HELP DIAGNOSE THE DEAD JOHNRUDE!!

[Instigator]

'99 JohnRude 250 V-6 Ocean pro (same as 225 HO). I was running these motors (twins on a Sonic V-bottom) close to the surface last sesason @ about 62-6400 RPM's w/103 hrs no problems, and box stock. Installed nose cones and Bobs exhaust snouts this Winter. Had the breather off for ease of idle adjustment (Gohr says no change in tuning for this, and ran 2nd half of last season w/o them)while coming in from 3rd or 4th pass the starboard motor developed the death knock! Did Autopsy and found #3 (middle hole starbord side)piston/rod/sleeve to be destroyed. Rod is in two pcs but has one bolt hole still in tact?? Threads are still in rod and bolt (found in case) is also still in tact?? One bolt is broken. Combustion chamber was "steamed" clean!Local dealer thinks I ran lean from the exhaust snouts. My problem with this is: 1.I was already surfacing the units which mostly relieves the exhaust anyhow 2.where I mounted the snouts (almost to the cavitaion plates) I drilled six 3/8" dia. relief holes through the tuner 3. only ran a few minutes with the exhaust's open which means it would have had to be way lean to nuke that quick 4. holes above/bellow, and opposing cylinder bank are perfect! 5. You can see on the inside of the case where the rod bolt had backed out and cut a grove into the water jackets and then "hydrauliced" the motor at speed! 6. dealer says: lean condition seized piston, steretched rod bolt which backed out and went through motor?? 7. Whats left of that piston is hammered into the shape of the top edge of the combustion chamber, and not as much aluminum "smeared" on insides as you would expect for a "lean seizure". I could more easily accept this scenario if there was signs of lean conditions in adjoining holes? The motors have stock jetting!! I think if it was close enough to a lean condition from the factory to where the snouts would have this much of a effect that it would'nt have lasted 103 hours w/o the snouts?? I have run this thing WFO (6200) for 30 to 40 mile stretchs several times. I just have a hard time believing that I would not have "seen" a lean condition 10 miles into one of these runs??? My scenario is, loose rod bolt from the factory???? Trying to do my home work before destroying second motor and or cooking the same one a second time! Proffesor O/B where are you??? Any suggestions/help would be greatly appreciatted. Thanx, Instigator

[Ray Neudecker]

Very common every spring. A combination of really good cool air and engines which have set up during the winter.If the motor was even close to lean previously, a slight restriction in a carb due to gelling of fuel combined with the great air you get in the spring often results in this problem without reliveing the exhaust also. i would clean and check all carbs and try a slightly richer jetting before runnuing again.

[LaveyT]

I know how you love projects,Time for some pyrometers and thermocouples!I guess the plug was to destroyed to read??Im not sure about leaning out, on the crossflows they were very fat.Gota go ,Dave