Motor Mounts for 454

[DSnyde34]

I am currently rebuilding the motor on a 1974 K20 that has a 454. When we pulled the motor out we noticed that it was sitting lower on the driver's side and that the oil pan was just barely rubbing the crossmember underneath. As a result, I decided to put new motor mounts on the truck. I am running into problems finding the right ones. The truck previously had a 350 in it and still has the 350 mounts. Is this why the motor was sitting too low? When I got new mounts for the 454 I discovered that the bolt holes on the mount don't line up with the holes on the frame perches. Has anyone run into this issue before and come up with a fix? Should I just buy new 350 mounts and stick it back in there or should I try and drill a new hole in the current perches? I tried to see if you could just buy new perches that the 454 mounts will bolt onto but so far I haven't been able to find anything. Any help would be appreciated. Thank you in advance!

 

[85K304SPD]

Just buy the small block 350 mounts. They are the same other than the bolt pattern on the frame.
I have been through all of this before. The factory big block trucks had the larger bolt pattern. The part that the motor mount bolts onto is the same on both.

 

[DSnyde34]

Just buy the small block 350 mounts. They are the same other than the bolt pattern on the frame.
I have been through all of this before. The factory big block trucks had the larger bolt pattern. The part that the motor mount bolts onto is the same on both.

Thank You! That is the path I was leaning towards. My only concern is that the new 454 mounts I have look to be just a little bit taller than the 350 mounts that were on the truck (Maybe a 1/4" taller at the most). Is this just because the old ones are worn out or were the 454 mounts slightly taller from the factory?

 

[85K304SPD]

I can't answer that for sure. I think it is probably just that they are worn out. Buy the ones that fit your truck and try them out. There is always surprises when you are doing a conversion.

 

[bucket]

The mounts are just wore out. When they sag a bunch, the engine gets real close to the crossmember. The old mounts in my '77 K5 were bad enough that the 8" balancer rubbed a hole in the crossmember. It's just a small block too.

 

[DonL]

I am currently rebuilding the motor on a 1974 K20 that has a 454. When we pulled the motor out we noticed that it was sitting lower on the driver's side and that the oil pan was just barely rubbing the crossmember underneath. As a result, I decided to put new motor mounts on the truck. I am running into problems finding the right ones. The truck previously had a 350 in it and still has the 350 mounts. Is this why the motor was sitting too low? When I got new mounts for the 454 I discovered that the bolt holes on the mount don't line up with the holes on the frame perches. Has anyone run into this issue before and come up with a fix? Should I just buy new 350 mounts and stick it back in there or should I try and drill a new hole in the current perches? I tried to see if you could just buy new perches that the 454 mounts will bolt onto but so far I haven't been able to find anything. Any help would be appreciated. Thank you in advance!

Nope. Big block frame brackets AND clamshell insulators are different than small block ones.(2WD)
Probably the cups that attach to the engine as well, but I don’t know that for sure

 

[bucket]

Nope. Big block frame brackets AND clamshell insulators are different than small block ones.(2WD)
Probably the cups that attach to the engine as well, but I don’t know that for sure

Yes, it's true that they are different. But using the small block mounts with a big block works just fine. 2wd and 4wd. It's been done over and over again.

 

[DonL]

Yes, it's true that they are different. But using the small block mounts with a big block works just fine. 2wd and 4wd. It's been done over and over again.

Yes, it's true that they are different. But using the small block mounts with a big block works just fine. 2wd and 4wd. It's been done over and over again.

Perhaps. Maybe I should have said that C10 frame brackets are much LONGER than the. C20 version.

 

[82sbshortbed]

I swapped a 305 with a 454 and used old brakets with no problems in my 82. Drove it Saturday. Long tubes too. Nothing rubs. Did put bb front springs in too.

 

[bucket]

Perhaps. Maybe I should have said that C10 frame brackets are much LONGER than the. C20 version.

No, I'm saying that if you drop in a 454 in anything at all, the 350 mount setup will work. Trucks, Chevelles, Camaros, Impalas, etc. It's been done over and over and over again for decades.

Also, C10 and C20 frame brackets are the same size. It's the C30 brackets that are different because of the frame rail differences. But a big block will still work with the small block mounts.

 

[82BBC20]

I had trouble with my 82 C20 w/factory 454 when I tried to upgrade my mounts to urethane, everything I ordered was too small even just replacing the insert using original clam shells. I finally ordered stock mounts for my truck & got a tube of windshield urethane from our glass guy at the shop & filled all the voids with urethane, let ‘em set 24 hours & good to go! That trick might help using small block mounts to firm things up a little!

 

[DSnyde34]

What I ended up doing was using new small block mounts and then we put aluminum plates as shims between the mounts and the perches to raise the motor up a little bit. So far it has worked out great!

 

[DonL]

Perhaps. Maybe I should have said that C10 frame brackets are much LONGER than the. C20 version.

I’m speaking from experience.

1976 C10 frame brackets are absolutely different than the ones from my donor truck 1979 C20 3+3 Camper Special. (I’ve later salvaged a 1974 C20 454, and they were the same as the 79)

As Paul Harvey would say: “And now for the rest of the story.”

I’m putting a 454 into my 1966 GMC.
That’s the frame in both pics.
Squarebody front suspension clip.

When the C10 brackets are set on the crossmember and 2 bolts inserted into the lower holes …. The bracket sits up above the frame about an inch, which would require a spacer.

When you do the same with the C20 brackets … they lay much flatter on the top of the frame rail. I did need to trim the upper edge of the frame rail about 1/4” in order to make the lay perfectly flat.

I am not the only one to experience this. 60-66 GM Truck group members on Facebook have found the same thing

 

[DoubleDingo]

I’m speaking from experience.

1976 C10 frame brackets are absolutely different than the ones from my donor truck 1979 C20 3+3 Camper Special. (I’ve later salvaged a 1974 C20 454, and they were the same as the 79)

As Paul Harvey would say: “And now for the rest of the story.”

I’m putting a 454 into my 1966 GMC.
That’s the frame in both pics.
Squarebody front suspension clip.

When the C10 brackets are set on the crossmember and 2 bolts inserted into the lower holes …. The bracket sits up above the frame about an inch, which would require a spacer.

When you do the same with the C20 brackets … they lay much flatter on the top of the frame rail. I did need to trim the upper edge of the frame rail about 1/4” in order to make the lay perfectly flat.

I am not the only one to experience this. 60-66 GM Truck group members on Facebook have found the same thing

That sounds like apples to oranges in the context of this thread.

 

[bucket]

I’m speaking from experience.

1976 C10 frame brackets are absolutely different than the ones from my donor truck 1979 C20 3+3 Camper Special. (I’ve later salvaged a 1974 C20 454, and they were the same as the 79)

As Paul Harvey would say: “And now for the rest of the story.”

I’m putting a 454 into my 1966 GMC.
That’s the frame in both pics.
Squarebody front suspension clip.

When the C10 brackets are set on the crossmember and 2 bolts inserted into the lower holes …. The bracket sits up above the frame about an inch, which would require a spacer.

When you do the same with the C20 brackets … they lay much flatter on the top of the frame rail. I did need to trim the upper edge of the frame rail about 1/4” in order to make the lay perfectly flat.

I am not the only one to experience this. 60-66 GM Truck group members on Facebook have found the same thing

Even though it's a C20, the 3+3 part of it is the key here. Crew cab C20's have the same frame as a C30.

Like @DoubleDingo said, what you are doing doesn't really apply to an engine swap. You are mixing and matching frame parts.