BIGT82

hey guys thanks for having me here this is a great place to thread and gain knowledge i have a 82 cutlass that im swapping a 307 out for a 425 and i have a ton of questions like motor mounts, engine questions primarily tips on rebuilding my 425 but ya thanks for having me and just feel free to contact me !! Happy 4th of July!!

olds425

I think you just need to use the motor mount and frame mount as the same. Meaning if you use the small block mounts you need the frame and motor mounts for the small block, and if you use the big block mounts you need the big block frame and motor mounts. I think if you have never rebuilt an engine before you need to get a book on rebuilding engines in general at the least. You will need a torque wrench and a good machine shop to check out the engine.

BIGT82

well i have rebuilt many engines im just making sure everythings gonna bolt up cuz it s a bigger motor ive been reading on here to get a new flywheel i have a 350 unibell trans im just cconcerned with fitment in that respect because i know alot of olds are interchangeable ie water pump, fule pump, starter depending on application but this motor i bought only had 70 k and a spun rod bearing so the rebuild will be easy its just fitment to the application of the unibell im pretty sure it should bolt on but as i said im just wanting som solid info on that

Oldsguy

Welcome to CO. I personally think bigger is better too.

joe_padavano

There are no "big block" motor mounts for a G-body. The 307 mounts bolt directly to the 425 and it drops into place.

ALL 1964-1990 Olds V8 motors use EXACTLY the same bellhousing bolt pattern, front cover, water pump bolt pattern, and motor mount bolt holes. The difference in water pumps is length, which is a function of A/C or HD cooling, not engine size. You must use water pump, pulleys, and accessory brackets as a matched set to avoid belt alignment problems.

The flywheel/flexplate is different between 1964-1967 motors and 1968-1990 motors. You need the early one for the 425. The crank flange bolt pattern is the difference.

The 307 starter will bolt to the 425, but is unlikely to have enough torque for a freshly built big block motor.

The 307 exhaust manifolds will bolt to the 425, but are excessively restrictive and a waste of time. If you want manifolds get the 1969-1972 W/Z manifolds.

When both BBO and SBO were in production, the accessory brackets had two sets of holes to fit both. The 307 brackets do not. If you want to use them on the 425, you will need to weld tabs to the A/C compressor bracket to extend it down to the holes in the block. You will also need to use a spacer and longer bolt between the alternator bracket and the PS pump bracket. Of course this means that you'll need longer belts for the alternator and A/C.

You'll need a radiator upgrade.

Other that the items I noted, this is a bolt-in swap.

Jamesbo

Welcome aboard

See it didn't take ya long to get the Olds Guru Mr. P to help ya out.

BIGT82

ya thanks guys imjust having an issues my current flywheel on the 307 is chwed up and beat can you guys direct me to a cheap flywheel site also ya i bought a huge radiator from like a 73 chevy its massive i barely got it to fit in the holder is there anything special when i pull that motor out im pretty sure i was looking yesterday its like 5 or 6 tranny bolts and 4 motor mount bolts and im gonna take the starter out with the wiring assembly and the electrics are gutted out so no computer there im trying to think if im missing anything.remove the fan tranny bolts, radiator hoses, exhast at my 2into 1 three bolts its pretty simple sounds like i have the 425 on a stand and im in the process of replacing the rod bearings in it the guy i bought of told me it was a one owner motor with 70k on it and it just had a spun bearing , im hoping that its that simple but im not gonna risk it im going thru rockauto and getting a gasket kit and ring bearing kit for it also what would you guys recommend as far as a stall converter im on a strict buget i was thinking of just putting the same tc back on it cuz its unibell but i also dont think im gonna need a regular cam im trying to keep it as stock as possible now to get running until i get the body done on it. but thanks for the input i really appreciate it ive heard of those sswap outs being pretty easy and i just wanted confirmation on it! thanks guys im gonna stay on here as long as i can!!

BIGT82

also was wondering about what type of exhasut headers i should put in there for cheap i was thinking heddman

J-(Chicago)

It's easiest to run shorty headers in a G body, since the cars are so small.

P.S. How is the Foundry? Every sewer grate in this whole state must have come from Neenah.

BIGT82

well thanks for that advice im trying to see will the oil pan i have on y 307 work for my 425 and where can i get a cheap flywheel 166 tooth>? and any other advice you have for me would be great thnks

joe_padavano

The 1964-1967 Olds motors use a different crank flange bolt pattern than the later Olds motors, so you must use the correct flexplate for those years. These are available new from Summit and Jegs. The 307 oil pan will bolt to the 425, though I would recommend getting a correct BBO oil pan. The big block pans were shaped a little differently, presumably for oil control.

BIGT82

thanks joe ya ive realized that im seeing that they have different pattern what did you mean by BBO oh duh (big body olds) ya ok i get that so do i have to get a different oil pick up also or can i use the same one off that motor? cuz my oil pu is smashed on my 425?

joe_padavano

Actually BBO = big BLOCK Olds, SBO = small block Olds, SBC = small block Chebby, etc. The 307 pickup will work with either SBO or BBO oil pans, but not with the Toro pan.

64Rocket

If you have a spun rod bearing , you WILL have to have the crank machined and the connecting rod resized and new rod and main bearings. You should put a new oil pump and shim the pressure spring.
Like others have said you need to use the rubber engine mounts for the 307 and the flex plate has to be for the early 400/425. You should be able to use the water pump from the 307 and all your pulleys should line up.

Gene