93 200hp burned #2 piston. Flywheel magnet possible cause? Dhadley?

[np90fxr]

I have a 93 200 Ocean Pro that fried the #2 cyl with almost no warning while running along @ 5800rpm. All other cylinders OK exc #2,appeared to be detonation/preignition. Motor is recent rebuild possibly 50hrs. Prior to problem motor ran fine except for intermittantly having one cylinder drop off. Power pack was new and Compression was run, good on all 6. Upon dissasembly noticed one of the 6 flywheel magnets was loose and was not in its original position. Could this be a potential cause (i.e. changing the timing or causing problems in just that one cylinder?)

 

[Dhadley]

Re: 93 200hp burned #2 piston. Flywheel magnet possible cause? Dhadley?

The outer magnets were probably not the cause. How's the center hub magnet? Why did it have to be rebuilt the first time?<br /><br />Most (not all) #2 failures are related to cooling issues. What spark plugs were you using? What grade fuel? Oil? What was the water pressure at 5800?<br /><br />Was it "fried" on the top edge by the exhaust port? In the center of the dome? Or is the damage related to the skirt area? If so, only on the exhaust side or all the way around? What brand pistons?<br /><br />Let us know!

 

[np90fxr]

Re: 93 200hp burned #2 piston. Flywheel magnet possible cause? Dhadley?

Plugs L77JC4, Fuel 87oct, Oil Pennzoil. Piston was fried I along the edge I believe along the top exh side (I'll have to verify) Motor was rebuilt because water got into the oil tank and burned several pistons. Tank was of course completely drained cleaned and refilled after. Do not have a water pressure gauge but I do have a temp gauge w\a sensor in each head. Temps at that rpm around 160-175. Wiesco pistons. Not sure about the inner magnets didn't notice anything obvious but I'll take a closer look.

 

[np90fxr]

Re: 93 200hp burned #2 piston. Flywheel magnet possible cause? Dhadley?

Checked damage to piston it is on lower edge from about the 4-8 O'clock position. Center magnets appear OK.

 

[Dhadley]

Re: 93 200hp burned #2 piston. Flywheel magnet possible cause? Dhadley?

Thats about where the exhaust port is - give or take. Look real close at the center hub magnet. It must be flush with the hub and in the correct position. If it has the apperance of a "spun prop hub" then it has most likely moved and thrown off the timing.<br /><br />Thats a bit hotter than we like to see. How do the thermostats look?

 

[np90fxr]

Re: 93 200hp burned #2 piston. Flywheel magnet possible cause? Dhadley?

Center magnet is within .010-.020" of being flush.I cannot turn it by hand. How can you tell if it moved or is in the right position. Also if it did move wouldn't it change the timing on all cyls. If so then why am I only seeing a problem on #2. all others OK. <br /> Thermostats open at 140 I even had drilled a 1/8" bypass hole in them to ensure some flow at all times (water temp where I live is normally above 70deg) Running temps I told you before are probably closer to 160 than 175. <br />Back to my original post, what effect would one of the outer magnets being out of position produce?

 

[np90fxr]

Re: 93 200hp burned #2 piston. Flywheel magnet possible cause? Dhadley?

One other thing I noticed. Don't know if it makes a difference. Whoever did the previous machine work seems to have installed something other than the "correct" water diverter in the location adjacent to the #2 hole. The other two in the block by the #5 and #6 holes are the "correct" red plastic OMC parts. Looking in the water jacket holes it seems that the OMC diverters are necked down to a smaller diameter (maybe allowing some flow around them) while the "incorrect" one by the #2 hole looks to be just a straight cylindrical "dowel" (which appears to block the whole passage)

 

[Dhadley]

Re: 93 200hp burned #2 piston. Flywheel magnet possible cause? Dhadley?

Have your dealer verify the center hub magnet location. If its not flush it may move when the flywheel warms up. If #2 was running the warmest (possibly due to the diverter) it will detonate first. <br /><br />If the motor hasnt been taken apart already you can have the dealer run it and check for double firing on that cylinder also.<br /><br />Good luck!