Cracked piston on high mileage stock bottom end

[Alky V6]

I was running Q16 and alky on a 10.8:1 target. Alky was a little over 10% of the mix. If there was any detonation at those levels the rod bearings would be hammered after one instance. There would be deformation and evidence of crank to bearing contact particularly in the top half of the bearing. A little detonation is not ok. All the rod bearings looked great on tear down.

Let me tell you about my first alcohol engine I put rods through.

Stage II off-center block, stock rods, Arias pistons, stock crank.

I was way off on the fueling target. Too lean, with too much boost. CR was 10.25:1. It was only 30 psi boost, and that should have been just fine for that CR, but the a/f ratio was way too lean. Soon after the car left the line I heard loud knocking. I got off the throttle for a split second. The engine sounded fine. I made the big mistake of getting back into the throttle. Soon, again the knocking came back, escalating in loudness until I heard parts of the camshaft and rods bouncing off the bottom of the car. It happened so fast the second round that I couldn't even react fast enough to get off the throttle before the parts started flying.
This is the video of that pass.
YouTube - Grand National Alky Buick V6 v1.0

Amazingly, the bearings, head gaskets, heads, and piston tops looked perfect. I swear, I could have thrown the bearings in the next engine. I was amazed. I didn't even surface the heads. Just threw them on the next engine, and they're on the present engine now.

There is no question that the engine went into pre-ignition. Yet, the bearings looked perfect. Stock crank, stock journal width.

 

[bison]

This type of damage on high mileage engines could be simply metal fatigue too. Just keep the feelers out and check for patterns.

This type of damage, pre-ignition type damage lacking the other typical signs of detonation or pre-ignition looks like the type of damage you see in a methanol engine that's been tuned too close to the edge.

Keep in mind these engines all have eutectic cast pistons to Don. I dont know of any alky engines that were ever built around a factory stocker. Fwiw the wrist pin bores were worn on mine. Hard to say how much since i cant easily remove the pistons to measure and they would be deformed after pressing them apart. One thing about all these engines in this thread is that they have seen a lot of WOT time. Its not like it happened on a fresh engine with forged pistons with no run time. If there was auto ignition it is still an uncontrolled combustion event that woudl put a lot of strain on the head gasket sealing too. It may not resonate the block at the same frequency as gasoline detonating but it will cause the same damage like hammered bearings and evidence of compression leaks in the head gasket sealing areas

 

[bison]

Let me tell you about my first alcohol engine I put rods through.

Stage II off-center block, stock rods, Arias pistons, stock crank.

I was way off on the fueling target. Too lean, with too much boost. CR was 10.25:1. It was only 30 psi boost, and that should have been just fine for that CR, but the a/f ratio was way too lean. Soon after the car left the line I heard loud knocking. I got off the throttle for a split second. The engine sounded fine. I made the big mistake of getting back into the throttle. Soon, again the knocking came back, escalating in loudness until I heard parts of the camshaft and rods bouncing off the bottom of the car. It happened so fast the second round that I couldn't even react fast enough to get off the throttle before the parts started flying.
This is the video of that pass.
YouTube - Grand National Alky Buick V6 v1.0

Amazingly, the bearings, head gaskets, heads, and piston tops looked perfect. I swear, I could have thrown the bearings in the next engine. I was amazed. I didn't even surface the heads. Just threw them on the next engine, and they're on the present engine now.

There is no question that the engine went into pre-ignition. Yet, the bearings looked perfect. Stock crank, stock journal width.

This is not the norm from what ive seen. Most of the bearings ive seen that came out of alky engines (which may not be a god comparison since they had roots blowers on them) looked like the pistons were hit with sledge hammers and flattened them out. Ive only seen a couple engines of that type.

 

[Alky V6]

On an ohv v-6 with the engine built to run high boost and about 8.5:1 CR id guess its upwards of 50psi. You have to take into consideration the pistion design and rod length vs stroke.

C16 by itself, or methanol by itself, should operate under those parameters without a problem. Keep in mind that you're mixing two different fuels that operate on two totally different operating temperature slopes.

 

[Alky V6]

Keep in mind these engines all have eutectic cast pistons to Don. I dont know of any alky engines that were ever built around a factory stocker. Fwiw the wrist pin bores were worn on mine. Hard to say how much since i cant easily remove the pistons to measure and they would be deformed after pressing them apart. One thing about all these engines in this thread is that they have seen a lot of WOT time. Its not like it happened on a fresh engine with forged pistons with no run time. If there was auto ignition it is still an uncontrolled combustion event that woudl put a lot of strain on the head gasket sealing too. It may not resonate the block at the same frequency as gasoline detonating but it will cause the same damage like hammered bearings and evidence of compression leaks in the head gasket sealing areas

That has not always been the case in my experience. I know it sounds crazy. Imagine freely spinning what's left of a rod around your crank journal and then taking it apart to find the bearings reusable.

 

[Alky V6]

This is not the norm from what ive seen. Most of the bearings ive seen that came out of alky engines (which may not be a god comparison since they had roots blowers on them) looked like the pistons were hit with sledge hammers and flattened them out. Ive only seen a couple engines of that type.

I'll be the first to admit that my engine configuration is not typical, but Bison, I have no reason to lie to you. All I'm trying to say is keep your mind open. You can have pre-ignition and not hammer the bearings. I've seen it in both of the engines that I had it happen to. I really can't explain it. I'm just relaying the information to you. Both engines did have bent pins too.

 

[bison]

I'll be the first to admit that my engine configuration is not typical, but Bison, I have no reason to lie to you. All I'm trying to say is keep your mind open. You can have pre-ignition and not hammer the bearings. I've seen it in both of the engines that I had it happen to. I really can't explain it. I'm just relaying the information to you. Both engines did have bent pins too.

Im open bud. Actually im running the same alky setup on the current one with 112 octane. It makes about 100hp more than the one with the cracked piston. I hurt once already by not removing the injector cut out that was set to 6300. Alky stayed on and injectors shut off.

 

[dr_frankenstein]

Bump......

tell me more gentlemen.

:biggrin:A.j.

 

[Super6]

add me to the list

i will post pics tomorrow night..#3 is cracked across the pin..i will post details tomorrow too........Bob

 

[bison]

i will post pics tomorrow night..#3 is cracked across the pin..i will post details tomorrow too........Bob

That sucks

 

[Alky V6]

Daaang. Well, at least it didn't hand you that rod we were talking about.

 

[pacecarta]

sorry to hear it bob .atleast it gave you a nice mph on that ptc converter
i wasnt bummed about mine , its just a stock piston .. pop another in


mine is back together but i plan to retire that block to lighter duty in the 87 behind a te44 ,
the 86 will be getting the 87's shortblock , forged 30 over trws and 4 steel billet mains
..

 

[Boost231]

I was running Q16 and alky on a 10.8:1 target. Alky was a little over 10% of the mix. If there was any detonation at those levels the rod bearings would be hammered after one instance. There would be deformation and evidence of crank to bearing contact particularly in the top half of the bearing. A little detonation is not ok. All the rod bearings looked great on tear down.

bison, im just trying to make sure. in one post you said you had the alky cranked all the way up and in this post your saying its alittle over 10% alky is that # correct? also what size nozzle/nozzels are you running? whats the settings on the alky both internal and on the controler? im spraying about 25% alky to fuel.

 

[bison]

bison, im just trying to make sure. in one post you said you had the alky cranked all the way up and in this post your saying its alittle over 10% alky is that # correct? also what size nozzle/nozzels are you running? whats the settings on the alky both internal and on the controler? im spraying about 25% alky to fuel.

Its cranked up as high as it can be on the knob but i have a 3.5 bar MAP sensor so it doesnt get full spray at 30 psi like a 3 bar does. 25gph total nozzle designation. I estimated the 10% based on data logged duty cycle numbers. Its a very close estimate, maybe a little bit more but definitely well under 15%. I doubt you are replacing 25% of the fuel needed if you are using one pump. Unless you are only making about 300-325hp. That would be a lot of alky. Keep in mind the engine i was spraying into was making over 700hp

 

[Boost231]

i was using my fast data logs to come up with this #. one pump dual nozzles.

 

[scrobbyd]

Figured I'd share my crack experience, piston that is! Hey Bison not trying to steal your thread here. But looks like a good place to post one of my trophies.

 

[bison]

i was using my fast data logs to come up with this #. one pump dual nozzles.

So your saying your DC drops 25% with the alky on? Mine is about 10-12% less with it on. For the engine i posted about in this thread it would need to be replacing about 75 lbs/hr of fuel (or slightly more) to be feeding 25%. Not going to happen on a single pump.

 

[bison]

Figured I'd share my crack experience, piston that is! Hey Bison not trying to steal your thread here. But looks like a good place to post one of my trophies.

This is an open forum and you are posting on topic so any info is appreciated. What were the conditions when you had failure? Quarter mph and time under WOT before failure?

 

[Super6]

piston

ok guys this is the piston..it's #3..i knew i had problem before leaving for Reynolds but i was like i didn't want to know..the plug on this cylinder was a shiny color and smelled like gas.i almost did a leak down test but decided not to..the only thing i can figure is that i busted it on the one fuel pump on my 10.16 pass a month ago at my local track.i now have a DP'er.the knock gauge never went off but it went lean on that pass...i thought i let out in time but i must have not..i could free rev the car to like 3k and after the motor came back to idle it would puff smoke..i ran it about 6 times at Reynolds all in the low 10's at 134 to 136 and some change. i am very surprized it ran that good..the breathers on the valve covers got soaked with oil on about the 3rd pass..these are some tough little motors.it's my fault it happened..should have put a DP in the car long ago but i thought i could get by without it.my plan is to go back with another piston with the motor still in the car..it has never been out..the cylinder bore looks perfect and the oil pressure is still good..i really want that 9sec time slip with this motor. the cometics done there job..they look good.....thanks Bob

 

[Super6]

Daaang. Well, at least it didn't hand you that rod we were talking about.

hey hey..you were close...it was my fault though....

sorry to hear it bob .atleast it gave you a nice mph on that ptc converter
i wasnt bummed about mine , its just a stock piston .. pop another in


mine is back together but i plan to retire that block to lighter duty in the 87 behind a te44 ,
the 86 will be getting the 87's shortblock , forged 30 over trws and 4 steel billet mains
..

i'm not really bummed..just wish it wouldn't happen but we live and learn..good luck with yours..will you be in BG next year?