What caused my melted piston?

[Geronimo36]

I've lost 2 #5s and 1 #8 on two.

I think the blower size and intake style have alot to do with the moving air to the cylinders.

Always #5

I'm with you dude!!!

I also think GLH is right; I would think 9 lbs of boost, intercooled, with GM heads is kinda on the verge with pump gas. I wouldn't go any higher than 7 lbs on mine and once in the boat I turned it down to 6 lbs to be safe and even jetted up 1 size on the secondaries to be help with heat-soak on long passes.

Every time I've ever had a problem it happened so quickly you can't prevent it...even with a knock sensor... Once you're into detonation it's almost too late. The moment you see the engine lay down RPM it's done and we're talking 1/2 to fractions of a second at 5-6k rpms.

Also, what was total advance? If too much you'll detonate, if too little you can smoke the exhaust valves. contrary to popular belief, blower engines like timing. I ran as much as 34* on the dyno but run 31/32* in the boat. I see some guys run 28* but every dyno I went to EGT's were very high at 28*. Of course this depends on the style heads you have.

I think if you really want to prevent it from happening again I'd look into getting some AFR's or turn the wick down!

[Tomas Wallin]

I'm with you dude!!!

I also think GLH is right; I would think 9 lbs of boost, intercooled, with GM heads is kinda on the verge with pump gas. I wouldn't go any higher than 7 lbs on mine and once in the boat I turned it down to 6 lbs to be safe and even jetted up 1 size on the secondaries to be help with heat-soak on long passes.

Every time I've ever had a problem it happened so quickly you can't prevent it...even with a knock sensor... Once you're into detonation it's almost too late. The moment you see the engine lay down RPM it's done and we're talking 1/2 to fractions of a second at 5-6k rpms.

Also, what was total advance? If too much you'll detonate, if too little you can smoke the exhaust valves. contrary to popular belief, blower engines like timing. I ran as much as 34* on the dyno but run 31/32* in the boat. I see some guys run 28* but every dyno I went to EGT's were very high at 28*. Of course this depends on the style heads you have.

I think if you really want to prevent it from happening again I'd look into getting some AFR's or turn the wick down!

Actually I just installed a J&S Safeguard knock retard controller that controls the timing individually, I'll get back with report on how it's working later on... So far it works very good! I will play around with the timing a bit to see what will happen.

Total advance was locked at 28.5deg around 1400F EGT's@6k

I don't remember what my AFR gauge said at that moment.

I will detune the engine to 8PSI (that has worked very well earlier) until next season!

[WeaponX]

I'm with you dude!!!

I also think GLH is right; I would think 9 lbs of boost, intercooled, with GM heads is kinda on the verge with pump gas. I wouldn't go any higher than 7 lbs on mine and once in the boat I turned it down to 6 lbs to be safe and even jetted up 1 size on the secondaries to be help with heat-soak on long passes.

Every time I've ever had a problem it happened so quickly you can't prevent it...even with a knock sensor... Once you're into detonation it's almost too late. The moment you see the engine lay down RPM it's done and we're talking 1/2 to fractions of a second at 5-6k rpms.

Also, what was total advance? If too much you'll detonate, if too little you can smoke the exhaust valves. contrary to popular belief, blower engines like timing. I ran as much as 34* on the dyno but run 31/32* in the boat. I see some guys run 28* but every dyno I went to EGT's were very high at 28*. Of course this depends on the style heads you have.

I think if you really want to prevent it from happening again I'd look into getting some AFR's or turn the wick down!

Aluminum heads is a must. And at 1400 degrees loss of water to the block even for a short period of time would finish the piston.

1250 degrees is a safe # on temps in my book.
It's crazy the differance heads can have on timing the last power I put together with Big Cheifs hated timing. I had heard it was that way but had to try it for myself made it to 31* and lost some power on the top end but the torque was better on the low side. Going to put a 4100 rpm retard on it for next summer to get the best of both.

[Geronimo36]

I've heard that about the Big Chief's, JC originally told me about it! How did the Chief's hold up long-term?

Sounds like a cool idea with the timing retard!!

[Real Baja]

I do not know about 4 stroke engines, but on multiple (triple) cylinder 2 strokes I have seen a loose plug create an extreme lean condition and quickly burn a hole in the piston. The plug gets so hot it glows and even with a bad connection the engine runs smooth, until the piston gives way.

[MikeyFIN]

I've heard that about the Big Chief's, JC originally told me about it! How did the Chief's hold up long-term?

Sounds like a cool idea with the timing retard!!

If the "Heads/engine" hatre timing it Works!!!
The more timing the worse the breathing.

[MikeyFIN]

I do not know about 4 stroke engines, but on multiple (triple) cylinder 2 strokes I have seen a loose plug create an extreme lean condition and quickly burn a hole in the piston. The plug gets so hot it glows and even with a bad connection the engine runs smooth, until the piston gives way.

This one is a force fed engine so it doesn´t got lean or draw air from the loose plug. Otherwise I agree with you but I believe this as a cooling issue.
Tomas just went over the hill...

[tango]

if it was not a blown (pressurized) intake charge, but strictly a naturally aspirated engine I might suggest a bad intake valve seal which would allow oil to be drawn into that "1" in particular cylinder and thus start the detonation process, just a secondary thought. also look @ the plug threads in the 1st post "oil" soaked ? is that a result of it being loose before or after the initial detonation process ?

[Tomas Wallin]

This one is a force fed engine so it doesn´t got lean or draw air from the loose plug. Otherwise I agree with you but I believe this as a cooling issue.
Tomas just went over the hill...

Yes, maybe...

But a loose plug can still cause the cylinder to pre-ignite because of the insufficient heat transfer between the plug and the head that caused the plug to glow.

It was loose enough to easily remove by hand. But if it was loose before or if it came loose during the "accident" I will most likely never know.

[JupiterSunsation]

What caused my melted piston?


Capt. Obvious says "HEAT" caused it.

[Tomas Wallin]

What caused my melted piston?


Capt. Obvious says "HEAT" caused it.

Capt. Stubborn says: What caused the heat.

[JupiterSunsation]

Capt. Stubborn says: What caused the heat.

Just saw you were from out of the country, Mr Obvious is a radio skit (I turned it into Capt. since it was boat related).
http://www.youtube.com/watch?v=5XZMC1M9o04

[Geronimo36]

Some pretty good suggestions have already been given. Depends what you choose to do with them!

I remember a while back suggestions were given from a reputable builder about your engine as well...

[Tomas Wallin]

Just saw you were from out of the country, Mr Obvious is a radio skit (I turned it into Capt. since it was boat related).
http://www.youtube.com/watch?v=5XZMC1M9o04

Yes I know that

[Tomas Wallin]

Some pretty good suggestions have already been given. Depends what you choose to do with them!

I remember a while back suggestions were given from a reputable builder about your engine as well...

Yup, and I'll do my best to use everyones opinion! Started this thread since I had some new info with the loose plug - and to gain some tech talk to the forum...

[MERPerformance]

i'AM NOT GOING TO SAY THIS IS WHAT HAPPENED. I had a N/A 540 CID 12.5:1 with iron heads, tapered seat plugs, paint was on the seat area of the head for the plug, well after awhile of running the plug would miss- fire and break the center electrode out of the plug and ding the top of the piston. If the plug was loose I feel it would have done the same either N/A of forced induction.

[WeaponX]

I've heard that about the Big Chief's, JC originally told me about it! How did the Chief's hold up long-term?

Sounds like a cool idea with the timing retard!!

Titanium intake valves are the trick to the Big Chiefs lasting. $1500. but it worth the cost.

We will see after another 42 hours.

[jeffswav]

Detonation almost always fractures the tops of the pistons around the ring lands. How about a cam lobe?

I am only on page 4 of this huge post but that happend to me on a flat tappet cam. I am sure he must have a roller cam. I have since switched to a roller cam after blowing a hole in the piston from going lean. A cam lobe can definatly do some damage.

[jeffswav]

That marking on the top bearing is consistent with pre-ignition/detonation. Oil actually gets squeezed out and the crank and brg touch.

I did the same thing a few years back. I destroyed the tops of the rod berrings. Machine shop said the most likley problem was pre-detination, most likley bad fuel. It was the first trip out in the spring with E10 fuel using stabil. I have since never stored E10 fuel more than 1 month. Man you are bringing back some bad memories.

[jeffswav]

...and we're back to why just one cylinder.

Ok, I have blown mine up way to many times. When I had a cam lobe go down it only blew one piston. May not play a part in this one.