Blown up KB 107 pistons findings
#2964901
09/17/21 07:50 AM
09/17/21 07:50 AM
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Joined: Jan 2003
Posts: 6,426 Abilene, Texas
fastmark
OP
master
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OP
master
Joined: Jan 2003
Posts: 6,426
Abilene, Texas
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I’m not sure which post I talked about my issues with this customer’s motor so I’ll start a new thread. My complaint was how easily these KB 107 pistons came apart. No, I did not build the motor. I just inherited a guys misfortune on a car he just purchased. I have had problems with these pistons before with 383. So, to all the KB fans out there that always say “ the motor was built wrong”, here’s my findings. The ring end gap on the other cly was .035, which is plenty big enough. My piston the wall was about .004. I think they are designed to run tighter than than because they are supposed to be low expansion pistons. There was no signs of scuffing on the skirts. There was no signs of detonation either at 9.25 CR. My machine shop said he “could see no apparent problems. These pistons will just come apart.” Incidentally, I called THE most respected Mopar guru in the world looking for pistons availability and his words were,” those pistons are f***ing junk made out of melted down beer cans. At least I feel I’m in good company.
Last edited by fastmark; 09/17/21 07:53 AM.
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Re: Blown up KB 107 pistons findings
[Re: J_BODY]
#2964935
09/17/21 10:14 AM
09/17/21 10:14 AM
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Joined: Aug 2008
Posts: 941 Texas, USA
ChrgrCuda
super stock
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super stock
Joined: Aug 2008
Posts: 941
Texas, USA
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What are all of those small looking gouge marks on the top of the pistons? I've also been using KB pistons on customer cars and so far so good.
68 Cuda Notchback [Email]10.86@120[/Email]
69 Charger R/T 440/505
2009 Challenger SRT8
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Re: Blown up KB 107 pistons findings
[Re: ChrgrCuda]
#2964948
09/17/21 10:47 AM
09/17/21 10:47 AM
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Joined: Jun 2006
Posts: 5,165 CT
GTX MATT
master
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master
Joined: Jun 2006
Posts: 5,165
CT
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What are all of those small looking gouge marks on the top of the pistons? I've also been using KB pistons on customer cars and so far so good. Those pistons look like they’ve been rattled to death to me, but that could be debris damage from the broken ring land. What do the other piston tops look like? What do the rod bearings and the bottom of the main caps look like? Hyper-eutectics are prone to breaking ring lands when they’re detonated.
Now I need to pin those needles, got to feel that heat Hear my motor screamin while I'm tearin up the street
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Re: Blown up KB 107 pistons findings
[Re: fastmark]
#2964970
09/17/21 11:49 AM
09/17/21 11:49 AM
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Joined: Jan 2005
Posts: 12,422 Kalispell Mt.
HotRodDave
I Live Here
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I Live Here
Joined: Jan 2005
Posts: 12,422
Kalispell Mt.
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The way that ring land broke looks like someone stuck something solid in the ring groove (rings butted together) and pried it up and snapped it off. I also would have rounded off the edges of the valve relief. Oh and that is too much piston clearance. Don't follow the directions don't complain when it fails.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: Blown up KB 107 pistons findings
[Re: fastmark]
#2964974
09/17/21 12:08 PM
09/17/21 12:08 PM
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Joined: May 2005
Posts: 2,005 Apollo, PA.
B1MAXX
top fuel
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top fuel
Joined: May 2005
Posts: 2,005
Apollo, PA.
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"The ring end gap on the other cly was .035, which is plenty big enough." Did that piston come apart? I get it some don't like them and won't run them , which is ok. But I have seen these used and pounded for thousands of passes/miles. Hell two of my personal engines have them. They have been getting beaten since the late 90's/ early 2000's.
Last edited by B1MAXX; 09/17/21 12:10 PM.
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Re: Blown up KB 107 pistons findings
[Re: B1MAXX]
#2965019
09/17/21 02:56 PM
09/17/21 02:56 PM
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Joined: Jan 2003
Posts: 5,486 SoCal
Brian Hafliger
master
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master
Joined: Jan 2003
Posts: 5,486
SoCal
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Melted down beer cans... THE most world renowned sb mopar GURU...WOW! Just wow....
Brian Hafliger
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Re: Blown up KB 107 pistons findings
[Re: fastmark]
#2965026
09/17/21 03:18 PM
09/17/21 03:18 PM
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Joined: Jan 2005
Posts: 12,422 Kalispell Mt.
HotRodDave
I Live Here
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I Live Here
Joined: Jan 2005
Posts: 12,422
Kalispell Mt.
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What's the bore size and how much for the other 7?
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: Blown up KB 107 pistons findings
[Re: HotRodDave]
#2965048
09/17/21 04:42 PM
09/17/21 04:42 PM
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Joined: Mar 2003
Posts: 6,341 Heaven
EvilB1Dart
master
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master
Joined: Mar 2003
Posts: 6,341
Heaven
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I had a cheap, hard-headed buddy that used some 15-20 yrs ago experimenting. Hit the motor with 300 from an NX Gemini Twin Stage-6 plate and MELTED ALL 8 to their A$$! It was on a serious 60' though LOL!!!!!!!!!!!!!! Funniest thing I've ever seen in my life.
"Any fool can know. The point is to understand"
- A. Einstein
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Re: Blown up KB 107 pistons findings
[Re: EvilB1Dart]
#2965136
09/17/21 11:19 PM
09/17/21 11:19 PM
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Joined: Jan 2003
Posts: 8,032 Tulsa OK
Bad340fish
master
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master
Joined: Jan 2003
Posts: 8,032
Tulsa OK
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I hate to see that, my KB107s were awesome. 4 drag weeks in the mid-low 11s, several thousand miles on top of that. Then I sold the motor and it has since been sold again(in a car). As far as I know they are still kicking.
68 Barracuda Formula S 340
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Re: Blown up KB 107 pistons findings
[Re: Moparteacher]
#2965165
09/18/21 05:51 AM
09/18/21 05:51 AM
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Joined: Feb 2007
Posts: 2,578 sweden
1Fast340
master
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master
Joined: Feb 2007
Posts: 2,578
sweden
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Was the piston dropped during or prior to assembly? That would be my guess. Shhh dont disturb those who already knows it all with comon sence.
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