DieselWalt

[jlshields]

where are you? About that #5 scored cylinder in a Mercruiser 5.7LX, on your advice I gave the mains and rod bearing on each side a good look and guess what. Well you already know. #3 and #4 main bearings. The upper shell was down to the copper in one area but it didn't look like wear, it looked like something had splashed on it and ate the babbit off???? This engine is raw water cooled so it wasnt anti-freeze. Crank was standard throughout. New mains Plasti-gauged at .002 and so did old rod bearings. Also #5 ex. valve seat cracked. Will finish assembly tomorrow but won't get to run it till it warms up some. Thanks John

 

[Trent]

Re: DieselWalt

If ya want Walt..E-mail him at Walt@boatdoctor.com

 

[Walt T]

Re: DieselWalt

Glad you found it. Sorry I havent been on, My house is being painted inside, man is that disruptive. <br />The splash look actually isnt caused by liquid, it's just what the bearing looks like when it goes. Ok, now you have to find out why those bearings failed. Water in the oil is a possibility, but I would think all bearings would have a problem. You have the new mains plastigauged good, did you check all the oil holes in the crank? If it were me, I would have that crank checked for straightness. If the engine was ever hydrolocked, even if just with the starter, it's possible the crank could be bent. The crack on #5 exhaust seat points to hydrolock. If the crank is bent, then the block must be checked along the crank bore. You can try checking the #3 and #4 main journals with plastigauge, this time check 4 different times with the crank rotated 90 degrees each time. If it's bent, you'll get different readings. This is not a precise way, but you may be able to find it. You should also have the rod checked. It could be bent, but I would think the bearing would be damaged also.<br />I dont think you've found the actual cause of the failure yet. The bearings are a symptom, and you'll do this again if the cause is not found.

 

[jlshields]

Re: DieselWalt

DieselWalt, I did have the crank checked for out of round or tapered journals and bent. Oil passages clear. Had block cleaned at machine shop and heads rebuilt, valve springs checked and shimmed .030, three angle valve job, new cam bearings, (my shop guy builds race engines and he didn't like the position of the cam bearing oil holes), and 2 bent valves. I guess top of piston ready to come off. Never hydrolocked since in my possession. (I bought it new). According to serial # and stencil on block and heads and casting date inside piston it's a '97 and I didn't purchase it till July of '99. Maybe sitting around at dealer it suffered some condensation? Also the #1 wrist pin was a smidge tight. John

 

[Walt T]

Re: DieselWalt

Bent valves, damaged piston pin.........it got water in it at some point. Make sure manifolds and risers and riser gaskets are okay.

 

[jlshields]

Re: DieselWalt

Thanks Walt, I'll look for that. Thanks, John

 

[Walt T]

Re: DieselWalt

If the machinist is confident in the crank and rod, I'd certainly take his word for it.

 

[geriksen]

Re: DieselWalt

If you don't know what blew this up yet, have you thought about fuel dilution of the oil? We somtimes see and ignition or carb problem repaired but the oil not changed. When the engine is cranked excessivbly without spark enough gas can get into the oil that after the engine warms up the oil thins out and oil pressure goes away. Was there any fuel or ignition system work done on this boat before this happened?

 

[jlshields]

Re: DieselWalt

geriksen, no problems, just started knocking. The #5 sparkplug (in the affected cylinder) was loose and had been very hot but no one seems to think that was the cause. The #8 plug was also running hot and they are on the same intake plane. DieselWalt feels lack of lube caused the wrist pin to go and my shop guy leans toward a vacuum leak that let that cylinder run hot, scored the cylinder walls, then the wristpin let go. I'm still at a loss. Looking at your theory, wouldn't all cylinders been affected? Thanks, John

 

[geriksen]

Re: DieselWalt

The loose spark plug could have been the culprit. the heat from the plug transfers through the threads to the cylinder head where it is cooled by the cooling system. If it is loose, the heat does not transfer and the plug gets very hot. Too hot a spark plug (just like having the wrong heat range plug in there) an you can have a recipie for detonation. Were there signs of detonation on that piston? Was the electrode of the plug melted off? Also are 5 and 8 across from each other on the distributor? If they are losing one cylinder ofter makes the opposite one on the cap quit firing. Just an idea....

 

[John Carpenter]

Re: DieselWalt

Amen on the loose spark plug. I had the exact same thing happen to me a few years ago...#6 plug was loose, the electrode was gone and the piston had a hole melted in the top the size of a half dollar. What I couldn't believe was that the engine ran fine once rpm's were above 2000 or so...also hard to imagine that with all the metal in the pan there was no damage to the cylinder walls. We replaced the #6 piston and a head because of cracks from overheating & put it back together. That was three years ago I think & it is still running fine...knock on wood

 

[jlshields]

Re: DieselWalt

Thanks all. Got the engine running and my computer shut down. $213 and we're back on line. Bad hard drive AND modem. Don't know what caused THAT either. Maybe it's a Communist plot. Engine sounds fine. Did find signs of water in exhaust manifold and questionable man. to elbow gasket. Water in cylinder?? Going to watch #5 and 8 reeeaaal close. Several who looked at piston said detonation or water. That loose plug wasn't burnt up yet but it had been hot enough the ground electrode was real easy to bend. Thanks again.