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Mystery Motor Mounts

Discussion in 'Tech Discussion' started by rehoward, Sep 1, 2019.

  1. rehoward

    rehoward Junior Member

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    Location:
    Everett, Washington
    First Name:
    Randy
    Truck Year:
    1976
    Truck Model:
    3/4 ton Silverado
    Engine Size:
    454
    I am working on a 1976 3/4 ton Scottsdale that I bought 10 years ago. The previous owner did a 4wd conversion on it and pretty much screwed up installation of the engine and trans. BTY motor is 454 and it has an auto trans, most likely a 400. I assume these are not the original motor and drivetrain because of the poor installation. Anyway I am trying to piece together factory mounts and have tossed out all the junk he cobbled together.

    I think I now have the correct front crossmember . See pics. I also thought I had bought the correct engine mounts but the "new" mounts (they are 10 years old) do not fit as the old ones do. The old mounts fit my crossmember and have a staggered 3 bolt pattern. The new mounts are a little longer and have a symmetrical 3 bolt pattern. These mounts are not interchangeable. See pics. The dirty mounts are the ones that fit the crossmember that I have, the new ones do not.

    So what Have I got going here? It looks like the old mounts put the long mounting bolt in the correct location but the new mounts do as well. The new mounts will not bolt up to the crossmember bolt pattern and are longer as well. What year/model/part number will allow me to bolt up my 454 to the old mounts with the staggered bolt pattern? Many thanks.

    Crossmember 1.JPG Crossmember 2.JPG Engine Mounts.JPG
     
  2. 75gmck25

    75gmck25 Full Access Member

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    First Name:
    Bruce
    Truck Year:
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    Truck Model:
    K25 Camper Special TH350 NP203
    Engine Size:
    5.7
    The 454 was a factory option for your truck, so the parts you need are available from both OEM and aftermarket. I don't know how any PO could screw up an engine swap when it was a standard factory option, but you never know.

    Since you aren't sure which mount is right, you might look up the parts numbers (Rock Auto works well), and go to Autozone or other parts store and compare their new part to the two mounts you have. At least you would know which one is correct. And if it does not match the cross member, that may be incorrect.

    GM used the 454 in both 3/4 ton and 1 ton, and I know there are frame size differences when you go up to the 1 ton. I don't know if this might have changed the crossmember enough to affect motor mounts.

    Bruce
     
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  3. Charlie

    Charlie Mopar by Birth. Chevy by Choice.

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    :welcome:
     
  4. legopnuematic

    legopnuematic Licensed Junk Dealer Supporting Member

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    Dart Swinger, Sierra 10, C10 Cheyenne, C10 Big Ten, Silverado 10
    Engine Size:
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    For a 2WD a 454 was a factory option, in 1976 no 454's were offered for 4WD trucks. Since yours was born a 2WD, the engine could be original.
     
  5. Craig 85

    Craig 85 Full Access Member

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    First Name:
    Craig
    Truck Year:
    1985
    Truck Model:
    K30 SRW
    Engine Size:
    454/TH-400/NP205
    My truck is a K30, so I'm not sure of the cross member is quite the same for a K20. Here's pictures of mine when the engine was out last year.

    FYI I've had some issues with getting the correct fuel pump. The 454 4WD takes a shorter one due to cross member clearance. The ones currently marketed by Carter (#M60191) are the wrong pump (See photo #3). I have a 3 port pump, not sure if you do. I had to find some NOS ones off eBay to work, Airtex 41615 or BWD 41615. FYI NAPA and Oreilly's are now using the Carter pump. In the picture, this was the last Napa pump with the correct labeling. I had them order in a few more and all new Napa stock is the Carter M60191.

    IMG_1765 (2).jpg IMG_1767 (2).jpg
    IMG_1352.JPG
     
  6. rehoward

    rehoward Junior Member

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    First Name:
    Randy
    Truck Year:
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    Truck Model:
    3/4 ton Silverado
    Engine Size:
    454
    Well, it looks like what I have are motor mounts for a 350 not 454. So the old used motor mount in the pic is for a 350. I really don't see much difference other than the base of the new mount is longer which means the bottom hole will be off the edge of the crossmember. As I said the location for the long mating bolt for each motor mount appears to line up to the engine bracket. So I am thinking of just using 350 motor mounts with the 454 since they seem to be a bolt on affair. Any comments on this?
     
  7. bft305

    bft305 Member

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    Truck Year:
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    Engine Size:
    350
    I had an issue finding motor mounts once but mine was a 350 and yes the ones you have look like they are for the 350. Now my truck frame is a 1976 and body is an 1985, so this kind of stuff happens to me all the time! Not sure if the 454 had different ones. I just brought my old mounts into Napa to compare. I think I asked for 1982 k10 mounts and 1976 mounts. Forget which worked but I did find ones that did.
     
  8. skysurfer

    skysurfer Full Access Member

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    Even without the possibility of an engine swap, finding the correct mounts can be challenging. Standing at the NAPA counter, the guy tells me there are two possible mounts for my truck. Not wanting to make a second trip to the store, I buy both sets. Neither fits. I ended up cutting apart one of the new sets and removing the rubber isolators inside. Cut apart my old clamshells, installed the new rubber, and tacked the shells back together with a mig welder.
     
  9. Dooley

    Dooley Full Access Member

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    donnieray likes this.
  10. climb-101

    climb-101 Full Access Member

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    if i remember right, there is a height difference on motor mounts between the small block and the big block but i think that was on the engine side of the mounts.
     
  11. rehoward

    rehoward Junior Member

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    First Name:
    Randy
    Truck Year:
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    Truck Model:
    3/4 ton Silverado
    Engine Size:
    454
    Thanks Craig and Dooley for advice on a fuel pump for a 454 conversion.

    I was Googling stuff about 454 conversions and found this article:

    https://gordonfrench.com/454-swap-350-power/

    It shows pretty much exactly what I am working with and talks about the 454 mounts being longer, not taller, meaning that both the 350 and 454 mounts place the long crosswise bolt in the same location. This is what I found too. Some good pics of the two different motor mounts except the 454 mount as shown is upside down I think. The single bolt hole should be pointing down, not up. Both mounts use three bolt holes, two on top and one on the bottom.

    I ordered two 350 mounts from Rockauto last night so we will see. Be back on it in a week or so. Thanks everyone for all the help.
     
  12. Remo76C15

    Remo76C15 Full Access Member

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    Engine Size:
    350
  13. highdesertrange

    highdesertrange Full Access Member

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    Truck Year:
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    Truck Model:
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    Engine Size:
    454
    I ran into this engine mount issue when I installed a 454 in my 78 that had a 350. the 454 mounts wouldn't fit(well the bolts didn't line up) so I just used 350 mounts and everything worked fine. highdesertranger
     

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