Maybe because of the step or raised portion for the bolts. The oem tin covers are flat all the way across.

 

I just put M/T covers on mine with some very thick SCE cork gaskets. 3/4" worked just fine.

 

Thank you for the replies.

 

I’m in the process of rebuilding a 460. I am going with M/T valve covers and S.S. bolts. A couple sites say that the 3/4” bolts won’t fit aluminum covers with one piece Fel Pro gaskets.
Does anyone know why they won’t fit?
Thanks.

I use Fel Pro rubber ones with no issues. On 2 460s and my 331 stroker. But I use ARP studs for alum valve covers.

 

I did see the studs and like the idea but I like the look of cap screws.
thanks

 

It may be unconventional but I just fire up the old internet and go to McMaster Carr or MSC and buy set screws in whatever diameter and length I want. I can get them in stainless and the added bonus is that they have an allen wrench receiver in the end so they are easy to install or remove.

 

McMaster Carr is my go to usually but I noticed buy sets from an online place was less costly but they also claimed that they didn’t fit with aluminum valve covers and Fel Pro caskets.
I ran a 1” bolt in for a mockup but it bottomed out with about 1/8”-3/16” of thread left.
I guess I’ll get both 3/4” and 7/8” and have both on hand. It’s not like I’ll never need a 1/4-20 again.
thanks

 

HI
That's because with the thickness of aluminum valve covers at the flange and the thickness of the gasket is to much for the 3/4" bolts to have very much thread to screw into the head and be secured. You could be able to use 1" tho and be OK I would think

good luck take care be safe
tim

 

I have valve cover spacers and Moroso T nuts. I use the Moroso Perm-Align gaskets (well worth the money). I couldn't find studs long enough, so I grabbed some 1/4-20 threaded rod, cut to length and loc-tite them in. As for the spacers, I run Jomar stud girdles, taller covers won't work for me because I can't pull them off with the AC stuff in the way. The shorter covers clear the girdles and AC.