Piston failure 97 merc 150

[bdc]

After adding 20 gallons of 10% ethanol gas and running 30 minutes the
engine failed with #2 piston disintegrated all other 5 were fine with oil. Mechanic says it was caused by fuel starvation caused by the ethanol freeing up some contamination in the alum gas tank and clogging the carb

Prior to owning the Merc my Johnson 235 hp blew the #2 piston on two different occasions with all other pistons ok.

Why is it it always the #2 piston-what is unique here.

 

[Bondo]

Re: Piston failure 97 merc 150

Why is it it always the #2 piston-what is unique here.

Ayuh,... Just a Guess,... Is #2 the farthest from the waterpump,..??
Farthest from it's carb,..??
It's carb farthest from it's fuelpump,..??

You really otta sort out your Fuel System,... Seems you're burnin' thru a Pile of pistons....

 

[j_martin]

Re: Piston failure 97 merc 150

Which one toasts first is purely chance. It's the one that gets a piece of chit in the fuel system and leans out. Here's what I suggest:

Don't use ethanol contaminated fuel
Replace the fuel lines and primer bulb, as well as internal fuel lines.
Install a fuel/water seperator-fuel filter.
Go through the entire fuel system (carbs, fuel pump)

Enjoy boating more than mechanics.

hope it helps
John

 

[Faztbullet]

Re: Piston failure 97 merc 150

I totally disagree with your tech's findings as that motor has a 20 micron filter AFTER fuel pump to the carbs so any "chit" from boats fuel system will be caught there. Now a rubber line after filter could be degrading internally and passed a piece of "chit" to carb but others should be showing signs of problems or flooding due to debris hung under needle & seat(single float carb). Also if it has the factory idle stablizer box still installed, it could have went bad and affected the bia's circuit causing that pack to run a higher timing. I would check electrical system good and index flywheel and check pack timings per cylinder.

 

[j_martin]

Re: Piston failure 97 merc 150

I totally disagree with your tech's findings as that motor has a 20 micron filter AFTER fuel pump to the carbs so any "chit" from boats fuel system will be caught there. Now a rubber line after filter could be degrading internally and passed a piece of "chit" to carb but others should be showing signs of problems or flooding due to debris hung under needle & seat(single float carb). Also if it has the factory idle stablizer box still installed, it could have went bad and affected the bia's circuit causing that pack to run a higher timing. I would check electrical system good and index flywheel and check pack timings per cylinder.

The Idle stabilizer pulls on the bias circuit, which alters timing on all 6 cylinders.

I think the thumb sized filter is a 100 micron screen. It's pretty worthless if there's some actual filtering to do.

hope it helps
John

 

[Dukedog]

Re: Piston failure 97 merc 150

Two and five are the hottest clyinders on tha Merc. Merc use to put one size larger mains in those clyinders in some carburators a while back but eventually got away from it. True, check the electrics and lose the idle/advance stabilizer, but pay closer attention to the carbs, filters and fuel lines. Also the cooling parts. You might show good pressure but may be low on volume............

 

[Faztbullet]

Re: Piston failure 97 merc 150

I have seen packs with damaged bia's circuits run higher timing on one bank than the other, the stablizer and advance modules vary the resistance to ground to alter timing on packs thats why we did not run them on our race boats. I will have to check the size but still a 100 micron will catch any debris large enough to stop up a jet, (100 micron about thickness of piece of paper) I myself would look heavly toward ignition system ....my $.02

 

[j_martin]

Re: Piston failure 97 merc 150

If you look at the trigger terminal on a switchbox with an oscilloscope, there is a clear transient artifact when the plug fires. It's the easiest way to check for premature firing. At a steady speed, the artifact should be at the same place, roughly half way up the waveform, on each cylinder. If one is firing early, the artifact will be to the left and lower on the waveform.

hope it helps
John

 

[Faztbullet]

Re: Piston failure 97 merc 150

Talked to a buddy at Merc and filter is a 20 micron, also checked with Don @ Serria and their replacement (18-7830) is also a 20 micron. Dont know about the o'scope testing but indexing flywheel will show the same resullts if pack is double firing or is off.