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Jonny Hotnuts
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« on: June 28, 2009, 01:49:36 AM » |
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I made a homemade positive piston stop to degree the cams. I noticed today that it put a scratch in the top of one piston. The scratch is small but I am sure you could feel it with your finger if the head was off.
Is this anything I should be concerned with?
I dont want any hot spot to form......
~JH
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jonny_hotnuts@hotmail.com "Sometimes it is impossible to deal with her, but most of the time she is very sweet, and if you caress her properly she will sing beautifully." *Andres Segovia (when Im not working on the car, I am ususally playing classical guitar)
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Milwaukee Midget
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Age: 53
Location: Beerhaven, Wisconsin
Posts: 3176
If in doubt, it probably IS a mistake.
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« Reply #1 on: June 28, 2009, 02:50:56 AM » |
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Jonny,
We don't know how bad the scratch is, but let me pose this question.
After all the time, money, and effort you've put into your car, how would you feel if the engine failed due to something you were aware of and didn't address?
It's frustrating, this having to make decisions.
Chris
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"Information - we want - information"
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McRat
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« Reply #2 on: June 28, 2009, 09:34:33 AM » |
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I'm not too fussy myself. I know pistons can be screwed up pretty hard and still make big power.
I have often punch marked piston crowns and haven't run into any problems, and that's deeper than a scratch, and hand cut valve reliefs with a power drill. Anything less than a 2-3 thou is getting filled in with carbon anyhow.
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« Last Edit: June 28, 2009, 09:39:40 AM by McRat »
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Dean Los Angeles
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« Reply #3 on: June 28, 2009, 09:41:26 AM » |
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The flame front rapidly heats the piston during the power stroke. At the end of the power stroke it starts cooling, and the incoming charge cools it further. The piston would rapidly fail if it was continually exposed to the high heat of combustion.
The scratch you describe can allow the heat to reach that area in a non-uniform pattern, but the amount with a small scratch isn't going to be much. If you leaned the engine out enough to melt the piston, the scratch isn't going to accelerate that point.
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Well, it used to be Los Angeles . . . 50 miles north of Fresno now.
Just remember . . . It isn't life or death.
It's bigger than life or death! It's RACING.
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panic
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« Reply #4 on: June 28, 2009, 11:21:54 AM » |
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Ignore it, if your subconscious lets you.
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desotoman
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« Reply #5 on: June 28, 2009, 11:44:04 AM » |
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Polish it out with a buffing wheel. That will take the sharp edge off.
Tom G.
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"Got'Cha" was first run in 1974. Bill Temple entered both 2 clubs in 1976 with records in AA/BGR. At El Mirage 201.79 and Bonneville at 220.
In 1977 Greg Temple started driving "Got'Cha" and entered the El Mirage Dirty 2 club in 1979 @ 201.97. Greg went on to set two records at Bonneville, one in 1981 at 241.848, then in 1991 he set another record at 262.230
Bill and Greg were the first father and son to enter the El Mirage Dirty 2 club. They broke the D/BFR at Bonneville in 1981 @ 241 with top speed of 249. This record still stands today. In 1991 they set the A/BFR @ 262 which was later broke by Duane McKinney.
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McRat
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« Reply #6 on: June 28, 2009, 11:51:57 AM » |
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Has anyone actually seen a lower knock point with scratched piston? I remember when lots of guys were polishing pistons before they found it had either no effect, or a negative effect. Seems the spark plug electrode and exhaust valve lip will ignite the fuel way before you can ignite it with anything made of aluminum.
The only hard evidence I have is when I hand cut some LS6 pistons, which leaves a very large scratched surface finish. After tuning for max power, the timing before onset of KR (spark knock indicator) was pretty much the same. But that's not a Hayabusa, nor turbocharged.
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1212FBGS
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« Reply #7 on: June 28, 2009, 06:37:21 PM » |
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was the dome coated?
kent
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Jonny Hotnuts
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« Reply #8 on: June 29, 2009, 06:09:42 PM » |
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was the dome coated?
kent No, Off the shelf JE 81mm turbo pistons  Heres a pic after I remove the sharp edges and polished the duke out of them. Pizzes me off 'cause I took so much time getten 'em shiney. ~JH |
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jonny_hotnuts@hotmail.com "Sometimes it is impossible to deal with her, but most of the time she is very sweet, and if you caress her properly she will sing beautifully." *Andres Segovia (when Im not working on the car, I am ususally playing classical guitar)
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Jonny Hotnuts
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« Reply #9 on: June 29, 2009, 06:14:37 PM » |
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BTW:
Motor fired for the first time on Sat......dry blocked it for a few seconds and without the blower....but the SOB sounds heathy and fired in the first 3 crank turns.
And there was no "clickety-clack"!
Would be a shame to have to pull the head off.....
~JH
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jonny_hotnuts@hotmail.com "Sometimes it is impossible to deal with her, but most of the time she is very sweet, and if you caress her properly she will sing beautifully." *Andres Segovia (when Im not working on the car, I am ususally playing classical guitar)
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Peter Jack
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« Reply #10 on: June 29, 2009, 11:10:15 PM » |
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Jonny: If you hadn't made them so nice and shiny you wouldn't notice the scratches!   Pete |
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My avatar shows Tok, a 100# Alaskan Malamute.
He's the one who runs everything around here.
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davidp
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« Reply #11 on: June 30, 2009, 03:19:33 AM » |
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Forgive me if I am beating a dead horse. The hottest object in the combustion chamber is the exhaust valve margin area. Aluminum readily convects heat and will sustain combustion temperatures that are well in excess of it's melting point if it's given enough time to transfer heat to the cylinder wall and the oil being squirted on the bottom by the piston cooler jet. It will be fine.
Keep in mind I have no experience with LSR vehicles and everything I know is from drag-racing. Some assembly required, batteries not included, your mileage may vary.
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