30h c-mod build

[rabbitears2]

Need advice. Putting together a 30h c-mod motor. What is the best product out there to use when sealing the filler block to the exhaust port area? I used a high heat gasket material to seal it and in a short time blew some of the seal out of the exhaust pipe. I am just taking a stock C 30h mercury motor and simply adding a hustler exhaust system to it. Can I use the existing water exit peep holes for the water to exit the same way a stock motor would exit water without adding holes to the exhaust plate or exterior water jacket? Trying not to alter the motor from original stock except for the new exhaust. any help would be appreciated.

[ZUL8TR]

exhaust seal

On the Yamato mod exhaust Cliff Johnson uses RTV High temp. Maybe the blowout was because to much of a gap between filler block and cylinder wall?

[Guest]

30 mod

Over the years I have used a number of sealers for our MOD engines. All our,30, 40 and 44 filler blocks are sealed with Permitex black high temperature silicone. Think it is good for 700 degrees. The only time that we have had a failure was when we didn't fit the filler block to block correctly. Also you must have it absolutely clean! Also try to have the mating surfaces a little rough to allow the sealer to bite better.

Alan

[Dave M]

The Right Stuff

A product named "The Right Stuff" is what we use currently. It seals the 44's filler blocks very well. The trick is to make sure your filler block is fit correctly and not a lot of slop to fill in with goop.

A lot of folks also use Devcon. That is an old stand by. It works very well too.

Not all Hi Temp silicones are made equal either. If using that, use a good brand name, and get the one that is good for above a 1000 degrees. I don't recall the exact temp rating on the one we have used but if memory serves me right, it is 1200 degrees or something close to that.