What should I check when buying a used Mercruiser 4.3L engin?

[gilmour]

Greetings everyone, I am a new member to this forum, been learning a lot by reading and learnign from other's experience in this forum. Lately I have decided to buy a used boat (1995 Bayliner 1850 LS), with an inboard "Mercruiser 4.3LX Thunderbolt 4 ignition" engine - I assume the engine is also 1995.

Any advice on what to check/test, or what to look for in these engines?, I have a lot of experience in outboards engines (Jhonson 2 strikes), but never had an inboard, I have some tools available if there is a need to disassemble parts to look beneath

Oh, one thing i forgot to mention, that the boat was out of the water for about a couple of years, and once in a while the owner runs the engine on muffs for a couple of minutes. Currently I can only test the boat outside the water.

 

[imported_TheMan]

Re: What should I check when buying a used Mercruiser 4.3L engin?

I'd say two of the bigger things are:

1. Cylinder Compression
2. Inspect for cracks around the block, exhaust manifolds, and ejected freeze/core plugs.

If it runs, it means that at least the rest of it is in decent shape. Since you can't take it out on the water, I think they don't recommend going above 1200 RPM on muffs? I'm sure someone else knows the number better than me. If it runs, you might have to replace a few parts yourself or tune it up for top performance, but at least the engine should be sound.

As far as the boat.. stomp around on the floor a bit to make sure there aren't any soft spots and the wood is in good shape underneath. Test the outdrive trim system a few times and make sure the boat goes in forward and reverse on the muffs. Poke around the transom to make sure it isn't rotted.

IMHO, this is pretty sufficient to decide if it is an acceptable boat or not.

Why can you only test the boat outside the water?

 

[gilmour]

Re: What should I check when buying a used Mercruiser 4.3L engin?

Thanks for the prompt response , Since it was not in use for a while, to drive to the lake I need to take care of the trailer registeration, insurance, pyrotechnic equipment - things that I need to do once I buy it.

by the way, what should be the cylinder compression? (is it the same as outboard engines ~125 -+10 for all?)?

 

[imported_TheMan]

Re: What should I check when buying a used Mercruiser 4.3L engin?

I believe a new 4.3 has compression in the 180 range, so I would expect to be around 150 or so?

From what I've heard/read, it is more important that all cylinders are within 10% of each other and that compression is acceptable, rather than just high compression (although it certainly is good).

 

[Don S]

Re: What should I check when buying a used Mercruiser 4.3L engin?

Make sure the oil look ok and note the level on the stick. Hook up the muffs and run it till it warms up, and watch the engine for water leaks that would indicate freeze damage. It should idle smoothly at around 700 rpm. Shift to fwd and rev. and make sure there are no grumbling noises or serious vibrations. Turn the wheel left and right, shouldn't make any odd noises.
After running, do the compression test, like this.
http://www.boatfix.com/merc/Bullet/97/97_25.pdf
Examine the plugs when you pull them out. They will probably be sooty black from just running on muffs, but you want to make sure none of them show signs of water, or rust. A perfectly clean shiny plug indicates water leak that is steam cleaning engine.
Check the gear lube reservoir for the outdrive. It should be a dark green color. Not black (burned) or milky (water in lube).
Recheck the engine oil. If it is milky and the oil level is noticibly higher, walk away. Very good possibility the block is cracked.