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#1
02-02-2013, 08:19 PM
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Bravo 3 runout
I was looking at a counter-rotating bravo 3 today and wondering what the allowable runout on the stern/trailing prop is? I think I detected .060-.090 with the eye-crometer.
Last edited by FishStretcher; 02-02-2013 at 08:22 PM. 
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#2
02-03-2013, 10:19 AM
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Quote:
a bravo III drive,it has a set of counter rotating props - in a twin installation,there's no changing rotations...these drives all have the same forward rotation... "run out" ?? could you explain "run out" are you referring to prop shaft run out ? as in,the prop shaft has a bend ? or are you referring to the prop itself ? "eyeomete" - it can read .060-.090" ??
__________________
do not let common sense get in your way
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#3
02-03-2013, 11:39 AM
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This is what I was looking at. The props run in opposite rotation, cancelling the torque and increasing propulsive efficiency, they say. The props are opposite hand as well.
There is a modest amount of what you might call wobble. I eyeballed it at 1/16-3/32" when spinning, comparing one prop from the other. I didn't pull the props and put a dial indicator on it. so it could be the sum of shaft straightness, hub concentricity/non coaxial error, or prop variation/damage. It looks ok to me for a single prop outboard, but I don't know I/Os or counter rotation in stern drives. The counter rotation drives I am used to are bigger and custom. There are a few things wrong with the install- like the antifouling paint masking. But I can't afford a new one Last edited by FishStretcher; 02-03-2013 at 11:42 AM.
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#4
02-03-2013, 11:49 AM
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Quote:
not sure what this means "There are a few things wrong with the install- like the antifouling paint masking. But I can't afford a new one" take a good look - did you notice the lower unit is new,and the transom assembly,along with the upper gear case are older ? i can see the aluminum oxide in the pictures - the white powdery stuff - its' on both the upper gear case and the transom assembly.trim cylinders are new too. this tells me,this was an older bravo III drive,the ones that were prone to corrosion,due to a design flaw... i'm still not sure what you're referring to ?? wobble ? that's a standard bravo III drive - been around for a while now - pretty trouble free unit.volvo builds a similar set up... did you check the shift ? as in attempt to shift it - reason i ask is there's a potential for problems with the bushings for the shift - this is upper gear case... you may want to have some one proper experience check it out for you -no offense,it seems as though you're not very experienced with these power systems..."bigger custom power systems " ? care to explain ?
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do not let common sense get in your way Last edited by pelican; 02-03-2013 at 11:58 AM.
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#5
02-03-2013, 12:09 PM
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No, I am not familiar with the I/O at all. It was moored, and the I/O is older, the lower unit is almost new. He said a friend botched something in the install/adjustment of the previous lower unit/ prop, so he got a new one. I saw receipts for the work. I ran it, it shifted nicely, although I am used t outboard "dog clutch" shifting, so anything is quieter. When running with the steering wheel turned hard over there were no odd noises (I was told to listen for gimbal bearing growl).
I am not sure of the generation of Bravo 3 it is. It is old enough to be either generation- installed ~2004. I think it might be older? I had a mechanic help with the de/re winterizing and running. But he knows the seller. My mechanic wasn't available. I get the feeling that the install wasn't top notch first time out- it was pulled and redone once, early on. And maybe the Bravo 3 lower unit dissolved. I don't know. This will be a trailer queen for a year while I sort it out and make sure the zincs and mercathode is done right. Your input is appreciated. As for my wobble comment- Standing behind the I/O with it at idle in gear, I could just see that the prop tips hat a bit of wobble. Not worse than my outboard when I do the same thing on the trailer. But I don't know Bravo 3 I/Os. Last edited by FishStretcher; 02-03-2013 at 12:16 PM.
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#6
02-03-2013, 03:16 PM
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I had one on my 1999 proline 251 great out drive but keep an eye on corosion I see you have an extra zinc on the propshaft I didn't started to see corosion and installed the mercathode system and it stopped it
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#7
02-03-2013, 03:35 PM
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Quote:
"gimbal bearing growl" - that noise,if bad gimbal bearing,would be apparent at all times , when the wheel is hard over - on the steering stop,this is a test for u-joint noise... there's a test for corrosion protection - all these units had mercathode systems... there's a test for that system as well - a common problem is,the power is only available to the unit,with the battery switch in the "on" position - this unit needs to have constant power to function properly... the early vintage bravo III had a corrosion problem,it was taken care of in the later model units - too much stainless,not enough zinc... i would pull that drive to inspect the bellows and the shift area i explained previous - with the aluminum oxide i see,i would highly reccomend you do that - but,with you being a "Mechanical Engineer for boats and marine systems ",i would assume you would know that...
__________________
do not let common sense get in your way
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#8
02-04-2013, 09:00 AM
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I pilot a desk chair and computer at work. I am not a marine mechanic, nor do I get paid to work on pleasure craft. I can wrench pretty well for a weekend warrior, but I need to know what I am looking at. So I don't know much about I/Os. Everything I know about this so far is from what I have asked the marine mechanics at work. So if I say something wrong, it's probably me, not the source of the info.
I showed pics of the outdrive to one of the mechanics, and he said he has seen lots worse. It will be a little gamble, I think. I think I have to pull the engine anyway for other reasons, so while I am in there I can address these issues.
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