Mercruiser 3.0 lx sea trial and compression specs.

[Guymontag]

Hello every one. I'm taking a boat on a sea trial this week and I have a few questions about the motor. It's a 94 mercruiser 3.0 lx with an alpha one gen 2. Before I buy the boat I wanted to do a sea trial and a compression test. Should I do the compression test after the sea trial or before? The owner says it runs fine. It's an old boat and motor I don't expect the world. But I don't want to buy if it's a rebuild in the very near future. From what I've read the 3.0 compression should be 140 and up to be considered in good condition? Is the lx model the same compression specs? I was thinking if the compression readings are under 140 I'm gonna pass

 

[Guymontag]

[No message]

 

[achris]

Hello guymontag, and :welcome: to iboats..

Do the test after the sea trial and while the engine is still warm. Actual readings depend on the gauge, but around 140 is good. The main thing is that maximum version across all cylinders is no more than 10%. Do a search, I listed exactly how to do a compression test for a couple of other members. Search for 'How to compression test'.

The one thing to check is for block and manifold cracks, freeze damage. Look for water in the oil after the test and external wear leaks on the engine.

Also, make sure the engine is making the right revs. I think for that engine at full throttle (and hold it there for a couple of minutes) is between 4200 and 4600... (I'm not near my manuals)...

Chris.

 

[Guymontag]

Just read it thank you. I'm a diesel inboard guy I've never owned an in/ob. Some you say the alpha one gen 2 is a good unit? Anything I should be looking for on it during the test? I assume the bravo is the successor to the alpha? What's the differences ?

 

[alldodge]

The Alpha gen 2 is a good drive and is designed for lower HP motors. The Bravo is heavier and is designed for high HP motors.

Alpha uses a dog clutch and needs a shift interrupter switch to shift into neutral. This switch makes the motor stumble when in the water and shifting into neutral. This is not used on dry land

Bravo uses a sliding clutch and no switch is needed, and shifts real smooth

 

[Scott06]

Not only is alpha great for lower hp small boats, 3.0 is great for a low cost, easy to maintain engine. How big is the boat. I had for 20 years a 3.0 lx in a 17 ft bow rider. Great on gas but as I and my kids got bigger it was underpowered. If you are looking at 19 ft boat with a 3.0 just think about how u want to use it. For me my kids their friend or two skiiing a 3.0 is under powered but $50 of gas went a long way.

Check compression as chris states, additionally if you have about 10 psi oil pressure per 1000 rpm hot and the drive lube is clean go for it. Tubing and skiing I really beat on mine and it lasted wonderfully, 4000-4500 rpm for an hour straight, no major repairs required. I had 140 psi compression and 45-50 psi oil pressure at WOT when I sold it with about 800 hours.

 

[Guymontag]

Thank you I will do . The motor is in an 18ft performance boat. I assume it's underpowered but as long as it gets up on plane I'll be happy. My other boat is a 36' sailer so.... I will be using it just to hit the swimming holes and grabbing lunch ,no skiing. What's the max rpm I should run at for extended trips?

 

[alldodge]

For extended runs try keeping it under 3800

 

[achris]

Also, crack open the bottom drain plug on the drive and check a bit of the oil. Should be clean and not milky, and not burnt.

Chris....

 

[Guymontag]

At 3799. From the info I've read there's nothing really to do to the 3.0 to increase perfomsnce? I've read it's kinda moot you'll need to add 10h.p just to etch out 1or2 mph. I've read youd spend thousands just to shorten lifespan and not gain much. With out getting to technical adding an aftermarket (carbs,heads,props etc) is not worth it from what I've read here? The boat came with the 4.3 or the 3.0 lx. I wish it had the 4.3. but oh well the boats in good shape and good looking. in the future if I were to smoke the 3.0 I'd be curious to repower with the 4.3. I assume I'd need to add stringers for diff. Motor mounts. Should the alpha 1 gen 2 work with the 4.3? Seems these motors can be had for 3 or 4k which I feel is in the budget but not if I'd need to replace the outdrive too. Just some Fwd thinking.

 

[Guymontag]

What do you mean by drive pan? The oil pan for the crank case?

 

[achris]

The stern drive unit. The bit on the outside of the boat, the 'leg'... At the bottom is the oil drain plug. Right at the front, on the port side.

 

[achris]

At 3799. From the info I've read there's nothing really to do to the 3.0 to increase perfomsnce? I've read it's kinda moot you'll need to add 10h.p just to etch out 1or2 mph. I've read youd spend thousands just to shorten lifespan and not gain much. With out getting to technical adding an aftermarket (carbs,heads,props etc) is not worth it from what I've read here? The boat came with the 4.3 or the 3.0 lx. I wish it had the 4.3. but oh well the boats in good shape and good looking. in the future if I were to smoke the 3.0 I'd be curious to repower with the 4.3. I assume I'd need to add stringers for diff. Motor mounts. Should the alpha 1 gen 2 work with the 4.3? Seems these motors can be had for 3 or 4k which I feel is in the budget but not if I'd need to replace the outdrive too. Just some Fwd thinking.

You pretty much nailed it. If you feel the need for speed, easier and cheaper to find the right boat from the get go. Trying to modify a boat can lead to empty pockets.

It's the same drive, but the internal gearing is different. And it's an expensive exercise to just change the gears.

Chris....

 

[Guymontag]

Thank you every one to recap..
140 compression or more on each cylinder with 10% max mariation.
Should rev to 4500 rmp for 2 mins straight.
10 psi oil pressure per 1000rpm.
no oil on dipstick an no milky oil in the drive leg. Any thing outside this think I should pass up the boat?

 

[Guymontag]

P.s. is there a more modern direct replacement for the 3.0 lx? I saw this motor Mercury MerCruiser 3.0L TKS Alpha I (One) (135-hp). Is that the same motor refurb or is that a modernized replacement.

 

[achris]

The 3 litre engine's been around since Adam was a young lad... The only major 'update' it's had is MPI, but that was more about complying with C.A.R.B. than anything else. Still 140hp.

There's been a few fiddles with the ignition system, but that's it.... As for the TKS, most clever people toss that thing and put a 'standard' carb back on...

If you're being thorough on the inspection, check the bellows too (inside the gimbal housing. Turn the steering wheel hard over one way and look in, and feel the bellows, then hard over the other way)...

Chris........

 

[achris]

Thank you every one to recap..
140 compression or more on each cylinder with 10% max mariation.
Should rev to 4500 rmp for 2 mins straight.
10 psi oil pressure per 1000rpm.
no oil on dipstick an no milky oil in the drive leg. Any thing outside this think I should pass up the boat?

Just checked my manuals... Max revs are 4400-4800... and towards the upper end is better.

Chris.....

 

[Guymontag]

Thanks so much! The bellows are rubber and should feel ....well "rubbery" still? The owner claims to have replaced the outdrive last year . Paint and exterior wear would suggest that but haven't really gotten into it. The outdrive is kinda like vodoo majic to me ha ha. I'm a diesel inboard and packing gland kinda guy.

 

[achris]

Never trust what someone selling tells you, verify it... Just do a search here on some of the stories :facepalm:

Chris....

 

[Guymontag]

Just curious should the 3.0 and the 3.0 lx have the same compression? The 3.0 just has smaller ports and heads? But same block and pistons? My knowledge of the inner workings of motors is limited. But I assume a bigger piston and cylinder would yeild more compression or is it all mostly the same. Just asking b/c most 3.0 "lx" Google searches bring me to the 3.0 specs.