replacing engine, odd combo of parts, please advise, BOND-O and other SBC gurus!

[duped]

I have a 1986 merc 305, block, casting # 14088551, in need of replacement.

This motor sort of an odd-ball, because it has a one piece rear main seal, 14" flywheel (staggered starter), and yet it has the perimeter bolt valve covers. I knew all center bolt valve cover motors were one piece, but up until today I did not know there was a transition motor and that this 305 that has one piece seal, without center bolt covers.

MY ONLY QUESTION! Did the crank flange diameter change with the one piece rear seal, or at a later time...put differently, does my one piece rear seal 305 use the same flange pattern as 1987+ 350s, or the earlier pattern? I need to know because I am looking at 87-95 truck TBI 350s and need to know if I can retain my flywheel/coupler...

I know I will have to switch intakes and find one with the straighter center bolt holes, also am aware of needing electric fuel pump, core plugs, etc so I wont ask any silly questions about that. Gantry is built and motor is ready to be pulled.

 

[Bondo]

Re: replacing engine, odd combo of parts, please advise, BOND-O and other SBC gurus!

I have a 1986 merc 305, block, casting # 14088551, in need of replacement.

This motor sort of an odd-ball, because it has a one piece rear main seal, 14" flywheel (staggered starter), and yet it has the perimeter bolt valve covers. I knew all center bolt valve cover motors were one piece, but up until today I did not know there was a transition motor and that this 305 that has one piece seal, without center bolt covers.

MY ONLY QUESTION! Did the crank flange diameter change with the one piece rear seal, or at a later time...put differently, does my one piece rear seal 305 use the same flange pattern as 1987+ 350s, or the earlier pattern? I need to know because I am looking at 87-95 truck TBI 350s and need to know if I can retain my flywheel/coupler...

I know I will have to switch intakes and find one with the straighter center bolt holes, also am aware of needing electric fuel pump, core plugs, etc so I wont ask any silly questions about that. Gantry is built and motor is ready to be pulled.

Ayuh,.... Wow,... Yer confusin' Block vintage, 'n Head swappin',...

While the Head changes might coincide with the block changes, that don't change any bottom lines,...
It Sounds like you've got the 1 pc. seal block, with earlier heads,...

The Chevy bellhousin' flange bolt pattern, has been the same, almost since the dawn of time, 'n their All the Same,...
That's the Beauty of the Chevys,... 2.5l to the 8.1s are the same,....

The SBC crankshaft bolt pattern, aka; the Flywheel bolt pattern went from 3, 1/4" to 3" with the 1 pc. seal,...
12", or 14" flywheels can be found in either pattern,....

Movin' this to the Non-repair forum,....
'n, btw,... Don't call me out by name in yer title,...
I'll find ya anyways,...

 

[Scott Danforth]

Re: replacing engine, odd combo of parts, please advise, BOND-O and other SBC gurus!

1985 to 1986 is a transition period for the SBC. GM went with the 1 piece cranks, however had more heads than cranks. by the 1987 model year on motors, this was straightened out.

There is no difference in the intakes or mating surfaces between the center-bolt non-vortec heads or the perimeter bolt non-vortec heads. the only difference is vortec to non-vortec.

Vortec heads are 1996 and later