Gear ratio wrong... swap gears?

[erikgreen]

I drained the lube from my secondary (my extra) sterndrive today, to see what work would be needed to replace the seals on the drive. There was no water in the drive lube, thankfully, and the Ujoint and splines seem in good shape.

The gears inside looked useable (no chips or worn spots) but when I counted the teeth of the gears under the top cap, I found that the gear on the input shaft had 24 teeth, and the gear it drove on the vertical (drive?) shaft had 20 teeth. Am I right in reading that this gear ratio means it's a 1.98 to 1 ratio drive?

I got it off an older boat that had a V-8 engine, but I doubt the PO who worked on it would have had any clue about drive ratios, so he may have just run it with the wrong drive.

I was hoping to replace the seals in this one and use it instead of my primary sterndrive, which was damaged in a car accident.

Secondary question - am I right that swapping those gears out from the 1.5:1 drive to this one would require specialized tools and is hard to get right?

Erik

 

[MikDee]

Re: Gear ratio wrong... swap gears?

Something don't sound right here Eric? reduction gearing means just that, the engine shaft should have less gear teeth then the (vertical) drive shaft, if you have the numbers reversed, I still get a 1.2X1 drive ratio??? You should recount the gears.

Replacing gears, unless you have the right tools, don't do it,,, I replaced a bad set of 1.5X1 gears once on a Type 1 drive, and ended up with a groaning drive

 

[whywhyzed]

Re: Gear ratio wrong... swap gears?

wrong thread, sorry...

 

[ziggy]

Re: Gear ratio wrong... swap gears?

i forget, which drive and engine package do you have eg?

 

[John_S]

Re: Gear ratio wrong... swap gears?

If Alpha GenII, from the service manual:

http://www.boatfix.com/merc/Servmanl/14/14a3.pdf

Drive Unit Gear Ratio Identification All drive unit gear ratios are identified on each drive in two places. It is important to note the ratio of the drive unit before preceding with any repairs. The first place to look is on the decal on the port side of the drive shaft housing. It will have a number such as (1.50R) and then the serial number. The second place to look will be on the universal joint splined yoke. It will be identified with a letter such as (F). This method is explained in the following chart.
ALPHA
A 2.0:1
B 1.98:1
C 1.62:1, 1.65:1
D 1.81:1, 1.84:1
F 1.47:1, 1.50:1
H 1.32:1
K 2.40:1
M 1.50:1 MAGNUM

A drive unit could have had the gear ratio changed for high altitude, which would void any application of the above chart. The gear ratio then would have to be determined by counting the teeth on the drive gear and the driven gear in the drive shaft housing and using the following chart for
reference


Tooth Count Ratio Drive Driven
14-28 2.40:1 20 24
14-28 2.0:1 24 24
17-28 1.98:1 20 24
17-28 1.81:1, 1.84:1 17 19
17-28 1.62:1, 1.65:1 24 24
17-28 1.47:1, 1.50:1 22 20
17-28 1.32:1 20 16



Eric, You can review the service manual to see if you want to tackle the job. From the special tools involved, I would be looking at an SEI replacement drive.

 

[achris]

Re: Gear ratio wrong... swap gears?

If you are right about the tooth count, then that is a 1.98:1 drive. That ratio was only ever fitted, as standard, to the 2.5 litre and 3.0 litre 4 cylinder engines. If the PO changed it at some stage then that could account for the 'wrong' ratio for a V8.

MikDee. The lower housing has a reduction of 1.65:1, so any ratio in the top box must be multiplied by 1.65 to give an overall ratio... (until 1995 when Merc changed to tooth count in the lower box of the Gen IIs, to give 1.62:1)...

Tooth count Total ratio
20-24 1.98:1
24-24 1.65:1
17-19 1.84:1
22-20 1.50:1
20-16 1.32:1

Cheers,

Chris...........

 

[MikDee]

Re: Gear ratio wrong... swap gears?

Thanks achris,

I thought all the gear reduction was done in the upper case, so be it. That makes sense then, but he had the numbers inverted, in actuallity then the 24tooth gear, being the lower shaft gear, and the 20 tooth gear being the engine shaft one, that made it confusing. Either way, it's not good news for Eric.

 

[erikgreen]

Re: Gear ratio wrong... swap gears?

i forget, which drive and engine package do you have eg?

Well, the engine is the long block I put in last summer, which is a Chevy 350. The broken sterndrive came from the 305 (Merc 228).

The "extra" drive is from a Formula Thunderbird boat I bought to get one part off of, then parted out. The formula had a chevy 350 in it, so I was hoping it had a useable drive too, but given the overall condition of that boat I'm not surprised it's off.

Looks like I may need to just sell this drive. Hmmm... the only thing really broken about the 1.5:1 drive is the mountings for the trim cylinders... that's on the upper, right? So I can't swap the uppers.... can I swap the drive casings?

Erik

 

[erikgreen]

Re: Gear ratio wrong... swap gears?

Thanks achris,

I thought all the gear reduction was done in the upper case, so be it. That makes sense then, but he had the numbers inverted, in actuallity then the 24tooth gear, being the lower shaft gear, and the 20 tooth gear being the engine shaft one, that made it confusing. Either way, it's not good news for Eric.

Actually I'm pretty sure I had the counts right... 24 teeth on the input gear, and 20 on the lower one. I'll re-count today and take a pic.

Erik

 

[MikDee]

Re: Gear ratio wrong... swap gears?

Eric Wait!!!, If you have 24teeth on the drive gear, and 20 teeth on the driven gear, then that upper set is overdrive! (.83) according to my calc.,,, Not, reduction gearing, and if Chris is right, and you multiply that times the reduction gearing of 1.65 in the lower unit, it comes to 1.3749 reduction gearing combined total!
If you miscounted and the upper gears are actually, 22t, and 20t, then you would have the 1.50 gearing you want!

Don't make any sudden moves , Don't sell it yet, either!

 

[achris]

Re: Gear ratio wrong... swap gears?

.... and if Chris is right ....

Wadya mean, "If Chris is right"??!?!?! Are you suggesting that I may be wrong??? I resemble that comment???

I did the 24/20*1.65 calc too... Didn't think that if Eric miscounted and had 22 teeth on the driven it would be 1.5:1... Good catch....

Cheers...

 

[MikDee]

Re: Gear ratio wrong... swap gears?

Wadya mean, "If Chris is right"??!?!?! Are you suggesting that I may be wrong??? I resemble that comment???:

You can't always be right? That would be my wife

Good catch....

That's Why I'm here, to keep you guys on your toes,,,!
Or, fall on my Face,,,, LOL,,, Cheers!

 

[Maclin]

Re: Gear ratio wrong... swap gears?

Is the drive together enough to spin the input shaft around and see how many turns it takes to turn the prop shaft once?

 

[erikgreen]

Re: Gear ratio wrong... swap gears?

Okay... I re-counted.

Note: Edited for correct terminology per Don's post below.

Bottom line, it's the correct drive for a V-8. It has a 22 tooth drive gear driving a 20 tooth driven gear.

Additionally, I was able to locate the serial number with some sandpaper and determine it is 4945949, which corresponds to a 350 V8 made between 1978 and 1982.

So, now I just need to locate a set of seals for it. I already have a new water pump kit. I'm going to clean it up, repaint, re-seal, and then use the drive in the spring.

Thanks everyone for correcting my incorrect information!

Erik

 

[achris]

Re: Gear ratio wrong... swap gears?

Part number for the seal kit for the top box is 26-32511A1.

 

[Don S]

Re: Gear ratio wrong... swap gears?

Just so we are all on the same page.

 

[erikgreen]

Re: Gear ratio wrong... swap gears?

Part number for the seal kit for the top box is 26-32511A1.

Thanks. I ordered this, plus a lower seal kit, plus a transom service kit. I see many evenings of questions on this board in my future as I rebuild the thing

Erik