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Old 01-12-2018, 03:20 PM   #1
sick472
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'76 350 into an '85 3/4 ton 4x4

I have my old '76 2wd that has a GM 350 crate motor with 70K miles on it and my '85 3/4 ton 4x4 is burning a lot of oil (like a quart every 1000 miles. maybe more). The '76 is almost see-through due to rust. Both are automatics and AC trucks. Neither have any real power to speak of. The '85 has an edelbrock intake and Holley carb with unknown heads and is a 350 ci as well.

My questions...what should I be aware of if I chose to swap the motor from the '76 into the '85? Would it be straight forward or will I have to make mods?

I'd love for this to be a one weekend chore should I pull the trigger.

Thanks in advance!
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Old 01-12-2018, 03:25 PM   #2
natedogg
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Re: '76 350 into an '85 3/4 ton 4x4

This will be a easy swap. All the pulleys and brackets from your 85 will swap over to the 350 out of the 76. You and a buddy should be able to do this in a weekend.
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Old 01-12-2018, 07:40 PM   #3
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Re: '76 350 into an '85 3/4 ton 4x4

Should be a piece of cake, especially if you're going to use the intake and carb off the 85's current engine. But there's always some little issues to iron out. Seems like 85 engines had passenger side dipstick, whereas 74 had drivers side. But that shouldn't be any big deal. I would transfer any parts like intake manifold, oil & temp senders, and kick-down cable bracket while both engines are out. And that's also the time to make sure the 74's starter will bolt to the 84's electrical connectors.
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Old 01-16-2018, 09:38 AM   #4
sick472
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Re: '76 350 into an '85 3/4 ton 4x4

Thanks for the encouragement folks!

I guess it's time to just wait for the old 85 engine to expire or use so much oil that I can't take it anymore. I think it is constantly leaking by the valve seals as I never see any oil smoke or leaks big enough to compare to the oil loss. The spark plugs need to be freshened-up/changed every year or so (5000 miles) because of oil fouling. Compression is from 170 to 200 psi and the pcv valve has been changed. There is no coolant loss either. Anyhow, this may be something for a different thread. Thanks again!
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Old 01-16-2018, 01:44 PM   #5
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Re: '76 350 into an '85 3/4 ton 4x4

If the dipstick is on a different side, you may have to swap out exhaust manifolds...which means your exhaust pipes will no longer fit -> trip (tow?) to muffler $hop. I think a lot of the crate engines had dipstick provisions on both sides though. You'll just have to check I guess.
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Old 06-29-2021, 08:09 AM   #6
sick472
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Re: '76 350 into an '85 3/4 ton 4x4

Well, it's time to do the swap. I have the 76 engine on the stand and hope to use the original cast intake with the original Quadra Jet carb (will rebuild). I plan to replace the water pump and fuel pump, but have not closely compared the two truck's pumps....

Should I buy the replacement pumps for the 85?

The 76 did not have a return line on the fuel pump and I think the 85 does. I am assuming that both the 85 style pumps will bolt up to the 76 motor.
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Old 06-29-2021, 10:18 AM   #7
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Re: '76 350 into an '85 3/4 ton 4x4

You want the fuel pump for the frame truck your going into. Also be aware in 1986 SBC used a 1 piece rear main seal and different flex plate. Always something to look out for when swapping engines. Guessing one truck is a th350 and the other is a 700r4? i know your going into an 85 and not an 86 but who knows what has been changed.

This is a great time to replace the rear main seal and oil pan gasket. I like the one peice felpro oil pan gaskets. Its a great time to knock in new freeze plugs and give it a nice coat of paint. Do you need too? Maybe not but after having to do a rear main seal in a rig a week after a swap i will always do them on the stand before.
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Old 07-14-2021, 11:08 AM   #8
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Re: '76 350 into an '85 3/4 ton 4x4

Thanks for everyone's help...it turns out the 76 motor had some issues (one scarred crank bearing and one booger'd piston). I found this while breaking it down to change the rear main seal. Good 84 400 suggested that, otherwise I'd never seen the crank bearing. So...time for rebuild. I am sure I will still be mixing and matching parts as the 76 block should be a good base to build from with the 85 block as a back-up.
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