Help diagnosing 240 low compression

[Ladiesman]

Hey Everyone,
Just joined this site, I am a new owner of a 2001 Challenger 1800 240efi. I bought the boat for $3000 knowing that one of the cylinders on the port side was reading low compression. I personally didn't test it myself yet. Before I start tearing into the motor, I am just curious If anyone has had this problem before and knows what it could be.
Thanks

 

[poinddexter]

Its probably not going to be good lol. Its most likely going to be a failed piston or rings usually caused by low oil or a failed oil pump. Pull the head or get a scope and go in through the plug hole. Hopefully the damage is minimal. If this is the case then at best its going to be a complete tear down, honing of the cylinder, and build back up with an over size piston.

 

[Dr Honda]

Yep... what he said.

it's a 15~16 year old 2-stroke engine. It lost a piston. BUT, I won't point a finger until I see the piston crown. So... pull the heads, and lets get a look.

 

[Ladiesman]

How hard are these engines to work on ? I have never owned a sideways inboard 2 stroke..lol..i am fully capable of rebuilding this motor but i know nothing about 2 strokes. How do i drain the oil and fluids to tear it down ??! Lol
I am trying to find a good repair manual also..having trouble finding a legit copy.
There are not a lot of resources on the web for these boats.

 

[poinddexter]

The engines are quite easy to work on. There are no fluids in engine since its a 2 stroke, just the small oil tank right there on the top. PM with your email address and I can send you my copy of the manual. Its not the greatest but definitely helps.

 

[Ladiesman]

Thanks, i tested the compression as follows
Looking at the transom from inside the boat
4-105psi, 1-0psi
5-0psi, 2-95psi
6-105psi, 3-105psi

A guy at the local WEST MARINE told me that if the 1st cylinder was the one with low compression then, it is most likely a cooling issue. for example the intake sucks up a bag and cuts the water to the engine. then the bag clears after cylinder already damaged.

on ebay i have seen complete engine overhaul kits which include pistons, rings, wrist pins, lots of gaskets, etc. for around $1200

my local machine shop said he could rebore the cylinders for around 50-100/cylinder..
and resurface the deck

 

[Dr Honda]

I wouldn't' point at cooling.... YET. Need to see inside.

The Mercury 2.5L V-6 engines have a plastic drive gear on the oil pump. That's GENERALLY the issue. It finally give up, and the engine melts from lack of oil. But... it can also simply be a time thing. When the rings start to give up... the hot combustion gasses get past them, and in turn... over heats the piston skirts, and the piston melts.


The WSM Mercury parts are actually pretty good. I used them on my boat, and this will be the 5th season on my engine.

FYI... you may not need to bore the entire engine. Once again.. take it apart first. You only need to over-size the bad cyl's. SO... get it apart, and measure the "Good" cyl's first to see where we stand. Then... order parts accordingly.


If you want to see the inside of these engine... look at my project thread. (i'll go look for it)

 

[Ladiesman]

where is a good source of parts ? the rebuild kit was the only parts i could find

also, why just oversize one or two cylinders ? wouldnt that offset the engine balance ?

 

[Dr Honda]

If you want to do all 6... that's fine. It can save you a few hundred $$ if the other cyl's are in spec.

As far as balance... it's not that big of a deal on these engines. If you want to build a race engine, turning +10,000 RPM... then yes... it will make a BIG difference.

The WSM parts can be bought on eBay as a "kit". But I think our sponsor is now a WSM dealer, and I'm sure he will beat any eBay prices. (use the parts link at the top of the page)

Any parts that that he can't get... I would recommend using Boats.net. The prices are pretty good, and they generally ship quick. I know there was a few gaskets I needed, and I wanted OEM.

Here's my project page.

http://www.seadooforum.com/showthre...ndia-Project-(Engine-rebuild-and-other-stuff)

 

[Ladiesman]

thank you so much for the knowledge.
Ill keep this thread updated once i pull the motor apart.

 

[Ladiesman]

Here's my project page.

http://www.seadooforum.com/showthre...ndia-Project-(Engine-rebuild-and-other-stuff)

I see your project and have some questions. how do you pull the motor out all assembled, minus wiring and hoses etc.
where can i get an eyelet to jack motor out ?
and the engine bay cover on my challenger opens back toward transom so should i remove the cover completely to jack motor out ?

 

[Dr Honda]

It's really an easy engine to get out.

On ebay... you can get a combo lifting eye/flywheel puller tool for about $35.

http://www.ebay.com/itm/Mercury-Mar...m4184d15412:m:mG7AWZoZaOMOvzqz31zQZyg&vxp=mtr


The engine in our boats is basically an outboard engine, mounted inside. So, it's actually pretty easy to get out.

1) Disconnect the round plug on the starboard side of the engine.
2) Disconnect the fuel hose at the lift pump. (electric, rectangle shaped pump)
3) disconnect the oil hose.
4) Remove the nuts on the bottom of the mounting plate.
5) Remove the rubber hoses on the exhaust.

6) LIFT !!

I think I had mine out in about 30 min. It took longer to get the tools together, and ready. On your boat... yes... it will be easier to remove the deck lid, than to try to pull it from the side. The lid is heavy, so get a helper on that one. The islandia hinges were nice. It just opens all the way. I was scared I would have to get 2 or 3 guys to get it off. (It's over 100 lbs)

 

[Dr Honda]

Oh... I forgot about the throttle cable. That has to get disconnected too.

 

[Ladiesman]

Should i pull the heads first ?
or pull the whole motor ?

 

[Ladiesman]

The engines are quite easy to work on. There are no fluids in engine since its a 2 stroke, just the small oil tank right there on the top. PM with your email address and I can send you my copy of the manual. Its not the greatest but definitely helps.

Any luck emailing the repair manual yet ?
mrericsouza@gmail.com

 

[Dr Honda]

Should i pull the heads first ?
or pull the whole motor ?

Up to you. But since it's 0 on one of the cyl's... it's got to come out anyway. So... I guess I would just pull the engine.

 

[Ladiesman]

I read somewhere that low compression in the two cylinders could be bad reed valves, can anyone here partially agree ? It's going to be a week or so before i can pull the motor, I am in the middle of moving into a house.
But, what are the chances it could be a bad reed ?

 

[Dr Honda]

Low compression can be from bad reeds. Basically... the lower half has to compress to get good pressure into the combustion chamber. BUT... if you are down to 0... that means the piston is melted, and there's a big hole somewhere.

 

[Ladiesman]

So the motor is out finally got around to it..
One piston partially gone, u can see the rings! What do i do next ?