srcevo8

iTrader: (10)

Besides some of the bickering I found this thread to be quite an interesting read. So thanks everyone for all of the input.

There was a statement made that maybe the E85 itself is what caused the problem. I know that between 2 stations you can 2 different mixes of E85. So you've got to leave some margin of error in case you get a "bad" tank of gas...bad just being a slightly different mix ratio. Maybe the OP is getting some really inconsistent E85 mixes at the local stations?

94AWDcoupe

iTrader: (125)

you must have missed the part where I keep a 270 gallon tank at home. fuel was consistent. only filled storage tank once.

Garth

One thing to keep in mind, the rod looks bent, but it didn’t bend, it buckled. The rod is not subjected to bending forces. The ends of the rod are hinged so the rod is subjected to axial forces only. It is quite possible the force that buckled the rod occurred at top dead center. Try stomping on a bicycle pedal when it is at top dead center.

1outlaw

94AWDcoupe- what kind of plugs are you running?

I read this whole paper with interest but at least take a look at the excerpt below;

Subject: Methanol/Ethanol is engines- LOTUS Triflex



http://www.ecolo.org/documents/docum...l-Lotus_09.pdf



While identical spark advance was used with methanol

and ethanol, some pre-ignition was noticed using the

former fuel. Small amounts of pre-ignition can be

compensated for in the ignition timing table and this is

the route taken by Saab for their BioPower engines [34]

but methanol shows a greater propensity towards this

phenomenon due to the lower temperature at which it

decomposes, advancing the phenomenon into the

compression stroke. Fortunately, a significant reduction

in the propensity to pre-ignite can be achieved by

adopting spark plugs with electrodes made from nonprecious

metals. Replacing the standard iridium

electrodes with copper-cored versions was shown to

eliminate the pre-ignition issue up to 100% methanol

concentration in the fuel. There were no further hardware

modifications necessary.

Garth

The backfire did not cause the buckled rod, but the buckled rod probably caused the backfire.

R/TErnie

iTrader: (32)

haha. Cylinder pressure owned your rods.

94AWDcoupe

iTrader: (125)

Your theories are quite off as I see it. Bend and buckle differ by definition but in case of rod there is no difference by looking at bent rod. It is I suppose possible the rod buckled at TDC. But if that were the case everytime an engine sees detonation rods should buckle. Instead of seeing millions of threads on blown head gaskets and broke pistons we should see millions of threads of bent rods. In fact I have never seen one thread about someone bending or buckling a rod from detonation. not one...

In fact at TDC the the axial strength of rod is highest. thats why we never see bent rods from detonation. cylinder pressure with detonation is over 4000 psi...

Preignition on the other hand is a whole different animal. It allows cylinder pressure rise far before TDC. In which case the piston would be pushing down on top of rod but crank pin would be pushing up. rod angle no where near TDC. = perfect bending force with not much cylinder pressure needed. maybe 1000psi would be enough to bend rod on its way toward TDC?

After TDC piston is pushing down on rod. But crank pin is not pushing up. it is pulling the rod down in same direction. rods survive 3000psi. turn crank and make power.

legs of a chair are very strong when legs are straight. lean back 15 degress and their strength is reduced ten fold or more.

Garth

You can create bending in the chair leg because the top of the leg is fixed. The top of the rod is hinged. It cannot take a bending force, it can only take an axial compression or tension force. The axial compression strength of the rod is the same regardless of orientation. Crank angle does not affect the amount of force the rod can resist. This is a case of euler buckling, not bending.

http://en.wikipedia.org/wiki/Buckling

Garth

To be through, if there is an angle in the piston rod from square with the piston, there is an increase in the force applied to the rod. Combining these forces to get the force in the angled rod, at 30 degrees the rod will see about 15 percent more load. (proportional to the length of sides in a right triangle) I would suspect this pales in comparison to the rate of rise in the compression forces in the cylinder.

94AWDcoupe

iTrader: (125)

maybe pictures will clear this up a little since my text is lacking in accurate description.
1. rod at TDC. during detonation cylinder pressure rises above 4000psi. the crank pin is rotationing left to right. there are no forces on rod other than the green arrow compressive force.
2. rod after top dead center during peak cylinder pressures of a normal running engine making some serios power.. the green arrow still imparts compressibve force along length of rod. the red arrow indicates the crank pin force pulling down in same direction. stock rods have handled 600wtq with out bending.
3. rod in before TDC position with preignition expansion of gasses pushing from top indicated by green arrow. red arrow indicates crank turning force in opposite direction of green arrow. this is what I refer to as easy position for rod to bend. although it is still technically a compressive force. I beleive the direction of arrows is correct angle of forces. yellow indicates direction of the bend due to the forces.

Garth

I understand exactly what you are trying to say, that is why I registered with this forum and am trying to help explain forces in the rod. The eccentricity you are showing in the third photo is resisted by a force against the side of the cylinder bore, and an equal and opposite lateral force against the crank. There is not a bending force in the rod; it is a two force member. A two force member has hinges at each end and resists compression and tension forces. Since there is not a bending force applied, the direction of buckling could be either way and could be the opposite direction of the yellow arrow.

94AWDcoupe

iTrader: (125)

Okay. Guess you should correct everybody who says they bent a rod? since everybody is actually buckling them. you have some work to do...

mrfred

iTrader: (50)

do rods always bend the same way relative to engine rotation?