Alpha One Drive Gear Swap

[T & T]

Does anyone know about the gear swap from a 1.62 to the 1.84 ratio in an Alpha 1 drive? I have a 1990 Bayliner with the 4.3l engine and have moved the boat from near sea-level to 5000'. <br /><br />What is required? Can I just buy the gear set or do I need the full Upper Gear Rebuild Kit? I am swapping gears because the current ones are damaged and need replacing.<br />Thanks

 

[achris]

Re: Alpha One Drive Gear Swap

Hi T&T,<br /><br />Welcome to iBoats.<br /><br />Originally the 4.3 was supplied with the 1.65 gearset. This was found to be too 'tall' for the engine in that configuration, hence the change to 1.84. When the Gen+ engines (more torque) were released Mercruiser took the ratio back to 1.62. The difference with 1.65 and 1.62 (also 1.84 and 1.81, 1.98 and 1.95, 1.5 and 1.47) is due to a change of tooth count in the lower gearbox (to reduce gear noise).<br /><br />You didn't say which ratio you have. If you have the 1.84, then all you need to do is reduce the pitch of the prop. If you have the 1.65 try with a smaller prop, but you may need to have a gearset change.<br /><br />Hope this helps.<br /><br />Chris............

 

[T & T]

Re: Alpha One Drive Gear Swap

Thanks for the welcome.<br />I have the 1.62 (or 1.65?), the book stated it was the 1.62 (1.65 was the Gen II Alpha 1), but whatever. <br />I currently run a 15 and 17 pitch prop. The 17 pitch is too much for 5000', and I need a good hole-shot. I want to step up to the 1.84 ratio to get me back aroud a 17 to 19 pitch (and use the 15 pitch prop for the 9000' lakes).<br /><br />What I need to know is can I just swap the upper two gears or is there something else different about the gears (from the 1.62 to the 1.84) that I don't know about that would prevent a direct swap?<br /><br />Like I stated before the existing upper two gears are damaged, but everything else (shafts and bearings) appear to be fine.<br />Thanks

 

[achris]

Re: Alpha One Drive Gear Swap

T&T,<br /><br />No problem with putting just the two gears in the top box. All other parts are the same. Just make sure that the shimming is done properly or you'll be replacing the new gears pretty quick.<br /><br />As an aside the lower gearset was changed in late 1995, 3 years into the Gen II. It was only the gears in the lower unit that were changed, to reduce the gear noise some clients had complained about. I owned a boat shop and was a Mercruiser dealer at the time and the amount of info we received on the change was huge, just for a tooth count change. I have a 'pre-change' Gen II and don't have a noise problem. <br /><br />As your leg is an Alpha One, then the ratios will be 1.65 or 1.84 depending on the top gearset.<br /><br />Chris..............

 

[T & T]

Re: Alpha One Drive Gear Swap

Thanks very much for your help.<br />I appreciate it.

 

[Wart T]

Re: Alpha One Drive Gear Swap

Boats delivered from factories to high altitude cities like Denver nearly always require a gearset change at the dealership. I strongly recommend letting a dealer do this. If you mess it up..............

 

[T & T]

Re: Alpha One Drive Gear Swap

This is why I am asking the question, they wanted $600 for parts and $600 for labor simply for a gear swap, and I am trying to figure out what I am missing. The dealership mechanics I have dealt with actually order the boats from the factory with the "high altitude" gears, and the mechanics don't do a lot of gear swaps, couldn't get a straight answer from them. The gear set is about $180 and a complete rebuild set with all shims, gaskets and bearings is about $350. I'll take the time and care to do the labor myself (no mess-ups, I promise.).<br />Thanks.

 

[T & T]

Re: Alpha One Drive Gear Swap

Oh, and if you search on this board, a complete new 1.84 upper drive is only $1095 with no core and no S&H costs. <br />There is no real magic to installing the complete upper drive, so I am having a hard time justifying paying $1200 just to have a gear swap.

 

[tommays]

Re: Alpha One Drive Gear Swap

well the hard part is doing it with out the merc tools to measure the bearing preload and gear backlash<br /> <br />every set of gears,bearings and housings are just different enough to require carefull shiming or the drive will become toast<br /><br />tommays

 

[achris]

Re: Alpha One Drive Gear Swap

$1200 does sound a bit steep. The gearset can bought from www.mercruiserparts.com/partsbynumber.asp for $213.58. The labour involved in setting them up wouldn't be any more than about 4 hours (absolute tops), so that's $150/hr. Where do I join? <br /><br />The special tools you will need are the drive gear shim tool, 91-60523, the driven gear shim tool, 91-60526 and an in-lb torque indicator and access to a press. The service manual will also be required. Those shim tools are also available at mercruiserparts, for about $130 combined. <br /><br />Good luck.<br /><br />Chris...........

 

[Wart T]

Re: Alpha One Drive Gear Swap

That is steep. Around 700 total is what it should be.<br /><br />Good luck. Be very careful you do this correctly or you will be buying an upper AND a lower.

 

[FreeBeeTony]

Re: Alpha One Drive Gear Swap

I replaced the gears, bearing carrier, and seals in my pre-Alpha lower unit w/o any special tools. I replaced the shims just as they were originally. I also resealed the entire upper unit and replaced the yoke (had a groove worn in it). I know about the concern regarding the shims, but so far so good! I have at least 50 hours on it and have not had any problems. No leaks and shifts fine...

 

[achris]

Re: Alpha One Drive Gear Swap

Tony,<br /><br />If you replaced all that stuff in the lower unit without shimming, the first you'll know about it is when it all falls apart. Usually there is no 'signs' that it's not right. Just one day it doesn't.<br /><br />Chris............

 

[FreeBeeTony]

Re: Alpha One Drive Gear Swap

Chris,<br /><br />I kinda know I took a chance.......but I'm hoping its ok. Seems fine so far, I think if it was going to come apart it would have already. I changed the gear oil and it was clear. I think most of the variances are in the housings, the gears should be made to precision specs, that's why I feel that if I shimed it the way it was, the tolerances should be the same.<br /><br />Tony

 

[T & T]

Re: Alpha One Drive Gear Swap

Chris,<br />Just got the complete Gear Rebuild Kit (gears, shims, bearings, gaskets, etc) for $269.95 and the drive gear and driven gear shim tool and Retainer (Spanner nut) wrench all for 149.95 Been shopping for best prices and lowest shipping.<br />However, so far... <br />Total damage is about $420 for all parts and tools. <br />now all I need to locate is a shop manual. <br />Chris, you know where I could get a .pdf of the shop manual? Need gear backlash specs, etc.<br />Thanks

 

[achris]

Re: Alpha One Drive Gear Swap

Best place to get the manual is from Merc. No pdf (that I know of). The manual will pay for itself over and over and over. Just ask the other guys. You need more than just the specs. The correct sequence is also needed.<br /><br />Chris.........