OMC loud Clunking

cowlotter

Seaman Apprentice
Joined
Sep 1, 2019
Messages
30
You can build a brand new stroker motor for $4200. However its your money

i just mainly want something reliable and i dont personally build any of the engine or have tools to install it. i can put on the manifolds and other minor parts no problem, thats why i was considering the silver package from Michigan motorz. whats the deal with building a stroker engine vs just having this one shipped in the have the mechanic drop it in? if i decided to do the stroker what conversions would i need with my current 87 5.7 omc setup or do all parts just transfer and engine drops in and go? what brand of engine should i be looking at as well?
 
Last edited:

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,297
starting from scratch and buying new parts, a 5.7 and 6.2 are the exact same cost. the dimensions of the engines are the exact same.

your dealing with a small block chevy with OMC stuff bolted to it. your replacement motor will be a SBC with your existing OMC stuff bolted to it.

not sure by what you mean brand..... because the brand is General Motors, and you are dealing with the corporate marine motor which is a SBC.

the 315 hp is the flywheel hp for a 260hp motor/drive package

going to a vortec motor is vortec heads and a roller crank.

reliability is purely a function of maintenance.
 

cowlotter

Seaman Apprentice
Joined
Sep 1, 2019
Messages
30
starting from scratch and buying new parts, a 5.7 and 6.2 are the exact same cost. the dimensions of the engines are the exact same.

your dealing with a small block chevy with OMC stuff bolted to it. your replacement motor will be a SBC with your existing OMC stuff bolted to it.

not sure by what you mean brand..... because the brand is General Motors, and you are dealing with the corporate marine motor which is a SBC.

the 315 hp is the flywheel hp for a 260hp motor/drive package

going to a vortec motor is vortec heads and a roller crank.

reliability is purely a function of maintenance.

basically by brand i mean who would i buy a new 6.3 383 stroker from thats marine rated and a direct replacement for the 87 omc. i see a couple remaned ones on ebay linked here, what do you think.

1 - [url]https://www.ebay.com/itm/Reman-6-2L-383-Stroker-Vortec-Marine-Base-Engine-w-Intake-Volvo-Penta-97-up/263083384267?hash=item3d40fdddcb:g:zOIAAOSwqVBZZNY D[/URL]

2 - https://www.ebay.com/itm/383CI-Strok...kAAOSwrXVde5pY

3 - https://www.ebay.com/itm/ATK-Chevy-...240740&hash=item3f84cab8d9:g:BLwAAOSwKt5ZlxGq
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,297
No, I would buy a brand new virgin block and build a 377. a 383 is a 0.030" overbore in addition to the 3.75" stroke crank

read this (in its entirety) https://forums.iboats.com/forum/eng...outdrives/10804776-upgrading-to-a-383-stroker

there are GMPP links, etc.

a new 377 is $4200, a reman stroker from someone not price-gouging would be about $3k talk to your local machine shop

I built my 468 for less than $3k
 

cowlotter

Seaman Apprentice
Joined
Sep 1, 2019
Messages
30
No, I would buy a brand new virgin block and build a 377. a 383 is a 0.030" overbore in addition to the 3.75" stroke crank

read this (in its entirety) https://forums.iboats.com/forum/engi...-a-383-stroker

there are GMPP links, etc.

a new 377 is $4200, a reman stroker from someone not price-gouging would be about $3k talk to your local machine shop

I built my 468 for less than $3k

sounds good so i was reading here and it says to repower the 87 it might need new parts. will i need a new intake manifold, electric fuel pump? also will my current power steering pump and other belt pulleys hook right up to this 6.2 from center state? also u stated in the other forum about the intake manifold and a 715cfm carb hooked up, u also mentioned new mainfolds for the exhaust. i believe i have a 600 holley and i have brand new exhaust manifolds and risers for my current 5.7. would i need a upgraded carb and get new exhaust manifolds aswell?
http://vi.vipr.ebaydesc.com/ws/eBayI...rsion=d04531b9
 
Last edited:

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,297
yes, vortec heads have different bolt pattern for the intake
vortec blocks (unless you go GMPP block) do not have a mechanical fuel pump pad that is machined

your exhaust manifolds will bolt to any SBC (from 1954 to today)

600 CFM is a bit small for a stroker
 

cowlotter

Seaman Apprentice
Joined
Sep 1, 2019
Messages
30
yes, vortec heads have different bolt pattern for the intake
vortec blocks (unless you go GMPP block) do not have a mechanical fuel pump pad that is machined

your exhaust manifolds will bolt to any SBC (from 1954 to today)

600 CFM is a bit small for a stroker

so just a new intake manifold, fuel pump and carburetor if i did the conversion? the old belt pulleys will bolt right up with my old power steering to and is there any other new parts id need?
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,297
keep it a 5.7 and your 600 CFM would be fine
 

cowlotter

Seaman Apprentice
Joined
Sep 1, 2019
Messages
30
without pulling it apart, its a guess

could be valve train, could be broken piston, could be bearings.

either way, your motor is coming out.

since ill probably be replacing the motor but i cant until next spring would i be fine not changing engine oil or filter during winterizing this season and just treat gas, fuel filter and drain water and call it a day. im trying to avoid spending money on something im going to replace anyways. what are your thoughts?
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,297
my suggestion is drain the fluids, pull the motor and drive now, and work on them over the winter. this allows you to see what is wrong with your current motor, assess what you need, and to do all the maintenance to your drive in the comfort of your garage or basement.

fuel system, I would simply drain and burn in the truck/car
 

cowlotter

Seaman Apprentice
Joined
Sep 1, 2019
Messages
30
my suggestion is drain the fluids, pull the motor and drive now, and work on them over the winter. this allows you to see what is wrong with your current motor, assess what you need, and to do all the maintenance to your drive in the comfort of your garage or basement.

fuel system, I would simply drain and burn in the truck/car

thing is i dont have the tools to pull engine. its going to have to get pulled and replaced by a shop when a new one is shipped in or diagnosed and fixed unfortunately. i have drive off in garage which just needs new fluid before winter.

is there an easy way to drain the fuel out tank and past the anti syphon valve as needed. thing is boat had about 60 gallons in it before the incident and i dont have anywhere to put that much fuel.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,297
for $30 you can build a gantry to pull the motor.

a shop will charge you about $3k
 

cowlotter

Seaman Apprentice
Joined
Sep 1, 2019
Messages
30
No, I would buy a brand new virgin block and build a 377. a 383 is a 0.030" overbore in addition to the 3.75" stroke crank

read this (in its entirety) https://forums.iboats.com/forum/eng...outdrives/10804776-upgrading-to-a-383-stroker

there are GMPP links, etc.

a new 377 is $4200, a reman stroker from someone not price-gouging would be about $3k talk to your local machine shop

I built my 468 for less than $3k

hey so im still looking at rebuilding my 5.7 350. quick question. it seems like if i got a remaned 5.7 block that going from the 87' pre vortec which i have to a 97' and up Vortec i get a decent amount of extra power and the two blocks costs the exact same when a reman is ordered from center state. the 377 might be a little to much money. Do i need to upgrade anything else besides the intake manifold to convert all my old parts from the 87 pre vortec to the 97 vortec? as seen in link i believe the vortec engine does accept a mechanical fuel pump as well.

this is the linked 5.7 vortec block im looking to convert to.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,297
The 96 and up is a roller cam, you would also need an electric fuel pump

The power comes primarily from the vortec heads
 

Scott06

Vice Admiral
Joined
Apr 20, 2014
Messages
5,542
I think also the flywheel is a different diameter necessitating a different coupler between engine and drive. Use harmonic balancer from newer block.
 

cowlotter

Seaman Apprentice
Joined
Sep 1, 2019
Messages
30
I think also the flywheel is a different diameter necessitating a different coupler between engine and drive. Use harmonic balancer from newer block.

can i reuse the coupler from my current 87 350? all these extra parts might not be worth even switching to a later model engine
 

Scott06

Vice Admiral
Joined
Apr 20, 2014
Messages
5,542
can i reuse the coupler from my current 87 350? all these extra parts might not be worth even switching to a later model engine

I would call Michigan motorz and ask they can give you more definitive answers than I. When I did my repower I found both Loren Haus and Roger Abjean there to be very helpful on mix and match combos like this. I took out a 4.3 and bought a 5.0 silver package from them that they tweaked the components to take advantage of what components/accessories I could use off my 4.3.
 
Last edited:

Scott06

Vice Admiral
Joined
Apr 20, 2014
Messages
5,542
I did a little research and looks like the flywheel is the same 1986 and up so should work. Only thing to versify since your original motor is close to change over year is if in fact your engine is an 87, my 1991 boat had a 1990 engine with (by serial number ) one of the last Alpha one gen one drives, so you can’t always go by boat year alone
 
Top