone needing one can contact me.