Switching from SB Chevy to BB Chevy

[CaptnReinell]

Hey all,
Been a while since Ive been on here.
I have a 1976 24' Searay With a merc 260 and merc trans.
My question is is there some kind of adapter plate available if I would want to put a big block in this or is the tranny made for big and small blocks respectivley??
Any advice would be appreciated...

 

[rodbolt]

Re: Switching from SB Chevy to BB Chevy

is this a stern drive unit or an actual inboard with a velvet drive transmission. if its velet drive then what is the gear ratio stamped on the trans ID tag.

 

[Bondo]

Re: Switching from SB Chevy to BB Chevy

Ayuh,... The motors are interchangeable without adapter plates...
Depending on the rest of the driveline of course...

 

[TilliamWe]

Re: Switching from SB Chevy to BB Chevy

Ayuh,... The motors are interchangeable without adapter plates...
Depending on the rest of the driveline of course...

Exactly

 

[CaptnReinell]

Re: Switching from SB Chevy to BB Chevy

is this a stern drive unit or an actual inboard with a velvet drive transmission. if its velet drive then what is the gear ratio stamped on the trans ID tag.

Its a merc ll trans with the monster OD. I am pretty sure 1.5 or 1.47.

 

[Don S]

Re: Switching from SB Chevy to BB Chevy

I'm thinking it's a II-TR, and you have a 255TR, which should have a 2:1 gear ratio.

Go up to the Adults Onlys sticky at the top of this forum, and download Mercruiser service manual #2. Then look at section 2C. Let us know what you find.

 

[Bondo]

Re: Switching from SB Chevy to BB Chevy

Ayuh,..That should take a BBC, just Fine...

 

[picklenjim]

Re: Switching from SB Chevy to BB Chevy

TRS drives started in 1973. The TR didn't start until 1977. 73'-74' was the 255 TRS which used the 351 Ford motor. 75'-76' was the 280 TRS which used the 350 GM motor. TRS has a 1.5:1 ratio and the TR has a 2:1 ratio. TRS will only take up to a 15" diameter prop where as a TR will take up to a 20" diameter prop. With the drive off see how many revolutions you have to turn the drive shaft to make the prop shaft go around once.

SB to BB....No problem.

FYI: The MercTrans ll bell housing is drilled to accept both Chevy and Ford motors.

 

[CaptnReinell]

Re: Switching from SB Chevy to BB Chevy

TRS drives started in 1973. The TR didn't start until 1977. 73'-74' was the 255 TRS which used the 351 Ford motor. 75'-76' was the 280 TRS which used the 350 GM motor. TRS has a 1.5:1 ratio and the TR has a 2:1 ratio. TRS will only take up to a 15" diameter prop where as a TR will take up to a 20" diameter prop. With the drive off see how many revolutions you have to turn the drive shaft to make the prop shaft go around once.

SB to BB....No problem.

FYI: The MercTrans ll bell housing is drilled to accept both Chevy and Ford motors.

It's the big prop, 19 spline instead of 15. prop shaft is bigger too. So if I am understanding this right a BB Chevy should be no problem. Thanks for you input.