Compression and scared cylinders

[ppidgursky]

The repair shop called and told me they have removed the head and found that 2 of the 3 cylinders are scared up. They are saying I must get the head bored and the rings replaced. Does this sound right. Is that the process when the cylinder is scared?
When I ran the boat last I was good for about 4 mins. of full throttle the she would die. I would have to let it cool down and then I would be able to go again. If I tried to start it before it cooled, it would be a slow crank, but I could usually get it started but would die when I try to give it gas. We tested the compression and they tested good, but we did test them when the engine was cooled. My problems seem to happen when the engine is hot. Could this be it, or am I getting raped, and not even getting dinner first?

 

[yamamarinetech40]

Re: Compression and scared cylinders

Let's just say you are overheating, which you would know if you put your hands on the top of the heads when this happens.....when an engine severely overheats the piston swells quickly compared to the greater mass of the cylinder and 'sticks', thus scarring the walls with the rings....and when you try to start an engine that's overheated the starter is trying to move this swollen piston against the walls of the cylinder and can't spin fast....that's why you DON'T start an overheated engine, you have to wait LONGER for the internals to cool down. Yes you do need to have a bore job and rings, regardless of compression....which should be done on a cool engine...now if the compression was low then you could try it warm and usually it would come up a little....but that's not your problem....you need to find the overheat source and doesn't your gauge have a bar flash over the temp symbol when overheats? Should.....

 

[Ray Neudecker]

Re: Compression and scared cylinders

Their story makes good sense. Exactly what happens during a seizure. You must get the original problem cured also or it will reoccur. Sounds like you overheated. That is what the buzzer and light are for.

 

[ppidgursky]

Re: Compression and scared cylinders

Now I know the water is circulating thru the motor because the stream coming out the rear is constant and warm. The guy at the shop SAID he tested the thermostat and it opened at the right temp.
If the water is circulating, and the thermostat is opening, what else could make it overheat?

I am supposed to go look at the motor tomorrow. I will see exactly the damage when I get there.

 

[yamamarinetech40]

Re: Compression and scared cylinders

That pee stream does not mean water is circulating throughout the complete engine...and it isn't trying to tell you it is...it is only telling you that your water pump is functioning. Also, what do the valves and other parts look like? Lack of oil can overheat also but should be able to tell which one....

 

[Ray Neudecker]

Re: Compression and scared cylinders

Normally an oiling problem would have had the rod bearing for that cylinder for lunch. When apart you will have a much better idea what happened.

 

[Capt Ken]

Re: Compression and scared cylinders

If you checked the compression and they all was close to being even, then you probably don't need a rebuild. It is not unusual for some scoring in the cylinders on an older engine. Would be nice to know which 3 cylinder engine you are speaking of. It may be that the engine's age may play into the decision to rebuild or not. Sometimes the engine just ain't worth it.

 

[ppidgursky]

Re: Compression and scared cylinders

Well unfortunatly we had to go with the rebuild. Top and bottom had 130 lbs, center had 15. I took it apart and the center piston was eat up. I found the cause....the water pump. The "wonderful" place I took the boa to trouble shoot the problem told me "It can be the water pump, you have water coming out the rear." Welll I took it apart and the impeller was missing a few fins and the rest were melts to a 90 degree angle..... nice huh.
Anyway I had the block bored 20 over and put new pistons.....wasn't as bad as I thought... total rebuild (boring, pistons, rings, and gasket set $330... put back togther myself with the shop manual by my side.

 

[JUSTINTIME]

Re: Compression and scared cylinders

Well unfortunatly we had to go with the rebuild. Top and bottom had 130 lbs, center had 15. I took it apart and the center piston was eat up. I found the cause....the water pump. The "wonderful" place I took the boa to trouble shoot the problem told me "It can be the water pump, you have water coming out the rear." Welll I took it apart and the impeller was missing a few fins and the rest were melts to a 90 degree angle..... nice huh.
Anyway I had the block bored 20 over and put new pistons.....wasn't as bad as I thought... total rebuild (boring, pistons, rings, and gasket set $330... put back togther myself with the shop manual by my side.

good to hear

 

[micel]

Re: Compression and scared cylinders

Where did you get parts?I can't even get gaskets for that,much less piston(s),ring set plus machine work.Hopely I will not have to use your source but if I do it would be good to know.I was planning on getting a new df175
if I have any major problem,but prices like that I will keep 2 stroke.