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Author Topic:   Damaged pistons - pics - opinions?
fairlaniac
Member
posted October 18, 2003 02:28 PM
Our last race out we encountered the damage shown in these pictures (see links). Can anyone offer some ideas on what may have happened? It's a .040 Chevy 350 with 11.5:1 lightened Wiseco pistons, 2.02 heads, Brzezinski 4bbl intake with a Carter AFB. If there is any more info you need, I can supply best to my knowledge. I notice how the damage occurs near the piston ring end gap? We're looking on correcting this for next year. Oh yeah, we're running 1/2 Sunoco 94 and 1/2 Cam2 racing gas.
Pic links: http://home.dejazzd.com/thebenders/images/cyc2-2003.jpg http://home.dejazzd.com/thebenders/images/cyc3-2003.jpg http://home.dejazzd.com/thebenders/images/cyc4a-2003.jpg http://home.dejazzd.com/thebenders/images/cyc4b-2003.jpg

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Doug
"Lift for a second, that's where you'll finish!"


sdhnc29
Member
posted October 18, 2003 05:48 PM
After looking at your pictures , this is an easy one . Judging by the color of the pistons , even the burned ones , you have not been running too lean in the past . But the burned pistons are caused from being too lean . This problem was most likely caused from a fuel pump failure , or another problem in your fuel system .

The giveaway on the lean condition is the fact that the intake side of the piston is burned . If this were caused by detonation , the center of the pistons and toward the exhaust side would be damaged .

I'd go over your entire fuel system this winter . I'm sure this is where you will find your culprit for the burned pistons .

Steve

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


fairlaniac
Member
posted October 20, 2003 09:37 PM
Steve,
Thanks for the response. We'll definately look at the fuel system this winter.

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Doug
"Lift for a second, that's where you'll finish!"


rocket36
Member
posted October 21, 2003 06:07 AM
steve, what about plug heat range. would that be a possibility?

last season we melted 2 pistons down in our late model engine similar to this picture (top ring land melted and a piece of ring then pounded away inside the chamber eventually imbedding in the top of the piston) this wasn't too lean (a little on the rich side actually) but we ended up finding the head gasket had walked up (snagged) on one of the head studs when the head was talked down, causing it not to seal properly and slowly leak water into the cylinder, eventually the combustion temperature increased dramatically (lack of cooling water) leading to detonation and the end result one dead engine. this all happened in less than 2 laps in a heat race and from in the cockpit the only sign i had was the engine went flat and started to "lay down", too late.
we learned from that to lay the head gasket on the block during assembly and then screw the studs in (through the gasket) to avoid the gasket fouling the studs and make sure the gasket is flat on the block.
might be something else to keep in mind (cost me $7000 to learn)

[This message has been edited by rocket36 (edited October 21, 2003).]

[This message has been edited by rocket36 (edited October 21, 2003).]

[This message has been edited by rocket36 (edited October 21, 2003).]

sdhnc29
Member
posted October 21, 2003 06:10 PM
rocket36
No , plug heat range would not really produce the burned piston affect that we see in his pictures .

Your burned piston problem that you had is definitely a strange one ! I've only ever seen this head gasket problem when people do not use dowel pins in the block . The fact that your intake pocket was burned , and your sure it was not run lean for even a 1/10th of a second , could definitely be a result of a hot spot in the cylinder due to the leaking head gasket . But the detonation on the intake side was a result of the head gasket problem , and not the sole reason the piston was burned . Look at my next post for some examples and explanations for burned pistons .

Steve

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


sdhnc29
Member
posted October 21, 2003 06:13 PM
Ok , if you look at the first photo that I attached , you will see a classic and somewhat extreme burned piston from a lean condition . Now I have not made myself clear on defining a piston that is burned from running lean , or one that is burned from detonation . In every case there is detonation occurring . When a cylinder runs too lean , the intake side of the piston heats up dramatically . This is due to the fact that the intake side is where the oxygen is ......thus producing the most heat in a lean condition . This is especially true with alky engines , due to the fact that alky has oxygen in it , where standard race gas does not . So what happens in a lean condition , is the intake side heats up and causes detonation resulting in the intake pocket being burned . Refer to photo 2 for an extreme view of this .

A burned piston that is caused from detonation alone (too much timing generally) , the entire piston will heat up . But ...the intake pocket will still be the hottest due to the most oxygen being on that side . Once this occurs the piston will generate a hot spot , usually on the intake side , and pre-ignite . Once this occurs , the flame from the pre-ignition and the flame from the spark plug will both burn to the center of the piston . This results in a hole in the center of the piston or a little off to the exhaust side , the center of the piston caved in , and yes even the corner of the intake pocket burned , or all of the above . Refer to picture 3 for a prime example of a burned piston caused by detonation alone .

At any rate there is always a cause for a burned piston . So when I or another engine builder refers to a piston being burned by being too lean , then I'm referring to the actual cause of the burned piston , not the fact that detonation has occurred since this is a given .

As a side note , the first and second photo's are from a SB2.2 headed , 406ci , turbo charged drag motor . This is from a customer of mine who run's in the Outlaw 10.5 inch tire class . This particular engine run's 30lbs of boost , and produces right around 2,200 HP . He burned this piston at a race in Florida last weekend after qualifying 2nd at a 7.31 / 197mph out of 80 cars . He had a problem with his injection system in the 3rd round and created what the picture shows .

The 3rd photo is from a limited sportsman circle track engine . This is from a customer of mine who bought a new adjustable timing light . He then adjusted his timing light to 36 degrees , and proceeded to time his engine on the 36 degree mark on the damper . Giving him a grand total of .................72 degree's !! I asked him if it was a little hard to start .......LOL

Hope this short explanation of burned pistons helps out !

Steve

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


rocket36
Member
posted October 22, 2003 06:57 AM
thankyou, very interesting.


dirtracer14
Member
posted October 22, 2003 09:02 PM
Steve you are the man thanks for the info above.....i have burned up to diff motors with what i would have to say was detonation ....from to much timing. Now were can a guy get a good timing light? and what is the correct way to set tdc with the motor together and apart. I think this will be somthing that really take more time with in the future! Thanks again, Craig Moore


sdhnc29
Member
posted October 22, 2003 09:37 PM
Craig ,

I feel lazy tonight , so I looked up a previous answer that I'd given to the TDC question , copied it and pasted it .....lol

"The simplest way to check for exact TDC if your engine is together would be with a piston stop . You can take an old spark plug , knock the porcelain out of it , and tap it for a 3/8 bolt . Use a long enough bolt so you can use a nut to lock the bolt in place . Once you insert the piston stop in the head , turn the engine over by hand until you are close to what you think is TDC . Run your bolt down until it touches the piston . Rotate the engine by hand until you are just off the piston stop , and turn the bolt maybe 1/2 to 1 more turn and use your lock nut to keep it in place . Next you will rotate the engine by hand the opposite direction until you come up and the piston touches your stop . Mark your timing tab in correspondence with your zero mark on your damper . Next you will turn the engine back the other direction until you touch your piston stop again . Mark your timing tab once again in correspondence with the zero mark on your damper . Exact TDC on your timing tab will be found half way in between the two marks that you made on your timing tab ."

With the heads off , you can use a dial indicator on the top of the piston and follow the same directions .

As for a good timing light , good luck ....lOl

Steve

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780

[This message has been edited by sdhnc29 (edited October 22, 2003).]

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