86 Larson DC21 Engine Help Please...

[4mula97]

Hi Team!

I have an 86 Larson DC21 with the 4.3 litre OMC and a cracked block/ water jacket. Boat and trailer is in good shape for the age otherwise.

Can I swap the GM vortec block from an S-10 truck or similar vehicle? I've searched the old topics and I don't see a thread that gives me a straight answer.

Please, and thank you!

 

[matt167]

If ( IF )the boat is in nice condition. Grab a rotted 4.3L mercruiser boat that runs and swap everything. You’ll be happier

 

[Bondo]

Hi Team!

I have an 86 Larson DC21 with the 4.3 litre OMC and a cracked block/ water jacket. Boat and trailer is in good shape for the age otherwise.

Can I swap the GM vortec block from an S-10 truck or similar vehicle? I've searched the old topics and I don't see a thread that gives me a straight answer.

Please, and thank you!

Ayuh,..... Welcome Aboard,.... Yes, that can work, but only the Long Block, not the complete motor,....

 

[4mula97]

If ( IF )the boat is in nice condition. Grab a rotted 4.3L mercruiser boat that runs and swap everything. You’ll be happier

Thank you, the OMC set up is not my favorite by any stretch. I'm also looking to a friend, i think he had a 350 mercruiser set up but dang, that's a lot of work.

 

[4mula97]

Ayuh,..... Welcome Aboard,.... Yes, that can work, but only the Long Block, not the complete motor,....

Yes, just the long block. My guess is that the motor mounts and bolt patterns should be the same, yes?

 

[Bondo]

Yes, just the long block. My guess is that the motor mounts and bolt patterns should be the same, yes?

Motor mounts,..?? yes,.....

 

[Scott Danforth]

If you pull a 4.3 from a truck, get the same vintage

remember, you are basically using the short block and heads. nothing else from the truck

you will need to swap core plugs to brass, use marine head gaskets and a marine circulation pump. from there, bolt on all the marine front accessories, your intake with marine rotating electrics and the marine exhaust manifold.

by vortec, do not go by the valve covers, true vortec V6's have the vortec heads (8 intake manifold bolts) and the balance shafts. these are 1996 and later motors.

 

[4mula97]

If you pull a 4.3 from a truck, get the same vintage

remember, you are basically using the short block and heads. nothing else from the truck

you will need to swap core plugs to brass, use marine head gaskets and a marine circulation pump. from there, bolt on all the marine front accessories, your intake with marine rotating electrics and the marine exhaust manifold.

by vortec, do not go by the valve covers, true vortec V6's have the vortec heads (8 intake manifold bolts) and the balance shafts. these are 1996 and later motors.

Thank you. If i remember right, the valve covers for mid to late eighties, vehicle engines, do not have the corrugated shape like the one in my boat does but you're right, I'll need marine style freeze plugs and gaskets if i go this direction.

I may decide to sell it a is stone i didn't pay a lot for it anyway.

 

[Scott06]

Thank you, the OMC set up is not my favorite by any stretch. I'm also looking to a friend, i think he had a 350 mercruiser set up but dang, that's a lot of work.

Less work than you think as long as there is 4" in front of the 4.3

if you friend has a complete merc pulleys to prop and boat is in good shape this is the way to go. Otherwise yes a 4.3 out of a wrecking yard is cheapest way

 

[Lou C]

First thing if you’re keeping the OMC drive system which one do you have, Stringer or Cobra? Reason being is that the stringer drives used pre 1986 engines with 2 piece rear main seals, the Cobra drives all used one piece main seals. So with that the flywheels are different so you have to stick with what your drive system originally came with. 1986 IIRC is when Chevy changed over to the one piece main seal. A 1986 boat possibly could have a 1985 drivetrain….