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Replacing 280 duo prop

Z

zapper1

New member
Good day to all.
I am a newbie to the forum .I have a 26 FT hourston glascraft with a volvo aq 260 and origanally came with a 280 sp.outdrive I've receintly changed the lower out to a duo prop WOW what a difference that made.
My question is that i am slowly piecing together a 290 outdrive I have the newer style transom with the larger pins that attach to the suspension fork,but the leg that i have is a DP A that has the smaller diameter hole on the suspension fork .Is it possible to change the suspension fork to the newer style on the DP A
Question#2 I am also thinking about getting a new crate motor a 330 HP Vortec long block. I know that I will need a new intake manifold Iam going to stay with carb. New starter new flywheel and possible a new cam. Will my egsisting bellhousing bolt up to the larger flywheel. If there is anything else that i need to chage over any input would be greatly appreciated
Thank You in advance Cheers
 
Yes, what a difference it can make!
I have a small V/P business, and I have switched many boats over to the Duo Prop over the years....., including several of my own.
I currently have a 28 foot SND F/B with twin 5.7's with Duo Prop drives..... so I know exactly what you mean. Big Grin! :D

IMO, you'd be far better off to go later than a 290, and get away from the Reverse Latch unit and the SS anchorage bracket.
This would be a C drive or later drive. (some call this the "large pin" 290.... it is NOT!)
Your Duo Prop will bolt up, minus the proper shimming!
The driven gear bearing size increases, and the gear box thickens, making this a stronger transmission, IMO.
The no reverse latch unit makes this quiet during gear engagement.

If you do go this route, consider a 275 A transmission!

If staying with the 290, then the transmission driven gear bearing diameter will allow you to stay with your Intermediate housing, and change the suspension fork, I believe.
This will allow for the 290 suspension fork to mate to the 290 transom shield.
All else will work as long as your helmet pin is compatable! But your 280 will have the single pin! You may need to have a special bushing made..... or switch to an early 275 bearing box clamping collar. (Again, shimming is imperative)

Just an FY I here..... Note the common misnomer re; the horse power rating of the Vortec engine.
It is rated @ either 5,200 or 5,400 rpm..... an rpm that we don't run at.
The eariler 260hp is rated at a much lower rpm.
Just an FYI on that, and I love the idea of the Vortec!


Now, I have to ask if you are aware of three things when you installed the DP:
**Using only the 1.95:1 over-all gear ratio for your SBC engine.
**Shimming of the vertical tapered roller bearing race (extremely important.... or the gear set can become damaged). This is a Negative pre-load.... not a Positive pre-load.
**Switching to GL-5 gear lube (also very important). Your single prop drive used engine oil!

Re; your existing "flywheel cover" (aka "bell housing" in the auto world):
If you go to a later engine, the typical 168 tooth flywheel becomes an issue as it will NOT fit within the AQ series flywheel cover.
You must find a 153 tooth flywheel that mates to the later crankshaft!
This is a Camero car flywheel if you can't find it any other way.


Have fun!:)
 
Last edited:
Thanks for the quick responce.
Yes Idid use a 1:95 ratio
I did put a neg pre load
I used a synthetic gear lube (AMSOIL) 75-90 I think
It runs great I've put about 20hrs.on it since the change
I have a complete upper transmision #DP-D1
I was going to try and use a 290 intermeidiet housing with this transmision
Then would it be possible to use the newer style H bracket to complete this drive
This flywhell that has 153 teeth is it a 12"that I would be needing
 
zapper1 said:
Thanks for the quick responce.
Yes Idid use a 1:95 ratio
I did put a neg pre load
I used a synthetic gear lube (AMSOIL) 75-90 I think
It runs great I've put about 20hrs.on it since the change
I have a complete upper transmision #DP-D1
I was going to try and use a 290 intermeidiet housing with this transmision
Then would it be possible to use the newer style H bracket to complete this drive
This flywhell that has 153 teeth is it a 12"that I would be needing
Click to expand...

The DP D1 will be large bearing.... it will not work with a 290 Intermediate housing. You'll need a large bore Intermediate housing for this transmission to work.
The bracket that you refer to is the "Suspension" fork!
I wish that I knew more about the interchangeability..... but I have fairly good reason to think that it will interchange. Pivot tubes and needle bearing kits are same.

Yes, there are only the two flywheels for the SBC..... 153 and 168.
 
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