alpha 1 gear ratio help?

1990 wellcraft eclipse 4.3l v6 alpha 1 drive# 0D354785.

The drive went out and I am looking for a replacement. I found one from a 1989 bayliner 4.3l with a supposed 1.84 gear ratio. I would love to know if this would fit. However I can't find any definitve info on my drive. A link, forward, or a "yes that would fit" would make my day. Thanks in advance.

Re: alpha 1 gear ratio help?

Best way is to count the teeth on on the drive gear & the driven gear. 1:84 is the proper ratio for a V-6.
Drive gear has 17 teeth, driven has 19.
The top cover has to removed but no other disassembly is required.

Re: alpha 1 gear ratio help?

Brad4g63 said:

1990 wellcraft eclipse 4.3l v6 alpha 1 drive# 0D354785.

The drive went out and I am looking for a replacement. I found one from a 1989 bayliner 4.3l with a supposed 1.84 gear ratio. I would love to know if this would fit. However I can't find any definitve info on my drive. A link, forward, or a "yes that would fit" would make my day. Thanks in advance.

Click to expand...

Your drive serial number comes up as an Alpha One 1.84 (provided the ratio hasn't been changed since factory), so if the replacement really is 1.84, yes, it will bolt straight up...

Re: alpha 1 gear ratio help?

Brad4g63 said:

1990 wellcraft eclipse 4.3l v6 alpha 1 drive# 0D354785...

1989 bayliner 4.3l with a supposed 1.84 gear ratio. I would love to know if this would fit...

Click to expand...

Direct bolt on, even if the gear ratios weren't the same.

Re: alpha 1 gear ratio help?

not to hijack the thread, because I think this would also help the OP.

but what is the difference between all the gear ratio's, I have had people tell me it doesnt matter.

I know from what little reasearch , all the drives use the same shaft that ties into the motor.

and that there is maybe 1 or 2 gears inside that are the main difference.

Is there a "all you ever wanted to know post"

Re: alpha 1 gear ratio help?

menglor said:

not to hijack the thread, because I think this would also help the OP.

but what is the difference between all the gear ratio's, I have had people tell me it doesnt matter.

I know from what little reasearch , all the drives use the same shaft that ties into the motor.

and that there is maybe 1 or 2 gears inside that are the main difference.

Is there a "all you ever wanted to know post"

Click to expand...

As far as the drive itself goes, yes the only difference is the 2 gears inside the top box. All the shafts, bearings, seals and housings are the same.

As for performance there is a HUGE difference. The gear ratios are selected so as to have the engine's torque curve utilised to the best possible effect. That means working out what sort of size boat that engine is typically going to be installed in, what the maximum and cruising speeds are likely to be, and then getting the ratio so the 'right prop' is in the range that is manufactured. eg, you could have a V8 with a 2.3 ratio leg, but you'd need a prop of around 29" pitch mark... and that's not too practical. Alternatively you could put a 1.32 ratio behind a 3 litre engine, but try finding an 11" prop for it!!!

When you look at the ratios you see that as the engines get more powerful the ratio decreases...

3 litre (140hp)- 1.94:1
The old 470 (170hp) - 1.84:1
4.3 litre (175 to 220) - 1.62:1 (some older models were delivered with 1.84:1 drives)
V8s (200hp to 300hp) - 1.47:1

Chris..........

Re: alpha 1 gear ratio help?

Ok so that makes sooo much more sense, as my 2.5 liter a 1.98 and the Ford 233hp has a 1.34.

So, could the OP then buy wich ever drive and then change the Gear ratio?

How practical is doing something like that?

In the OP's case it sounds like he has a replacement, so its not something he would need to change. but if he found one from a V8, I would guess he could take the gears out of his current. But I understand there are some other factors like MC-1 vs Bravo vs Alpha Gen 1 or Gen 2.


anyway, thanks much solving my questions

Re: alpha 1 gear ratio help?

It's not practical at all. The reason for different gear ratios is the torque and HP of the engine and the sizes of the props.
The props need to be in a certain range of pitch for best performance. Usually in the 17 to 21 inches of pitch range. The prop diameter is set by the size of the drive. So the only thing you can adjust is the gear ratio to get in the pitch range of the prop, then fine tune the adjustment of engine WOT rpm with prop size.
The manufacturers know what ratios are needed for each size engine

Re: alpha 1 gear ratio help?

menglor said:

...So, could the OP then buy wich ever drive and then change the Gear ratio?

How practical is doing something like that?...

Click to expand...

Buying a drive with a different ratio and putting a new set of gears in is expensive. Even if you were to use the gears from an existing drive, you would need to buy the shimming tools, also not cheap. And if you haven't done it before, it can be a little daunting.....

There are special cases when for reason of engine/boat application a ratio change is used to get the required performance. There was one post up here a few months ago with a 5.7L V8 engine in a very big boat (for the size of engine) and it was recommended to him to change the ratio from 1.5 to either 1.65 or 1.84. That would have got him back into the 15"-19" prop range. There is also cases to go the other way. A V8 in a small high speed boat would do well to go to 1.32 in the leg, but once you reach about 60 knots (I use marine terms in a marine environment ) you are getting into the areas where special drives and surface piecing props are needed. And that is a whole new ball of wax, and requires VERY deep pockets!