What caused this????

[jlw1972]

1997 JOHNSON 115 X FLOW

I bought this boat knowing the power head had piston damage. One of the cylinders had been previously rebuilt with a .020 piston and the other three were stock. I was told the boat ran fine after the first rebuild/patch job, For a couple years. Then it dropped the other three stock cylinders. I was able to size all cylinders at .020 over when I rebuilt it this time. Today I checked my spark advance using Joe Reeves method. I had not moved the adjustment during the rebuild. After locating TDC which was exact with the TDC mark on my fly wheel, I checked it with a timing light. It was 8 degrees higher than what it is supposed to be. The correct deg. is 28 so I set it at 24.

My question is, Could this be what caused this piston damage?? I know the rings breaking is what ate them up so bad but why did the rings break?? Could it have been the high spark advance? One of the pistons(The .020 from the first rebuild) looked ok but the 3 stock pistons were demolished. Why 3 cylinders at one time and not all 4??

 

[jlw1972]

Re: What caused this????

Or could it have been from the first rebuild?? They removed all the pistons and only rebuilt with one new and reused the 3 original. Maybe they changed the wear pattern on these three is the reason they failed and the one replaced with a .020 was still good. I dunno.

I am really just more curious than anything as the motor runs fine now since I rebuilt it this last time. Sure would like to know what happened though. So I don't make that mistake.

 

[F_R]

Re: What caused this????

One oversize piston is not the problem. I've rebuilt lots of them that way.

But correct timing is absolutely essential. Too much advance is especially destructive. "Advance" means the spark occurs while the piston is still on the way up. That is normal, as it takes time for the fuel to ignite, and by then the piston is ready to go on it's downstroke. But too much advance means the piston is not high enough when the spark occurs, and the resulting ignition tries to push the piston back down the wrong direction. You can imagine the battle going on in the cylinder when that is happening.

The other absolute essential thing is correct fuel to air ratio. Too lean causes pre-ignition, which breaks things, like pistons and rings. That commonly happens due to dirty or incorrect carburetor jets or insufficient fuel supply to the carburetor. Also serious lack of fuel on one or more cylinders means lack of oil to those cylinders also.

Did we mention correct propeller? Over propping is like driving up a mountain all the time.

 

[anzomcik]

Re: What caused this????

Do you know how the motor was scattered the first time? and the second time? That would be my first thing I would want to know, was it cooling related, oil related, over reving... I think those would be the first major clues.

Also which pistons went this time around, that could also help as well.

Just a question here, did you freshin up the 4th cylinder while you were in there?

 

[jlw1972]

Re: What caused this????

Yes, the 4th cylinder was freshend up so all four match.

3 pistons went this time. The three stock pistons.

F_R I thought about the fuel-air mixture but I would have thought that all cylinders would show signs. Or at least show sign in accordance with the carbs they were paired to.

Would the 8 degree advancement be enough to cause this much damage. I'm not sure how much 8 deg. really is in terms of being a little to advanced or a lot to advanced. In my mind the book say's 28deg so it should be run at 28deg. Guess what I'm asking is how much can a motor deviate from the 28deg before it would be destructive??

 

[boobie]

Re: What caused this????

Are you still using the VRO and are you getting the proper oiling ??

 

[jlw1972]

Re: What caused this????

No VRO. As for proper oiling, The previous owner knows how to mix the oil so all I can do is ASSUME that he mixed it properly. He bought this boat and motor new and owned it for 13 years and used it often.

The boat has a built in 30 gal. tank so maybe he wasn't premixing the oil with gas before adding it to the tank when filling up???

Can't say for sure on this...

 

[Bosunsmate]

Re: What caused this????

I wonder if they all went at once, it seems a bit more catastrophic than what i would expect from advanced timing. Advanced timing will get it in the end but not all three at once, perhaps they didnt all break at the same time.

Which cylinder did the ok piston come out of? port side/lower?

 

[emdsapmgr]

Re: What caused this????

It's ok to mix a new oversize piston with the 3 originals. The top ring let go on the piston. That's from an overheat. Either the piston was not cooled properly or ran on a lean fuel mixture (overheat.) In any event, it got hot enough to break the top ring and that destroyed the top of the piston. First thing to do is to inspect the main fuel jet on the side of the carb that feeds the destroyed piston. Maybe it has some dirt/debris in it, restricting fuel flow.... If it looks ok, you need to check the cooling passages around the piston's cylinder liner. If the rubber water diverters are positioned incorrectly, they can restrict water flow around that cyl, causing an overheat. See attached pic. The middle diverter is correctly placed. The right one is not. Also, remove the cyl head cover and check for water restrictions inside the head cooling passages. These type of water restrictions can overheat/destroy just one cyl and you may never get an overheat warning from the hot horn. 28 degrees max advance is ok on that engine. It has low compression bathtub heads on it and was made to run on 87 octane at 28 degrees +- one degree.

 

[Faztbullet]

Re: What caused this????

Check cooling system as theres a lot of coke on them pistons, sign of running to cold.

 

[Joe Reeves]

Re: What caused this????

Perfectly okay to rebore one cylinder and reuse the other good pistons as you've mentioned has been done in the past.

Spark advance too far advanced would definitely cause the damage pictured.

Another cause that results in damage as you've pictured would be fouled (lean running) carburetors. Be sure to dismantle, clean thoroughly, and rebuild the carburetors to new condition. Make sure that the high speed jets (2 to a carb) that are located in the bottom center portion of the float chambers are absolutely clean.

I assume you're using a 50/1 mixture as required and nobody has run the engine without lubrication.

 

[jlw1972]

Re: What caused this????

Perfectly okay to rebore one cylinder and reuse the other good pistons as you've mentioned has been done in the past.

Spark advance too far advanced would definitely cause the damage pictured.

Another cause that results in damage as you've pictured would be fouled (lean running) carburetors. Be sure to dismantle, clean thoroughly, and rebuild the carburetors to new condition. Make sure that the high speed jets (2 to a carb) that are located in the bottom center portion of the float chambers are absolutely clean.

I assume you're using a 50/1 mixture as required and nobody has run the engine without lubrication.

Thanks Joe. Everything on/in the power head is new except rods and crank. Including rebuilding carburetors and fuel pump. Motor runs great now. I was just curious as to what caused the initial damage because it happened in three cylinders.

I am running a double oil mixture right now for the 10 hr. break in.

The gas I drained from the tank after purchasing the boat looked to have oil in it. Plenty of water also.

 

[Joe Reeves]

Re: What caused this????

Wishing you continued good luck with the finished rebuild job.

Double oil... good idea.

Previous fuel tank... water for possible internal cooling... not too good a idea!