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Merc stern drive

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harleyheadfred

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"I have what I believe is one

"I have what I believe is one of the old Alpha drives on a 1989 boat. I'm getting a loud low pitch whine, which I belive is probably coming from the drive. This happens whether in gear or not. My neighbor was over recently and he said he thought he could hear my "center bearing" going. This was the week before I noticed it. What's a center bearing? 2nd question: If I replaced this drive, could I increase the ratio to give me more top end speed? FOr example, I have seen drives advertised with a 1 to 1.6 ratio, and others advertised as a 1 to 1.8 ratio. I would think increasing the ratio would give me more top end."
 
"I believe that he is refering

"I believe that he is refering to your gimble bearing when saying center bearing. this bearing turns constant when the engine is running. it is located in the housing that bolts to the transom. it has a lube zirk on the starbord side of gimble housing. with your 2nd question you dont state what engine you have, also your altitude. also with that think of a car, with the lower ratio your highway gears, with the higher ratio your stop light to stop light. the higher the ratio the more prop you can run but then again there is a limit. you have to try to balance the best of both worlds and the designers did that. they also gave most engine/drive combos 2 ratios, one for sea level and one high alt with all the drag ratios and weight worked out. find what ratios were offered for your boat, look at your ratio on the drive. maybe your at high altitude using sea level gears and will notice a perormance plus with that new ratio. hope that helps."
 
agree. probably the gimble bea

agree. probably the gimble bearing.

Secondly... if you are considering the drive ratio... making prop pitch changes is the first step. But boats are "load limited" much more often than they are "RPM" limited. Unless you are easily reaching 4800 RPM at wide open throttle (depending on your engine) - close to red line - than you've got the right drive ratio. Your WOT RPM should be 4500 - 4800 in my experience. If you up the ratio or the prop pitch you might end up with a slower start and a similar top speed but at only 4k RPM.
 
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