SBC - BBC Swap 77SWB

[Matt]

Are the motor brackets different for a BBC than a SBC?  I know the BB motor mounts are different but not sure on brackets (brackets that bolt to Block). Converting from BB to SB and the BB is setting to high and to far back, and the brackets and mounts do not line up perfectly.  Can I just move the mounts to different locating holes and make it work?  Thanks

[Captkaos]

Nothing is different but the accessories.
Remove SBC, unbolt the motors brackets from the engine, bolt them on the BBC and drop it in.

[Captkaos]

Can I have the motor mounts in the wrong locating holes? I replaced the motor mounts and set the BB in - I can only get one pin (bolt) through motor bracket/mount - other side does not line up.
Thanks

How is it not lining up?  I would imagine it isn't going down far enough.  Jack up on the motor with the one side in and see if you can move the engine over to get it aligned.

[malibu795]

Can I have the motor mounts in the wrong locating holes? I replaced the motor mounts and set the BB in - I can only get one pin (bolt) through motor bracket/mount - other side does not line up.
Thanks

How is it not lining up?  I would imagine it isn't going down far enough.  Jack up on the motor with the one side in and see if you can move the engine over to get it aligned.

i have found out that GM made at lest 2 different hieght engine mounts..

and x2 on capt stated

[Engineer]

The 454 does use a different "clam shell", or engine side mount.

However, the SB mounts will bolt up, and do work on the 454.

The SB's mounts will cause the engine to set about 1"~1.5" lower in the truck than if you are using the proper 454 mount. But again, it should work. This could cause a problem if you are using the OE 454 fan shroud. The SB mounts will allow the fan to hit the bottom of the fan shroud opening. The SB fan shroud will not work with the BB engine without major modifications.

The rubber mount (frame side) is the same for both SB, and BB. This is by the part numbers.

Your accessory brackets (alt, PS pump) are completely different for the SB, and BB. The SB's will not work with the 454. Period.

However the crankshaft, and water pump pulleys will interchange. But, there are different part numbers for the SB, and BB crankshaft pulleys. You should use the 454's crankshaft pulley just because of the way it center's itself on the harmonic balancer.

If you need the OE GM part numbers for any of this swap, just ask, I have all that you need. 

[Captkaos]

I have swapped out a number of SBC to BBCs over the years and I have never had any issues with the motor being 1-1.5" lower or hitting the shroud.  The factory 73-79 1/2T 454's I have worked on  had the same motor mounts also.

[Engineer]

I don't know Capt.

My experiences have always been with 4x4 trucks, maybe that is the difference? I know that using the SB mounts on a 454 in a 4x4 will cause the shroud to hit the fan. Again, maybe this only applies to the 4x4s?

Maybe the 4x4s frame is different enough that the SB engines can set lower, but the 454s need to set higher. I also know that the shroud part number is the same for both a 1985 K-30, and C-30 with the 454 engine. So however it is set up, the engine sets in the same postition relative to the radiator in the 30 series 4x4s, and 4x2s with the 454.

One other difference when working on a 4x4, you can drop the oil pan on a SB with out taking the motor mounts loose, but the BBs need to be lifted out of their mounts to remove the oil pan.

I have only worked on 1 '77 C-10 with a factory 454 in it, but I never had to pull it. So comparing the engine mounts never was an issue.

As I say, the small block mounts will work on the 454. I know this because my 1977 K-30 originally came with a 400SB, and I swapped in a 396 using the 400SB mounts. The 396 is/was no different than the 454 that I now have in the truck. However, there are some mounts that are different. When I bought my 454 it's engine side mounts had the hole drilled approximately 3/4" farther away from the engine mounting surface than did my 400SB mounts.

Since I couldn't use the shroud that I had bought for my 396, I deceided to try the 454 mounts, and this allowed me to use the shroud with my 454.

Just for grins....Here is the OE GM part number that is stamped on the steel mounts that came on my 454 (14067103). My 454 is originally out of a '73 C-20. When chasing this P/N is shows to fit 454s up to 1991.

[Engineer]

Here is another thought, if my 400SB was supposed to have those little spacer plates that the transmission strut rods bolt to, and didn't this would explain the slightly different height.

I know that it never had these, but if the mounts were supposed have the spacer in order to work properly, that would explain the shorter height of the mount.

My truck was used, and a half when I bought it. The #s on the 400SB showed it to be a '75 model, so if my original engine was gone, then so could the original mounts. If you run the numbers, my truck was an original 400SB truck, but I have no explanation as to why the engine that was in it when I bought it was a '75, other than to say it was swapped in.

My son's '79 is a perfect example of this, his truck has the strut plates, but since his truck is a 4-speed there is no torque converter cover to bolt the struts to. If a "shadetree" mechanic was working on his truck then ol' shady might be inclined to leave the plates off.

Hmmmm.......Well anyway.

[Captkaos]

AHHH, 4x4 ARE different.  In fact you couldn't get a 1/2T - 1T K series with a 454 up until about 1989 or so and it was only in a K30, from the research I have.

[Texcuda]

So if I follow correctly, since my truck has a 305, i can use the original clamshells and new small or big block mounts? has anyone verified the 1-1.5" drop on the motor. That would be a nice bonus as it would increase hood clearance, not that it's much of an issue. I plan to use dual electric fans so fan shroud clearance isn't an issue. Thx

[Captkaos]

EVERY Truck I have swapped over from a SBC to a BBC used the EXACT same frame mounts and engine mounts.