Low Compression, Low $ Advice

[Kola16]

Hey all, just need some experience, thoughts, or opinions. You can skip all the intro if you want and scroll to the last two paragraphs, but here is the backstory. I just bought this used 1996 Yamaha 130TLRU 2 stroke for pretty cheap as a "mechanic special." I already deleted the oil injection and will just mix the oil and gas. I put it on a used 18' aluminum bass boat that I just got that had a smaller, older, falling apart 50 HP engine on it. So I replaced the older crappy engine with the Yamaha. I bought the Yamaha and knew the compression was low before I bought it so no surprise or grief there.

The compression numbers the marine mechanics had on it where the guy I bought it from took it to had it at:
110, 98, 90, and 115. (25 PSI or 24% difference between high and low)

I tried working some magic to hopefully see if I could raise the low cylinder by using Seafoam Deep Creep, then Marvel Mystery Oil in the cylinders, and Amsoil Power Tuner while it was running. After doing these three separate treatments I didn't get much. On my compression tester that reads higher than other compression testers, but consistent, I got:
117.5, 107.5, 105, and 125. (20 PSI or 17% difference between high and low)

So a little improvement, but still not quite what one would want.

The problem is that I do not have $1,500 to spend on a rebuild. I just do not. I just rebuilt everything on my offshore boat, and have spent a lot on fixing my truck and car.

MY MAIN QUESTION...
For $200 or so, could I potentially just buy new piston rings (and associated gaskets) to get my compression even again? I would be taking out all of the pistons, using one of those ball hones to deglaze the cylinders, then putting standard size new rings in it with the existing pistons. Would that help the engine last a season till I could afford a full rebuild? Or do you think that the cylinder walls are too worn away with my compression numbers to just be deglazed and have the same pistons and new rings go in them? Obviously, I need to measure the bore and current ring gaps for y'all to know more specifically, but the engine is fully assembled and running right now so I have not taken it apart.

I am not looking for a performance outboard, this will just be used for duck hunting 10 miles roundtrip on the weekends and fishing maybe once a month. It is plenty of HP as the old engine was only a 50 HP. Just want it reliable. Should I just wait the 8 months or so till I have the $1500 to do the full rebuild with the overbore? I will lose a lot of duck hunting time if I have to do that, and that would be tragic. Has anyone been successful just replacing the rings and deglazing?

I do not mind the extra work of honing and new rings and gaskets 1 year, then a full rebuild the next. It is spending that cheese that is just not doable right now. All opinions are welcome. Thanks!

 

[KJM]

You seem to know more about engines then I do, but if its running fine now, would just using it as is be a bad thing until you can get it done properly?

 

[99yam40]

Run it with Yamaha Ringfree Plus for a few months to see if it gets better

 

[boscoe99]

If it ain't broke I would not go fixing it.

 

[Scott Danforth]

If running ring free for a few weeks doesn't help, start saving for a power head

 

[flashback]

No knowledge here, but Yamaha tends to pig out on rich mixture at least with their twin motorcycles...

 

[racerone]

Start saving for overhaul parts or a new motor.

 

[boscoe99]

No knowledge here, but Yamaha tends to pig out on rich mixture at least with their twin motorcycles...

What does that have to do with the OPs report of low compression?

 

[airshot]

While your comp numbers are not great, they are not that terrible either. Your not looking for optimum performance so just get it running as good as you can and go !! Decide down the road if you want to rebuild or not.

 

[brodmann]

I was thinking the same thing. Those numbers aren't too bad. I have a 1999 115 Yamaha that has 135 compression and my mechanic says it's as good as a new one. My last boat had a 115 Yamaha also. I had a piston come apart and store the cylinder pretty bad. Our local Yamaha dealer was a high school buddy of mine and he gave me a used piston from a recent rebuild. I got rings for the used piston and honed the cylinder as good as I could and threw it back together and used it like that for a couple of years. The compression on that cylinder was 85! The other 3 were between 120 and 125. My boat was a little overpowered with the 115 on it, so it reduced my top end speed from 52 to around 40, but that was plenty fast for me. I'd say got with what you've got and throw a little "magic in a bottle" in the tank every now and then and just use it as is. Use good quality 2 stroke oil and try to forget those numbers. I know you've got that in your head and it will be hard to forget, but as long as it remains dependable, I'd go with it.

 

[flashback]

What does that have to do with the OPs report of low compression?

Running pig rich causes excessive carbon deposits and stuck rings among other things.

 

[stresspoint]

run it like you stole it , chances are a good blast will bring up the numbers.
IMHO that motor will probably live as long as the boat.

funny thing about compression numbers and how people get to thinking a motor is dead because of a number that is 10 or 15 PSI low on a cylinder.
news flash >>> its not the end of the world , the motor will run fine , maybe just not make the full HP , but in the big picture it will still run and get you on the water .

now that said . start stressing when you see 50 or more psi difference .

enjoy your new motor and stop stressing ., iv seen much worse and still running strong.

 

[wmgeorge]

Never done an outboard engine but motorcycles and snowmobiles, pull off the heads and re-ring. Break the glaze on the cylinders and put it back together. Those engines I did had needle or ball bearing rods and mains. Plain bearing, wait for that full tear down.

 

[stresspoint]

Never done an outboard engine but motorcycles and snowmobiles, pull off the heads and re-ring. Break the glaze on the cylinders and put it back together. Those engines I did had needle or ball bearing rods and mains. Plain bearing, wait for that full tear down.

easier said than done with an outboard .

 

[flashback]

run it like you stole it ,

On my side of the planet they call it an "Italian tune-up!

It works sometimes and sometimes not.. worth a shot...

 

[boscoe99]

Running pig rich causes excessive carbon deposits and stuck rings among other things.

There is a benefit to running pig rich. Less chance of leaning out a cylinder. Better to have rings with carbon build up than a seized piston.

 

[wmgeorge]

easier said than done with an outboard .

That why I said what I said, but the prices quoted seem so expensive.

 

[QBhoy]

Hi. Firstly. These things are known to be only breakable by ridiculous human error. Otherwise I’ve yet to know if one that’s failed.
Forget all the silly additives. Get her a strong dose of oil mix (by the way…these have a great oil injection system as they are)…run her on load…then do a test again. They are either broken or they aren’t, these things. Nothing in between. Any I’ve known that have broken, were to do with either water getting into the oil supply tank in the bilge…or folk not knowing there was one in the bilge..and alarm not working or paid attention to.
As it happens, I bought a boat cheap years ago with one of these..it suffered from getting water in the oil tank. It actually ran like that for weeks unknown to the owner.
Looking into rebuilding it…just wasn’t financially viable. Parts were extortionate. As it happens though…turns out they are also worth a fortune for spares or repair. Actually sold it for almost the same money as it cost me to buy a 150 merc v6 from around the same age !!

 

[Kola16]

Thank you for all the responses y'all! Incredible help! It seems like the consensus is a full rebuild rather than honing and new rings, so I will save some $$ in the mean time.

The funny thing is, I posted this thread before I took it out on the water. I bought it as a "mechanic special" and was told it did not run under load so I did not even attempt to put it on the water. When I first started it on the hose, it seemed to idle okay, but did not sound happy when I raised the RPMs. That could have been from going into limp mode from no oil in the reservoir though IDK. I already had premix in my gas tank. I took the carbs apart to clean them and I did find very few particles and one small jet maybe blocked, but the biggest thing I found was water in the fuel filter that's on the engine. Also found fuel lines with no zip ties or hose clamps or anything, just fuel hose slipped over the barb connector and that was it. So once I fixed the fuel system, I deleted the oil injection, gave it the full treatment of sea foam deep creep, Amsoil power tune, marvel mystery oil, and Yamaha ringfree plus thanks to your guys' suggestion. The Ringfree plus stuff is pricey. I did a heavy shock of ringfree. No change in the compression, but worth a shot. Oh well, I thought, it does sound WAY better at high RPMs so I will take it to the lake to see what it does.

On the lake, the engine was pretty BA. It was fast and sounded pretty good for the most part. It did sometimes have this weird thing where it would kind of struggle to get on plane for like 2 to 3 seconds, kind of like a misfire, but it only did that sometimes. Most times it would jump up like a bat out of you know where. Once on plane at WOT, there were no issues whatsoever. The hesitation may be due to a missing carb gasket (orange O-ring on a jet? that broke and will be replaced), or just the heavy shot of ringfree, but I do not believe it is compression related. Could be wrong. The latest compression numbers with the engine warm and the carbs wide open were 119, 110, 107, and 127.5 PSI (17.5% or 20.5 PSI difference) just FYI.

Anyway, I am going to run the engine till it really dies, then do the full, proper rebuild. I have a bow mount that will get my home wherever I plan on taking this boat. I got the engine for cheap, and am very happy with it for the money so far compared to the other engine I had.