425 engine mount dimensions needed
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500, 472, 425, 368 Discussion, 425 engine mount dimensions needed in Cadillac Engine Technical Discussion; All, I am new to the forum and am conducting a Cad 425 swap into a 1953 GMC 1/2T. Look ...
  1. #1
    hitorq is offline Cadillac Owners Member
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    425 engine mount dimensions needed

    All, I am new to the forum and am conducting a Cad 425 swap into a 1953 GMC 1/2T. Look forward to future discussions. I was wondering if someone can tell me what the distance is from the back of the block (bellhousing surface) to the centerline of the engine mounts on a 425? Also, wondering what the width of the mounts on the block are?

    I assume this is the same as the 472/500.. I have yet to pick up the motor, so cannot measure it myself at this point.. I am using a chassis engineering crossmember which already has the chev biscuit crossmember mounts welded in place (one on each shock tower as it wraps around the frame). I am either going use the top half of a stock cad mount on the block and fab/run an adapter plate to a chev mount (biscuit), or might have to cut those chev mounts off and put frame mounts further up on the frame (although with the shock towers/R&P not sure if I willl have enough space..

    Anyway, thanks for the assist.

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  3. #2
    Roadmaster75's Avatar
    Roadmaster75 is offline Cadillac Owners Member
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    Re: 425 engine mount dimensions needed

    Hi
    I applaud your engine swap choices!

    I recently installed a 455 Buick in the same chassis as your (51 Chevy Panel). I have modern power steering and disc brakes
    but retained the straight axle. I did not have to modify the firewall and I don't think you will either esp. since your distributor
    is up front. I had mine in and out of the frame about 12 times to get it perfectly located, but you get good and fast after the first
    try!
    Unfortunately
    You'll probably have to cut off the already tabbed small block mounts (too narrow in that dimension) & you are correct;
    the Mustang ll set up impacts engine placement on a motor of this size.

    Go the the "StoveBolt Forum" in the HiPo thread… There are guys that have already done this swap.

    Best thing to do is get your steering column hardware, your engine and trans ( with exhaust manifolds & motor mounts attached ),
    and mock up the fit a few times with the whole rig on the engine crane. Have your new 32 or 33 inch steering column loosely installed, too.
    (column shift or floor shift? Column shift means more space needed between engine and shift linkage arm)
    Get a Transdapt or similar trans mount for a TH400 for your chassis
    and have it loosely sliding on the frame rails. Once you've determined exactly the fore and aft mounting locations, loosely bolt the trans mount to the trans
    and clamp it in the frame with C clamps or vice grips. This is now your point of reference for fine tuning the fit.
    Also, Put the radiator support in so you can determine fan to radiator distance clearance. In my case
    I use an electric "pusher" to save space. Once the engine/ trans assembly is set (remember the 3-5 degree tilt
    required for driveshaft angle) THEN, you can begin to fab up or modify what you need for engine mounting. TransDapt
    also sells a variety of "perch" style hot rod mounts. These use the urethane "donuts" between the mount and the
    frame perch. They can be cut to fit and welded into the frame, but…again… some interference with the Mll
    may have to be dealt with.

    Considerations:

    Did your engine come out of an Eldo or a rear drive DeVille? The motor mounts are entirely different.
    You'll need the Deville mounts.

    An Eldo oil pan is usually preferable due to its rear sump location & will clear your Mll crossmember better, I believe.

    Space will tight up front around the radiator esp. if installing A/C … Get a fairly large trans cooler and mount it to the right and rear of the trans
    under the floor.
    This will save space by relocating the cooling lines out of the trans. More room for exhaust.
    Consider a rear mount under bed fuel tank, too.

    Good luck and have fun with it!
    mike

  4. #3
    deVille33 is offline Cadillac Owners Connoisseur
    Automobile(s): 1977 Coupe (blue), 1977 Coupe (yellow), 1977 Coupe (green)
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    Re: 425 engine mount dimensions needed

    From the back face of the block (trans mounting surface) to the center of the mount is roughly 19". The stock mounts are 4 1/2 " long, unless you cut the location guides off. These mounts use a long bolt as a pin to locate the engine. The mount is encased in a metal enclosure. If you pick up that engine, ask for the engine mount brackets that mount to the engine. They have different set back on right and left. This is due to the location of the mounting bosses on the block.

  5. #4
    hitorq is offline Cadillac Owners Member
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    Re: 425 engine mount dimensions needed

    Thanks Mike, good info. I think the model I am getting it out of is a Deville. What is the difference in the mounts? I figure I would only be using the top plate at this point (without the rubber)... Yeah, I was concerned about the chev mounts on the CE IFS. I would rather know they won't work for an adapter plate prior to mocking in the motor / trans so I can remove them prior.. if I end up removing (sounds like this will probably be the case thus far), I will have to figure out how much rail space I have between the rad x-member and the R&P, and whether to box a small amount of the frame or bolt/weld on top and inside the rail, etc.. No A/C will be ran. I will run a floor/tunnel shift to lessen interference. I do not have my column yet, so a little concerning. I do have a 500 driver side exhaust manifold (deville) so that will be thrown on prior to the mock up. Tracking on the other items. More to follow..

    Brian

    ----------

    Quote Originally Posted by deVille33 View Post
    From the back face of the block (trans mounting surface) to the center of the mount is roughly 19". The stock mounts are 4 1/2 " long, unless you cut the location guides off. These mounts use a long bolt as a pin to locate the engine. The mount is encased in a metal enclosure. If you pick up that engine, ask for the engine mount brackets that mount to the engine. They have different set back on right and left. This is due to the location of the mounting bosses on the block.
    Thanks for the quick response on dimensions. I will keep the mounts once pulled from the car.

    B

  6. #5
    Roadmaster75's Avatar
    Roadmaster75 is offline Cadillac Owners Member
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    Re: 425 engine mount dimensions needed

    Brian
    DeVille has a great point here…

    It occurred to me that it might be good to have both Deville & Eldo motor mounts
    in hand while you are trial fitting the assembly… I believe that the Eldo mounts
    were designed to get the motor to sit higher in the cradle than was necessary for the
    rear drive Cadillacs. If that's the case, then the actual dimension between the mounting bolt
    centerlines MIGHT be narrower on the Eldo mounts. That might be enough to
    allow you to modify the small block mounts instead of cutting them off. Go look at
    both on eBay or wherever … & maybe score some cheap used ones for fitting.
    Don't cut anything until you trial fit them & make a final determination. I believe
    that it is better to modify the frame side mounting points to allow the use of a STOCK rubber
    vulcanized engine mounts than messing with the motor side mounts…. You don't want any
    undo flex or stress on that nice light weight block casting by compromising the motor mount's
    ability to do it's job. That's MY opinion, but thought I'd bring it up.

    Also, don't worry about steering column if you don't have one. A 32 or 33 inches should be
    short enough to allow a shallow angle of attack for the connection to the rack. I used a 33, but
    ended up moving the exit point in the firewall over and down about 2 inches; just to give me
    more room for the column shift I desired.
    Regarding exhaust manifolds… I had to relieve the passenger side frame rail about 1/4 inch
    for the big block Buick; but I mounted mine as low (and far back) in the frame as I could get it.
    You may or may not have to do that, but better have a passenger manifold handy if you can.

    I used a recored , but stock dimensioned radiator in the stock radiator support and the front of the water pump is about 1 inch from the radiator.
    Ensure that the core support is perfectly square with the frame… you don't want it leaning back & give you a false clearance
    measurement for the water pump snout. also, the core support is critical in lining up
    the inner fenders/fenders/and grille. Expect to trim away some of the inner fenders as needed to
    clear things like power steering pumps, pulley drive belts, brake lines, etc etc

    IT's all quite a dance to get it all right..but, a great brain exercise! BTW, I suspect that
    once the motor and trans are in, it may, in fact, weigh slightly LESS than a stock cast iron stove bolt,
    cast iron, bell housing, cast iron trans and torque tube.

    mike

  7. #6
    hitorq is offline Cadillac Owners Member
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    Re: 425 engine mount dimensions needed

    Thanks again Mike, great points. The GMC has about 3 extra inches of length in the engine bay over the Chev, so that works well for me. Will post some pics once I get it mocked in.

    Brian

  8. #7
    hitorq is offline Cadillac Owners Member
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    Re: 425 engine mount dimensions needed

    Engine Mock.jpg

    Well, if the picture comes up, just threw it in and tacked a few things in place to help with alignment. Have since rasied it a bit. I need to get the r&p bolted up and start threading the linkage.. More to follow.

    Brian

  9. #8
    Roadmaster75's Avatar
    Roadmaster75 is offline Cadillac Owners Member
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    Re: 425 engine mount dimensions needed

    Looks like you're sneak' up on it!

    At this point I'd mount ALL the motor's accessories in place.

    Oil pump, oil filter, pulleys, power steering, harmonic balancer, alternator/brackets, fan etc.
    Get all this stuff mocked up with belts, before you make the final positioning
    permanent, Eliminates surprises. In my case, The harmonic balancer cleared the front cross member, but with the
    crank pulley installed I had to clearance the cross member a fraction of an inch to clear enough to be
    able to change belts. Set the radiator support & radiator in place, too measure whether or not you
    can run stock fan; or go to an electric.

    I had interference with the oil filter on the 455 Buick in my panel.

    Trans-dapt makes a neat oil filter re-location kit (with 90 degree oil line fittings) that eliminated the
    necessity of cutting the front frame cross member. I put the filter up on the pass. side fender well.

    Do you have the trans on the motor in the pic?

    You'll need to make sure the 3 to 5 degrees of tilt is determined with the trans at or near
    it's trans mount bolt down point. A couple of degrees could make the difference
    laterally or fore and aft final positioning.

    Good luck!
    mike

  10. #9
    hitorq is offline Cadillac Owners Member
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    Thread Starter

    Re: 425 engine mount dimensions needed

    Yeah, working through it. I am clearancing the front support x-member, so will have plenty of room for the oil filter. I also have plenty of room for the fan, fortuneately.. I have the R&P on at this point so will be fitting steering linkage and building motor mounts in the next few weeks. I have the carb base level, which gives me the degrees needed; the trans is hooked up. The only shortfall I have is that I do not have the suspension on and at the truck at final ride height. I plan to set it up fairly level, so should be able to buy a few degrees once I bracket the trans, which I will set last at final height. More to follow... So far I have adequate room, more than I thought I would have.

    B

    Quote Originally Posted by Roadmaster75 View Post
    Looks like you're sneak' up on it!

    At this point I'd mount ALL the motor's accessories in place.

    Oil pump, oil filter, pulleys, power steering, harmonic balancer, alternator/brackets, fan etc.
    Get all this stuff mocked up with belts, before you make the final positioning
    permanent, Eliminates surprises. In my case, The harmonic balancer cleared the front cross member, but with the
    crank pulley installed I had to clearance the cross member a fraction of an inch to clear enough to be
    able to change belts. Set the radiator support & radiator in place, too measure whether or not you
    can run stock fan; or go to an electric.

    I had interference with the oil filter on the 455 Buick in my panel.

    Trans-dapt makes a neat oil filter re-location kit (with 90 degree oil line fittings) that eliminated the
    necessity of cutting the front frame cross member. I put the filter up on the pass. side fender well.

    Do you have the trans on the motor in the pic?

    You'll need to make sure the 3 to 5 degrees of tilt is determined with the trans at or near
    it's trans mount bolt down point. A couple of degrees could make the difference
    laterally or fore and aft final positioning.

    Good luck!
    mike

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