Confused about ratio's, yoke length and MC-1 to Alpha compatibility.

[adamjr]

So I have the drive pulled on my 68 merc 120. The drive serial tells me the drive is a 1973 which at some point in the vessel's history must have been a replacement.

I am picking up a salvage boat (1987 or 1988 Four Winns Horizon) for the purpose of the tandem axle trailer it is on but it happens to have an Alpha 1 with power steering that I might adapt in the future. The outdrive is off but the bell housing and all other components are there. I want to use the Alpha because of the hockey puck trim and trim limit senders as opposed to the original MC-1 buried tilt limit switch that I am wrestling with.

While discussing the outdrive with the current owner of the salvage boat he tells me that the Alpha outdrive will bolt right up to my MC1 bell housing. Now I don't know if this is true or not. I am also beginning to doubt some things I thought I knew. He also keeps calling the drive Gen II. I didn't correct him but didn't the Gen II cut in in 1991 or 1992? I did print out the two different ID docs supplied by Don S (my hero) so I will have them on hand. According to the serial from the gimbal housing it is a 1988 Alpha 1.

Yoke Length: I checked the yoke length of my 1973 outdrive's gear housing. The end that goes into the coupler is 8" long. Reading through some Mercruiser literature "earlier" drives have a yoke length of over 9". When did the length get shortened to the 8 1/8" length? I want to be sure I am not risking major damage to the yoke or coupler if I am supposed to have the longer yoke.

Drive compatibility: Can I bolt up my MC1 outdrive to the Alpha bell housing without issues provided the yoke is the correct length as it appears to be?

Can I bolt up the Alpha outdrive to my MC1 bell housing without issues provided that the yoke is the correct length?

Which gasket do I use? The one that is correct for the drive or the one that is correct for the bell housing? The concern there is mating the flat top of the Alpha with the hump top of the MC1.

The motor that is in the salvage boat is a 3.7 motor which if the outdrive is correct is a 1.84 ratio. The correct ratio for the 120 is a 1.98:1. While the ratio's are close I am not doubting that the Mercruiser engineers had a reason for the drive ratios chosen for a particular motor. In some of the ID literature motors above the 120 and 140 were paired optionally with ratios 1 step higher or lower. If I am correct the ratio higher number is the turns of the input shaft. So that would mean if I use the Alpha drive on my 120 the prop will turn at less than 8% higher RPM than the stock drive. Is running this drive on the 120 going to damage the drive or the motor or both?

Like the old Steve Martin tag line "I'm so CONFUSED!"

Thanks in advance for the great help I know I will receive here

 

[adamjr]

Re: Confused about ratio's, yoke length and MC-1 to Alpha compatibility.

Nobody? Bond-O and DonS must be working, sleeping in, or on vacation.

 

[Don S]

Re: Confused about ratio's, yoke length and MC-1 to Alpha compatibility.

You need the 1.98 gear ratio with a 120. The 3.7 is 170 hp, a lot more than your 120.

The change in shaft length was in 83 with the start of the R drive. 1982 and earlier was the MC-1 drive.
Below is from service manual #6

 

[Don S]

Re: Confused about ratio's, yoke length and MC-1 to Alpha compatibility.

Gee, get all worried because you didn't get an answer in the first 3 hours, even call out people by name for not jumping on your question, then when you do get a reply you can't even acknowledge you read it ?????????? I can see you was back on the forums about an hour ago.

 

[adamjr]

Re: Confused about ratio's, yoke length and MC-1 to Alpha compatibility.

Gee, get all worried because you didn't get an answer in the first 3 hours, even call out people by name for not jumping on your question, then when you do get a reply you can't even acknowledge you read it ?????????? I can see you was back on the forums about an hour ago.

Don,

I don't think I meant post #2 the way you took it. That's the problem sometimes with the written word. You can't hear a tongue in cheek when you're reading. As far as when I read that I was unable to respond as I was doing something I should not have been doing while reading a forum post. Driving.

I wholeheartedly appreciate the expert advice that you provide. When I made that comment I was on a break from a training class. It was totally tongue in cheek. I do not know where you and Bond-O find the time to answer so many posts with such great information. Not that I expect for you to spend the time looking at all of the threads I have posted looking for advice but if you did I think you would find an enthusiastic "Thank You" for every answer I receive.

For your advice I thank you. I hope there won't be any hard feelings based on what I wrote appearing to be ignorant of the fact that most people have lives and jobs that keep them from spending 24 hours a day answering newbie questions.

As far as the yoke question you actually answered it in a previous post where you attached a diagram of the two yoke lengths that came from Manual #6. Problem was I read it wrong with regard to which yoke is which. Reading is fundamental and I failed the fundamentals. What I did not see in the car was that you posted that same very valuable excerpt on this post. I was trying to pay more attention to driving than to reading.

http://forums.iboats.com/attachment.php?attachmentid=84033&stc=1&d=1298688323

I hope this was more clear as an apology then my previous statement was as a joke.

Thanks again for your help.

 

[Bondo]

Re: Confused about ratio's, yoke length and MC-1 to Alpha compatibility.

What I did not see in the car was that you posted that same very valuable excerpt on this post. I was trying to pay more attention to driving than to reading.

Ayuh,.... That comment alone is enough for Me, to Never, EVER answer a question for ya....

Drivin' a car is a Full Time operation, that needs yer Undivided Attention...

I have NO tolerance for Morons drivin' 'n readin' or textin' nor anything else, other than Drivin'....

People Die every single day from such Foolishness....

 

[achris]

Re: Confused about ratio's, yoke length and MC-1 to Alpha compatibility.

You know what I call people who drive and text (or talk on the phone or read books)?.... Temporary Australians!!!

I did have a whole lot of info for you, but after reading that you were on the internet while behind the wheel of a death machine, well, I just forgot it all....

'nough said!!! (I just feel for the family of the person YOU kill!)

 

[adamjr]

Re: Confused about ratio's, yoke length and MC-1 to Alpha compatibility.

pparently I started an S- Storm with my comment about driving and reading a post. If y'all ever drove through Cook County Illinois you would understand the method. I'm not talking about reading while rolling. While waiting at a stop light, 50th in line, knowing full well I am going nowhere for at least 5 minutes I clicked on my email. I saw DonS's had responded to my post. I read the two sentences and tapped the link to see if that was the only response. Then I set the phone back inthe cup holder and waited four and a half more minutes for the light to change.

So I am sorry if I offended anyone. Understand this PLEASE; If my foot isn't firmly on the brake pedal and the car isn't 100% stationary the phone is in the cup holder. My bluetooth tells me who is calling and more than half the time I don't even answer the phone when I'm rolling. I am not one of those driving multi-taskers.