Approx. cost to swap 305 and 350 merc engines?

[John_S]

Re: Approx. cost to swap 305 and 350 merc engines?

I'd have the seller do the install, and reserve the final payment to after the test drive. If the motor happened to not be as good as advertised, you will end up paying your mechanic more just to remove it.

I believe what coors is refering to is the 2-piece oil seal vs 1. The engine you are considering should have a 1 piece seal. The 1 piece is better at preventing the dreaded SBC rear main oil seal leak.

As Bondo has mentioned before, the crank changed on the newer vintage. This drove flywheel, coupler, and starter changes. All of which I suspect the seller has from the old engine.

 

[erikgreen]

Re: Approx. cost to swap 305 and 350 merc engines?

Guys, I am close to a decision on buying this engine. I'm trying to understand how tough a swap this is......assuming my engine is a 1985 305 and the one I'm buying would be a 1987-1992 vintage 350. So, basically, what changes in the install or modifications will be needed. I won't understand the specifics, likely, just trying to ballpark how much mod work the mechanic will need to do.

So far, no bids so it's at $500 but the eBay reserve isn't met....so I'm hoping to get it for $1,000 or so. My local mechanic says I can't go wrong at that price if it's in decent shape. It's the whole engine, not just the block. I called two shops and one guy who does marine work on the side. Looks like somewhere between $350-500 to install. I may go with the "on the side" guy, NOT to save $$$ but because he'll let me help and I'd love to see how it's done.

I'm pretty sure the newer engine will use a different flywheel. That will require a different bell housing to fit it, a different transom plate to fit the bell housing......lotsa $$. You need an older motor.

You need to get a 1985-ish vintage 350 if you want to swap it in like you're planning. The cheapest way to get one is to get a truck block, the 350 as used in a truck will have about the right cam for boat use. Replace the gaskets, freeze plugs, and install marine bolt-ons and you're good.

For $1000... I wouldn't buy a used motor. Too risky. Just get a crate motor of the right year or a reman from a good shop, and bolt on the 305 accessories. I did this last summer in my '83 sea ray, went well.

Erik

 

[Bondo]

Re: Approx. cost to swap 305 and 350 merc engines?

assuming my engine is a 1985 305 and the one I'm buying would be a 1987-1992 vintage 350. So, basically, what changes in the install or modifications will be needed.

Ayuh,...... This'll be an Easy Swap,......

While I agree that it appears you're going from the early 2 piece seal motor to a later 1 piece seal motor,....
Seirra has come out with a retrofit Coupler that simplifies the Swap,....
Instead of swapping the flywheel, they have an early style Coupler with the late style bolt pattern.... This only applies to the small round couplers...
Or,.....
If this complete motor comes with it's own Flywheel,.... It's a moot point as it'll accept the coupler from your original motor, if it's the triangler 1...
If Not,+ you have the small round coupler,... You'll need an 18-2172(which should be available right here from iboats.com) to convert the early bolt pattern to the late model pattern....

 

[tmh]

Re: Approx. cost to swap 305 and 350 merc engines?

OK, thanks you all for the help! I'm doing the swap only if I get a good price on the engine. I'll let you know how it goes.

Thanks again.

 

[tmh]

Re: Approx. cost to swap 305 and 350 merc engines?

Just going thru some old threads where I asked for help and rec'd it - wanted to thank all who gave me advice in this thread about swapping a 305 to a 350 engine and give the "results" so you know the help led somewhere.

I wound up with a 350 Mag Vortec mercruiser from around 1992 I think, so it must have been modified for the Vortec (as I found out they were not around in 1992). (Long story, but my 305 wound up cracked anyhow so I needed a new engine!) Cost me $1,200 for complete engine which I think was a great deal.

As was said, it was a pretty easy swap (had a high school senior kid who's a gear-head and works at a marina during the past few summers do it for me) for $400. Fit right in place, minor exhaust piece needed to be installed I think. He changed oil and plugs, rebuilt the carb and now it's been operational fora month or so.

Results: Speed went from maybe 41 to 48 mph (may get more when I change props again). Mid-range acceleration is great. Cruises at 35-38 effortlessly. I'm very happy with the upgrade! Only issue is starting isn't as good as my previous engine as we're having some choke issues I think (different thread). All-in-all I'm pretty happy with the swap, especially considering as things wound up I needed a new block and manifolds anyhow!

So.....THANKS for the help! I'd have been lost knowing what to look for without the folks here at iBoats forums!

 

[Coors]

Re: Approx. cost to swap 305 and 350 merc engines?

Glad it worked out.

 

[Limited-Time]

Re: Approx. cost to swap 305 and 350 merc engines?

Nice to see someone taking time to post results......................and thanking those who took the time to help.

 

[tmh]

Re: Approx. cost to swap 305 and 350 merc engines?

I'm guessing I'm at around 280 hp so I never really floor it from a dead stop - it doesn't need this to take off fine. I assume it will be OK if I don't push too hard too often. I think Alpha one is rated to 300 hp, correct? Anyhow, I doubt the short time at top end will kill the drive as long as I don't pound it off the start.

 

[tmh]

Re: Approx. cost to swap 305 and 350 merc engines?

Be aware, if you more than 260 or so ponies you WILL have problems with the Alpha 1 outdrive.

Darn you, Bubba!!!!!!! You jinxed me but good! Don't know if it was due to the hp, but......I just went out, was doing a short WOT run (more prop performance testing), was trimming out, maybe trimmed too high.......then all of a sudden the prop stopped spinning and the boat stopped. Neither forward nor reverse work now, although the engine idles fine, runs in forward but dies in reverse.

I'm pretty sure it's not just a spun prop as I checked it and it's not spinning freely by hand so I think I'd get some movement from it. The marina guy said maybe it's the coupler or the gear box. They'll be looking at it whenever they can get to it.

CRAP!!!!!!!!!!!!!!!!! Just add this to a long list of costly boat work this year......

 

[bruceb58]

Re: Approx. cost to swap 305 and 350 merc engines?

Is your engine overheating? If it is not, your coupler is still good.

 

[tmh]

Re: Approx. cost to swap 305 and 350 merc engines?

Well, not sure if it's overheating because I only ran it a few seconds after it wouldn't go. I waited a while then tried to go again, but only for a few seconds - it was obvious I wasn't going anywhere so i got towed in.

I guess I'll have to wait to see what the problem is from the marina mechanic.