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Identifying gear ratio

T

Tony B

New member
I have a 20' wellcraft with a 350 chevy in it. It has a frozen penta 280 outdrive which I am trying to replace. I need to find a way to identify the gear ratio in the existing drive so I can replace it with the proper one. Any suggestions or help would be greatly appreciated. The serial number on the old drive is 28003206 B. Thanks Tony.
 
The 1.61:1 over-all ratio is the correct drive ratio for your engine and size hull. The "B" in the serial number denotes that yours is the correct ratio, but ONLY if the lower unit has not been changed in the past.
No other ratio will work in a 280 s/p 5.7L scenario!

I usually have these in good used condition, if interested.

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Ricardo, I appreciate your help! I have a line on what appears to be a good used unit right now(serial #28161515 B), however the owner is telling me that it is a 1.91:1 ratio. I am hoping he is confused. If not, what I am gathering is that the lower unit has been replaced. To verify the ratio on the used unit I am going spin the prop. one rotation and count the rotation on the input. I believe this will give me the correct ratio. If this does not pan out I would be interested in what you have. Thanks again for the help!
 
I.m a big fan of rotating the input shaft in gear (10 times) and count the prop shaft revolutions.
what is stamped and what gears are inside doesn't always agree
 
A couple of people now have told me to rotate the input shaft ten times, but why ten. After do I divide the number of revolutions on the prop. by ten?
 
Tony, the 280 ratios are: 2.15:1, 1.89:1 and 1.61:1....... there is no 1.91:1 ratio in the V-8 Single Prop 280 drive. I assure you......, the 1.61:1 is the correct ratio for the V-8.
Other ratios are for different engines and/or some of the high performance Single Prop drives.... of which the 280 is not!
Duo Prop ratios are yet entirely different as well.

Do as Joe suggests. Remove the ring anode just ahead of the prop. Wire brush the area of the prop shaft bearing carrier. The numbers will be right there..... and will very likely read 1.61 only! (omitting the " :1 " )

However, if a gear set had been changed, and if the carrier did not get re-stamped, this would be incorrect!

The reason for rotating ten times is two-fold.
One......... Ten is an easy number to do the math with.
Two...... the sliding sleeve must be locked firmly into the gear cup. You may not get this upon first attempt. Once engaged, do not stop..... keep pressure on the sleeve/cup until you have gone ten times.
Now do the math!

Doing this removes a margin of error.

NOTE: the ratio is a result of both transmisson AND lower gear sets..... hence the term "Over-All" ratio.
So if you are testing a lower unit only...... it will not be accurate!


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Thanks guys, I was able to verify the ratio behind the zinc anode on my drive. It was in fact the 1.61 ratio as you previously suggested. What I now need to do is have the owner of my potential drive verify his. I am going to have him spin the input shaft 10 times. I believe I am looking for 16.1 rotations on the prop shaft. As for the sliding sleeve and gear cup...(I don't mean to sound ignorant) but if the drive is fully assembled do I have to worry about this? Once again, thank you!
 
The Cone Clutch does not lock-up immediately like Dog Clutch engagement does.
It may require some movement and pressure to squeeze the oil from within the sliding sleeve conical surface, and from the gear cup surface.
Once the oil film is deminished, and once friction is realized......., the two lock-up (figuratively speaking), and begin rotating 1:1 with each other.

.
 
Well good! :D

May we assume that the numbers worked out to be 1.61:1 ?

FYI: there is a also a 1.89:1!
Not that these are all that close to one another, but a slight error could cause you to think it is correct.
Just say'n............

.
 
Hey Ricardo-

I completely understand what you are getting at. He told me that when he spun the input 10 times he came out with 6.5 rotations on the prop. 10/6.5 gives me 1.54 ratio. Any slight oversight can change the ratio drastically. 10/6.2 gives me 1.61 which I am looking for. That is only .3 prop. revolutions difference. Hopefully he was just off a little.

I won't know until I can find a mechanic in his area(Orange County, CA) to verify. I am about 7.5 hours away, which is making this very challenging. I can't just go check it out for myself. Unfortunately there are no reasonably priced units in my area (Sonoma County, about 1 hr. north of San Francisco). I have gotten quotes on rebuilt units in Sonoma County that vary from $5,000 to $11,000. My father-in-law paid $10,500 for the boat 8 years ago, which makes it hard to justify spending that kind of money. This is his boat, I am just earning my keep so to speak (he will never take gas money from me) as far as doing the leg work on trying to replace the unit.

Do you have or know of any units if this does not pan out? As far as price what do you feel is fair?

Thanks Again---Tony
 
Volvo stuff does not wear out... well, at least not like some of the other drives. Therefor the used market is soft, so to speak.
A good used 280 1.61:1 lower unit will usually sell for $600-700 tops.
We also do not normally rebuid this lower unit due to the good used market..... it's just not cost effective!
Gear set is about $850, bearings another $250, labor for set up may run $450.....

A used 290, which is basically the same, may bring slightly more...... only because of the 290 style.... of which only involves the exhaust outlet flapper.
The 280 had the flapper on the production models only. They are somewhat rare!

How much is he asking for this used 1.61:1 lower?

.
 
He wants $600 for the whole outdrive and transom assembly. He purchased the unit three years ago for his boat from someone in Arizona. The unit is supposedly only been in fresh water. Between the time he purchased it and installed it he came across a 280dp, which he opted for. It appears the price of things around here is slightly inflated.
 
Tony, I was estimating a cost for you regarding a "lower" unit only!
$600 for all (transmission, Intermediate, suspenion fork, Rev Latch, and lower unit) is an excellent deal!
You could use the lower unit (re-shimmed correctly), sell the transmission and Intermediate via e-Bay.
A used transmission (nothing having been done to it) will bring an easy $400. An Intermediate will bring and easy $150. And if you were to remove the suspension fork and rev latch unit......, and sell separately, you may do even better.

Keep all shims for future.
Make certain that each lower unit is accompanied with it's original vertical shaft tapered roller bearing race.
(this race will be installed in the Intermediate.... and must be removed and kept with the corresponding lower unit) It will require a new shim value to be calculated prior to the race being re-installed.

When removing/installing, remove the transmission first/install last. Much easier this way. Cost is two O-rings ONLY!

Rather than type this all out, here is a link to a web page where I have posted links to many threads that help explain removal/installation, using "heat", and shimming procedure, etc.
It will be "read only" for a non-member, but you will find quite a bit of AQ series info there.

.
 
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RicardoMarine said:
Tony, the 280 ratios are: 2.15:1, 1.89:1 and 1.61:1....... there is no 1.91:1 ratio in the V-8 Single Prop 280 drive. I assure you......, the 1.61:1 is the correct ratio for the V-8.
Other ratios are for different engines and/or some of the high performance Single Prop drives.... of which the 280 is not!
Duo Prop ratios are yet entirely different as well.

Do as Joe suggests. Remove the ring anode just ahead of the prop. Wire brush the area of the prop shaft bearing carrier. The numbers will be right there..... and will very likely read 1.61 only! (omitting the " :1 " )

However, if a gear set had been changed, and if the carrier did not get re-stamped, this would be incorrect!

The reason for rotating ten times is two-fold.
One......... Ten is an easy number to do the math with.
Two...... the sliding sleeve must be locked firmly into the gear cup. You may not get this upon first attempt. Once engaged, do not stop..... keep pressure on the sleeve/cup until you have gone ten times.
Now do the math!

Doing this removes a margin of error.

NOTE: the ratio is a result of both transmisson AND lower gear sets..... hence the term "Over-All" ratio.
So if you are testing a lower unit only...... it will not be accurate!


.
Click to expand...
I believe I have a 2 80 outdrive Volvo Penta with dual engines and wanting to replace one
 
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