Can I buy a used 302 and use parts from my bad motor to convert it to marine?

[cameron92]

Bought a boat on marketplace only to find out I got scammed.

Seller put fresh oil in so it looked good. I took it out on the lake and now there's water in the pan. Not sure where it's getting in. I took one compression reading on the plug I could get to and not sure if I did it right but I got 100psi which is low.

Wondering if I can buy a used 302 for a car and convert it easily with the parts I have from this motor. The motor I have is EFI 1993. Model 50FAPRJVN

 

[Scott Danforth]

first, check your exhaust manifolds. most of the time water getting in is from failed exhaust manifolds. Check that first

do a leak down test to see if you have rusty valves from a leaking manifold BEFORE you fire off a parts cannon

most automotive 302 motors share a few parts with the marine motors. Truck motors are much closer to spec. the marine motor is normally using a 351 Marine cam and the better HiPerformance GT40 heads which is not what you will find in your average mustang

If I were to recommend anything retaining Ford and OMC, it would be get a 347" stroked short block and have your heads re-conditioned. then pull the EFI and toss it for a Mallory YLM distributor and a good 4-barrel manifold. Add heat exchanger cooling while you are at it.

Or get rid of the Ford/OMC powerplant and get a Mercruiser or Volvo Penta long tail

 

[Lpgc]

Yes you can. Probably a different cam, water pump, headgaskets, distributor, oil pan, etc but you can use parts from your engine.

I might've done the same instead of rebuilding my boat engine but I'm in the UK and used 302 Windsor engines are not as available over here so I rebuilt mine. If I had wanted an already rebuilt / upgraded 302 it would have been no problem, if it was a more recent 5L Ford from a late model Mustang etc that I wanted, or if it was an old Chevy engine there would have been plenty to choose from over here. I was surprised I couldn't buy an old used Ford Windsor, seems the rebuilders buy any old Windsors usually before they're seen up for sale by most other people.

Post crossed with Scott's. My 95 Windsor just has the E7 heads but I replaced the exhausts during the rebuild, it was cracked exhausts that killed it in the first place.

 

[Lou C]

Agreed you need to do a couple days of investigation first. Pull off the manifolds and check them, see if you have rust trails in the bottom of the water passages....that can put water in a cylinder and into the oil
Then pressurize the cooling passages with air and see if it holds pressure (12-15 psi)
You can also do a compression test/leakdown test and see what that shows
If you have to pull the engine, and could get a Merc or Volvo long tail with a carbed 5.7 V8 you'd be miles ahead.
Make sure though that the rest of the boat is structurally sound, the deck, transom, engine stringers, stringers outboard of the fuel tank, etc.

 

[cameron92]

Other side. Will do compression next

 

[cameron92]

Agreed you need to do a couple days of investigation first. Pull off the manifolds and check them, see if you have rust trails in the bottom of the water passages....that can put water in a cylinder and into the oil
Then pressurize the cooling passages with air and see if it holds pressure (12-15 psi)
You can also do a compression test/leakdown test and see what that shows
If you have to pull the engine, and could get a Merc or Volvo long tail with a carbed 5.7 V8 you'd be miles ahead.
Make sure though that the rest of the boat is structurally sound, the deck, transom, engine stringers, stringers outboard of the fuel tank, etc.

Would a Merc bolt up to my outdrive?

 

[Scott Danforth]

The ford flywheel housing pattern is different than the Chevrolet. So.... No, not directly However the out drive bolts to the transom assembly. You would need to find a GM transom assembly for your OMC. At that point, it would be cheaper to replace all of the OMC stuff

 

[Lou C]

You’d have to get the OMC bellhousing for the GM engine. I agree at that point I’d look for a complete Merc drop in power package.

 

[Lpgc]

Question for @louc and @Scott Danforth

If an engine / drive combination was available with either a Chevy or Ford motor, is it just the bellhousing that needs to be changed if swapping between the different motors or would you need to change the coupler and transom stuff too?

 

[Scott Danforth]

the flywheel, coupler and the flywheel housing assembly, exhaust, and most of the plumbing are specific to the manufacturer of the motor.

at that point, its cheaper to buy a longtail and swap everything over.

 

[Lou C]

Like Scott said, everything aft of the flywheel is different, if you want to check the only way to know, is to head over to marineengine.com and look at the OMC parts catalog for your year and model, and then compare parts #s and the reality is, most of those parts are NLA, even if you wanted to convert your OMC to a GM engine. That leaves you with Ebay and NLA marine parts, lol.
I kept mine OMC because the drive and transom mount have been relatively trouble free all this time even in salt water use and moorage, and I never had to pull the engine. But if I had to pull the engine, it would really make much more sense to convert it all over, if keeping the boat.
I was talking to an acquaintance the other day, who has a 2005 Merc powered boat, that isn't even moored like mine but used in the same salt water, and he had to spend about $10K at a local shop to replace:
The entire transom mount
exhaust Y pipe
and associated bits and pieces
due to a chronic leak in the transom mount
so with the engine pull and using brand new OEM parts, that's what it came to.
He was shocked when I told him I have a 38 year old OMC moored in the same salt water for at least 25 seasons that has not had that problem!

My thought, if your engine isn't so bad, and can be re-vitalized with an in the boat top end overhaul, leave the boat OMC for now but if not, bite the bullet and do it right. I did it this way and 9 years later it is still running fine. I have a whole spare Cobra transom assembly, trim rams, and a spare drive that's good for a rebuild in the garage.