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73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: knightrider84 on May 20, 2025, 02:12:43 pm

Title: Big Block Fuel pump clearance on frame for Crew Cab K20
Post by: knightrider84 on May 20, 2025, 02:12:43 pm

Hello all-
   I recently removed a 350 engine from my 1976 K20 3+3 Crewcab truck and I dropped a 454 into it. I changed the rubber (frame side) motor mounts to new ones (at first I bought ones for a 1976 K20 with a 454 but the bolt holes on the lower side of the mount did not match up to the frame, so I purchased mounts for a 350 and those bolted on). I was dropping the big block in and the mechanical fuel pump makes contact with the frame. So much so that it bent the lines coming out of the bottom of the pump. I removed the fuel pump and was able to seat the engine in place, insert and tighten the bell housing bolts and lower the brackets that are bolted to the engine block down onto the new rubber motor mounts, insert my big bolts and everything went fine and the engine is bolted into place.
   The fuel pump I have is a stock mechanical one that we used to run the engine on the stand, it is the "taller" one (I mean it looks like the small block one but is "deeper"). This pump will not work because of clearance issues. My questions is; what is wrong here?
   -Are there other motor mounts that are "taller" so the engine sits higher and the stock fuel pump clears?
   -Is there a "shorter" fuel pump for the Big Block?
   -Is the fact that it is a crewcab creating this issue?
   -And, no I don't want to block it of and run an electrical one!

      Any help would be appreciated,

 thanks!

Title: Re: Big Block Fuel pump clearance on frame for Crew Cab K20
Post by: VileZambonie on May 20, 2025, 05:18:48 pm

You need 454 mounts in the correct location

Title: Re: Big Block Fuel pump clearance on frame for Crew Cab K20
Post by: VileZambonie on May 20, 2025, 05:22:03 pm

See image

Title: Re: Big Block Fuel pump clearance on frame for Crew Cab K20
Post by: knightrider84 on May 21, 2025, 08:28:44 am

Thanks Zambonie,
   But when I had the 454 mounts, the holes would not line up no mater what I did.
-I am thinking I had the wrong "454" mounts
-Or does the fact that it is a Crewcab have something to do with this? (I noticed the note saying: ALL EXCEPT MOTOR HOME CHASSIS

    What do you think?

Title: Re: Big Block Fuel pump clearance on frame for Crew Cab K20
Post by: ehjorten on May 21, 2025, 09:29:56 am

The big block motor mounts have the mounting holes in a triangle pattern. The small block ones are in a rectangle. The Big Block motor mount has the lower mount in the center. Also the Big Block motor mount sits a little taller. I have included 2 pictures with dimensions.

Title: Re: Big Block Fuel pump clearance on frame for Crew Cab K20
Post by: ehjorten on May 21, 2025, 09:33:10 am

I also believe that the engine side mounts for the big block are different than the small block. I think they are shorter? I can't remember.