What to check when buying a used mercruiser 3.0

[mattyrich]

I have been on the hunt for a used 3.0 mercruiser 140 hp to replace the seized one that's in this boat I picked up. My buddy was moving, and gave me the boat. I promised I would get her going again. Anyway, I found a few different motors being sold for roughly the same price. One that im really considering is supposedly in excellent shape and looks like new even though its is a 1981 motor. I know a bit about what to check on outboards (compression, gear oil, spark, etc...) but i'm new to inboards and I want to do as thorough of a check as possible before I shell out 500 bucks ( i know that this would be a great deal for a running motor). She seems very trustworthy and we have been communicating a lot but you never know. She also said that her mechanic came over and was going to go through the motor because she didn't want to sell a motor that didn't run. I say, well that sounds good to me!!! lol... He supposedly did a compression test and she said it was 180,185,180,185.. I said, OK? knowing that it is supposed to be 140 psi. from the manual that i have, I questioned her and she said that the test could not have been accurate because the motor was winterized and filled with Oil so it wouldn't seize or dry out the gaskets. Does this sound right? seems crazy to me. I know that you can fog the cylinders and/or put oil in them to try to free them up if seized, but i never heard of filling cylinders with oil just for storage. What is she talking about? I don't think that she is trying to screw me over. she is even going to go and renew the registration on her flatbed trailer and let me use it and bring it back after dropping the motor off at my house... If someone has a list of what to check for before i purchase this motor that would be AWESOME!!! THANK YOU!

 

[thumpar]

Re: What to check when buying a used mercruiser 3.0

Foggy oil maybe. I use it in my water toys when winterizing.

 

[mattyrich]

Re: What to check when buying a used mercruiser 3.0

Anyone? I only got until Thursday morning before the motor is sold to "her mechanic." Thanks...

 

[stonyloam]

Re: What to check when buying a used mercruiser 3.0

She seems very trustworthy and we have been communicating a lot but.......

There you go! If you can't hear it run sometimes you just gotta trust the seller. Compression is good (numbers are high but very close to each other), and you know it spins over and her mechanic is willing to buy it, all good signs. You could ask for a guarantee that the block is not cracked. Can't think of much more. Good luck.

 

[mattyrich]

Re: What to check when buying a used mercruiser 3.0

Thanks for your incite guys, this is pretty much what i was thinking but I didn't want to miss anything. I'm pretty excited. This lady says that there is absolutely no corrosion on the motor and it looks like new! I put a wanted ad on craigslist for a 3.0 mercruiser 140 and got lots of replies, but this one seems like its a sweet motor. Hopefully it will plug and play, drop right in, you know. How should i drain the oil out of this motor, the petcocks/drains on the block? let me know if ya have any recommendations on what to do before swapping these motors. Thanks again guys. I'll post pics of the motor swap.

 

[stonyloam]

Re: What to check when buying a used mercruiser 3.0

How should i drain the oil out of this motor...

There should be a drain plug in the oil pan, just like a car. When the motor is installed in the boat you can either attach a drain hose kit to the pan drain, or suck the oil out through the dipstick tube, which on a boat goes to the bottom of the pan.

 

[mattyrich]

Re: What to check when buying a used mercruiser 3.0

Thanks for the advice. I was pleastantly surprised when i went to look at the motor today when I found that it actually already has the oil drain hose on the motor. NICE!!! score. Come to find out, This motor was apparently rebuild a while ago by a guy who wanted to put it in a boat. He sold it to the lady i got it from after rebuilding it because he apparently need to pay bills? I have no idea, but what i do know is that he replaced the head, alt,starter,fuel pump,carb, coil, exhaust manifold, belt, oil, distributor, and maybe more. She gave me all of the old parts preciously mentioned. Seems good to me, im hoping that someone wouldn't spend all that money on a motor if they didn't think it was a good runner. It sounds great and cranks real strong. The oil in the motor was new, and the compression was 160 across all four cylinders. I am super pumped to switch over some stuff from the motor in the boat, and get this puppy goin. I will be sure to post pictures of the process. I am going to have a few questions about the swap of the ignition, valve cover, etc... hopefully i can find some answers

 

[NHGuy]

Re: What to check when buying a used mercruiser 3.0

That motor does sound like the right choice. Now don't go getting too far ahead of yourself, though.
Try to find out what seized the old motor and eliminate that happening on the replacement. Read through some repower threads for ideas about what to check.
Sounds like you are off to a good start though.

 

[mattyrich]

Re: What to check when buying a used mercruiser 3.0

Ok, update time. Got the 1991 3.0 Mercruiser 140 hp that may be seized, out of the boat today. pulled out surprisingly easy. thank god for pneumatic tools. I've talked to quite a few people about swapping this motor to an earlier (1981) of the same model that i have been pondering on craigslits. Everyone says,"it will drop in no problem", so I was convinced that it would be compatible and I bought the motor. I was hopeful that the gimbal housing on the new (older motor, 1981) would match up with my mercruiser alpha one transom assembly (1991). Much to my dismay, when i pulled the 1991 and set it next to the 1981, they were different. the older motor has motor mounts that are about 6 inches further apart! Uh Oh... Fortunately, the housing that covers the flywheel (i think its the gimbal housing) was in good shape on both motors and looks like it should swap out nicely!!! kept it off to clean it up first, but looks compatible to me. So thats where I stand; both motors side by side on a trailer. I am considering swapping over some parts from the 1991 to the 1981 that I am dropping in, but there is some obvious differences. I am going to post some questions that I hope someone can help me with. Should I take the closed cooling system (pretty rough condition, but may still work... full with clean coolant) off of the 91 and put it on the 1981 that im prepping to drop in? What do ya think? Is it worth it? I am also considering taking the electronic ignition (distributor, coil etc) to replace the breaker/points system that is on there. It does work, but i figured the electronic one is more advanced and maintenance free so to speak... Is this a possible swap. I am also going to have to adapt the shift throttle control plate... the boat was set up for a motor (1991)with the shift/throttle connections on the valve cover. the motor im putting in (1981) has, or had, the shift/throttle connections on the exhaust manifold just under the carb. Is it going to work if i just swap the valve covers? those are my two biggest questions right now; ignition/wire harness swap, and valve cover/shift connection swap.... Any body stilllllll reading that could provide some much needed knowledge... THANK YOU, im learning, and I DO read my crappy Seloc manual. lol Here is some pictures of today's activities... Iv'e got limited time and funds, so any help would be greatly appreciated and it might help someone else out as well...

 

[fishrdan]

Re: What to check when buying a used mercruiser 3.0

The 3.0 and 140HP are similar, but have differences. Here are things to check

- Manifold/head port configuration, small, large, combined
- Rochester carb = old, Mercarb = new
- Riser and exhaust down tube
- your EST ignition will fit and work in the 140HP, I have one in my 140HP
- fuel pump? filter on top or bottom
- flywheel, 12.5" or 14"
- crank, old has studs for the coupler and flywheel, new one has bolts for the flywheel
- crank rear main seal, old is 2 piece, new is 1 piece
- starter (for 12.5 or 14" flywheel)
- rear engine mount, you saw this one
- coupler, old ones mount to the crank, new triangle style bolts to the flywheel
- outdrive input shaft
- shift linkage locations


Putting a closed cooling system on an engine that's been raw water cooled can cause problems, rust flakes clogging heat exchanger.

 

[mattyrich]

Re: What to check when buying a used mercruiser 3.0

Guys... Should i just change over the complete wire harness with the ignition system, valve cover (for the throttle shift connections), and the exhaust elbows are different. the one out of the boat is at a 45, and the one im dropping in is straight back... can u just use the exhaust downpipes to match up near the transom or do i have to change the whole system one way or the other? Also, just found something else. The carb on the motor im going to use has a manual choke (no connections for that in the motor compartment in the boat) the motor i pulled out has what appears to be an electric choke with a purple an black wire to it. How can i fix this problem. thanks, Matt.

 

[fishrdan]

Re: What to check when buying a used mercruiser 3.0

Someone has done a hack job on the carb's choke as it's supposed to have a spring choke assembly on there, similar to the electric choke on your Mercarb, but it's run off a small heated pipe connected to the manifold. Your 91 Mercarb won't fit as the bore size is bigger and bolt pattern is wrong.

Check the exhaust down pipes, they are probably different at the transom assembly, so you won't be able to swap them.

The easiest way to resolve a bunch of problems you'll encounter is to swap the heads and everything attached to it, but you are still going to have problems when it comes to the coupler and rear engine mount.

Pull the rear engine mount off the 91 and see if the mount, coupler and flywheel will fit the older engine, I don't think they will as the crank bolt patterns are different.

I hate to say it, but I don't think you are going to easily swap in that old engine, too many differences between the years. Go through the list I posted up earlier and start checking things. I have a feeling you won't like what you find.

 

[nitrosteve]

Re: What to check when buying a used mercruiser 3.0

I would swap manifolds, valve covers, all electrical items. Use your riser since it matches your down pipe.
I feel your pain I just swapped a 86 3.0 into my 98 Monterey 180 but I still had the other complete boat to steal parts. The only difference was ignition,shift cable ***.,valve cover,the 86 coupler still works just doesn't have the added grease extension, the down pipe and riser manifold is still 86 the 98 had to come off the transom plate since the riser was different angle. Granted it may have worked but I didn't want to chance it. It was a lot of work but the boat has ran great, lots of power maybe more than the 98 version had...

 

[mattyrich]

Re: What to check when buying a used mercruiser 3.0

Ok, thanks guys.

Is there anyone out there show me what the older spring type choke assembly looks like? Also I would like to see how the throttle and shift cables connect to the side of the manifold like the older motor (1981). I am going to post again in a minute to update the progress today... Its not to good! Im really starting to get desperate. I know it can be done. Just now sure which route I should take? More details to come... here's a couple pictures

 

[mattyrich]

Re: What to check when buying a used mercruiser 3.0

Thank you very much for all of your great information guys. I REALLY appreciated it!!! However, i have many issues. Can't believe that everybody i talked to, told me that these motors would swap out no problem. any how, i think it can work, just need to figure out the best plan of action???

Ok, so here's where I stand... Swapped the rear motor mounts with no problems and it worked like a champ. starter and flywheel stayed and match up fine, luckily. looks fine and works fine I think. Starter cranks and flywheel turns.

HERE'S A BREAKDOWN OF ALL OF MY PROBLEMS... ANY GOOD NEWS?

********************Ignition problems************************

I went ahead and swapped the ignition system from the 91' over to the 81'... ((IGNITION MODULE (think that's what it is?), IGNITION COIL, DISTRIBUTOR(electronic spark timing) , and the CIRCUIT BREAKER))

Everything seemed to go pretty smooth...I had to change a couple connectors but no major problems, I thought at least. However, for some reason, now I have NO SPARK ON ANY CYLINDER, OR FROM COIL TO DISTRIBUTOR? Why?

I did have strong spark with the other older style ignition system that i took off last night!!!(slave solenoid, coil, and distributor with rotor...thought it had points, but doesn't). The only reason that I changed it was because i didn't think i could just plug that harness into the female on the boat without problems? should I have left it or did I possibly hook something up wrong? my manual doesn't have a diagram of a est ignitions system. HELP! Can I test these components without the motor running. It Still turns over strong, JUST NO SPARK!!!

I swapped the valve cover so I could try to hook up the control cables in the boat the way they were on the old motor. I ran the wires to the neutral safety on the valve cover too but i guess right now they are just going to a dead end at the Mercruiser harness as the boat is sitting on a flat trailer next to the old motor. could this be my no spark issue? I tried bypassing it by connecting the black and purple/white wire together with no luck?

I Have two white wires coming out of the distributor that don't go anywhere.
I have one black wire that was spliced to a white wire going to the motor side of the harness... that's how i found it on the old motor before it came out. I saw videos on Youtube that looked the same?

my buddy gave me this boat and said the old motor was running before he broke a starter bolt and let it sit with no plugs for a year. I would assume that everything was hooked up correctly if it was running before.

************** Fuel pump****************

I have a total of four fuel pumps. one that"s on the older motor. two that came with the motor i just bought (filter on bottom) and one that is mounted on the motor(81') that i just bought. It looks different and not sure if i can get the fuel metal fuel line to the carb with this pump? have you seen one of these before? (should be visible in my attached pics). Which pump should i use and is there gasket/diaphragm kits for these? next issue....

*******Carburetor/ Choke/ throttle/shift linkage/ manifold/ exhaust******

As you can see in the pictures The old motor has a black carb. that i havent identified (mercarb?) that only matches the bolt pattern on the manifold from the old motor. (its in pretty bad shape)

The carb that came on the new motor (81') is a Rochester two jet that has no connection for the choke or does it??? This carb only will fit on the manifold that is on the new motor(81') as some of you know.

The problem is that the Rochester carb looks like it may work but there is nowhere for the wires from the harness (electric choke), the mechanical choke seems incomplete. ALSO, the linkage that should connect to the throttle cable(from the valve cover) doesn't have an arm to connect to? to short, and i cannot swap it from the other carb. Can i connect the cables on the manifold, and rig the existing, or non-existing mechanical choke, and swap the valve covers back? will this work? P.s. THE ELECTRIC CHOKE WILL FIT ON THE THE ROCHESTER CARB, BUT I STILL HAVE THE ISSUE OF THROTTLE LINKAGE... UGH!!!

I really dont have the money to spend on another manifold, and im not sure if i can get the old one off or if it will work. Furthermore, Im not sure if the Mercarb will work on the new motor(81) even if i do change the manifold? In that case I still need to figure out the spark issue and fuel pump.

Should I try to change the manifold and carb, and use the old carb that has the electric choke and definitely will mesh with the throttle cable linkage and deal the spark issue, the fuel pump issue, and i maybe a new exhaust elbow too? (how good of condition do the elbows need to be to work?)

On the other hand, could I leave the Rochester carb and the existing manifold on the new motor(81'),change back to the older style ignition and wire harness (if i can figure it out), and deal with the throttle linkage, choke linkage, fuel pump, exhaust and wonder what will happen when i plug the harness in on the boat? will everything get power still?

with either alternative i need to figure out the spark issue. two different harness's two different ignitions? I feel like i need the one harness that matches the neutral safety switch(On the valve cover), and the electric choke, but the other harness is the one that worked on the motor and had good spark, but im not sure if it will match the circuitry on the boat side???

WHAT THE HECK SHOULD I DO MAN!!!! AHHHHH. If i wasn't broke i would go buy the parts i need if i could find them. Actually, I guess if i wasn't broke i wouldn't be going through all this hassle. lol I do enjoy it but its frustrating.

IF ANYONE ACTUALLY MADE IT THIS FAR, YOUR AWESOME! THIS SHOULD BE A VERY HELPFUL THREAD TO LOTS OF PEOPLE IF I CAN GATHER ALL OF THE ANSWERS. THANK YOU ALL SO MUCH!!!!

 

[nitrosteve]

Re: What to check when buying a used mercruiser 3.0

Ignition problem could be the shift interrupter switch try unplugging it.

 

[fishrdan]

Re: What to check when buying a used mercruiser 3.0

Swapped the rear motor mounts with no problems and it worked like a champ. starter and flywheel stayed and match up fine, luckily. looks fine and works fine I think. Starter cranks and flywheel turns.


What about the coupler? That's the part that's going to give you the problem, adapting the old style coupler to the triangle coupler, if the 91 has a triangle coupler. The outdrive input shafts could be different lengths, thus the need for the different couplers.

It Still turns over strong, JUST NO SPARK!!!

I'd use the new harness as it will solve some wiring problems. The EST and points ignitions get wired differently, especially when it comes to the shift interrupt switch,,, points get grounded, EST gets +12V.

I Have two white wires coming out of the distributor that don't go anywhere.


These are for timing the EST ignition, you need to use the correct procedure for timing an engine with EST, it's not the same as points.

I have a total of four fuel pumps.

Use one from the 91 so your metal fuel line matches up. I'm doing that on my 140HP, new style pump going to Rochester carb. I had to buy an adapter fitting for the carb, but it works. On my engine,,, the block cutout for the pump is centered a bit low and the gasket only seals about 1/4", but it's sealing. (BTW, the fuel pump on the 81 is an automotive pump,,, get rid of it, it has no business being on a marine engine)

The problem is that the Rochester carb looks like it may work but there is nowhere for the wires from the harness (electric choke)

It didn't use an electric choke, thus no wire, it used a heat stove, thin pipe running from manifold to to choke.

the mechanical choke seems incomplete.

because it was a HACK from the previous owner

THE ELECTRIC CHOKE WILL FIT ON THE THE ROCHESTER CARB, BUT I STILL HAVE THE ISSUE OF THROTTLE LINKAGE... UGH!!!

That sounds do-able

I really dont have the money to spend on another manifold, and im not sure if i can get the old one off or if it will work.

need to check head port configuration

On the other hand, ........................................what will happen when i plug the harness in on the boat? will everything get power still?

check the cannon plug and see if they match, number of pins


















CHECK THE COUPLER!

 

[mattyrich]

Re: What to check when buying a used mercruiser 3.0

Thanks for all the wisdom Fishrdan, and you are correct; there are many complications in swapping a 1981 mercruiser 140 3.0 for a 1991 merc 140 3.0... just not going to happen i dont think. I already swapped over the whole wire harness and est ignition system, but i have no spark? I used the harness that was hooked to the est ignition before. Not sure what the problem is?

Not sure where to go from here, maybe I have i wire missing? gonna go through it once more with the diagram.

I pulled the flywheel covers back off of both motors, as i swapped them before and didn't make sure the drive shaft coupler was the same depth, which it is not. So, the flywheel on the 1981 does also have the triangle pattern so the other couple will fit, but the flywheel is held on by studs that come out from behind the flywheel and I would need a 3/8 inch spacer or six heavy duty thick washers to hold on the flywheel? Im not sure if this is possible... Any ideas? The flywheel from the 1991 is held on with bolts going in through the flywheel towards the block. The only way I can see to do it is to change the bolts that hold the flywheels on, if thats even possible, or to make a spacer that will fill the compensate for the gap where the base of the old style coupler bolted to the center of the flywheel The threads dont go all the way down so bolts/washers will fit flush to, and hold the flywheel on. anybody understand what im talking about out there.

THE ONLY WAY IT WILL LINE UP IS WITH THE NEW STYLE (TRIANGLE STYLE )ENGINE COUPLER BECAUSE I SUPPOSE THE SPLINES ON THE DRIVE SHAFT FROM THE ALPHA ONE ARENT LONG ENOUGH TO ACCEPT THE OLD STYLE ENGINE COUPLER... ITS DEEPER AS YOU CAN SEE IN THE PICS

Any miracle fixes to this, or know where i can get round plate machined/made with six holes drilled in it to fit on this flywheel. that,way the newer style triangle coupler will still fit flush and bolt on to the old flywheel(it clears the old bolts even though they are longer)...
If i can get this fixed and come up with a solution to my spark problem, use the manifold mount for the throttle cable, and hook up the electric choke, to my Rochester carb, then, i think we are in business... Please help!!!!
DOES IT SOUND LIKE THIS WILL WORK?
THANK YOU

 

[mattyrich]

Re: What to check when buying a used mercruiser 3.0

A couple more pics... ps. the good motor is the one with the better looking flywheel.

 

[mattyrich]

Re: What to check when buying a used mercruiser 3.0

Here's a few pictures of the motor after i swapped in the est ignition... still no spark. stopped dead in my track to get to the bottom of this engine coupler/drive shaft spline ISSUE...

ANYONE SEE A CIRCUIT IM MISSING OR ANY WRONG CORRECTIONS? IM NOT SURE THE STARTER IS WIRED CORRECLY? GONNA GO FUSS WITH IT BEFORE DARK. I WOULD LIKE TO AT LEAST GET THIS THING RUNNING LIKE I KNOW IT WILL SO I CAN SELL IT OR GET IT IN THE BOAT.

THANKS AGAIN, MATT