7.4L MPI Risers & Manifolds

Mr Mac

Mr Mac

Member
Feb 27, 2019
49
Apollo Beach, FL
Boat Info
1997 330 Sundancer
Name Slàinte Mhath!
Engines
Twin 454 Mercruiser with V-drive
Replacing these (finally) and need to know a couple of things. For the risers, do I need any gasket sealant for those gaskets?

Second, what are the torque specs for the manifold and riser bolts?
 
Thanks for confirming that for me. I had read it on another forum but wanted to be sure.
 
I don’t want to complicate anything, and I am not questioning the accuracy of your answer. I have read from others that they put gasket material on the manifold to elbow and leave the block to manifold dry.

Do you know the reason we can’t use a good gasket sealer on the upper joint? Since water will be passing over the joint, if seems the seal would be better.
 
DWABoat said:
I don’t want to complicate anything, and I am not questioning the accuracy of your answer. I have read from others that they put gasket material on the manifold to elbow and leave the block to manifold dry.

Do you know the reason we can’t use a good gasket sealer on the upper joint? Since water will be passing over the joint, if seems the seal would be better.
Click to expand...
OEM gasket is SS sandwiched between graphite which sticks like glue. His BB might not have the SS but def. has the graphite
 
Last edited:
scoflaw said:
OEM gasket is SS sandwiched between graphite which sticks like glue.
Click to expand...
Now that is the answer I have been looking for.
Good reason to go with a Merc gasket set vs “Other” brand, I guess.
Thank you.
 
I used a high temp Permatex gasket sealer because my matting surface was not smooth and I did not want to remove the heads to send them to a machine shop, when the Permatex gasket sealer would fill the gaps... My manifolds have be on now for three years with no problems... I used all merc parts, however, I needed to run a 9/16" tap on manifold threads that the riser and elbow stud screw into. I also ran a die over the studs removing the orange thread sealer...
 
rcknecht said:
I used a high temp Permatex gasket sealer because my matting surface was not smooth and I did not want to remove the heads to send them to a machine shop, when the Permatex gasket sealer would fill the gaps... My manifolds have be on now for three years with no problems... I used all merc parts, however, I needed to run a 9/16" tap on manifold threads that the riser and elbow stud screw into. I also ran a die over the studs removing the orange thread sealer...
Click to expand...
The head surface is not the critical area, there's no water there. This thread is about elbow to manifold mating where water is present and perfectly flat surfaces are paramount.
 
scoflaw said:
The head surface is not the critical area, there's no water there. This thread is about elbow to manifold mating where water is present and perfectly flat surfaces are paramount.
Click to expand...
You are correct, the question was regarding the risers... If the manifolds are also replaced, then the a sealant may be needed... There will be exhaust leaks if the head is not smooth... There is no need for sealant on the manifold to riser connection with the OEM gaskets as scofflaw had stated above...
 
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