1977 Mercruiser 140 replacement

[Irish Whip]

We have a 1977 aluminum Starcraft 18 SuperSport with a Mercruiser 140 (3.0L I4) motor and Mercruiser Alpha I outdrive. It's not the greatest or prettiest boat but it's great for our camping/tubing/skiing trips. Unfortunately I found a crack in the port side of the motor below the heat exchanger. My friend owns a decent-sized welding shop and he is going have his best old-timer take a crack at the crack since it can be done while it's in the boat and won't cost me a lot. Regardless of the outcome, I'm thinking of rebuilding a used motor this winter to replace the old one since it was showing signs of it's age (valve rattle & heavy exhaust). The question is what is a good choice for under $750 including the rebuild (<$500 motor, <$250 rebuild components)? I don't want to get to complicated with outdrive compatibility, motor mounting, exhaust hook-up, linkage hook-up, electronics (currently nonexistent), etc.

I know the simplest thing would be to replace it with another 140. Plus I could possibly use some components from my motor. However, my kids and I aren't getting any easier to get up on a slalom ski, so I'd love to add some HP's while I'm at it. Is there a 4-barrel carb for the 140 that would add some HP's?

It looks like the old Mercruiser 165 I4's are very similar to my 140 (mouting, components, etc), but I've heard issues with the closed-cooling system. Plus the short few-year production makes me nervous about the design and replacement parts.

It looks like the more-common Mercruiser 165 I6's are also similar, but likely longer but I may be able to accomodate that without too much problem. I am concerned about the extra weight for only 25 HP though.

Another option is a 1995 GM 4.3L V6 (throttle body) I have in a scrap truck. But I'm nervous about the outdrive compatibility, mounting, and all the hook-ups (aside from needing heat exchanger, riser, starter, water pump, freeze plugs, etc). Plus I've seen ratings as high as 180 HP for that motor which might be a bit much for our boat. But I've also seen ratings as low as 160 HP which might be perfect.

Any experience or opinions you can offer will be appreciated!

 

[Bondo]

Re: 1977 Mercruiser 140 replacement

The question is what is a good choice for under $750 including the rebuild (<$500 motor, <$250 rebuild components)? I don't want to get to complicated with outdrive compatibility, motor mounting, exhaust hook-up, linkage hook-up, electronics (currently nonexistent), etc.

Ayuh,... Using that as a guide line, your Only choice is another 140...
Btw,...
It'll Never happen within that budget...

 

[Irish Whip]

Re: 1977 Mercruiser 140 replacement

Which cost do you believe to be the issue? I haven't been looking very long and already found a number of 140's <$500. I haven't looked at or listened to any of them though. I haven't priced the rebuild components, but I have rebuilt engines in the past and thought I could get away with <$250 for a four-banger. Of course that all depends on reusing most of the main components and requiring very little machining.

Thanks for the input. If I stick with the 140, will anything in the '68-'82 and/or '82-'89 years be direct swaps? My serial # is 4649230.

 

[Bondo]

Re: 1977 Mercruiser 140 replacement

and thought I could get away with <$250 for a four-banger. Of course that all depends on reusing most of the main components and requiring very little machining.

Thanks for the input. If I stick with the 140, will anything in the '68-'82 and/or '82-'89 years be direct swaps? My serial # is 4649230.

Ayuh,... A Full Rebuild will run more than $250. I believe,...
Last 1 I was involed with went about a Grand for parts,+ machine work...

Any 3.0l/ 140 up to 1990 should be a plug, 'n play swap...

 

[Kainon]

Re: 1977 Mercruiser 140 replacement

Going to a Inline 6 165hp or Inline 4 190hp, aren't bad ideas, there great ideas, except even though you can find an engine for <$500 doens't mean the project wouldn't go over $1500

An Inline 6 though only about 25hp more, has more torque and uses a different gear ratio drive giving it more speed, and it has the torque to get there and there are some basic mods to get 200+ hp Easily, but requires a little $$$.

Same with the BIG Inline 4's with 4bbls @ 190hp is a decent upgrade, but again, you would need to change the upper section of the outdrive as the gear ratios are different from the 140 1.98R vs 1.65R for the Big Inline 4 and 165HP Inline 6 of 1.65R.

Check out the picture and you'll see the MPH difference the RPM's to Ratio makes with the same prop (given a modest 10% slip)

And if you have a light boat, you can probably use more Pitch with the larger engine, making an even more difference.

Also If you engine is tired, ( low compression, leaking valves etc.. ) You're not seeing the full 140hp you should, so makeing a jump to those engines would be even MORE substantial.

 

[Kainon]

Re: 1977 Mercruiser 140 replacement

Plus I've seen ratings as high as 180 HP for that motor which might be a bit much for our boat. But I've also seen ratings as low as 160 HP which might be perfect.

Actually the 4.3L V6 Vortec goes as high as 220hp with MPI, and 190 with a 4bbl, the non vortecs do 170hp with a 2bbl. And you'd need to change a few things and wouldn't be able to use your TBI with out some $$$ parts. Though Holley does sell Marine TBI Kits $1500-$2500

 

[Irish Whip]

Re: 1977 Mercruiser 140 replacement

The 160-180 HP values for the 4.3L are stock TBI values I found. Why couldn't I use the existing throttle body? Cooling porting? I'm not looking for a huge jump in HP because I'm assuming the hull isn't designed to or young enough to handle a whole lot more.

 

[Bondo]

Re: 1977 Mercruiser 140 replacement

Why couldn't I use the existing throttle body? Cooling porting?

Ayuh,... How are you going to power the Efi,....

 

[Irish Whip]

Re: 1977 Mercruiser 140 replacement

I thought about that too. I'm not real familiar with throttle bodies. I guess they're ECU controlled like more modern multi-port fuel injection? How do you think an S-10 dash would look in a Starcraft?

 

[Irish Whip]

Re: 1977 Mercruiser 140 replacement

Hey Bond-O,
What are the major components you're including in your $1000 rebuild estimate. I was just hoping to get away with rings, bearings, seals, pumps, etc and reuse pistons and shafts. Further hope to only hone cylinders and not flatten any decks. A guy can hope right? Is that too much hope? There are full rebuild kits for $500-600 on ebay.

 

[Irish Whip]

Re: 1977 Mercruiser 140 replacement

Same with the BIG Inline 4's with 4bbls @ 190hp is a decent upgrade, but again, you would need to change the upper section of the outdrive as the gear ratios are different from the 140 1.98R vs 1.65R for the Big Inline 4 and 165HP Inline 6 of 1.65R.

So Kainon,
Is my outdrive gear ratio only suited for the 120 & 140 motors? Would a bigger motor blow/wear-out my outdrive or just not perform optimally? I'm basically wondering if I could "upgrade" in stages. Do you know what would be involved in mounting and connecting one of the motors you mentioned in place of my 140? If the weld sticks on my current motor, I can take my time in installing a motor and outdrive after the season. If it doesn't I'll be trying to get a motor in for an August camping trip, but I'm afraid I won't have time to do the full rear-end swap. I have seen some deals on scrap boats with running 165's and outdrives, so it's possible I could do the full monty in time if the retrofit isn't a nightmare.

 

[Irish Whip]

Re: 1977 Mercruiser 140 replacement

Just found parts for '91 Mercruiser 4.3L:
(2) heads
intake manifold
2 barrel carb
$100 for all

Would that make my 4.3L go in my boat? That gives me the marine cams and gets rid of the throttle body. Still the issue of the outdrive. Which outdrive bolts to the 4.3L?

 

[Kainon]

Re: 1977 Mercruiser 140 replacement

an Alpha 1, Gen I or II and pre-'s are good to about 350hp +- depending on their true condition

you can use your current outdrive on a 4.3, however you would need to use a bigger prop, 21p instead of 19p, you should change to a 1.84:1 Ratio drive instead of the 1.98:1 Ratio you have now, but that's another story.

PS.. the gear ratio parts are in the upper section, so you would only need an upper with the correct ratio.

Yea.. you can use the block from the truck, make sure it has Brass Freeze/Frost/Casting Plugs.

 

[Bondo]

Re: 1977 Mercruiser 140 replacement

What are the major components you're including in your $1000 rebuild estimate.

Ayuh, a Full rebuild,... Bore, 'n hone the cylinders, new pistons, rings, bearings, etc....

Would that make my 4.3L go in my boat?

You'll only be lacking another Grand worth of Stuff to do it....

It's the outdrive Gear Ratio that's different...

 

[Irish Whip]

Re: 1977 Mercruiser 140 replacement

Kainon,
I'm new to the outdrive gear ratio topic, so please forgive me. The two issues I can think of that a difference of 1.98 to 1.84 ratios would cause is lower RPM's for a given prop/boat speed (about 300 RPM?) and faster boat speed at idle. Is the problem that it can (or will) put you in the wrong portion of your power curve and either bog down if you keep the RPM's low or thrash the prop if you go up to WOT?