BBC piston weight change
Moderator: Team
BBC piston weight change
I have a BBC 461 in the shop that I did 10 years ago and some how the guy grenaded a piston .
The replacements are 27 grams lighter .Is this enough of a change to effect balance ?? 6K Max on RPM.
The replacements are 27 grams lighter .Is this enough of a change to effect balance ?? 6K Max on RPM.
-
- Guru
- Posts: 4607
- Joined: Sun Sep 18, 2011 11:31 am
- Location: Heading for a bang up with Andromeda as we all are.
Re: BBC piston weight change
Find out how much the pins weigh in the new pistons and then look for replacements that are heavier.
The cost of 8 new pins might save the guy the cost of another balance job.
The cost of 8 new pins might save the guy the cost of another balance job.
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
-
- Guru
- Posts: 1762
- Joined: Wed Aug 26, 2009 8:30 pm
- Location: Beautiful Southern Maryland
- Contact:
Re: BBC piston weight change
rj,
What pistons are they ? I have had some luck in the past finding single older pistons on E-bay. Also like mag said you can try to find a heavier pin.
What pistons are they ? I have had some luck in the past finding single older pistons on E-bay. Also like mag said you can try to find a heavier pin.
Bill Koustenis
Advanced Automotive Machine
Waldorf Md
www.enginerepairshop.com
Advanced Automotive Machine
Waldorf Md
www.enginerepairshop.com
-
- Pro
- Posts: 461
- Joined: Sun Feb 13, 2005 11:27 am
- Location:
Re: BBC piston weight change
From what I am reading you only need one piston. The .150 wall pins weigh roughly 152 grams. The .180 wall pins weigh around 180 grams. Replace the .150 pin with the new piston with a .180 assuming all the other pistons have .150 pins.
Another way to look at it. I have a customer that insist I overbalance his engines 1 percent. The bobweights are around 2300 grams. One percent would be 23 grams. He has never complained about his engines shaking.
I don't think you would be able to tell the lighter piston was in the engine. I would still put a heavier pin in and get it closer.
Another way to look at it. I have a customer that insist I overbalance his engines 1 percent. The bobweights are around 2300 grams. One percent would be 23 grams. He has never complained about his engines shaking.
I don't think you would be able to tell the lighter piston was in the engine. I would still put a heavier pin in and get it closer.
-
- Guru
- Posts: 4607
- Joined: Sun Sep 18, 2011 11:31 am
- Location: Heading for a bang up with Andromeda as we all are.
Re: BBC piston weight change
I would still like to know how one piston went south if it was not from a valve dropping!
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
-
- Guru
- Posts: 6389
- Joined: Tue Jul 24, 2012 11:15 am
- Location: Roseville, Michigan (just north of Detroit)
- Contact:
Re: BBC piston weight change
Use a heavier pin ...
http://www.rmcompetition.com
Specialty engine building at its finest.
Specialty engine building at its finest.
Re: BBC piston weight change
I read it he's replacing all eight pistons and asking is rebalance necessary.
Agree, rebalance is not absolutely necessary. Choosing 50% of recip is the general rule, but a couple of percent (or more) either way is common practice for certain applications.Old School wrote: ↑Mon Aug 15, 2022 11:27 amAnother way to look at it. I have a customer that insist I overbalance his engines 1 percent. The bobweights are around 2300 grams. One percent would be 23 grams. He has never complained about his engines shaking.
Jack Vines
Studebaker-Packard V8 Limited
Obsolete Engineering
Studebaker-Packard V8 Limited
Obsolete Engineering
Re: BBC piston weight change
Just a thought, what about using the current pin (you have it) and putting a 27 gram slug in it. Perhaps a light fit with some Loctite?
-
- Guru
- Posts: 6389
- Joined: Tue Jul 24, 2012 11:15 am
- Location: Roseville, Michigan (just north of Detroit)
- Contact:
Re: BBC piston weight change
I missed that ... I thought you were only replacing One.
Unless the engine was already "overbalanced" I would not worry about it but, you could get 8 heavier pins if it bothers you.
http://www.rmcompetition.com
Specialty engine building at its finest.
Specialty engine building at its finest.
Re: BBC piston weight change
Thanks for the replies. yes I'm changing all 8 pistons to forged. It had KB 207's in it and is a strong runner
but it sits for long periods ( bad Gas?) and I get ZERO feedback from this guy. Says It just blew up. Yeah right.
I did the install and tuning and there are no signs of detonation. BUT the piston that failed completely crumbled,
The pieces were like gravel. Then of course the pin (press pin) punched a big bole in block. I do not think this thing
has 1500 miles on it. The rest of the parts looked like new. It only bent the 2 valves in bad cylinder.
Thanks RJ
but it sits for long periods ( bad Gas?) and I get ZERO feedback from this guy. Says It just blew up. Yeah right.
I did the install and tuning and there are no signs of detonation. BUT the piston that failed completely crumbled,
The pieces were like gravel. Then of course the pin (press pin) punched a big bole in block. I do not think this thing
has 1500 miles on it. The rest of the parts looked like new. It only bent the 2 valves in bad cylinder.
Thanks RJ
-
- Guru
- Posts: 1762
- Joined: Wed Aug 26, 2009 8:30 pm
- Location: Beautiful Southern Maryland
- Contact:
Re: BBC piston weight change
Is the engine fuel injected ? I did a Mercruiser 454 recently that had one burnt up piston and it turned out to be from a bad injector. Maybe a vacuum leak to that cylinder somehow ?rjpower wrote: ↑Tue Aug 16, 2022 5:17 am Thanks for the replies. yes I'm changing all 8 pistons to forged. It had KB 207's in it and is a strong runner
but it sits for long periods ( bad Gas?) and I get ZERO feedback from this guy. Says It just blew up. Yeah right.
I did the install and tuning and there are no signs of detonation. BUT the piston that failed completely crumbled,
The pieces were like gravel. Then of course the pin (press pin) punched a big bole in block. I do not think this thing
has 1500 miles on it. The rest of the parts looked like new. It only bent the 2 valves in bad cylinder.
Thanks RJ
Bill Koustenis
Advanced Automotive Machine
Waldorf Md
www.enginerepairshop.com
Advanced Automotive Machine
Waldorf Md
www.enginerepairshop.com
Re: BBC piston weight change
IIRC, the KB207 is hypereutectic and it doesn't take a licking and keep on ticking. Even momentary detonation from stale gas might have been enough.
Jack Vines
Studebaker-Packard V8 Limited
Obsolete Engineering
Studebaker-Packard V8 Limited
Obsolete Engineering