Question about engine knock

[Andys Delight]

I have an older 1985 Mercury 2 stroke 115 O/B.  I dropped the boat off to the nearest boat service center (not going to name names) for spring service before getting out on the water this year.  I normally use a traveling boat mechanic (again, not naming names), but my last trip out for Stripers last year resulted in my engine bogging down on me quite a bit and even stalled on me.  I got back to the dock, trailered it home and realized when I got home that stupid me forgot to replace the fuel water seperator recently and had a good deal of water in it (damn ethanol!!!!).  I replaced it and the boat ran fine on muffs at home so I completely winterized it.  I wanted to be sure that everything was looked over thoroughly this year so I opted to use the expensive, huge service center here as opposed to the traveling service guy thinking they had better equipment/knowledge to fix it. 

The mechanic told me that the engine seemed ok, but he did hear a bit of a knock in one of the cylinders.  He said he didn't want to go too deep into the engine since it could get costly and maybe not worthwhile on an engine that old, then started recommending I might want to consider buying a new engine or boat soon. 

What's your thoughts on this?  Prior to the last trip the engine ran fine and he said it ran fine for him as well, just didn't want to go digging too deep in an engine that old. 

My question is could the engine knock have caused the engine to bog down under a load, and if so is there anything I can do to remedy the situation short of his recommendation to buy one of the lovely new boats on his lot (It's a boat dealer as well). 

Anyway I replaced it and the boat ran fine on muffs at home so I completely winterized

[Hotrod]

I ran my 115 Evenrude for a full season with half a piston   I didn't know it until I did a compression test..and found a low cylinder..

If you lose a rod....this will be the death of the Motor..

I would Call Matt from Task Marine..

Or if you have Seatow or BOat USA..  run her till she blows

[Andys Delight]

I ran my 115 Evenrude for a full season with half a piston  I didn't know it until I did a compression test..and found a low cylinder..

If you lose a rod....this will be the death of the Motor..

I would Call Matt from Task Marine..

Or if you have Seatow or BOat USA..  run her till she blows

I have Boat US unlimited towing and trailer service.  Wouldn't dare go out without it.  It was described as a "small knock".  The service center has been extremely busy.  It sat on their lot for 3 weeks before they even looked at it.  I just kind of got the feeling they didn't feel like going too in depth on mine because of how backed up they are with jobs and how old the engine is.  I've seen Matt's info listed but he's a hell of a long way from me (I'm in Bridgewater).  Not sure if it's practical for me to tow it all the way down to him.  

I was basically told other than the small knock the engine looked good and to just try and burn off the existing gas or replace it.  I have no idea where to get rid of 30 gallons of gas so I'll just not go WOT and keep a close eye on the fule water seperator..........and pray ahaha!

[kezsr]

I would do a compression check and see if all ok,here's a link to a site I found helpful,go there and register and pose your question,and if your boat is sitting at a shop that starts with an L,I'd get it out of there, a few years ago mine spent a month there,costly repair as to there reccomendation and never fixed the problem and myself found a cylinder down and replaced motor.http://www.marineengine.com/boat-forum/forumdisplay.php?f=30

[Andys Delight]

I would do a compression check and see if all ok,here's a link to a site I found helpful,go there and register and pose your question,and if your boat is sitting at a shop that starts with an L,I'd get it out of there, a few years ago mine spent a month there,costly repair as to there reccomendation and never fixed the problem and myself found a cylinder down and replaced motor.http://www.marineengine.com/boat-forum/forumdisplay.php?f=30

Thanks kezsr, definitely does not start with an L.  I'll check out the site and see what I can find.  I'm headed over now to pick it up. 

[Hotrod]

I would do the Compression test..  Then do a Decarb..   Or just do the decarb.. 

and remember 1 Thing!.  2 stokes live for WOT. 

When ever possible.. push the throttle down and let her scream

[Andys Delight]

Got it back and spoke alot more in depth with the service manager.  I definitely was put a little more at ease.  They ran a compression check on it, it came back 125, 100, 125, 125.  The knock was coming from cylinder 2 but was not dramatic.  He said it could even go away once I burn through the fuel.  He also said run it at WOT as much as possible (thanks Rod  ) and get it good and hot.  He basically said he didn't want to go tearing into an old engine and cost me thousands when the problem could just have been the fuel.  He gave me the company line that "old engines could blow any day" but then said he felt with the proper maintenance and care I could probably get another 5 years out of it. 

She splashes on Thursday 

[L.T.]

Can  I assume that the knocking from cyl. 2 was the one with 100 lbs. compression as opposed to the others at 125 lbs.? 

[Andys Delight]

Can  I assume that the knocking from cyl. 2 was the one with 100 lbs. compression as opposed to the others at 125 lbs.? 

Yes it was.

[Hotrod]

Decard   Yea..  the 100 isn't good.. but could just be a stuck ring..  Decarb can re that up.

[Andys Delight]

Decard   Yea..  the 100 isn't good.. but could just be a stuck ring..  Decarb can re that up.

Exactly what I was thinking of trying.  Hopefully this rain quits for a little while.

[Hunter 2]

Dont forget to use STABIL ethanol treatment or a similiar product.  One 32oz bottle will treat 320 gallons. You may be able to siphon some fuel off the bottom of the gas tank with a hose and check it for water or contaniments in a clear container.

[Andys Delight]

Here's something interesting-Went to the shop to pick up some Yamaha Ring Free today and happened to run into the mechanic.  He adamantly said not to use ring free or decarb at all.  He said the carbon buildup in an engine as old as mine might actually be contributing to keeping the PSI up as high as it is right now, that loosening up the carbon might actually drop the pressure and potentially kill the engine.  I've never heard of such a thing and now I'm left 

[Hotrod]

Yea.. well.. I guess anything is possible.. but Carbon holding the engine together..  sounds a little tough to believe..

You looking to burn off carbon that could be sticking the rings.  I don't think the Decard is going to take all the carbon off the top of the piston..      But.. what do I know..

[Andys Delight]

Yesterday I felt a little better after meeting with the mechanic there and having him explain in detail what he found with my engine.  Now I'm back to being skeptical.  I have never heard decarbing being a bad thing, especially when one cylinder is low.   

[Hotrod]

I would just run it... and Fish

[Andys Delight]

I would just run it... and Fish

She gets wet tomorrow, wish me luck.   

[Capt. Carl]

i heard the same thing about the decarb cleaners...if your rings are worn down,the carb build up could possibly be giving you the compression...clean those off and you left with no pressure....thats what i was told and im sticking with it! 

[Andys Delight]

Well, now she ain't getting wet till Friday.  Then the fun begins.  Let you guys know how it goes.