Going from 290 to 280

[danielkelsas]

My question is a bit of a long winded one. I know some will say I need to install a new transom blank. Without doing that. Would it be possible to install a 280 transom shield in a 290 hole? With obvious grinding way back and feathering in a strong fibreglass “patch” at the top where its smaller? Maybe even an angle iron bolted to the inside? That way I can just install my two v8’s with my two matching 280 drives. OR. would it be better to split the lower units off the 290 drives (already installed in the boat) and re shim/install the 280 lower units? (The existing 290’s are geared for 4 cyl). If I go that route I need new y-pipes and a different spline in the flywheel cover correct? How much typically are these parts worth? Having trouble finding 290 flywheel covers or exhaust that bolts from the inside of the transom shield rather than the outside. Thankyou for your help.

 

[DRCrowe]

danielkelsas, Sounds like an interesting project. There are a few questions that go beyond the outdrive. You elude to the current setup for 4 cylinder engines being swapped to v8's is that correct? If so you will need to solve some exhaust issues if you plan on keeping the 290 transom shields.
Assuming you have addressed this issue, swapping the 280 lower onto the 290 and shimming will work. You mention the 280's are paired with the V8's so I will also assume you are using the correct gear ratio (maybe 1.60 or 1.95)?
I don't know what would involve the full 290 to 280 transom shield swap. I'm sure there are guys here a lot smarter then me that can help.

 

[danielkelsas]

Update. I have decided that since I already have all the 280 parts. including the exhaust y-pipes and correct flywheel covers with matching splines. That I will be going with the fibreglass route. Installing older 280 drives in bigger 290 c transom plate holes. Tapering back and installing some thinner core material. Probably 3/4” ply. I finished the grinding today. I had to go a lot deeper than I would have liked. There was some moisture in the bottom edge. Also some voids where the transom is tabbed into the bottom of the hull. Has anyone else ever attempted this without installing a whole new blank transom? What height should I install the transom plates? Will the output shaft of the flywheel cover need to be at the same height for the v8’s as it was for the 4cylinders?

 

[DRCrowe]

Wow, That will be a project. Looking forward to following your progress. I did a partial transom repair on a Barefoot Ski Centurion a couple years ago. It turned out good, but was a lot of work. I used West Systems epoxy instead of cheaper poly resin. You get what you pay for. Do you have any pics? I hope you end up with room to work on the motors after you install them. V 8's are a lot wider then 4's! You will probably have some stringer/motor mount work ahead of you too.

 

[Scott Danforth]

why not simply keep the 290 and swap the lower with the 280

the gear ratio change is in the lower. the transmissions are the same, and the 290's have a better tilt and trim.

 

[danielkelsas]

why not simply keep the 290 and swap the lower with the 280

the gear ratio change is in the lower. the transmissions are the same, and the 290's have a better tilt and trim.

I was having trouble sourcing two 290 y-pipes and flywheel covers. Also unsure about the condition of the trim pumps and cylinders. Also a little worried about splitting and re shimming the bottom ends.

 

[Scott Danforth]

I was having trouble sourcing two 290 y-pipes and flywheel covers. Also unsure about the condition of the trim pumps and cylinders. Also a little worried about splitting and re shimming the bottom ends.

the shimming is super easy and covered in the manual.

the PDS housing should be the same

Y-pipes are on CL and ebay

 

[danielkelsas]

the shimming is super easy and covered in the manual.

the PDS housing should be the same

Y-pipes are on CL and ebay

 

[danielkelsas]

I know your right. I thought this might save me time/money. Fibreglass isn’t cheap either though. Once I started grinding away I got into some soft core spots and some shitty layup with voids. So maybe it’s a good thing? I finished grinding the transom inside and out. Now my worst fear is coming true. I am going to have to do some pretty extensive modifications of the stringers to accommodate the wider stance motor mounts. And maybe even at the front for the Harmonic balancer/pulleys? How high can the drive be mounted? So the exhaust fin is inline with the bottom of the hull?

 

[Scott Danforth]

match the height of the 280's you have

I wouldnt go higher

 

[danielkelsas]

match the height of the 280's you have

I wouldnt go higher

Thankyou for your help. Is there a shorter v8 motor mount that I could use underneath? Or maybe a different one that comes Down from the block at a steeper angle? Rather than 45 degrees to create a narrower stance?