Turning to the smart guys on Mercury 40 hp 2 stokes.

[crossroads123]

I want to ask the experienced operators here for their oppinion on my 40 hp 2 stroke motor serial #OD120859. My motor is a 1992 2 stroke which starts great and runs great. She has no noise or leaks of any kind. I am retired (yeah right) and of couse live on a fixed income, which makes buying a new $ 40,000. rig out of the question. Now to the problem, she runs great and starts every time but the compression is very low. I have tested it twice, warm motor, WOT and even done the decarb and it still is low on ALL cyl. She reads 75 psi on all 4 cyl.

I was wondering if I can open her up and install a new set of rings without tearing the motor completely down? I am NOT a boat or outboat motor mechanic, but am very mechanically inclined. 1) Would that be possible while bolted on? 2)Would it be possible to do this without completely tearing the motor down? 3) IYHO would I accomplish anything by doing this? 4) If I do this can you tell what gaskets, seals are needed? I have found a rebuild kit but, trying to avoid the $700 price tag. I know cheap scape, but on fixed income in the "Golden Years" I need to save all I can.

Well anyway thanks for listening and for the answers in advance. Any and all suggestions WELCOMED. Thank you all and happy boating.

 

[Laddies]

Re: Turning to the smart guys on Mercury 40 hp 2 stokes.

First what type of oil were you using at the time of the test ans what ratio, were the carb butterflys open? As far as a overhaul many times we will simply put in a fresh set of rings and light hone the bore on our 44 cu. in. racing engines which is the same basic engine you are running. These places love to sell kits with many parts one does not need to people that have no idea what they need but will use the parts because they already paid for them.
The engine will have to removed from the driveshaft hsg and completely torn down. I really doubt if you can do it without help and a OEM manual.

 

[Silvertip]

Re: Turning to the smart guys on Mercury 40 hp 2 stokes.

Carb butterflies don't need to be open on a two stroke when doing a compression test. They can be but there is no advantage. And no -- the engine must be totally disassembled to remove the pistons. These engines are not built like auto engines.

 

[Moody Blue]

Re: Turning to the smart guys on Mercury 40 hp 2 stokes.

Be forewarned, that once you open it up you are likely to find more than you bargained for. With compression numbers on the low side across all cyls, you may find scored cyl walls or damaged pistons. On the positive side, all your compression numbers are equal, indicating that there is not a catastophic problem in any one cylinder.

I tore my motor down this winter expecting to replace just a couple internal seals. Ended up swapping in an entirely different block and crankshaft, replacing the seals, two pistons, two bearings, reed blocks and so on. My motor had 155PSI -160PSI across all 4 cylinders but I had water in the lower cyl. It ran reasonably well for a 41 year old motor.

From my limited experience, I would suggest running the motor as it is for as long as you can unless you are prepared to spend a few hundred dollars or more to do a partial rebuild. Again, until you open it up you don't know what you are in for.

 

[crossroads123]

Re: Turning to the smart guys on Mercury 40 hp 2 stokes.

So what is the consenus tear her down or run her like she is? She runs great but I would hate to completely destroy my motor. Advice please.

 

[carholme]

Re: Turning to the smart guys on Mercury 40 hp 2 stokes.

Before I did anything, I would get another compression gauge and re-test it. With everything as well as it is and the compression so even, it would be a shame to commit to tearing it down when you might just have a bad compression gauge.

Gerry

 

[crossroads123]

Re: Turning to the smart guys on Mercury 40 hp 2 stokes.

I have checked it twice with 2 different gauges including a brand new one with no notable differecne in pressure.

 

[ultra353]

Re: Turning to the smart guys on Mercury 40 hp 2 stokes.

Well, if you never tested the compression and didn`t know what the numbers were would it bother you. If it runs great , to me, theres nothng to worry about. You probably are down a bit on power but being on a fixed income i would run it and enjoy it. Just my 2 cents.

 

[Silvertip]

Re: Turning to the smart guys on Mercury 40 hp 2 stokes.

Rent a bore scope which is a lighted optical tube that you can check the cylinder bores looking through the spark plug holes. If the bores look ok (no scratches or obvious issues) then go ahead and run it as the low compression merely means the engine is tired and worn. At this point you would need to have the engine bored and oversize pistons and rings installed which is something you cannot do (boring that is). If the cylinders are scored, the engine doesn't have long to live anyway and a rebuild now would be in order, or a catastrophic failure down the road which may prevent an overhaul of any sort. Only you can make those choices. They all involve money.

 

[Laddies]

Re: Turning to the smart guys on Mercury 40 hp 2 stokes.

Pull the intake port covers off the starboard side of the engine and you can look at the pistons, rings and bores for the cost of 2 gaskets if you are unlucky and tear the old ones. Those engines seldom need boring we are still running 1987 engines that have not been bored and have been raced ever year since they were new and won D Stock National Marathon Championship last summer. That engine has been re rung ever 3 or 4 years but never bored or had bearings replaced. Many years ago we ran a rental fleet with about 15 of the 44cu.in. engines in it and they were rented ever day that it did not rain and sometime on rain days most of the time at WOT to make the 87 mile waterway we were on and they averaged 3 to 4 year of misuse on a overhaul.

 

[crossroads123]

Re: Turning to the smart guys on Mercury 40 hp 2 stokes.

I really want to thank everyone for their answers. I will be be pulling the intake port covers off and see what I can see. Gentlemen I really want to say THANKS.