The Stovebolt Site Forums The Parking Lot Big Bolts '56 engine swap

I have a '56 model 424 (10 ton) with a 6 cyl 302 that is about to throw a rod. What more modern engines (8Cyl?) would bolt up with minimal adjustment?

conventional cab? the 283 is a direct bolt-in w/ the repro front mounts, any SBC should fit fine w/ the adapter crossmember for the side mounts - 350's are common as flies

Bill

I believe Firefox has a GMC, so the Chevy small block isn't a drop-in. The 302 GMC is longer and has different motor mount spacing. I don't think the bell housings are the same either.

Mike

the GMC and Chev frames 55-59 are virtually identical, and came from the factory w/ provision for a V8 - the bell housing from any 6 will be different than any 8, especially the floor start 6's - any V8 is shorter than any 6 - 6 cyl mounts not involved - he inquired about V8's - having a 58 that has the [optional] 283 in place of the original 235, I can attest that it's a piece of cake - maybe a pontiac V8 would be more "appropriate"? they mount the same way, but are less common

Bill

I DO have a GMC, and a 350 is preferrable, do I understand red58 correctly that I would only need to adjust motor mounts to go with a 350?

PS- It is also a conventional cab with no floor start. please see gallery entry: David Inscore's GMC "Tanker" Truck - in the 55 - 59 section.

yes David, but not adjust, add - to mount a 350 you'd just need to add a crossmember at the position of the 350's side mounts, and if the 302 has the bellhousing mounts, like the 235, you're home - not sure if the 302 bellhouse fits the 350 [235 don't], but a standard shift 350 bellhouse will fit the trans - prolly hafta rig a fan shroud because the 350 will be back too far for good cooling at low speed/extended idle - also the throttle linkage will change I expect, but repro V8 linkage is available

good lookin "worker" ya got - w/ the best GMC grill for the year

Bill

Back in the last century, I pulled the spun bearing-cracked main 235 from my 54' chevy half ton and replaced it with a 270 GMC. I used the chevy bell housing (The torque mounts were different on the older GMC bellhousing) it buckled right together. I did have to move the front motor support and radiator about 2" forawrd, as the jimmy was a bit longer. Can't remember what flywheel/starter combo I used. Both engines were floor starts. Doesn't the 350 have the mounting bosses in front for the pencil mounts? And I am ALMOST sure that the 235 bellhousing fits the small block V8 (You will need it for the torque mounts) Hope this helps more than hinders!

Dave - the front mounts were only on the 283 - I think the 327 still had the holes cast, but not threaded and one hole wasn't full depth because it goes into the crankcase or an oil gallery and leaks w/o the mount bolt to plug it! - not sure 350's even had the holes - the front peg mounts [nearly identical to 235 mounts] were only used until 60-62 I think, and even earlier in cars, but they do make it easier to drop in the 283 rather than a 350 - all stick shift SBCs had the bellhousings w/ the mounting ears, but I remember the 235 one not fitting the V8, and don't know what was used on the 302

Bill

Thanks for the help guys, I think I'm off and running. We'll see what comes up. I spoke with someone today who thought just about any GM engine would bolt to the tranny, so I'll see how much torque I can get. Glad you like the grille Bill. Actually, I have the stock GMC emblem and I'm modifying a chrome Chevy p/u grille to fit that gaping hole!
Dave

Early Chevy 350's still had the front motor mount holes drilled, I have a 350 in my '56 Tow Truck, it dropped right in using the stock front mounts and the side bellhousing mounts.

I don't think the GMC 302 6 cylinder bellhousing will bolt to a Chevy SB. If you can find a Chevy Truck V8 (not car) bellhousing your in business. You might need to get the Chevy V8 front mount brackets that are sold by most vendors.

Mike

that's useful info Mike, I've never seen a 350 w/'em, but the way to tell is if there's an apparently useless bolt in the block lower left front that actually is keeping the oil in!! I know 327's had that bolt - also be careful not to put too long a bolt in there Dave, or you'll bend the fuel pump push rod

Bill

I know I've seen those front mount bolt holes in a 350, but I don't know which ones have them and which don't.

The bellhousing behind the GMC 302 will NOT fit a Chevy V-8.

The 'minimal adjustment' V-8 approach is probably a Chevy V-8 using a truck or pickup V-8 bellhousing from a '55 to '66 or '67. Actually, starting in '63 a six bellhousing should be the same.

I think the GMC motor even has the same flywheel bolt pattern, so its possible the flywheel and clutch will work... I'm not real sure of that...

I'd front mount the motor if you are still using the bellhousing mounts instead of messing with a new crossmember.

Use a cable type throttle. You'll change a few wires and move the radiator and should quickly and easily be back in business.

Don't forget the saddle front mount from the E. 60's one ton & bigger trucks with V-8 has 2 sets of holes;the mount is drilled for a smallblock AND a bigblock. At least my 62's is. So,with that front mount,and a bellhousing from a V-8 truck '55 to middle 60's,you could install a bigblock with factory mounts.If you run a 396,427,or a 366 or 427 tallblock (the 402 and 454 are externally balanced),you can even run the stock smallblock flywheel and clutch. A cable throttle from a 70's pick up is easy to install and eliminates linkage binding. For a truck that size,I think a bigblock would be worth a look. BTW,unless the tranny is close to grenading already or you have no finesse with a clutch,the stock transmission will probably out last your next couple of sets of tires. Remember,you'll be hammering the brakes more,so check your lining thickness more often.

Also,I doubt the GMC flywheel will fit anything but a GMC engine. It might bolt up to the crank,but the diameter,ring gear tooth count,and back spacing will all have to be the same or you'll have big headaches. (been there,done that,got the T-shirt)