400 to 350

[Gator]

I made a thread awhile ago looking for help regarding an issue I was having in my 400. I never officially figured out the issue, but I am sure it is a main bearing that went bad.

Anyway, I've decided to swap it out and picked up a 70's 350 a few weeks ago. I've never done a motor swap however, and after researching, I can't find any information that will help me. Both motors are from the 70's and are carb'd.

I have a few questions about this situation. Will the 350 be a direct swap (motor mounts and all)? How long much time should I look at spending on this swap? I'll be removing the hood, have the tools, cherry picker, etc and work at an auto part warehouse so tools and parts won't be an issue. Lastly, how do I do the swap? I intend on breaking it up into parts because of the winter. I know to remove the distributor but I can't think of much else to remove before unbolting it from the mounts and transmission (besides the 3 fuel lines and radiator hoses). I appreciate any help and would appreciate any directions to any guides that may help.

Thanks.

 

[Rusty Nail]

You'll want to use the original clamshells to the truck (from the 400). I recommend installing (factory) exhaust manifolds prior to putting it in the truck. Don't try to it last, the ******* manifolds CHANGE SHAPE and tweak. It's WAY EASIER to do it with the motor on the stand, rather than bent over in the engine bay.

Verify the correct flywheel / starter prior to installation.

Everything else is straightforward.
I did this last year and those things proved the most frustrating
Good luck, safety first.

 

[1987 GMC Jimmy]

I made a thread awhile ago looking for help regarding an issue I was having in my 400. I never officially figured out the issue, but I am sure it is a main bearing that went bad.

Anyway, I've decided to swap it out and picked up a 70's 350 a few weeks ago. I've never done a motor swap however, and after researching, I can't find any information that will help me. Both motors are from the 70's and are carb'd.

I have a few questions about this situation. Will the 350 be a direct swap (motor mounts and all)? How long much time should I look at spending on this swap? I'll be removing the hood, have the tools, cherry picker, etc and work at an auto part warehouse so tools and parts won't be an issue. Lastly, how do I do the swap? I intend on breaking it up into parts because of the winter. I know to remove the distributor but I can't think of much else to remove before unbolting it from the mounts and transmission (besides the 3 fuel lines and radiator hoses). I appreciate any help and would appreciate any directions to any guides that may help.

Thanks.

Yes, it's a 100% direct swap. As far as the time invested goes, it really depends. You have all the tools and access to more tools if needed, which is a big plus. However, you've never done this before, and you have to account for interruptions. Having a buddy there when you start to hoist that sucker out of there would be good and putting the other one in, too. I'd shoot to spend a weekend or the equivalent of one on it since you're breaking it up. Maybe Friday night taking everything off, undoing things, unbolting things and making sure you're ready to go. Hit the ground running Saturday pulling the motor out and getting the replacement back in and hook as much up as you can. Same mentality for Sunday except work on getting it going good. That's how I would approach it. It shouldn't be too bad, but I wouldn't expect it to go completely without a hitch, even if the hitch is a small one. The way you've gotta think about it is untethering the engine as much as you can so it can be pulled without resistance. That means undoing the starter wires, undoing the ground cables that touch the engine, removing the fan shroud, undoing the upper and lower radiator hoses (maybe even pulling the rad just to protect it), undoing the heater hoses, removing the carburetor which includes the cabling, removing the fan and clutch so they don't get squished, unplugging your distributor, removing your flexplate cover, removing your torque converter bolts, removing your bellhousing bolts, undoing your motor mounts, and unbolting your headers/manifolds. That's all I could think of. I think with my eyes a lot, and I'm 120 miles away from my vehicles so I can't look at them and make a visual checklist so I'm spouting this off from memory. I don't know why you'd have to take your distributor off. If that's standard procedure for pulling a motor, that's a whoops on my behalf. That's about it, though. How complete is this other motor, and how much are you gonna have to take off this one to make it work? I would suggest getting you a little build stand and a tarp to store this 400. They're cool engines. Maybe you can go back sometime and tear it down and go through it. I found this run stand in New Orleans that this little shop was getting rid of for thirty dollars, and I grabbed it. They're a good tool to have.

 

[WFO]

Just don't put the harmonic balancer from the 400, on the 350. 400s are external balanced.

 

[CSFJ]

Flex plate/flywheel is different too, if I remember correctly.

 

[PrairieDrifter]

Flexplates and flywheels are different on a 400. Correct. Same as the balancer. Everything else is completely the same

 

[Gator]

You'll want to use the original clamshells to the truck (from the 400). I recommend installing (factory) exhaust manifolds prior to putting it in the truck. Don't try to it last, the ******* manifolds CHANGE SHAPE and tweak. It's WAY EASIER to do it with the motor on the stand, rather than bent over in the engine bay.

Verify the correct flywheel / starter prior to installation.

Everything else is straightforward.
I did this last year and those things proved the most frustrating
Good luck, safety first.

Clamshells should be the motor mounts right? How many of them should I expect to find and will they be on the bottom of the motor? I intend on doing a lot of part swapping with it on the stand, since I put a bunch of 350 parts onto it. It's running headers so I shouldn't need to worry about manifolds.

Yes, it's a 100% direct swap. As far as the time invested goes, it really depends. You have all the tools and access to more tools if needed, which is a big plus. However, you've never done this before, and you have to account for interruptions. Having a buddy there when you start to hoist that sucker out of there would be good and putting the other one in, too. I'd shoot to spend a weekend or the equivalent of one on it since you're breaking it up. Maybe Friday night taking everything off, undoing things, unbolting things and making sure you're ready to go. Hit the ground running Saturday pulling the motor out and getting the replacement back in and hook as much up as you can. Same mentality for Sunday except work on getting it going good. That's how I would approach it. It shouldn't be too bad, but I wouldn't expect it to go completely without a hitch, even if the hitch is a small one. The way you've gotta think about it is untethering the engine as much as you can so it can be pulled without resistance. That means undoing the starter wires, undoing the ground cables that touch the engine, removing the fan shroud, undoing the upper and lower radiator hoses (maybe even pulling the rad just to protect it), undoing the heater hoses, removing the carburetor which includes the cabling, removing the fan and clutch so they don't get squished, unplugging your distributor, removing your flexplate cover, removing your torque converter bolts, removing your bellhousing bolts, undoing your motor mounts, and unbolting your headers/manifolds. That's all I could think of. I think with my eyes a lot, and I'm 120 miles away from my vehicles so I can't look at them and make a visual checklist so I'm spouting this off from memory. I don't know why you'd have to take your distributor off. If that's standard procedure for pulling a motor, that's a whoops on my behalf. That's about it, though. How complete is this other motor, and how much are you gonna have to take off this one to make it work? I would suggest getting you a little build stand and a tarp to store this 400. They're cool engines. Maybe you can go back sometime and tear it down and go through it. I found this run stand in New Orleans that this little shop was getting rid of for thirty dollars, and I grabbed it. They're a good tool to have.

Thank you for the list of most, if not, all items that will need to be removed. I've been looking for one because I didn't use one when I dropped the trans years ago and snapped the TV cable. Took a few months to figure it out.

I've read that it's good to take the distributor off to avoid breaking it along the firewall. Doesn't matter much since it'll have to come off to go on the other motor. The new motor is 100% complete. I have parts from my 400 which I'll be swapping over (intake manifold, carb, valve covers, fuel pump (only has 10 miles on it and is a 350 pump)). I'm not sure what I'll do with the 400 yet, I've had offers for it a few weeks ago but no one was consistently interested. I want to know where the problem comes from so I may look into tearing it down, but I just have to see where it goes with school and work.

 

[1987 GMC Jimmy]

Clamshells should be the motor mounts right? How many of them should I expect to find and will they be on the bottom of the motor? I intend on doing a lot of part swapping with it on the stand, since I put a bunch of 350 parts onto it. It's running headers so I shouldn't need to worry about manifolds.



Thank you for the list of most, if not, all items that will need to be removed. I've been looking for one because I didn't use one when I dropped the trans years ago and snapped the TV cable. Took a few months to figure it out.

I've read that it's good to take the distributor off to avoid breaking it along the firewall. Doesn't matter much since it'll have to come off to go on the other motor. The new motor is 100% complete. I have parts from my 400 which I'll be swapping over (intake manifold, carb, valve covers, fuel pump (only has 10 miles on it and is a 350 pump)). I'm not sure what I'll do with the 400 yet, I've had offers for it a few weeks ago but no one was consistently interested. I want to know where the problem comes from so I may look into tearing it down, but I just have to see where it goes with school and work.

Oh, and add power steering lines, A/C lines, and the alternator hot wire to that list if you have those accessories. You're welcome. I'd do a little homework before you swap intakes. Some people use the gasket kit, some people use RTV and some use both. The lore out there and the way I've done it says that you're best off using the gaskets on the actual heads, but the two small pieces that go on the front and back of the motor are best done with RTV. If you do that, just be careful with the oil pressure port on the back. I think whatever you do with the motor should be contingent on your interest. If you don't have the time to wrench on it, it's probably best to get rid of it now while it's fresh out. If you do feel like you will, I'd definitely get a little build stand and something to cover it up with. If space isn't a concern, I'd keep it anyway. Those motors were around for only four years so they're pretty special.

 

[77 K20]

I think everyone else pretty much covered everything. One thing I will add is don't be afraid to take a bunch of pictures on your digital camera/phone before you tear it apart. They are free to take, and each pic is worth 1000 words later if you are confused.
I did that on my old 400 before I removed it. And there were a lot of snags (my replacement engine was newer). Not as "direct" as I thought it was going to be.
So it took a lot longer than planned. I forgot small details of how things were, or how they were hooked up. It was nice to go back thru and look at prior pictures. (vacuum lines, whatnot)

 

[1987 GMC Jimmy]

Yes, agreed!

 

[Rusty Nail]

What I'm calling the "clamshell" is the part of the motor mount that bolts to the engine block, not the truck's frame.
In my experience, they can be specific to the TRUCK, and that is good advice.

As is returning a bolt back to the place it came from. The intention being to NOT end up with a huge pile of bolts and have to determine where they go.

Good luck!

 

[Gator]

Oh, and add power steering lines, A/C lines, and the alternator hot wire to that list if you have those accessories. You're welcome. I'd do a little homework before you swap intakes. Some people use the gasket kit, some people use RTV and some use both. The lore out there and the way I've done it says that you're best off using the gaskets on the actual heads, but the two small pieces that go on the front and back of the motor are best done with RTV. If you do that, just be careful with the oil pressure port on the back. I think whatever you do with the motor should be contingent on your interest. If you don't have the time to wrench on it, it's probably best to get rid of it now while it's fresh out. If you do feel like you will, I'd definitely get a little build stand and something to cover it up with. If space isn't a concern, I'd keep it anyway. Those motors were around for only four years so they're pretty special.

I think I've done it both times, with the most recent being with all RTV. I was removing and installing it on a monthly basis it felt like.

What I'm calling the "clamshell" is the part of the motor mount that bolts to the engine block, not the truck's frame.
In my experience, they can be specific to the TRUCK, and that is good advice.

As is returning a bolt back to the place it came from. The intention being to NOT end up with a huge pile of bolts and have to determine where they go.

Good luck!

Ah, that clear it up. I've seen the term around while researching but wasn't sure. Thanks.

 

[Camar068]

Thanks for the clamshell bit, I've wondered if it was the whole thing, top or bottom half as well. Like they said above, tons of pics of everything and def test the exhaust to make sure it fits. I wasted hours at the yard looking for a set that would fit. On the third trip he said take these 2 sets and bring me back the other today. Course he was 1/2 hour away, a lot of wasted time on a daily driver.

 

[Gator]

Rather than making a new thread, I'll add on to this one

I pulled the 400, swapped over the fuel pump, valve covers and motor mounts/clamshells. I haven't put the manifold on yet because I'm using that section with the leveler.

My problem is that as I'm installing the new motor (350) is that I can't get the 2 pins on the 350 to get into their holes on the trans. I have the 3 motor mount bolts on each side in their holes, but not bolted up. The flexplate is rubbing into the driver side part of the housing. It looks like the transmission or motor (probably motor lol) needs to be rotated but I'm not sure how. I do have a jack support on the trans.