Old style Coupler on newer 4.3 v6 Mercruise

[dlogvine]

I was taking apart an old 1984 4.3 v6 Mercruiser. The crankshaft has a different flywheel and coupler connection, instead of a triangle and mounting bolts, old coupler goes on a set of studs and tightens with the nuts. Could I use this coupler and flywheel on the newer 1993 engine with the chevy block rebuilt for marine application? Thx. Also, how different is a triangle coupler and could it be used with the gen one alpha one outdrive shaft?

 

[Fun Times]

This ought to be your 1984 OEM coupler part number 76850A2 , which being an 1984 should of had the 12-3/4in. flywheel size as the later 1985 year models went to a 14in. flywheel size which needed the triangle coupler.

Plus there's a 1 piece vs 2 piece rear main seal to consider knowing of.... Along with the bell-housings sizes between the two for fitment back then.

Also just take note of the very small possibility of Mercruiser's 1 piece vs 2 piece rear main seal flywheel housing to transom plate assemblies engine mounting...The spacing of the 2- engine mount bolt holes of the rear motor mount (flywheel cover) between the 2 designs. Are they the same distance apart or is one wider ?.

Below are tones of helpful notes covering both types especially the first link as you click on each coupler.

https://bpi.ebasicpower.com/shop/me...gine-system-parts/couplings-couplers-and-kits

https://www.mercruiserparts.com/bam/subassembly/31470/979/140
https://www.mercruiserparts.com/bam/subassembly/31472/919/170
https://www.mercruiserparts.com/bam/subassembly/31472/919/250
http://www.mercstuff.com/page08.htm
http://www.mercstuff.com/couplers.htm
http://www.mercstuff.com/tricouplers.htm
MerCruiser GM Engine Identification - boatfix.com

Fits MCM 3.0L (1999 & newer), GM V-6 & V-8 (305 & 350 cid) engines (1993 and newer). This coupler is used with the 14 inch flywheel. If you are unsure as to whether you have a 12-3/4 or 14 inch flywheel, measure the distance from the center of the driveshaft splines to the center of one of the mounting holes. The 14" couplers will have a radius of 6.32

^ Also take note of the available conversion kit you may need.

 

[dlogvine]

This ought to be your 1984 OEM coupler part number 76850A2 , which being an 1984 should of had the 12-3/4in. flywheel size as the later 1985 year models went to a 14in. flywheel size which needed the triangle coupler.

Plus there's a 1 piece vs 2 piece rear main seal to consider knowing of.... Along with the bell-housings sizes between the two for fitment back then.

Also just take note of the very small possibility of Mercruiser's 1 piece vs 2 piece rear main seal flywheel housing to transom plate assemblies engine mounting...The spacing of the 2- engine mount bolt holes of the rear motor mount (flywheel cover) between the 2 designs. Are they the same distance apart or is one wider ?.


^ Also take note of the available conversion kit you may need.

I am piecing together a drivetrain for a new hull without an engine or an outdrive. I had a 1993 chevy 4.3 v6 block with a balanced shaft and bought a junk boat to get all the accessories and an outdrive. The engine appeared to be an older version, 1984 with an older Alpha one gen 1 outdrive. My rebuilt 1993 engine has a 1 piece rear seal and 14 inch flywheel. The old engine had a 2 piece rear seal and this older type coupler and crankshaft. Old engine had cracked everything, block, heads, exhaust manifolds, so I took it apart, saved the crankshaft, connecting rods, intake manifold and accessories and dumped it. Now I'm trying to figure out the easiest and cheapest way to combine the old bell housing, than some plate and outdrive with a newer 1993 engine. If I buy a new coupler triangular with a replacement shaft, should I use it with a newer flywheel? I need to check if it will fit in an old bell housing that matches the transom plate.

 

[harringtondav]

Fun Times I recall a long string some time ago detailing the hazards of mixing 4.3 balance shaft and non-balance shaft parts. Is the flywheel part of this issue?

 

[achris]

...Could I use this (84) coupler and flywheel on the newer 1993 engine with the chevy block rebuilt for marine application?...

In short, no.

Build the 93 engine complete, as a 93 (including a balance-shaft engine flywheel and coupler). Use the 84 gimbal housing and inner transom plate, and the 84 ('R') drive. The 93 engine will drop straight onto the 84 inner transom plate mounting points. At a later stage you could upgrade the drive to an Alpha One (up to 91)...

.... If I buy a new coupler triangular with a replacement shaft, should I use it with a newer flywheel? I need to check if it will fit in an old bell housing that matches the transom plate.

The flywheel housings are the same 84 to 93... The flywheel and coupler are not the same...

Might I suggest, abandon the 84 altogether. Find yourself a post-92 transom assembly and drive (Gen II)... Going to save yourself a lot of pain in the future. From a purely engineering stand-point, the Gen II is superior to the earlier drives. Things like oil bathed drive shaft splines, cast-in water pocket (no gasket to leak), SIGNIFICANTLY improved water pump design, better upper shift shaft seal system, more anodes, different gearsets (quieter operation), and being newer, easier in the resale market.

Chris............

 

[Fun Times]

Though I may be incorrect here I'd just like two remention (just in case) the 2 flywheel housings types as I seemed to recall (though not the exact specifics of where) some past members saying certain things comes into contact with each other when installing the flywheel housings and lower housing covers and they had to do some grinding to make things fit better...Just want you to watch out for that if you head down the mismatched road of parts fittings.
https://www.nlamarine.com/products/m...-7l-v8-305-350 ...< This link has notes regarding the 2 designs.
https://www.mercruiserparts.com/bam/.../31472/919/250 ....< Hover over the notes magnifying glass for basic info between the two flywheel and cover designs where used in that past timeframe.

harringtondav, Mostly you may had run into mounting issues, possibly sizing issues of fitment depended on which way you were going with your build but not necessarily weight issues of vibration from a flywheel as I don't believe they added weights to the stock/standard engine models for a balancing standpoint.

By chance maybe the following info below may help with some of your questions too...,

The original 4.3L Engine Model was released around 1985 as a non-balanced-shaft engine in the carbureted engine model family. This original version of MerCruiser 4.3 Engine was equipped with a mechanical fuel pump however in 1992 with Gen II series engines the fuel system was upgraded to include an electric fuel pump as well as standard engine mounts due to the introduction of the balanced shaft engine design to address the inherent vibration issues associated with 90 degree V6 engine configurations.
https://www.perfprotech.com/mercury-...linder-engines

https://www.mercruiserparts.com/bam/.../31468/919/170
222-6355 ,https://www.nlamarine.com/products/m...nt=41842458053
222-9518 ,https://www.nlamarine.com/products/m...ant=1110579788
https://www.nlamarine.com/products/m...nt=28863700357 ...Cylinder Block, Camshaft, Crankshaft, And Balanceshaft

https://www.thirdgen.org/forums/engi...ce-vs-two.html

 

[Scott Danforth]

I was taking apart an old 1984 4.3 v6 Mercruiser.

that would be a miracle. in 1984, it would have been a 3.8 liter as the 4.3 didn't become a reality until 1985. the 1985 is a 2-piece crank and basically a one-off year for the 4.3 subsequent 4.3's had a 1-piece crank

In short, no.

Build the 93 engine complete, as a 93 (including a balance-shaft engine flywheel and coupler). .

This is good advise. do not try to mix and match

 

[dlogvine]

Looks like this is the path I'm going to take. I am moving the engine and the outdrive from my 1993 Larson boat to 2007 Baja hull. This hull has it's own transom plate and bell housing, so I will just have to buy another Alpha one gen 2 outdrive and a correct coupler.