Replace Aquamatic 250 with 280

[jeffnick]

A little background -
I bought a 40+ year old boat. It didn't have the original drive train but had been updated to a 260A motor w/ 250 outdrive. I bought a complete spare 250 outdrive for parts, but it was for a 4 cylinder, not an 8 like mine. I tore up the anti-ventilation plates on my 250 and didn't want to change out the gearbox on the replacement 250 (4cyl), so I bought a complete 280 for my V8. I then decided to just repair my 250, so the original 250 is still on the boat and I have a working 250 4 cyl and a working 280 8 cyl in addition to the 250 8 cyl on the boat.

So I'm playing with the 280 in preparation to use it if/when. Here's the 280 8 cyl and 250 4 cyl which I have been told are pretty much interchangeable except for the lower section.

We know the 250 takes a short hub propeller and the 280 can take either. Is the only difference in the prop cone assembly the hole in the end of the cone?

I know the cone with the hole can be used with the 250 because that's what I have on the boat now with the 250 and it works just fine using the tangs without the center bolt.

So I need a 'long hub' line cutter and what else to mount the short hub prop on the 280?
And if I want to use a long hub prop on the 280, what additional stuff do I need in addition to the long hub line cutter? Maybe just an 850888 plastic washer?

The 250 isn't tapped for a cone bolt. I see cone bolts on sale for over $20 but they can be had at Home Depot for less than $2. All I really need to know is how long?

I'd asked if there might be a difference in the helmet bolt going from the 250 to the 280, but find that the 250 bolt fits just fine in the 280.

It's nice that they even have the torque spec etched on the top of the helmet bolt.

We talked about the oil fill hole on the 280 being substantially higher than the required level, so I'll use the level as shown on the dipstick.

So my last question for now is about the hose connecter on top of the outdrive. I need one and can't decide what part number it is...the 250 and 280 appear to be identical but some are only 2 hole and are some called 'thermostat housing'?

Oh, and when you use heat to free up a stuck bolt, do you apply heat directly to the head of the bolt or to the housing it's seated in? And if the bolt itself - how hot - do you need to get it red?

 

[RicardoMarine]

Man.... this reply is going to cost you!

A little background -
I bought a 40+ year old boat. It didn't have the original drive train but had been updated to a 260A motor w/ 250 outdrive. I bought a complete spare 250 outdrive for parts, but it was for a 4 cylinder, not an 8 like mine.
Yep... the 4 cylinder lower unit will create an over-all ratio of 2.15:1.

I tore up the anti-ventilation plates on my 250 and didn't want to change out the gearbox on the replacement 250 (4cyl), so I bought a complete 280 for my V8. I then decided to just repair my 250, so the original 250 is still on the boat and I have a working 250 4 cyl and a working 280 8 cyl in addition to the 250 8 cyl on the boat.
Is the 250 on the boat now a V-8 ratio???? (1.61:1)

So I'm playing with the 280 in preparation to use it if/when. Here's the 280 8 cyl and 250 4 cyl which I have been told are pretty much interchangeable except for the lower section.
Well... yes and no!
If the over-all ratio is 1.61:1, either will work for your V-8.
However, the 250 transmission is small bearing, and has a much smaller main drive gear male yoke splined shaft. I've rarely seen this shaft twist, but it can happen behind V-8 power.
Early 250's used a washer at the dip stick and drain plug.... later this became an O-ring.
The 250 transmission will not work with the 280 Intermediate housing, or visa-versa (small driven gear bearing -vs- larger driven gear bearing).
250 oil fill port is in the Intermediate housing. (no fill port in the transmission)
250 suspension fork has the anti-rotation pin "inserts", of which makes this fork not quite as stout.
The 250 torque tab/trim fin is not as effective as the 280 style torque tab/trim fin.
250 lower gears are bevel cut.... not Hypoid.
All AQ series lower units will interchange as long as the proper shimming procedure is followed.

All AQ series single prop drives require engine oil... not gear oil.

We know the 250 takes a short hub propeller and the 280 can take either. Is the only difference in the prop cone assembly the hole in the end of the cone?
The 250 prop shaft will use the 1 pc spinner, or both halves of the 2 pc spinner, and must use the SS locking tab washer.
The center locking bolt cannot be used due to the prop shaft not being internally threaded.
The 250 exhaust outlet housing location prevents the use of the large propellers.


Below, you are showing the 1 pc spinner on the left..... and both halves of the 2 pc spinner on the right.

I know the cone with the hole can be used with the 250 because that's what I have on the boat now with the 250 and it works just fine using the tangs without the center bolt.
Correct!
You have the 2 pc spinner w/o the center locking bolt installed on this prop shaft.

So I need a 'long hub' line cutter and what else to mount the short hub prop on the 280?

OK.... this is where many people have trouble.
The spacer/line cutter is proprietary to the prop shaft... not the prop, nor prop hub length.

250, 270 or 275 will always use the short spacer/line cutter, regardless of the propeller.
280, 285, 290 will always use the long spacer/line cutter, regardless of the propeller.

The correct spacer/line cutter causes the same net exposed prop shaft and splines of either style.

And if I want to use a long hub prop on the 280, what additional stuff do I need in addition to the long hub line cutter? Maybe just an 850888 plastic washer?
See above.


The 250 isn't tapped for a cone bolt. I see cone bolts on sale for over $20 but they can be had at Home Depot for less than $2. All I really need to know is how long?
5/16" NC thread.... but I don't have a length for you.
Just make sure that the bolt becomes tight against the spinner, before bottoming out in the female threads.

I'd asked if there might be a difference in the helmet bolt going from the 250 to the 280, but find that the 250 bolt fits just fine in the 280.
If the helmet pin fits both transmissions, you are OK to interchange them.
The 280 and later helmet pins underwent several changes...... ranging from thread diameter to the double bolt helmet pin.
Some of the later helmets used a rubber isolated bushing.

It's nice that they even have the torque spec etched on the top of the helmet bolt.
Yes!

We talked about the oil fill hole on the 280 being substantially higher than the required level, so I'll use the level as shown on the dipstick.
Correct!
Give the new oil enough time to enter the hollow area of the vertical shaft before taking your final reading.
Replace the red phenolic fill port washer.

So my last question for now is about the hose connecter on top of the outdrive. I need one and can't decide what part number it is...the 250 and 280 appear to be identical but some are only 2 hole and are some called 'thermostat housing'?
For years some venders have been calling this a 'thermostat housing'. I've even contacted a few to bring this to their attention. They have made NO change!
This is actually a Water Neck fitting or hose connection fitting!
Whether 2 holes or 6 holes, the aluminum water neck will fit your suspension fork.
The "bead" on the "beaded gasket" faces down against the pivot tube.
Since the bead rotates against the pivot tube, you will want to grease this surface.

Keep an eye on this part.
It is considered to be a "wear item" and requires routine replacement.
Corrosion like you show below will cause this part to breach suction....... resulting in engine over-heating.

NOTE: if the upper pivot tube bushing is worn (causing wobble), the beaded gasket will seal for a short time ONLY.

Oh, and when you use heat to free up a stuck bolt, do you apply heat directly to the head of the bolt or to the housing it's seated in?
The thread inserts are within the aluminum. That is where you want the heat.

And if the bolt itself - how hot - do you need to get it red?
Use either a small hand held Propane torch or a Mapp Gas torch.
NO Oxy-Acet unless you know exactly how to use an Acet rich flame, and avoid using a Neutral flame.

A few words to the wise:

Your red 1 pc V-8 flywheel cover houses a double bearing PDS. Engine must be removed in order to replace these bearings.
Always, always, always replace the PDS bearings/seals while you have the oportunity.
1- 6206, 1- 6007, and 2- 35x62x7mm TCM or Timken seals, and are industry standard parts.
Glue or stake FWD seal in place...... AFT seal installs in the Non-conventional direction!
Pre-fill the grease cavity prior to seal installation.


Install a new eccentric piston seal. (the new seals are directional)

Use new gaskets or O-rings at the dip stick and drain plug.

Do a Press/Vac leak-down test on the drive (oil drained for the pressure test).

Make sure that a FWD gear engagement is a result of the shift cable becoming extended at the yoke.
Cable extends for FWD.... retracts for REV.

Place the eccentric piston at dead neutral, then make alll cable adjustments from there forward.


.

 

[RicardoMarine]

A few images that will help you.

First one shows a single bearing PDS and related bearing and pilot nose arrangement. (yours will be the double bearing PDS w/o the pilot nose)

Second one shows a double bearing PDS like what you have.

Third image to the right shows an incorrect AFT PDS seal installation.
When installed correctly, the seal lip and tension spring will be visible from the rear.
Reason.... we want this seal to breach excessive grease gun quantity and/or pressure, so that the FWD seal is not pushed from it's bore.

Next one shows an 18" grease gun extension hose being used for a remote grease port.... highly advised.

Last two show the 280 style and 250 style (respectively) prop shaft lengths prior to the long and short space/line cutters being installed.
The correct space/line cutter renders each shaft the same in length.

 

[sandkicker]

I did that conversion on my 1969 Lancer. As purchased, the P/O had replaced the 250 drive with a 4 cyl ratio unit. Since the original engine was a 283CID 185HP engine, he almost got away with it. When I reengined to a 5.7L 260HP could never get a prop to work. I considerd just swapping the lower 1/3 of the drive (where the reduction happens) but decided to go with the 280 drive instead. The hypoid cut gears in the 280 drive run quieter and cooler than the bevel cut gears in the 250... Given the bigger CID of the engine, the larger bearings were a plus.

 

[jeffnick]

First off - thanks for all the help. I didn't really feel bad about the lengthy post/questions because I got an email encouraging me to post here.
So now I can order my long hub line cutter and water neck fitting (aka thermostat housing) with confidence

Anyway, when I had the engine out I did send the flywheel cover to a shop for new PDS bearings.

I'm guessing the bearings were installed correctly? Knowing what I've learned here, I'd do it myself next time.
How can we be sure I have the double bearing model? It does have the grease fitting and in my boat that fitting is easily accessible...should it be greased often?

Thanks for the tip on checking the bushing on top of the pivot tube...mine is snug.

And sandkicker - we lived aboard a B27 for 3 years. Bought it new and took delivery at the factory.

 

[RicardoMarine]

............................

Anyway, when I had the engine out I did send the flywheel cover to a shop for new PDS bearings.

I'm guessing the bearings were installed correctly?
Question how they were installed.
(I can't tell you how many incorrect installations that I've seen over the years by so called V/P Techs.)

Find out if "sealed" bearings were used, or if the correct "open" bearings were used.
Also ask if they pre-filled the grease cavity until grease came through the ball cages.
Ask how the two seals were installed.
FWD seal must be glued or staked in place.
AFT seal installs in the non-conventional direction.

Also ask what type of grease was used..... NO green Marine wheel bearing grease!!!!!!!!

Knowing what I've learned here, I'd do it myself next time.
How can we be sure I have the double bearing model? It does have the grease fitting and in my boat that fitting is easily accessible...should it be greased often?
See image below

Thanks for the tip on checking the bushing on top of the pivot tube...mine is snug.
Good!

 

[jeffnick]

Thanks Ricardo - The PDS work was done over 3 years ago. We put less than 100 hrs a year on the boat - 95% of that is @ 1800 rpm or less -- she's kept warm and undercover the rest of the time. Even if the seals are incorrect I'm not going to pull the motor to change them at this time...maybe when I do manifolds and risers and put on the 280?

I do have a question about the steering linkage though. Is there something that should hold this pivot pin into the transom shield? It never comes out any farther but just to be safe I've fabbed a spring like arm to keep it in place.


Am I the only one who can see the sailboat in my previous post?

 

[RicardoMarine]

................

Thanks Ricardo - The PDS work was done over 3 years ago. We put less than 100 hrs a year on the boat - 95% of that is @ 1800 rpm or less -- she's kept warm and undercover the rest of the time. Even if the seals are incorrect I'm not going to pull the motor to change them at this time...maybe when I do manifolds and risers and put on the 280?
When you remove the old drive, and while the AFT end of the PDS is visible, have a helper give the cavity several pumps of grease while you watch for the old grease to come out past the AFT PDS seal.
If after several pumps you see nothing, give a few more.
If still nothing, it means one of several things:

• The cavity was never pre-filled in the beginning as it should have been.
• The forward seal has already become dislodged from it's bore, and the grease is taking the path of least resistance.

NOTE: I can't begin to tell of what type of damage may occur if you were to lose the AFT PDS bearing!!!!!!
It is not pretty, nor will it cheap to repair !!!!!!


I do have a question about the steering linkage though. Is there something that should hold this pivot pin into the transom shield? It never comes out any farther but just to be safe I've fabbed a spring like arm to keep it in place.
Yes, it is missing a keeper plate.
This plate is secured with the two studs that secure the chrome water tube to the transom shield.
The plate prevents the steering linkage bell crank arm from moving forward and out... although it will never come completely out.

View attachment 10638

Am I the only one who can see the sailboat in my previous post?

 

[jeffnick]

Thanks again Ricardo - it's a comfort having you around.

 

[RicardoMarine]

You are more than welcome!

If you can view this ..... click on the image that shows the FWD side of the shield.
You'll be able to see the small bracket or retainer that prevents the bell crank arm from moving forward from it's bore.

http://www.2040parts.com/-volvo-pen...om-shield-867900-dual-relief-ports--i1036156/


.

 

[sandkicker]

Am I the only one who can see the sailboat in my previous post?

No, I see it as well. I always liked the lines of the B27 and wished I had one. The B22 does not have enough headroom for me to stand and my wife is slightly claustrophic and won't spend any time in the cabin, thereby limiting my use of the B22 to a "day sailer". A quite comfortable one mind you that shrugs off the pincushion seas and 3 to 4 ft short chop we often get in Barnegat Bay in the afternoon. Regrettably, I'm putting it up for sale, as my wife (an RN) now works every other weekend and is off 2 days during the week, and I often work during the week (semi retired engineer). This cuts down on sailing opportunities during the season ( April thru October). Last 2 years we had the boat in the water, we only went out 3 times each season. It was in the water for Hurricane Sandy and sustained minor damage, which did not get fixed until late Sept. It never made it to the water last year due to very late spring and the maintenance demands of my power boat.