1990 4.3L short block or 5.7L swap

[brian36578]

Engine died on my 4.3L on Monday, pulled the engine yesterday and disassembled today to find it threw a rod and cracked the block. I have been interested in a 5.7L since I got this boat, and I believe I would have enough room (though it would be very tight, I had seen someone online say you need 8" additional space in front of the 4.3L to fit the 5.7L?) plus my uncle has a cracked alpha 1 stern that came off a 5.7L so I would be able to swap the gearing right away as well. Other than the sterndrive gears, what else needs to be modified for this swap? I am also trying to get back in the water ASAP since its mid summer so I might just go with a 4.3L short block, does anyone know of any place that sells reman 4.3L, ideally within a couple hour drive of SE Michigan? Also, would I be able to swap in a short block from a vehicle if I get the same year? I think this would be the cheapest and quickest route.

 

[Bondo]

Ayuh,...... If you go with the 5.7l, you'll need a Fully Dressed motor, with All the bits, 'n pieces,.....

If ya go 4.3l, go with a long block, not a short block,......

Michigan Motors sells lotsa boat motors,.....

 

[Rick Stephens]

Needs a lot of stuff to convert to 5.7L. And you need to move the motor mounts up 3 inches.

 

[Furbird]

The Vortec 4.3's from the vehicles use the same head gaskets and freeze plugs that the Mercruisers do, so yes they are drop in, except you need to use the Mercruiser camshaft. However, yours is pre-vortec so I don't know about those. My boat has a 4.3 from a Chevy Express van and the previous owner (who did the swap and is a machinist by trade) verified that info before he swapped it. He put freeze plugs in it anyway since it was out. Been in there since 2009. Exponentially cheaper than a Mercruiser option.

 

[Rick Stephens]

The Vortec 4.3's from the vehicles use the same head gaskets and freeze plugs that the Mercruisers do, so yes they are drop in, except you need to use the Mercruiser camshaft. However, yours is pre-vortec so I don't know about those. My boat has a 4.3 from a Chevy Express van and the previous owner (who did the swap and is a machinist by trade) verified that info before he swapped it. He put freeze plugs in it anyway since it was out. Been in there since 2009. Exponentially cheaper than a Mercruiser option.

All factory motors use some sort of plated steel core plug. Those have to be replaced.

The cam in a pickup or van motor is just fine.

Headgaskets depend on if you are in salt water.

Water pump has to be changed as well as all the bolt on parts including ignition.

 

[brian36578]

I found a 4.3L local out of a 1991 GMC Safari with 86,000 for $200 so I will be checking that out. It will be used in fresh water, so head gaskets should be fine, correct? If I strip it down to the long block and use all the accessories off my motor should I be fine or do I need to put in different freeze plugs as well?

 

[Rick Stephens]

Have to change the steel core plugs to brass. Steel ones are great with coolant, not so good with plain water.

 

[Scott Danforth]

I found a 4.3L local out of a 1991 GMC Safari with 86,000 for $200 so I will be checking that out. It will be used in fresh water, so head gaskets should be fine, correct? If I strip it down to the long block and use all the accessories off my motor should I be fine or do I need to put in different freeze plugs as well?

you have to pull the heads and swap to marine head gaskets. not until 2007 were the automotive head gaskets the same as the marine gaskets

you need to change all the core plugs to brass or stainless. no such thing as a freeze plug, its a core plug to get the core casting sand out of the block casting at the foundry

while at it, you can swap in the mercruiser cam if you want, up to you

you then need to swap the marine circulating pump and all the accessories from your marine motor to the long block.

if you want more power, swap to vortec heads and a 4-barrel intake at this point

 

[nola mike]

It appears that at some point gm switched to brass core plugs. Mine were on my '01 and another guy says the same about his 02

 

[brian36578]

Thanks! I'll do the head gaskets and core plugs for sure. I will leave the pre-vortec heads and 2-barrel for now, the boat does about 38 knots which is good enough for this 19ft bow rider. Someday when I buy a mid 20ft cuddy or flybridge then I'll make this boat mean with a 5.7 swap and haul exhaust .
As for the cam, do you know what the profile difference is from the van to the marine application?

 

[Furbird]

Slang or not, every mechanic in the world calls it a "freeze plug". You walk into a parts store and ask for core plugs and they're going to look at you like an alien. Or they'll hand you heater core block off plugs which are rubber caps.

It appears that at some point gm switched to brass core plugs. Mine were on my '01 and another guy says the same about his 02

My 01 is the same way. Machinist changed them anyway since the block was out and he had been told they were not brass by boat mechanics. He cut several in half afterwards and verified they were brass originally. I believe the same guy you are referring to also said the head gaskets are identical and that has also been mentioned on other forums. It will never affect me because I won't run in salt water and neither did the previous owner. Plus a multitude of people have said running a raw water cooled I/O in salt water is a good way to put a boat mechanic's children through college.

 

[brian36578]

Also, what about oil pump? is that the same from automotive to marine?

 

[Scott Danforth]

Slang or not, every mechanic in the world calls it a "freeze plug". You walk into a parts store and ask for core plugs and they're going to look at you like an alien. Or they'll hand you heater core block off plugs which are rubber caps.



My 01 is the same way. Machinist changed them anyway since the block was out and he had been told they were not brass by boat mechanics. He cut several in half afterwards and verified they were brass originally. I believe the same guy you are referring to also said the head gaskets are identical and that has also been mentioned on other forums. It will never affect me because I won't run in salt water and neither did the previous owner. Plus a multitude of people have said running a raw water cooled I/O in salt water is a good way to put a boat mechanic's children through college.

since we have gone off topic

dont know a single SAE certified mechanic that calls them "freeze plugs"


welsh plugs - yes
core plugs - yes
block plugs - yes

however never once has one called them "freeze plugs" on the job

 

[brian36578]

Thank you for the history of freeze/welsh/core/block plugs, they will be replaced with brass ones. Lets get this post back on topic now:

- Oil pump for automotive, same or different from marine?

- Camshafts, I looked at new camshafts for a 1991 GMC Safari with a 4.3L on rockauto, They had 3 camshaft manufacturers all had different cam profiles....I have the service manual for the 4.3L merc, it shows the lift but not duration. I would prefer to keep the same cam in there since I do not have a cam bearing install tool and not interested in buying one. From those that have done a similar swap and left the van cam, did they notice any power difference? Harder to get on plane? Lower top speed?

 

[Scott Danforth]

Thank you for the history of freeze/welsh/core/block plugs, they will be replaced with brass ones. Lets get this post back on topic now:

- Oil pump for automotive, same or different from marine?

- Camshafts, I looked at new camshafts for a 1991 GMC Safari with a 4.3L on rockauto, They had 3 camshaft manufacturers all had different cam profiles....I have the service manual for the 4.3L merc, it shows the lift but not duration. I would prefer to keep the same cam in there since I do not have a cam bearing install tool and not interested in buying one. From those that have done a similar swap and left the van cam, did they notice any power difference? Harder to get on plane? Lower top speed?

the oil pump is the exact same for both. I believe Melling M-55, same as the SBC V8's pickup may be pan dependent. if swapping pans, us playdoh to check pickup to pan clearance. (put duct tape over the pickup screen, put a ball of playdoh on the duct tape, install the pan, then remove and measure the pickup to pan distance.)

not sure on the cam profile in the vans, however the truck profile is fine. GM had multiple cams available for the 4.3 depending on application.

I doubt you would notice any issues.

if the cam bearings are good, no need to change them even if you change cams. just keep the lifters with the cam lobes