Sounds like your manifolds are part of the closed side. You can just
use two of the regular gaskets with your existing block off plate or
there is also a different gasket that has the holes blocked off in the
gasket. Either will work, the objective is to block the water passages
between the manifold and the riser. The only opening should be the big
one in the middle for the exhaust.

I've also seen this used on raw water cooled engines to preheat the
water by running the incoming water through the manifold(s) before it
goes to the block. The dumping the water via the risers.


JohnH wrote:
On Thu, 01 Jun 2006 20:02:21 GMT, wrote:

Greetings,

I have twin 350 Merc's with full fresh water cooling......I'm in the
process of replacing the risers, and when I disassembled them, I found
the typical stainless block-off plate sandwiched between two
gaskets.....

Looking at the new Merc part number and schematic, it seems that only
a single gasket is now used, and the stainless block-off plate is a
thing of the past...

Can anyone kindly confirm if in fact the current set-up only requires
the single block-off gasket (Merc # 27-863725 1), or is the stainless
block-off plate still required?

I've seen manifold/riser "kits" available, and they too only have the
block-off gasket, but if I'm going to the trouble, I want to be
sure....I guess they could have changed the gasket design so the
stainless plate is no longer needed, but......

Thanks a bunch!!!

I don't have the fresh water cooling, but my manifolds and risers both use
only one gasket. Mine is a 350, 1997.