Piston Damage

[bjncj827]

Hi, all! I have tried to find a post associated with piston damage that I am experiencing. Can't find one. If anyone could steer me in the right direction, I would appreciate it.

I have a 90 hp evinrude (87'). She has always run a little rough (at leats for the last 5 years that I have had her!). Receently, it has gotten to the point where I can not even get the motor started. I rebuilt the carbs (they looked pretty clean though).

Through researching the post, I find out that I was using the wrong spark plugs (was using L82C instead of the L77JG4's per iboat posts - ouch!!). I think this is where my problem started!!

I checked the compression in all four cylinders. The two cylinders on the left when facing the plugs had about 105 psi. The two cylinders on the right where 0 psi on top and 20 psi on the bottom. I took the plates off to inspect the piston/cylinders. The pistons are severly worn and chipped. A lot a play also, hence no compression! The two left pistons look fine!

The cylinders themselves don't look bad, but I'd have to think that they will need some attention based upon the piston condition.

I had the incorrect plugs in all four cylinders, so I can not understand why the other two cylinders are not showing the same problems.

Where to go from here??? Any ideas on cost of repairs???

I must say that reading these posts and working on the motor myself has turned me into a boat grease monkey!!! A new hobby!!

 

[HybridMX6]

Re: Piston Damage

It's unlikely the spark plug did the damage on only half the engine. More likely you had a blockage in the carb that feeds those 2 cylinders. Have you pulled the head off that side to inspect the cylinder or is that what you mean by plates?
You/We will need to find the cause of the problem in order to properly fix it, so it won't happen again.

 

[bjncj827]

Re: Piston Damage

I was referring to the heads when I mentioned plates. I did pull them off and inspected the cylinders.

Here are a few photos of the cylinders, pretty ugly!!

http://www.facebook.com/album.php?aid=31394&id=1435996812&l=2ac28f1215

I cleaned the carbs. Is there a way to check for the blockage???

 

[jonesg]

Re: Piston Damage

Pistons are $130 ea, last time I looked.
Machine shop(marine) to bore 20 over is usually less than $200, have them fit the new pistons to the bore. Probably $600-800 total when you add gaskets , piston pins, bearings etc.

 

[HybridMX6]

Re: Piston Damage

From the look of that pic it looks like that lower cylinder ate the rings. Could be caused by no lubrication or no cooling. Does your motor have the warning horn or no?

 

[reeldutch]

Re: Piston Damage

if the carbs would be dirty wich would mean you would run lean at some point, it will show signs of lack of lubrication.
no gas means no oil.
if there is no scoring on the cylinder walls and there is a film of oil covering the cylinder walls i have serious doubts about the carbs causing this problem.

your rings might be stuck in the ring lands(groove)

of course when you rebuild you will have to rebuild the carbs.
take all the jets out the whole nine yards.
all im saying is i dont think that the carbs caused you this problem .
specialy because the way the cylinderwall looks and on the cf V4 the carbs feed or the 2 top or the 2 bottum ones.

i do think you have stuck rings and the wrong plugs might have given you the wrong heat range on the long term eating your pisons.

did you take both heads off?

 

[bjncj827]

Re: Piston Damage

Thanks for everyone's feedback.

It does have a horn for no water flow/cooling. It has gone off a couples times when out on the water. However, I am under the impression that that horn also can be trigger with low fuel or low oil levels. When the alarm did go off, I checked the motor and still had a stream of water coming out the motor. My fuel level was good, but I was running low on oil (not out though). So I brought her in and refilled the oil. Horn stopped the next time out.

I have been noticing that I was using a heck of alot more fuel than in the past. Don't know if this points to anything, running lean???

Cylinder #1 (top right) has quite a bit of oil reside on the head, minimal in the cylinder. The other heads look clean with a thin layer of oil/gas on the cylinder wall. There is an area at the top of cylinder #1 where it comes to the head that is dry. It looks like this is the area where I am losing compression.

 

[Faztbullet]

Re: Piston Damage

What you have is a ignition or a cooling problem. From the looks of #3 piston it looks as if rings broke due to coke/carbon build up from : engine over propped or this side running to cool due to defective or open t-stat. #1 piston eyebrow looks to be eroded, could be timer base or bias circuit in packs and this side running a advanced timing. I highly doubt it was a carb problem as chances of high speed jets lean same side are unlikely.

 

[HybridMX6]

Re: Piston Damage

I'm saying the rings are shot due to that's what it looks like from the pics. Those pistons look like the ring got torn up and pushed into the compression stroke, then beat to death by the piston, causing those nicks.

 

[emdsapmgr]

Re: Piston Damage

Agree with Fastbullet. Check the piston ring areas and piston skirts for carbon builtup. Also, the bottom cyl looks dry. I'd pull the carb apart that feeds that cyl and check the jets on that side of the carb that feeds that piston. You may have some debris in them, causing a lean condition. The piston tops should be black.

 

[HybridMX6]

Re: Piston Damage

If you can get a look in the ports through the exhaust plate area you will be able to see the rings, but I have a feeling from those pics there are no rings left. Looks like both cylinders ate the rings. Also, either that one dry looking cylinder has a blockage in the carb as mentioned earlier, or your head gasket blew out and let water in, steam cleaning the cylinder.
All this could also have been caused by overheating, which would be as easy as the head gasket went out some time ago, allowing the compression in the cylinder to push the cooling water away from this side of the engine, which over time resulted in the rings finally breaking down and tearing up in the cylinder, causing the damage you see.

 

[bjncj827]

Re: Piston Damage

I appreciate everyone's feedback. I am spending some time digesting all this. Piston rings are not something that I am familiar with, but I certainly am learning quite a bit. I am assuming the piston rings are what allows compression to take place (located between the piston and cylinder wall???). There is a lot of play in all the pistons/cylinders, no rings???.

It sounds like my next step is to get the cylinders honed, replace at least two of the pistons and rings and check for proper water flow to prevent this from happening again. The jets were open (not plugged) when I cleaned the carbs. I gave them a good soak anyway. What is the best way to check for proper water flow???

 

[HybridMX6]

Re: Piston Damage

You will most likely need to strip the block down and remove everything from it (you will need to remove it from the engine itself first), then take it to an outboard engine shop. Typical automotive machine shops are not used to dealing with outboards and I've heard some bad stories of people going to them with their outboard motor. They will then need to check the cylinders for roundness, as well as size. They will then let you know if you can hone them or if you have to bore them to the next oversize up. From there you will order the parts you need based on what they say/do.
The rings fit in grooves in the side of the piston, and they are what seals the piston and maintains the seal to build compression. If you can move them back and forth freely, most likely the rings are gone altogether.

 

[emdsapmgr]

Re: Piston Damage

If the carb jets were open, you should have had fuel into the bottom cyl. To get that "washed" appearance, you may have a water leak. Check the head gasket sealing surface on that cyl, and also check the exhaust cover and it's gaskets for water leakage into the exhaust chest. Exhaust chest water leaks tend to affect the bottom cyls first.

 

[HybridMX6]

Re: Piston Damage

Good info ^^^^^

 

[iwombat]

Re: Piston Damage

Looks like a blown head gasket was at least part of the equation. Chicken and egg on that one though. Bottom hole is shot. The low reading on the top was probably from the blown head gasket.

Two likely causes of failure (I'm sure there's more):

1) blown head gasket - water damage caused ring failure.
2) carb blockage - lack of lubrication caused cylinder to overheat. Blown head gasket and ring failure.