Model I Sterndrive Basic Questions

[myoldboat2]

I believe my 1974 Mercruiser sterndrive, serial number 390xxxx, is a "Late Model I". I have a few probably dumb questions:

1. Can the top cover be removed without messing up the preload on the vertical drive shaft?

2. In the parts diagrams, I don't see a gasket for the top cover; is there one?

3. Is this page the right parts page? My top cover has a liftting hole, and some other websites show separate pages with some different part numbers for each drive series (but I can't seem to match them up to my drive serial number).

Thanks.

 

[crazy charlie]

Re: Model I Sterndrive Basic Questions

You can remove it and there is a rubber o ring around it.Torx socket may be needed.Charlie

 

[ziggy]

Re: Model I Sterndrive Basic Questions

that link looks like a alpha1. try this link and pic your poision for your engine. http://www.mercruiserparts.com/selectModels3.asp?type_id=DRA

Torx socket may be needed.

i suppose it could be but i don't think torx drives were invented back in them days... maybe a 12 pt. socket will be the ticket though..
as far as for messing up the preload. i don't think it'll interfer to remove the cover because when you put the cover back on you'll torque the fasteners down to the same torque they were to start with so the cover will be right where it was prior to removal. i think i'll be preloaded the same.. and yep on the rubber oring for a gasket..

 

[crazy charlie]

Re: Model I Sterndrive Basic Questions

[QUOT i don't think torx drives were invented back in them days... maybe a 12 pt. socket will be the ticket though..
.[/QUOTE]

Thats what I meant.Charles

 

[myoldboat2]

Re: Model I Sterndrive Basic Questions

OK, I see, my sterndrive is under "120/140 1970-1977 Serial number 2791957 THRU 4893634".

Great, I think I will pop the cover in advance. The manual says to mate the drive gear teeth as before. Not sure if the teeth will be pre-marked or if I need to mark them. I'll pick up a new o-ring in advance.

 

[ziggy]

Re: Model I Sterndrive Basic Questions

Great, I think I will pop the cover in advance.

what ya going in there to look at?

Not sure if the teeth will be pre-marked or if I need to mark them.

i think only 1.65:1 gear ratio had marks on the gear teeth. if you separate them, i'd mark them. by taking the top cover only off you can't get the gears out of mesh. you need to remove the yoke and drive gear 1st...

 

[myoldboat2]

Re: Model I Sterndrive Basic Questions

hmmm, i was planning to mark the gear teeth through the top cover access, but it sounds like you can't see them? by pulling the vertical shaft we could replace the drive housing lower seals, or does that cause issues? so if you need to pull the u-joint assy out first, how do you mark the mating teeth between the drive gear and the other gear?

edit: i'm getting Upper Gear Seal Kit, Sierra SIE182648

.

 

[ziggy]

Re: Model I Sterndrive Basic Questions

i was planning to mark the gear teeth through the top cover access, but it sounds like you can't see them?

go look at the s/m. it has pics. yes, you can see them. probably mark them too. ya just can't separate them since ya gotta remove the drive gear first. fwiw. i expected my gears to be marked and they were. but it looked like someone used their electric pencil on it. from the factory i assume.
you can replace the lowest seal in the upper w/o taking anything apart. short of separating the upper and lower. the next seal going up. you have to remove everything from the upper to access it i think. i've never gone that far. i did note that when you have the drive gear out of the way, you can lift on the vertical driven gear shaft. i assume it just lifted out. better read up real close in the service manual if your gonna go for that 2nd seal. the one ya gotta get from the inside..

 

[myoldboat2]

Re: Model I Sterndrive Basic Questions

Thanks, I am trying to absorb all of this.

The service manual (pg 6A-20) says, "CAUTION: MerCruiser drive units with the same number of teeth on both gear (in drive shaft housing) have identification marks on drive and driven gears. These marks must be matched as shown in Figure 7, whenever gears are installed into drive shaft housing." I assume this is related to the gear ratio (not sure what mine is at this point). If the gears do not have the same number of teeth, then the indexing "walks around" each gear in normal operation--so then matching certain teeth isn't needed, right?

 

[myoldboat2]

Re: Model I Sterndrive Basic Questions

which drives have the same number of teeth on both gears?

 

[ziggy]

Re: Model I Sterndrive Basic Questions

to the best of my knowledge and from memory. the 1.65:1 ratio only. i think 24 teeth ea...

 

[myoldboat2]

Re: Model I Sterndrive Basic Questions

After being slowed down by rain and family commitments, I've got the new coupler and starter on and the engine remounted and aligned. I am going to install the new yoke assembly into the drive shaft housing.

I'm running out of time. I plan to use the boat the next three weekends and then I may replace all of the drive seals in the fall, when it's too cold here for the kids to tube or wakeboard. I have never had water in the gear lube.

QUESTION 1: Can I remove the universal joint / drive gear / bearing assembly without removing the top cover? I have the bearing retainer wrench and the drive shaft housing seal kit. I've read Mercruiser Service Manual Number 2 and it's not clear--it lists removing the top cover but it goes on to remove the whole vertical gear stack, which I don't plan to do at this time. I think I have a 1.98:1 gear ratio (the manual doesn't say; it's s/n 390xxx "Late Model I"), so assuming the upper unit drive gear and driven gear have different teeth counts, then they don't need to be marked for reassembly, right? If it's important to remove the top cover to remove the u-joint bearing assembly, then I'll do so.

QUESTION 2: Can someone explain a little more about the u-joint / drive gear / bearing assembly reassembly procedure. Assuming I have the small spacer, I apparently torque the u-joint shaft pinion nut to 85 ft-lb while turning the bearings, and this applies the correct preload on the drive gear bearing assembly. Manual #2 says to use a bar to hold the u-joint. Manual #3A also discusses the procedure, but shows the assembly sort of cradled over the handle of the retainer tool (which is in a vise) with a hose clamp around the large spacer (for what, to turn the bearing assembly, I suppose?). Any light you could shed on this would be helpful.

Thanks in advance.



.

 

[jtybt]

Re: Model I Sterndrive Basic Questions

You don't have to remove the cover to remove the drive/yoke assembly.

It's been a while but I think the lower seal for the short vertical shaft comes out and goes in from the under side...but you(should) have to remove the vertical shaft first. If you never had water in the drive, it can wait.

As long as you don't replace any gears or bearings, you don't have to reshim. Just keep all the shims in the same order when you separate the bearing pack of the drive/yoke assembly.

 

[myoldboat2]

Re: Model I Sterndrive Basic Questions

sounds great, i hope to go for it today. some day i'll figure out what jtybt stands for... thanks.

 

[myoldboat2]

Re: Model I Sterndrive Basic Questions

ok, it's done. that wasn't much fun. the retainer loosened up easily. the bearing assembly was not that easy to pull out. i also found that taking out the lube vent plug relieves the vacuum you set up when pulling the assembly out. i was really honking on the yoke shaft end nut, to the point where i thought i was going to bend something, so i ended up heating the nut up. i didn't want to do that, but i spent an hour before that with no movement at all. i'm not super comfortable with my torque value on putting that nut back on. the manual says it's critical to get the bearing preload right (85 ft-lb, i have the small spacer), how critical is it? for example, when i took the big hose clamp off to slide the assembly back into the housing, the bearing cups and large spacer could still be rotated and the spacer could slide if pushed. i found that out when it wedged on the way in the first time. with as hard as it was to break the nut free, i find it hard to believe it was assembled the last time at 85 ft-lb, probably a lot more with somebody's air wrench. i also got the big retainer nut near 200 ft-lb, but not sure it's exactly there. tomorrow i mount the sterndrive back on the boat.