Rear main seals/engine swap

I have a 1985 boat Searay with the original 260hp mercruiser motor (350 chevy). I’m under the impression that my motor would have the 2 piece rear main seal and that the motors starting in 1986 have the 1 piece rear main seal.

2 questions:
1. Am I correct to assume that the 1 piece rear main seal is better and less likely to leak?

2. If I were to get a rebuilt motor (long block) to replace mine, would there be any swap issues for external parts if I were to get a newer, 1986 motor?

Re: Rear main seals/engine swap

In maybe trying to rephrase my question... as long as the rebuilt motor comes as a long block (with the heads), would it be ok to upgrade my pre-1986 motor with a motor produced after 1986? I'm be bolting on the externals -- starter, alternator, distributor, water pump, power steering pump, carburetor, and maybe the intake manifold.

Re: Rear main seals/engine swap

The 1 pc. seals leak the same as 2 pc. I would make sure you get the same vintage motor as what you have.

Re: Rear main seals/engine swap

Agreed,......

The Year of Change is 1987,......
And,......
The Fitment Issue is the Crankshaft Bolt Pattern is Smaller on the 1 pc. seal motors,......
Hence,... The Flywheel,+ Possibly the Coupler will be Different...........

Re: Rear main seals/engine swap

Thank you for your answers.. I think I may save a couple of bucks by sticking with the same (my older) vintage. I don't think I'd pick up any performance with a newer vintage either unless I upgraded to vortec or fuel injection...and I can't afford all of that.

Re: Rear main seals/engine swap

You will save a group of money and keep the hassle factor down by sticking with the same vintage. There are actually very few things from your old engine that would work on a later model.

Re: Rear main seals/engine swap

A vortech engine with a 4 barrel manifold would run better just by design. steer clear of the TBI motors tho as they have thinner cast heads that tend to crack. A new manifold and flywheel would be necessary.

Re: Rear main seals/engine swap

1. yes.
2. no. if you buy a new longblock, everything should bolt right up. even the flywheel and manifolds, though, i would inspect the flywheel carefully. would be a shame to put one in with ground teeth while you have the motor out to begine with.

agree with seaman. the 4 bl is a better choice than the TBI. not performance wise, the TBI will smoke a 4bl, but for reliability stick with the 4bl.

and your in luck. the 5.7 is the cheapest engine to buy. they are even cheaper than 6 cylinders. and the externals will all bolt on.

Re: Rear main seals/engine swap

Cptkid570 said:

2. If I were to get a rebuilt motor (long block) to replace mine, would there be any swap issues for external parts if I were to get a newer, 1986 motor?

Click to expand...

rosco said:

.
2. no. if you buy a new longblock, everything should bolt right up. even the flywheel and manifolds, though, i would inspect the flywheel carefully. would be a shame to put one in with ground teeth while you have the motor out to begine with.

Click to expand...

If the Same Vintage Block is used,.......
Yes,... Everything Will Fit......

If the Newer Block is used,.... The Crankshaft Bolt Pattern is Smaller on the 1 pc. Seal Block,.... By 1/4".....
The Flywheels are Not Interchangeable between Pre- 87 motors,+ Post- 87 motors.........

I too would closely inspect the Ring Gear,.... If there are Any Bad or Dinged Up Teeth,......
The Ring Gear is Replaceable,..... Without replacing the Flywheel.......

Re: Rear main seals/engine swap

actually I think the change over to center bolt valve covers and one piece rear mains came in 85 from GM, then about 1990 or so the machined pad for the fuel pump was eliminated.
so depending on which 5.7 you go with you would have to swap flywheels,couplers and mount an electric fuel pump.
for ease of service I would reccomend either a bobtail engine or go back with the same style long block you removed.
the later style triangle coupler will work with either flywheel.
to me the extra HP of the vortec is not really worth the extra expense.
your going to gain up to a 325 HP engine over the current 260 HP and not really notice the difference.
the TBI and MPI engines start and idle well but you will pay the cost difference.