4.3 motor swap with truck engine

[timharper89]

I'm planning on swapping my knocking 1987 4.3L merc (s/n 0B459735) engine with a truck donor. Everything I've found is late 90s and later (vortec). What accessories can I keep from my old motor, and what won't fit? I know the intake manifold is different, but is there anything else?
As far as checking the new motor, compression test, take off the valve covers...anything else? I know I need an alignment tool. Any other non standard tools I might need? Any other advice here? I have next week off and am hoping to get it swapped out then. Thanks for any help

 

[itsathepete]

You can use your 1987 cylinder heads and intake with the donor if you like but you will get a significant power increase from the vortec heads. They will require a new intake manifold. Make sure you get one that fits your carb, be it 2 or 4 barrel spreadbore or squarebore. If you are going to be in saltwater you must get a marine intake. 99% chance there will not be a way to mount a mechanical fuel pump on the donor engine so you will have to convert to an electric fuel pump. Get a good name brand (Carter and Airtex are a couple) marine low pressure electric fuel pump. Also a fuel pressure regulator and an oil pressure cutoff switch and associated wiring supplies.
You will strip everything off the donor engine until it is just a block and heads. You will use all the accessories from the 1987 engine to put on the new engine. You may need to use the timing cover off the old engine if the balancer has a different seal size. Get an engine gasket kit, head bolts and silicone sealant. Get a set of brass core plugs and replace the automotive steel ones. It's a good idea to replace the rear main seal and oil pump while you're there.

 

[achris]

Just be aware that later 4.3 blocks may have some metric fastener threads, so you might need to replace bolts (things like starter motor bolts)...

Your 1987 is a 2bbl without a balance shaft, so the water pump may not fit. (too close to the block for the wider timing cover.)

Chris......

 

[Scott Danforth]

remember, you have to take the vortec motor or any truck motor, knock out the core plugs and replace them with brass or stainless

you also need to use marine head gaskets

the only thing you need from the truck is the block and heads unless you get a motor from a truck with a manual, then the flywheel too

you will not be using any of the accessories, brackets, pulleys, water pump, etc from the truck.

vortec marine intake manifolds can be gotten used, or new for about $300

I would upgrade to a PMGR starter

@nola mike did a mix and match of vortec and non-vortec in his thread

 

[itsathepete]

Just be aware that later 4.3 blocks may have some metric fastener threads, so you might need to replace bolts (things like starter motor bolts)...

Your 1987 is a 2bbl without a balance shaft, so the water pump may not fit. (too close to the block for the wider timing cover.)

Chris......

If the water pump doesn't fit because of the timing cover, the timing cover from the old engine can probably be used. It will be metal, and not stick out as far.

 

[Scott Danforth]

If the water pump doesn't fit because of the timing cover, the timing cover from the old engine can probably be used. It will be metal, and not stick out as far.

No, cant swap timing covers from a non-balance shaft motor to a balance shaft motor

 

[Rick Stephens]

If the water pump doesn't fit because of the timing cover, the timing cover from the old engine can probably be used. It will be metal, and not stick out as far.

There is no cross compatibility.

 

[Scott Danforth]

light reading. https://forums.iboats.com/threads/complete-history-of-the-4-3-liter-with-casting-numbers.693935/

 

[Rick Stephens]

light reading. https://forums.iboats.com/threads/complete-history-of-the-4-3-liter-with-casting-numbers.693935/

More like essential reading when you want to swap gen.

 

[itsathepete]

No, cant swap timing covers from a non-balance shaft motor to a balance shaft motor

Copy. Wasn't sure if it would work but can a thinner cover be used to allow clearance for the older water pump?

 

[Scott06]

Just be aware that later 4.3 blocks may have some metric fastener threads, so you might need to replace bolts (things like starter motor bolts)...

The bolts that are metric are side motor mounts, flywheel cover mounts, starter bolts. Metric is an M10 thread, US is 3/8-16.

Ironically on a metric block all other threads are US , not sure why GM did mix and match on same block. When I swapped my metric 4.3 for a 5.0 ended up costing about $40 for the bolts including the proper starter bolts.

 

[achris]

Copy. Wasn't sure if it would work but can a thinner cover be used to allow clearance for the older water pump?

No.

 

[timharper89]

You can use your 1987 cylinder heads and intake with the donor if you like but you will get a significant power increase from the vortec heads.

I think I'll start with what I have and make sure I can get it running before doing that. If I go vortec later I'll get a new 4bbl marine carb as well.

They will require a new intake manifold. Make sure you get one that fits your carb, be it 2 or 4 barrel spreadbore or squarebore. If you are going to be in saltwater you must get a marine intake.

If in freshwater only I don't need specific marine intake?

99% chance there will not be a way to mount a mechanical fuel pump on the donor engine so you will have to convert to an electric fuel pump. Get a good name brand (Carter and Airtex are a couple) marine low pressure electric fuel pump. Also a fuel pressure regulator and an oil pressure cutoff switch and associated wiring supplies.

Already have all this due to a fun project the previous owner left me with when I bought it. There is no mechanical fuel pump hole on my block.

You will strip everything off the donor engine until it is just a block and heads. You will use all the accessories from the 1987 engine to put on the new engine. You may need to use the timing cover off the old engine if the balancer has a different seal size. Get an engine gasket kit, head bolts and silicone sealant. Get a set of brass core plugs and replace the automotive steel ones. It's a good idea to replace the rear main seal and oil pump while you're there.

Thanks for this

 

[timharper89]

remember, you have to take the vortec motor or any truck motor, knock out the core plugs and replace them with brass or stainless

you also need to use marine head gaskets

the only thing you need from the truck is the block and heads unless you get a motor from a truck with a manual, then the flywheel too

Why the flywheel if it's a manual?

you will not be using any of the accessories, brackets, pulleys, water pump, etc from the truck.

I read something about maybe the belt would be different on newer motors. Is this anything to worry about?

vortec marine intake manifolds can be gotten used, or new for about $300

I would upgrade to a PMGR starter

What's the benefit of this?

@nola mike did a mix and match of vortec and non-vortec in his thread

 

[timharper89]

Just be aware that later 4.3 blocks may have some metric fastener threads, so you might need to replace bolts (things like starter motor bolts)...

Your 1987 is a 2bbl without a balance shaft, so the water pump may not fit. (too close to the block for the wider timing cover.)

Chris......

Can I just use the bolts from the donor?

 

[timharper89]

The bolts that are metric are side motor mounts, flywheel cover mounts, starter bolts. Metric is an M10 thread, US is 3/8-16.

Can I just use the bolts from the donor motor?

Ironically on a metric block all other threads are US , not sure why GM did mix and match on same block. When I swapped my metric 4.3 for a 5.0 ended up costing about $40 for the bolts including the proper starter bolts.

 

[itsathepete]

If in freshwater only I don't need specific marine intake?

Just use the intake you have if keeping old heads

Why the flywheel if it's a manual?

automatic trans uses a flexplate, manual uses flywheel, marine uses flywheel

I read something about maybe the belt would be different on newer motors. Is this anything to worry about?

You will be using all your pulleys and accessories so, no.

 

[achris]

If in freshwater only I don't need specific marine intake?

Freshwater is still corrosive. And an aluminium manifold bolted to iron heads forms a galvanic cell... The only time you don't need a marine intake is if you're running coolant (cars and close cooled marine).

Already have all this due to a fun project the previous owner left me with when I bought it. There is no mechanical fuel pump hole on my block.

? You have a Gen II block? If so that means it has a balance shaft, so the timing cover and water pump WILL go over to the new block.

I read something about maybe the belt would be different on newer motors. Is this anything to worry about?

The belts only drive 'accessories', and since you'll be using all the accessories from the old engine you can use the belt system you currently have.

Can I just use the bolts from the donor?

Most likely yes.

 

[nola mike]

The bolts that are metric are side motor mounts, flywheel cover mounts, starter bolts. Metric is an M10 thread, US is 3/8-16.

Ironically on a metric block all other threads are US , not sure why GM did mix and match on same block. When I swapped my metric 4.3 for a 5.0 ended up costing about $40 for the bolts including the proper starter bolts.

This confused TF out of me when I started stripping out the holes using nearly identical to M10 ⅜ bolts. Ridiculous.

 

[Scott Danforth]

I think I'll start with what I have and make sure I can get it running before doing that. If I go vortec later I'll get a new 4bbl marine carb as well.

Vortec heads are an honest 20hp because of the chamber shape. Used iron vortec manifolds are $50 or less

PMGR starter is 22# lighter than a direct drive starter, uses half the power and has twice the torque

You use nothing bolted to the truck block and heads. You have to use the marine stuff from your current motor

If you do not have a mechanical fuel pump boss, you may already have a vortec block in the boat. Post casting numbers

How many bolts holding the intake on the busted block? 8 or 12?