from NO compression to LOW compression in one cylinder

[Nina215]

I posted previously about my boat not going above 2200 RPMs. It's a 99 Sea Ray 215 with a 5.0. The boat has sat almost its entire life, minus 2 or 3 seasons. I bought it as a project, went over everything, got it running and it ran great all 2016 season. I winterized it and was too busy to use it last year so it sat another year and a half until this year. Since bringing it out of storage, it hasn't wanted to go above 2200 RPMs. I went through everything again and again before a mechanic found that the #7 cylinder had ZERO compression. ALL other cylinders have 180+. The boat/engine only have 155 hours, engine looks brand new, no wear on it, but a lot of sitting.

I took off the valve cover and found the exhaust valve for #7 was stuck open. The cylinder was full of carbon. I thought I might get lucky and just have a valve stuck open from carbon. I worked the valve a bit and cleaned it and eventually got it to close successfully. I removed the exhaust manifold and have a clear view of the valve and can see it is fine, not bent, and holds liquid if I fill the backside of it through exhaust port while holding it up. Did another compression test after freeing the valve and now I'm up to around 40psi.

I cannot see any damage to the piston through a scope. I sprayed a lot of seafoam in it today to clear a lot of the carbon off and it looks fine to me.

Any ideas what this could be?

I'm running out of options. I do not have the time to tear the head off. Nor do I want to put any money into this engine. I bought this boat as a project with the block cracked on both sides. I fixed it with marine tex, hoping to just buy me a season or two until I put a new engine in. But the engine is so clean and has run so good until now, and has perfect compression in all other cylinders. It'd be a shame go through the time and expense of a replacement if it's something simple.

Problem is, I'm about 2 months behind on more serious projects that I need to get done at home. I cannot devote any more time to major engine repair or replacement this year. I paid $2k for my dockage this year, ensuring the boat started and ran and sounded fine before forking over the cash. But since the very first ride of the season, it has had this issue so I haven't been able to enjoy my boat at all this season and just threw away 2k that I can't get back, nor am I allowed to sell my remaining dockage. So if it's something I can fix relatively easily, it'd be worth it to try to salvage what I can of the season and get something out of my $2k. Otherwise, I don't want to put money into an engine that is cracked and will just replace it with a 5.7 over the winter.

What are the odds that the rings are stuck? Could that cause such a low compression reading? I filled that cylinder with seafoam today and am gonna let it soak a day or 2.

 

[Rick Stephens]

I would have loved if you had continued the old thread... really nice to tie it all together. Whatever. I think you should add some marvel mystery oil to the engine oil and run it. What's to hurt? See if he super high detergents in MM oil clean it up and free it up. Go boating for a while.

 

[Searay240sd]

I would do a leak down test on that cylinder, that would tell you what is wrong

 

[Scott Danforth]

first, look down the bore with a bore scope. you could have rust in the bore from sitting with the exhaust valve open. then again, you could have had mice build a nest in the cylinder because the exhaust valve was open.

if its clear, then fire it up and run it....then check

in the future, if the motor is going to sit. back off the rockers. something an old machinist told my father 45 years ago. something that I do to this day.

 

[Benny67]

The valve isn't seating.

You run that engine, you are gonna burn the valve up.

Pull the head, re seat the valve.

It MIGHT run OKAY for a week or two...but after that, that valve is toast.

 

[Benny67]

I took off the valve cover and found the exhaust valve for #7 was stuck open. The cylinder was full of carbon..

Dollars to Donut's that carbon you are discribing is causing the valve to not seat properly and in turn is causing the compression to drop to what you see now.

 

[Benny67]

It will look something like this if you run it in that condition. Funny, cause I've had this burnt valve sitting in a old coffee cup on my desk at work now for 15 years..I can finally use it for something.

The hot combustion gas will leak past it and eventually burn it up...making it look like that

 

[Nina215]

The valve wasn't seating, it was stuck open. Now it is seating, since cleaning it. This has been verified by having it hold fluid, as stated. It will hold fluid until I release it. There is no damage to the valve. Now, something else is causing the vacuum leak? I'm thinking stuck rings.

 

[TurtleTamer]

As stated you're going to have to scope that cylinder and see what it looks like. You probably got rust in it. Think about it. With that valve hanging open your combustion stroke has now turned into an intake stroke, but through the exhaust. You very well could have been sucking in water and spitting it back out. This could have rusted the intake valve as well to some degree, even if it just got moist between uses. I'd say you scope it and see. If you really want to cut corners you could rotate the engine to where that piston is at TDC, remove the rockers, springs, keepers, and seals, chuck your valve into a drill and pull up on it while rotating. You couldn't get any lapping compound in but you should be able to clean the rust off. You'd have to be really careful not to overdo it. Your liquid test is promising but won't tell you what the valve is doing under pressure.

I'm doubtful you have an interference engine but if so it's not impossible you dinged the piston pretty bad and didn't bend the valve. Small hole would give you low compression.

 

[Benny67]

There is no damage to the valve..

Correct...The valve itself may be fine However, the area where the valve meets the head (seat) probably isn't sealing properly. If you pull the head and at least lap the valve into the seat it would probably solve the problem.

You said yourself, there was a lot of carbon build-up.

That's EXACTLY how burned valves get burned...too much carbon, that in turn effects the seating of the valve and then you get blowby of hot gasses, it then burns the edge of the valve.

I doubt it's sticking rings.

 

[Benny67]

A If you really want to cut corners you could rotate the engine to where that piston is at TDC, remove the rockers, springs, keepers, and seals, chuck your valve into a drill and pull up on it while rotating. You couldn't get any lapping compound in but you should be able to clean the rust off.

Not something I would do...but feesibly could get you through the season and then do your heads in the winter.

Not the WORST idea...definitely creative and COULD fix it. However, it's a gamble

 

[Nina215]

Like I said, when I hold the valve up in the seat, and fill the backside with fluid through the exhaust port, it will hold the fluid until I release it. Nothing wrong with it or the seat.

Yesterday, I filled the entire cylinder with seafoam and let it sit 24 hours, hoping it was just stuck rings. I went back 24 hours later and every drop of that seafoam was gone. It had leaked past the rings. I did another compression test and it was zero. I was like wtf, how did I go from 40 to zero? I thought that when I did the test yesterday, there was a little seafoam in the cylinder and maybe that basically made it a wet test. So I added a little 90w oil and did a wet test today, 15psi. So it is definitely worse than yesterday. How did that happen?

I am not pulling the heads or fixing this engine, as stated. I never intended to keep this engine. I will have to put a new engine in in the off season. My goal is to salvage what I can from this season since I spent 2k on a dock and can't get my money back and can't sell my spot to someone else. I'm not gonna put all kinds of time and money into this block when my plan was always to put a 5.7 in it eventually. But I just want to get something out of it this year.

 

[Scott Danforth]

do a leak-down test to see if its rings or valves

check if your spring is cracked. if so, 15 minutes with an on-head spring compressor and you can change the springs.

did you look in the hole with a bore scope?

 

[TurtleTamer]

Not something I would do...but feesibly could get you through the season and then do your heads in the winter.

Not the WORST idea...definitely creative and COULD fix it. However, it's a gamble

I appreciate that but I'm going by his/her mindset of trying to salvage some of the season before changing the motor this winter. That, to me would make it worth a shot.

OP, I missed it where you stated you shot the cyl with the borescope in your first post, which is how you know you have carbon and no apparent damage to the piston. But to me, it'd be just plain ODD for the rings in one cyl to be bad and not the others. Valves are a different story. What fluid are you using to fill the exhaust port? And to that effect, I'd bet if you did a leakdown test, with the fluid sitting in it, you'd see bubbles coming up (you're putting about zero pressure on the valve with your method whereas you're gonna put ~120psi with the leakdown test). That, and you can't possibly know what the intake valve looks like, unless your scope is the snaky sort that you can get down past your carb and into that intake port.

Also, to me, the seafoam leaking down past the rings means little. I've seen more than one hydrolocked engine sit for a short time and then turn over once the water leaked past the rings, and I can personally vouch for one experience where compression numbers across the board were 140+psi. Worn out? Maybe. Shot? No.

 

[Nina215]

I don't think the rings are "bad". I think they are stuck. From rust and/or carbon from sitting for so long and for being run at high RPM basically never. Even two years ago when I ran it, most of it was idle speed river cruises. So a lot of carbon build up. I've been reading about and watching videos about people who seized up rings from sitting for long periods of time. They filled the cyilnder with one thing or another and let it sit for days and then ran the crap out of the engine and were able to get them unstuck and bring compression up. But I haven't read a single instance where all the fluid drained past the rings in a day. These people all had to remove the fluid days later.

When I tested the valve, it was visible stuck at first. It was 1/4" open. I removed the spring and worked it free. Then I removed the exhaust manifold, held the valve up by hand, sprayed the backside of it with carb cleaner to where I had a small puddle, maybe 1/4" deep being held up by the valve. I sat there like that for awhile seeing if it'd drain out. It stayed at the same level until I released the valve. I took video and everyone who watched it agreed there is nothing wrong now with the exhaust valve. I cannot see the intake valve. I cannot turn the scope around to see it in the cylinder. When I put the seafoam in the cylinder and filled it, I filled it all the way past the exhaust valve so that the intake valve would also be soaking. From the valve cover, it appears that the intake valve is all the way up. I could remove the spring and work it the way I did with the exhaust valve.

 

[Searay240sd]

Are you against doing a leak down test? That will tell you exactly what the problem is.

 

[Benny67]

Are you against doing a leak down test? That will tell you exactly what the problem is.

What your saying is really the most logical next step..OP is looking for a quick fix.

The drill spinning the valve is the best short term quick fix..if it works..I'd suggest also pushing the Piston to tdc and possibly attaching a compressor into the spark plug hole in case the valve drops you stand the chance of the compressed air stopping it from dropping down..and also the Piston might be high enough to stop it from falling in as well.

What he's discribing with the valve is a classic example of carbon buildup dropping compression in the cylinder.

Anyway you look at it, that head needs to come off.

 

[Nina215]

I'm trying to borrow a compressor to do a leak down test. Mine is way too huge to take to the marina. I really feel like it's the rings at this point but I'm not totally ruling out the intake valve. I think if it's just the valve, I could clear it like I did for the exhaust valve which was visibly stuck open.

 

[Benny67]

Your liquid test is promising but won't tell you what the valve is doing under pressure.

This is spot on advice. Just because it's holding liquid that really means little to nothing.

Leak down test will confirm.

 

[Nina215]

I did a leak down test and found that the intake valve was leaking. I was hoping it was just carbon build up like the exhaust valve but found the valve to have a slight bend at the bottom. I decided to go ahead and take off the head but as soon as I got the intake manifold off, I found an internal crack in the engine, on the opposite side of the block. It's interesting because no water showed up on the dipstick and even marine mechanics said my oil was fine. So it's done. I'm going to put a 5.7 in. Who sells good remanned marine engines?