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Old 07-19-2012, 08:38 AM
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chevy smallblock 350

I want to know what i would have to do to put a 350 from a 1986 chevy pickup into a 1998 chevy z71. I have been told it will work and i have been told it wont. i would like to use the older 350 because it has low miles on a rebuild and i dont want to rebuild my newer one. i dont want to switch any thing else is it possible or not?

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Old 07-19-2012, 09:03 AM
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Quote:
Originally Posted by bglinde View Post
I want to know what i would have to do to put a 350 from a 1986 chevy pickup into a 1998 chevy z71. I have been told it will work and i have been told it wont. i would like to use the older 350 because it has low miles on a rebuild and i dont want to rebuild my newer one. i dont want to switch any thing else is it possible or not?
You will need to swap over some of the sensors and the FI system (Manifold etc) The engine will bolt right up. Is the 98 a Vortec, if it is you will not be able to bolt up the manifold to the old heads.

There are other systems in the truck that will need feedback from the ECM so the engine sensors will need to be in tact. you could get around this but it would be a ton of work and hardly worth it
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Old 07-19-2012, 10:42 AM
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it is a vortec. that is one thing that i dont know if it will work. i was told that the heads are set at a diffent degrees. i will need to get a diffent intak because the one i have on the 98 is cracked. so if there is a intake that i can put on the other moter and make it work so i can run my throdel body that would be ther best. the sensor thing is not a problem since it is a 350 there not hard to change at all.
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Old 07-19-2012, 11:21 AM
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Quote:
Originally Posted by bglinde View Post
I want to know what i would have to do to put a 350 from a 1986 chevy pickup into a 1998 chevy z71. I have been told it will work and i have been told it wont. i would like to use the older 350 because it has low miles on a rebuild and i dont want to rebuild my newer one. i dont want to switch any thing else is it possible or not?
This crosses a couple generation changes, the 86 should have a carburetor, the 98 is Vortec with sequential multi-port injection. Between them is the Throttle Body Injection, Swirl Port head engine which is a technical bridge between the two.

The 98 needs a special crank damper and uses a different timing case cover that positions a sensor that is triggered by the crank damper. It uses different heads (Vortec) with a different bolt pattern and different intake port size and height so old manifold such as the 86 will not fit the new heads. The 98's distributor is different taking it's instructions from the computer that runs everything else (transmission, speedometer, etc).

Given that everything about the 98 is different and computer managed you just can't drop the 86 engine in there and expect anything to work. You really have two choices you need to pick from as ways to go.

1) Simplest, use the bottom end of the 86 engine with the 98 engine heads and intake EFI system; the plastic timing cover from the 98; the crank damper assembly from the 98 (this stuff will bolt to the 86 block and crank); then it's likely that the 86 engine still uses the two piece rear seal this changed to the one piece your 98 has in 1987 production. The 86 will require using the 86 flywheel or flexplate for which ever type tranny you have. This should bolt to the 98 clutch or torque converter. The two to one piece seal change also changed the crankshaft flange bolt pattern and a bit of counterbalance so the fly/flex has match the rear seal type used on the crank.

2) The way more complex and I think undesirable from a cost and time standpoint is to use the carbed 86 engine in the 98. To get this to work requires a replacement or major modification to everything the computer, fuel injection, and emissions systems touch which includes the transmission especially an automatic, the fuel system, etc. Everything you can think of is impacted except maybe the seat covers and paint. If my description in paragraph number 1 seems complicated, you ain't seen nothing complicated and expensive till you go down this path.

So in my opinion go with door number 1. Or just buy a Vortec crate replacement, it's a couple thousand bucks but you'll have the truck up and running during your life time. GM part number 12530282 is the light duty that engine uses 2 bolt mains; the 12530283 is the heavy duty version with 4 bolt mains. Other than that these engines are identical.

Bogie
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Old 07-19-2012, 11:34 AM
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ok oldbogie. your saying that there is no differences where the heads sit. people have told me that you cant put 98 heads on a 86 block. i dont know that much about that i just want to know everything that i can before i take this project on.
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Old 07-19-2012, 12:55 PM
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Originally Posted by bglinde View Post
ok oldbogie. your saying that there is no differences where the heads sit. people have told me that you cant put 98 heads on a 86 block. i dont know that much about that i just want to know everything that i can before i take this project on.
The 98's heads will bolt on the 86 block and the electronic fuel injection will bolt to the block.

- The 86 uses a flat tappet cam the 98 a roller, with the 98 heads on the 86 block you will need to use the longer 86 push rods that are compatible with the shorter flat tappets. This just goes together; no problems set the lash adjustment just like it was all 86. The 86 uses push rod guides the 98 uses rockers that guide on the valve stem. So no further guide consideration is needed when using the 98 heads.

- The 86's metal front timing cover is removed as is its crank damper. The 98's plastic front timing cover is substituted (you will find that you may have to remove some locating pins and that the plastic cover does not use all the bolts the metal cover did. You can drill the cover to take these or leave them off which ever you're comfortable with. Here's a stopping point for another consideration. The plastic front cover might have clearance problems with the 86's timing set, go slow and check this cause if it doesn't clear and you start the engine it will eat a hole through the plastic faster than you can shut it off. Best solution here if it doesn't clear is to add a gasket or two. That's about it as pushing this further gets the damper and crank position sensor too miss aligned. But 1 or 2 additional gaskets ought to be enough.

- You will use the damper assembly from the 98 on the 86's crank, this should be removed from the 98 and slide on the 86; shouldn't be any more difficult than that. The 98 has a notch that is sensed by the Hall Effect gadget in the plastic timing cover to tell the computer where the #1 piston is at, so the 98cover and crank damper must be there. While the 86 and 98 dampers look different, they both are neutral balanced for the 350 and changing one for the other will not affect crank balance.

- The 98's distributor does nothing but distribute spark and tell the computer about cam position. It must be there. It just drops into the 86 block with the 98 EFI intake on it, should be no problem.

- You need to use the 86's style flywheel or flexplate to mate with the 98's clutch or torque converter. The crank flange bolt pattern is different between the 86 (large) and the 98 (small) to accommodate the different rear crank seals between these engines. The clutch or torque converter bolt pattern is the same so hooking up will not be a problem. An aside that should not affect you but worth knowing is that the 98 carries a small amount of external counter weight on the flywheel or flexplate. The clutch or torque converter across these years remains neutral balanced so swapping between the 86 and 98 will not be a problem.

- Buy or make a fuel pump close-off as you have no need for the mechanical fuel pump. Don't forget to pull the push rod out while you're there and put a bolt with some sealer into the hole used to lock the push rod when replacing the pump so you don't get an oil leak.

- All the serpentine belt brackets will bolt on the 86 engine. You need to use the 98's water pump and fan (if it's driven off the pump) as the 98 pump and fan rotate counter clockwise with the serpentine belt drive which is backward compared V-belt driven 86.

So in a nutshell

1) Use the 98's heads and EFI system bolted to the 86's short block. Use the 86's push rods with the 98's rockers.

2) Use the 98's front timing cover.

3) Use the 98's crankshaft damper

4) Use the 86's flywheel or flexplate.

5) Use the 98's distributor.

6) Remove the fuel pump push rod and close off the 86's fuel pump mounting pad.

7) Install the 98's serpentine brackets and accessories, use the 98's water pump and fan.

That ought to do ya.

PS edit; the starter on the 98 is one of those new super powerful things that are quite small, it should bolt onto the 86 without problem. You can use either but given the choice I'd go with the 98 mini.

Bogie

Last edited by oldbogie; 07-19-2012 at 01:00 PM.
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Old 07-19-2012, 01:29 PM
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If it's the plastic part of the intake manifold that's cracked on the 98 it's available from dorman much cheaper than you would think.
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Old 07-19-2012, 02:15 PM
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The 98 likely isn't in that bad of shape if you treated it right. I'd just rebuild that, the only cost difference you're looking at may be rings and bearings if everything checks out.
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