Help! Burned piston
 

This is the second time this motor has burned a piston. It had the same symptoms both times, and I think it was the same cylinder. I had it running rich, and 30 degrees timing. It never got over 180 water temp, or 220 oil temp. After breaking the motor in for about 5 hours, I turned it up to about 5k and within 2 minutes, the oil pressure dropped to zero and the motor lost power. I thought it was an oiling issue the first time so I put on a new 4" oil cooler from cp, canton high flow adaptor, all new 12n lines, and a huge oil filter. I have a 10 quart pan and ran plenty of mobil 1 oil. It has 5 lbs of fuel at the carb. The only thing I can think of that I don't know is the water pressure. Could low water pressure cause this? There's a crack by the intake valve but I am guessing I caused that on the 10 min idle back to the dock. Both times, it's like the top edge of the piston melts off. Any thoughts???

thanks!
Chris

Re: Help! Burned piston
 

Did you fry the bearings the first time. What compression ratio. what octane fuel? The chambers volume look small. Also the fire ring looks too close to the bore. What head gasket are you using?

Re: Help! Burned piston
 

Chris
30 degrees if timing makes the exhaust temp very hot people think this is safe when it actually does nothing but run the exhaust temp through the roof and reduces engines ability to make power efficiently. I believe and some guys will agree the valve was most likely damaged from heat from a lean condition which was also what damaged the piston I don't believe oiling had any part of damaging the piston either time you may have had bearings fail from detonation but oiling will not melt the piston like that pic shows. Give us some more details about fuel press and fuel oct. and we may be able to help you further. Best of luck in fixing it. Sincerely Laz

Re: Help! Burned piston
 

it is just shy of 10:1 with felpro 1037 head gaskets. I run 93 octane from a nearby exxon station. The 'expert' that built it said I was ok with up to 34 degrees... Looks like I was told wrong! When he dyno'd it, I noticed the exhaust temp slowly climbed until he stopped the run, he said that was normal. They are small GM oval port heads.
The bearings look fine, we replaced them although the builder told me they weren't too bad the first time around.

Re: Help! Burned piston
 

looks like a clear case of detonation to me... bet the plugs have little tiny round balls of al on them... my guess is compression ratio to high for the fuel or you just THINK you have 30 deg timing... and is really something else for some other reason... incorrectly calibrated timing marks... dist/ electronics doing something weird and giving you a lot more timing than you think... look at the other pistons ... see if the sharp edge is eroded on any others...... boy those chambers DO look small...don't they...

Re: Help! Burned piston
 

5 lbs of fuel pressure is just barely enough. Is that measured at idle or running wot? It that is at idle, you have a problem. What about the rest of the fuel system? Start at the tank pick-up and go forward. What size lines? Are there any brass fittings? filters? What type of pump? Estimated h.p. of that motor?

Re: Help! Burned piston
 

it uses a holley red pump, 6an lines all the way from the tank, through the pump, filter, to the carb. It has 5psi at idle and at cruise, I haven't been able to check at wot as the gauge is at the carb. the engine dynoed at about 660 hp at 4300 rpm. I've had a 'resident expert' tell me that the pump is too small. It has a demon 850 carb. What psi should I be looking for at wot? It has an msd dist and msd marine ignition.

Re: Help! Burned piston
 

All this talk about small heads, I'm starting to suffer from 'head envy'! What would be a good size head for a 540?

Re: Help! Burned piston
 

i would really re-cc the heads and check your math on the compression ratio...

chambers don't look lean to me at all

Re: Help! Burned piston
 

6an lines are too small. You should run 10 an. Make sure you have a 5/8" pick-up in the tank. Take off the stock check valve also. Sounds like you need an entire fuel system. Holley red, marginal at best. Since you dont have a guage on the dash, you dont know the pressure while running. Thats bad.. 5 psi at idle means 2-3 at wot. Not enough pressure or flow. You are making good power but need to feed it correctly. I would recommend Aeromotives marine pump and return regulator. I have it on my motor, it works well. I also have a mechanical pump hooked up for slow cruising or idling in conjuction with the electric. You cant have too much flow in the fuel system, the worst that will happen is that the regulator sends it back to the tank.