Pre detonation of fuel in the crank case

[Steven Bryant]

Hi guys

I took my MAC 45 engine out of my mono to strip it and clean it i noticed that the CONROD was burnt on the top 50% and the piston sleeve was showing signs of burning on the outside inline with the ports, this looks to me like the fuel was detonationg in the crank case. I always strip and rebuild my engine are each days running due to the water i run in is brackish (Salty water). I have never noticed this before with my engines and would like to know peoples views are.

Cheers

Steve

 

[John Finch]

Hi guys

I took my MAC 45 engine out of my mono to strip it and clean it i noticed that the CONROD was burnt on the top 50% and the piston sleeve was showing signs of burning on the outside inline with the ports, this looks to me like the fuel was detonationg in the crank case. I always strip and rebuild my engine are each days running due to the water i run in is brackish (Salty water). I have never noticed this before with my engines and would like to know peoples views are.

Cheers

Steve

Sounds like you just ran too lean or lost water cooling and over heated the engine. Predetonation would be seen on the head button and piston top. It would look like someone hit your head button and piston top with a sand blaster. Or they might be pitted like you tried to compress small pieces of dirt.

 

[anthony_marquart]

I have never heard of this.. it might be that you built up such heat that the metal turned color,.. I don't know really.. it would be hard to imagine ignition in the case and the engine still running..

 

[Steven Bryant]

Hi guys

I took my MAC 45 engine out of my mono to strip it and clean it i noticed that the CONROD was burnt on the top 50% and the piston sleeve was showing signs of burning on the outside inline with the ports, this looks to me like the fuel was detonationg in the crank case. I always strip and rebuild my engine are each days running due to the water i run in is brackish (Salty water). I have never noticed this before with my engines and would like to know peoples views are.

Cheers

Steve

Sounds like you just ran too lean or lost water cooling and over heated the engine. Predetonation would be seen on the head button and piston top. It would look like someone hit your head button and piston top with a sand blaster. Or they might be pitted like you tried to compress small pieces of dirt.

Hi John

I have noticed that the button head and and piston head look like they have been sand blasted and they do look slightly burnt as well., i will check the water cooling to make sure the engine is getting enough water running through it.

cheers

Steve

 

[Steven Bryant]

I have never heard of this.. it might be that you built up such heat that the metal turned color,.. I don't know really.. it would be hard to imagine ignition in the case and the engine still running..

Hi Anthony

I'll post a picture later on on to show you the discoloration on the conrod, it looks like someone has put a yellow flame to it and it has started to go black from the soot build up. the bottom of the rod is fine in color and the inside of the piston looks fine to me as well.

steve

 

[David Murany]

Sounds lean for sure but the discoloration inside the crankcase is new to me. Did you suck in any of the water possibly and not get it blown out before the next run? Also does the bottom of the piston go past the bottom of the exhaust port? Maybe it was drawing burnt fuel back in through the ex. port. Anyway hope you get it figured out.

 

[namba969]

I have seen discoloration caused from castor oil used in the fuel, especially when the motor gets hot and the castor burns. Could be that?

Andrew

 

[Steven Bryant]

Thanks for your replys guys, i found the culprit a small piece of gravel stuck in the water pickup on the rudder, looks like i didn't have enough water cooling on the last run of the day. at least the run was only a short run so the engine looks pretty good except the blackening on the rod.

thanks again

Steve

 

[John Finch]

Thanks for your replys guys, i found the culprit a small piece of gravel stuck in the water pickup on the rudder, looks like i didn't have enough water cooling on the last run of the day. at least the run was only a short run so the engine looks pretty good except the blackening on the rod.

thanks again

Steve

Glad you found it,

John