Converting 270T to 280DP

[Roadrager50]

Hello IBoats

I love this forum between those that have done it to those that are trying there is so much information on here. Okay enough with my raving about the site.

My question: I have a1974 V/P 270T. I was wondering if I can take the lower end and replace it with a 280DP. I have been looking at pics and diagrams. They look alike but I am not sure. If I have to I will replace the whole thing but that would be a little more than I was thinking. I might have to part it out and move on to another boat. any suggestions would be appreciated.

Smooth Waters and Blue Skies

 

[HorizonblueDK]

Re: Converting 270T to 280DP

Yes, the lowerunit can be switched. But you must check/replace the shims under the tapered roller bearing race, that is pressed into the upper unit. The race can be seen when the drive comes apart.

 

[Roadrager50]

Re: Converting 270T to 280DP

Thank You Horizon.
Now that I know that, I need some more info.
I am working on a 74 Thompson Laguna 18ft with a Waukesha 302.
So what I need to know is what should my final drive be?
I have not started on it yet.


Smooth Waters and Blue Skies

 

[HorizonblueDK]

Re: Converting 270T to 280DP

You need a lowerunit with a 1.95:1 gear ratio. The upperunit is not changed.

 

[billbayliner]

Re: Converting 270T to 280DP

You first need to determine which engine, before a ratio can be selected.

The 1.95:1 is typically used behind the small block V-8s. The 4and 6 cylnder engines typically call for the 2.30:1 and Big Blocks call for the 1.78:1.

The vertical shaft race is pressed into the intermediate housing, not the upper unit. Be sure to get this race with the duoprop lower unit!

The Volvo Penta OEM workshop manual will will explain the shimming procedure and will point out the "A" and "B" dimensions!

Gear oil is now GL-5.

 

[HorizonblueDK]

Re: Converting 270T to 280DP

You first need to determine which engine, before a ratio can be selected.

The 1.95:1 is typically used behind the small block V-8s. The 4and 6 cylnder engines typically call for the 2.30:1 and Big Blocks call for the 1.78:1.

The vertical shaft race is pressed into the intermediate housing, not the upper unit. Be sure to get this race with the duoprop lower unit!

The Volvo Penta OEM workshop manual will will explain the shimming procedure and will point out the "A" and "B" dimensions!

Gear oil is now GL-5.

We are thinking the same. I considered the upper gearbox and intermediate housing as the "upper unit", since that assembly is the upper one, when the outdrive is separated into two.

The OP mentions that his engine is a Waukesha 302, which must be a Ford small block V8, and he therefor needs a 1.95:1 ratio.