Merc 240 compression test?

[Bent]

Greetings, I'm considering purchasing a local 2002 utopia in nice "looking" shape with the Merc 240 hp engine, I'd like to make a compression test a condition of the sale - as well as try it out with the owner in the water to listen for anything out of place/poor performance.
What's involved to perform a compression test on this engine? do you simply remove all spark plugs and insert/thread the compression tester in one sparkplug hole at a time and crank till you get a maximum reading? Do you put the spark plugs back in the spark plug caps and ground the electrodes on the block when spinning the engine, or is this not critical?
(I highly doubt that you actually fire the engine up on 5 cylinders while reading the 6th one...).
I'm concerned about the condition of the pump already - as the owner doesn't seem to know much about maintaining it - he just claims it's reliable and it works every time.

 

[johnhibbs]

The lanyard kill switch will kill the spark but still allow you to crank the engine.

 

[johnhibbs]

I'm working tonight replacing the wear ring on my 240EFI M2. A 2002 boat is probably going to need a new wear ring and maybe a new impleller. If the jet pump is working good the acceleration should be very impressive. The top speed on a smooth lake should be 50 mph. The cost of a new wear ring is $460 plus shipping plus some o-rings. You need to be able to do a lot of your own work on these engines/boats. The impeller/stator should have new lube put in every year. How much are they asking? The impeller/wear ring is very hard to inpect without taking something apart. You might be able to get a miniature camera from ebay and connect it to a camcorder and push it through the grate and look at the impeller/wear ring that way. I would just assume you have to replace them both for $1000 with labor. I replaced the head gasket o-rings a few years ago. It's really very easy. Not like on a car engine. One day job on weekend.

 

[johnhibbs]

You might be able to use this to inspect the impeller/wear ring from the grate: http://www.amazon.com/Waterproof-Pl...-non-wireless/dp/B0035J4O7I/ref=cm_cr_pr_pb_t

 

[Bent]

will it be cost prohibitive to repair the pump when I ask him how often the fluids in the pump have been changed and he possibly tells me "never"?

OH, w.r.t. the scope, I have something similar, but it's for checking out stud cavities in buildings/houses for doing home theater installations.

 

[johnhibbs]

If he hasn't used the boat much the lube in the stator could still be OK. It can also leak out if the o-rings go bad. You usually want to check it once a year just to make sure nothing bad is happening. It's probably not the most important thing on the list to look for. I would be more interested in the wear ring and impeller condition. The engine compression is a very good test to do. You need to go for a ride to see if you like the way it handles in the water conditions you are going to be using it in. These boat don't like choppy water.

 

[Bent]

we are in a network of deep rivers, so there's always a corner to go to to stay out of the chop.
The boat I have now is a 15' fibreglass tri-hull, so anything will show a marked improvement from it.

 

[Bent]

Is there any visual indication as to whether the oil pump has been upgraded to the electric version - or if the plastic drive gear on the mechanical pump has been replaced? (I guess it's not too hard to do this though).

Regarding the compression test procedure - spin the engine with all spark plugs removed?
(what size spark-plug socket will I need - I know my kit had two, but one size is missing).

 

[johnhibbs]

You have to do a complete engine tear-down to replace the plastic oil pump gear. That's why it is such a big deal.

I would pull all the plugs out at once to do the compression test but it may not be necessary. Not sure of the size.

The electric oil pump should be easy to spot. I would just ask if its been done when looking at the engine. If they did it they should just point it out.

 

[Bent]

you guys who've been following this thread will prolly have the text of my original reply in your e-mails, opinions?
(I've edited my post in case he's reading what I wrote).

 

[Bent]

Ahhh nevermind guys, I found out that the two local Merc. dealers in my area no longer offer support for these units, so I called it off.

All the help was greatly appreciated though.