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 Post subject: Continental Io-520 BA or BB
PostPosted: 07 Apr 2011, 18:52 
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Please can someone explain the difference between an IO-520-BA and the IO-520-BB?

Many Thanks Steve


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 Post subject: Re: Continental Io-520 BA or BB
PostPosted: 07 Apr 2011, 19:05 
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Steve, first off, welcome to Beech Talk, glad to have you here.
The IO520BB was is the most up to date revision of the IO520 series for Bonanzas. The BB basically has the heavy crank case and VAR crank shaft, both are better than what the B has, and the BB case is better than the BA.
Don't let a BA scare you off, though I would be real nerveous of a B as they usually crack.
If you get to a point of overhaul, and are considering a Reman, get the BB, or better yet, get an IO550B.

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 Post subject: Re: Continental Io-520 BA or BB
PostPosted: 07 Apr 2011, 20:51 
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Username Protected wrote:
Steve, first off, welcome to Beech Talk, glad to have you here.
The IO520BB was is the most up to date revision of the IO520 series for Bonanzas. The BB basically has the heavy crank case and VAR crank shaft, both are better than what the B has, and the BB case is better than the BA.
Don't let a BA scare you off, though I would be real nerveous of a B as they usually crack.
If you get to a point of overhaul, and are considering a Reman, get the BB, or better yet, get an IO550B.


Close but not quite right! The "B" and "BA" have the same crankshaft but a slightly different counterweight configuration so one is no more likely than the other to break. Either can have a light or heavy crankcase. The "BB" differs in that the crankshaft has larger main bearing journals and the crankcase has larger main brearing bosses to accommodate the shaft. This was cooked up by TCM back in the early '80's when some of the smaller main bearing journal cranks broke. In the early '90's the great revalation was that it was really non VAR crankshafts that were breaking. All "BB"'s were built with VAR crankshafts. All non VAR crankshafts are AD'd to be scrapped upon removal. The sad part is that any and all of them still break once in a great while.


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 Post subject: Re: Continental Io-520 BA or BB
PostPosted: 07 Apr 2011, 20:51 
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Greg-

Could you please point me to your source of data? The IO-520 type certificate data sheet says nothing about case differences. It says there's a slight difference in the crankshaft between a -B, -BA, and a -BB.

I'm still trying to decipher the puzzle.

edit: Charles beat me to the submit button! Thanks Charles for the excellent info.


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 Post subject: Re: Continental Io-520 BA or BB
PostPosted: 07 Apr 2011, 21:48 
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I was under the impression that the heavy case has the case humps along the top and 7th stud cylinders.

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 Post subject: Re: Continental Io-520 BA or BB
PostPosted: 07 Apr 2011, 22:19 
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Username Protected wrote:
I was under the impression that the heavy case has the case humps along the top and 7th stud cylinders.

Originally when TCM came out with the BB series heavy "humped" case and larger main journal VAR crankshaft, they did not have the 7th stud. The 7 th stud came later. When I rebuilt my IO520CB's I had Divco add the 7th stud mod to my heavy cases. :)

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 Post subject: Re: Continental Io-520 BA or BB
PostPosted: 08 Apr 2011, 00:42 
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[/quote]Close but not quite right! The "B" and "BA" have the same crankshaft but a slightly different counterweight configuration so one is no more likely than the other to break. Either can have a light or heavy crankcase. The "BB" differs in that the crankshaft has larger main bearing journals and the crankcase has larger main brearing bosses to accommodate the shaft. This was cooked up by TCM back in the early '80's when some of the smaller main bearing journal cranks broke. In the early '90's the great revalation was that it was really non VAR crankshafts that were breaking. All "BB"'s were built with VAR crankshafts. All non VAR crankshafts are AD'd to be scrapped upon removal. The sad part is that any and all of them still break once in a great while.[/quote]

Instinct was the cranks were breaking because of insufficient "crank journal overlap", so they increased the size of the main bearing surface to compensate. Makes for a stronger crank, but more frictional loss as well.


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 Post subject: Re: Continental Io-520 BA or BB
PostPosted: 08 Apr 2011, 08:47 
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Just to throw in more useless information there were heavy cases without the bumps on the backbone. They were known a logo cases. Backbone cracks were not a major problem on permold front alternator cases. They were a major problem on the sandcast rear alternator cases. IIRC heavy cases found their way into production engines around December '76.


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 Post subject: Re: Continental Io-520 BA or BB
PostPosted: 08 Apr 2011, 10:40 
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So although the non-VAR AD (97-26-17) simply refers to IO-520s, because the TCM Service Bulletin (CSB96-8) refers to the IO-520A, B, BA, C, D, etc (specifically missing the BB), NO IO-520BBs have a non-VAR crankshaft, period. Is that right?

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 Post subject: Re: Continental Io-520 BA or BB
PostPosted: 08 Apr 2011, 10:53 
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This is confusing me. I have an IO-520 BA but with the heavy case. Does that mean I have a non-VAR crankshaft? Or is it an engine by engine thing with a BA? Sorry for the amateur question.


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 Post subject: Re: Continental Io-520 BA or BB
PostPosted: 08 Apr 2011, 12:15 
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There are no non VAR BB crankshafts. It seems that cranks manufactured after about the middel of '78 are VAR anf the BB wasn't built until around '80. The BA could have a non VAR or a VAR in it.


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 Post subject: Re: Continental Io-520 BA or BB
PostPosted: 08 Apr 2011, 13:49 
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Username Protected wrote:
There are no non VAR BB crankshafts. It seems that cranks manufactured after about the middel of '78 are VAR anf the BB wasn't built until around '80. The BA could have a non VAR or a VAR in it.

According to Larry Ball's book, all Bonanzas came with IO520BB's starting in 1979.

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 Post subject: Re: Continental Io-520 BA or BB
PostPosted: 08 Apr 2011, 14:17 
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Username Protected wrote:
There are no non VAR BB crankshafts. It seems that cranks manufactured after about the middel of '78 are VAR anf the BB wasn't built until around '80. The BA could have a non VAR or a VAR in it.


Is there any way to find out what you have in a BA without tearing the engine apart to do it?


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 Post subject: Re: Continental Io-520 BA or BB
PostPosted: 08 Apr 2011, 14:46 
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Username Protected wrote:
There are no non VAR BB crankshafts. It seems that cranks manufactured after about the middel of '78 are VAR anf the BB wasn't built until around '80. The BA could have a non VAR or a VAR in it.


Is there any way to find out what you have in a BA without tearing the engine apart to do it?


My last plane had a factory reman built in 1990. When I bought the plane in about 1997 I called Continental prior to the purchase and they pulled the records and confirmed that the engine had a VAR crank. Additionally, the crank was new at the time of the build. Even though a reman doesn't guarantee new components in the bottom end, they must run short of servicable components at times. I always figured a new crank at rebuild increased the likelyhood of reuse if the motor puked unexpectedly.

Robert

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 Post subject: Re: Continental Io-520 BA or BB
PostPosted: 08 Apr 2011, 19:53 
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Username Protected wrote:
There are no non VAR BB crankshafts. It seems that cranks manufactured after about the middel of '78 are VAR anf the BB wasn't built until around '80. The BA could have a non VAR or a VAR in it.


Is there any way to find out what you have in a BA without tearing the engine apart to do it?


There are "numbers" on the OD of the crankshaft flange that may or may not confirm VAR. That's a PITA and incurrs labor charges to r&r the prop. First explore the history of the engine. Who overhauled it when? Was it a factory rebuilt etc. Sometimes it is possible to determine form the paperwork that is could be a VAR or conversely that it could not be.... PM me what the logs show at zephyrengn@aol.com and I'll try to help make the determination. Charlie Melot

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