chewing up piston rings

[rustybeater]

I have a 1993, 90hp Johnson outboard it is the v4 sea horse. About three years ago it chewed up the piston rings on the lower piston on the right side. I believed that it was because of the vro2 fuel/oil pump not working properly. After I replaced that piston and re-ringed all of the pistons I started mixing my oil in the tank.I have probably put about 60 hours on the boat since i rebuilt it. Today I was out on the water and it was missing real bad. I found out that the top piston on the right side has chucked out the piston rings. That is the first time I have rebuilt a boat motor but I have rebuilt some car motors and do not believe that any thing was done wrong. I have a temperature gauge and and audible alarm for over heats and I mix my oil at every fill up at 50 to 1. I guess my question is would there be a reason why I keep chewing up piston rings and is there anything that would cause it to happen on the right side. I performed a compression check and all are at 110 except the bad one which is reading 90. Any ideas? thanks

 

[racerone]

This es OH SO COMMON on the V-4 crossflows.----Picture this and check how much slop is in the worn pistons near the ring lands.----Now look at this top ring and see that as the ring moves away from the piston the side clearance goes way UP and the ring is really sloppy in there.----The result is what you have ----KABOOM it goes.-----Putting new rings in a worn out ring groove is also a bad idea,----Look into a set of WISECO pistons for the fix.

 

[boobie]

When you put in the new pistons and rings make sure you radius the ports or run a ball hone down the cylinder to take the sharp edges off of the ports.

 

[rustybeater]

Ok, so as I said I am new to this but you think i should just go ahead and replace all of the pistons and and rings. Is there anything else I should do while I am in there? bearings? Plus the head has some nicks in it, I will probably replace that as well.

 

[boobie]

No need to replace the head if you can get the sharp edges smoothed out. Done a lot of them. Indentations won't hurt.

 

[emdsapmgr]

What was the determined cause of the first failure? Did you resolve that prior to the first rebuild? Did you pull the carbs completely apart visually inspect the jets to be sure they are not restricted. Did you visually inspect the water jackets to be sure they are clear? Are the rubber water diverters in normal position and not restricting flow by each cyl? Did you pull the head covers off both heads to be sure the internal water passages are not restricted? Are you sure one of the two stats is not stuck shut? It's possible to heat a cyl up to the point it fails because of one of the above cooling issues-and never get a hot horn.

 

[Faztbullet]

Also if the engine is running to cold it will cause excessive carbon to build up and chuck rings....

 

[rustybeater]

I believe that the first problem was caused by failure of the VRO2 fuel/oil pump. I corrected the problem by putting the older style fuel only pump and add oil directly to the fuel tank. I do not believe it was overheating but, the audible alarm sensors were not working. I went ahead and replaced them (one in each head) and I installed a temperature gauge only on one head (the one that is chewing up pistons). When I rebuild the motor the rubber diverter valves were not in there so I went ahead and ordered them and installed them. I also made sure that there was no water flow restrictions and I replaced both thermostats. While I was at it I rebuild both carbs and installed a fuel water separator. When I took the head off yesterday it does not seem like it has excessive carbon build up. I tried to load a picture but it just says the file size is too large to attach.

 

[Chinewalker]

I'm betting your initial rebuilt was not a result of VRO failure, rather was rectified by the carb rebuild. Your second blown cylinder may be due to lugging, cooling issue, or another gooped up carb. Lugging is an often overlooked issue with the V4s. The like to spin up. Propping them so that they peak in the neighborhood of 5700-6000 RPM is ideal. If they top out at 5000 or below, then you're lugging it - akin to driving uphill in fifth gear while towing a trailer...

 

[rustybeater]

I want to say that at wide open that motor runs at about 5500 rpm but usually I will cruse with it around 4200 rpm. I don't think that should really be lugging it? if I was lugging it there would be carbon build up correct?

 

[emdsapmgr]

If your engine makes 5500, that's fine. Not lugging. Once you get the engine to run that rpm at WOT, it means your economy, reliablilty and performance are optimized all other rpm's too. Did you ever have the head covers off the heads to check those cooling passages? It's also possible that the new pistons may not have been sized properly for the bores. Changing piston suppliers sometimes requires differences in piston clearances to account for thermal expansion. There are cast and forged pistons.

 

[rustybeater]

all the water passages look good. I cleaned them out real good on the first rebuild and they still look pretty good (no blockage). I keep trying to post pictures but It keeps saying the file size is too big. I even changed the mega pixel on my phone from 16 to 6 (as low as it goes) and it still wont let me. Last rebuild I only changed one piston and then re-ringed the rest. The one that I changed last time looks good. On the compression check all are at 105 except the chewed up one which is at 90.

 

[emdsapmgr]

Have you had the carb apart? What did the high speed jet look like that fed the bad cylinder?

 

[rustybeater]

No not yet, I have been working long hours. I am hoping to get off and have time to pull the carbs tonight. I will let you know.

 

[racerone]

When you get the engine apart measure the total clearance between piston and cylinder.-Report what you find at the bottom of the piston skirt and near the ring lands .

 

[rustybeater]

ok all I got done today is removing the carbs. Once again I had to stay late at work. I took the high speed jet out and it looks fine it is not gummed up at all. I took a picture but it wont let me attach it. hopefully I will be able to measure the pistons and the cylinders this weekend

 

[rustybeater]

No Title

finally able to attach pictures. In the picture with the head you can see it is darker but, something hit and closed the gap on the spark plug so I had to go about 2 miles back to the ramp without it firing. as you can tell from the head the one on the top is the bad one and the lower one is the one that went bad a couple years ago.

 

[racerone]

I do not have enuff fingers and toes to count how many times I have seen this problem !!!!

 

[emdsapmgr]

I'm concerned about the water flow around the cylinders in your picture. Seems to me that the upper rubber water diverter is a little too close to the sidewall, somewhat restricting water flow. Not closed, but restricted. Also, there looks to be some debris on the right side of the lower cooling passage. Will post a picture of what the optimal cyl water passages look like.. (The left diverter is ok, the right one is an example of one that is out of position.) You may want to clean as much of that lime-appearing crud out of the cooling passages as possible. Also, what you see inside the block is also inside the head cover. Pull the head cover off the head and see what the cooling passages inside look like. With blocks like this that have some water movement, a single cyl can overheat and the hot horn may not sound. The spark plug tip got bent over when the top piston ring disintegrated and blew out the exhaust. Likely you may find piston ring shards in the lower unit exhaust area just behind the prop.

 

[rustybeater]

No Title

That debris that you see on the right side is just some gasket material that stuck to it when I pulled the head off you can see it a little better in this picture. There is some restriction built up on the water passage but I don't believe that it would be enough to cause an over heat. Also the cylinder that chewed the piston up is the cylinder that my temperature gauge is on.