manifolds

[demaris]

ok, now i'm looking at the manifolds that are either removed or in the process of being removed. rust and corrosion obvious. manifold exhaust surface shows uneven levels perhaps due to the metal ring around the exhaust block exit on the gasket to the manifold exit. the question is; how much can be resurfaced to make the manifold a better seal. these were represented as stainless. not stainless. have yet to really see the heads.

need to carry a magnet next time i decide to have a lobotomy.

 

[Scott Danforth]

unless you have custom manifolds made by HiTek, or headers by companies like CMI, they are not stainless. only the elbows are stainless

so what is your problem?

 

[wingless]

Click save...

Twin 7.4L Mercruiser Bravo II Outdrives


My 454 (7.4L) has a flat exhaust manifold / head joint mating surface. Resurfacing was never required, just old gasket removal.

 

[demaris]

question is, can the manifold surfaces that mate to the heads be resurfaced or do they need to be replaced?

 

[Scott Danforth]

without a pic of the issue you have, its impossible to answer. however that surface should never need to be trued up

if the mating surface at the head is damaged, just buy new. my guess you will find other issues. if your in salt water, manifolds are consumables and last 7-10 years

 

[Scott Danforth]

if when you pull the manifolds you find rust in the exhaust ports, the manifolds long ago died.

time to pull the motors and go thru them. the number 1 reason of motors being replaced in salt water boats is lack of manifold inspection and maintenance.

 

[demaris]

has a split sys. manifolds and engine, fresh water. risers raw water. in single port pic, lower left is thin and varigated. upper face is just discolored. in manifold pic, no interior rust. ex-sailboater, diesel. new to gas powerboats. again sorry for rants. probably just wishful thinking to resurface?

 

[Scott Danforth]

that manifold is at least 5 years past its replacement time. spend the $200 on a new one (actually buy them in pairs)

while at it, update to the dry-joint

 

[Bondo]

has a split sys. manifolds and engine, fresh water. risers raw water. in single port pic, lower left is thin and varigated. upper face is just discolored. in manifold pic, no interior rust. ex-sailboater, diesel. new to gas powerboats. again sorry for rants. probably just wishful thinking to resurface?

Ayuh,...... I see Alota gasket residue on the manifold to head ports,.......

That point rarely fails, the other end of the manifolds, at the riser/ elbow joint is where they fail,......

Clean All of the gasket surfaces to Clean cast iron with whatever means ya got,.......

Then inspect 'em for potential replacement,.......

 

[demaris]

i've decided to replace the manifolds as y'all have suggested. spendy but piece of mind. the risers are stainless, original i would guess. they haven't been available for some time. they are, however. in great shape. no rust or corrosion and i know they'll fit. i'll stick with these,

as an aside though, i did notice that the two cylinders farthest back towards the transom appear to heat the manifolds the greatest. the damage to the manifolds is much worse with these exhaust ports. not sure how the passageways are configured but i'm thinking that the cooling water in the top middle and out the bottom middle doesn't cool the trailing cylinders sufficiently. any thoughts? manifolds with input forward and outlets aft?

 

[Scott Danforth]

99% of cooling issues is from lack of flow. find the lack of flow and fix.

external rust issues is from a salt-water leak somewhere

manifolds on raw water cooled and HX half systems, have raw water entering the manifold and then exiting the elbows

manifolds on HX full systems usually enter the bottom, exit the top and return to the HX

so what kind of system do you have?

 

[Lou C]

Judging by the 90* elbow fitting on the top of the manifold it looks like they are on the closed cooling circuit, so they may be internally ok as long as the mating surfaces can be cleaned up flat n true.

 

[demaris]

looks like i never said, my error. 1994 7.4l bravo II. risers are stainless and raw water cooled. manifolds are i think standard for fresh water cooling. fresh water in to the top and then out the bottom. or possibly bottom to top flow. hx=head xchanger? looks like i have a full system. while we're at it. any favorites for manifolds.

 

[Scott Danforth]

Manifolds are the same for that vintage no mater how its cooled

Water in the bottom, then out the elbows on top in a raw water cooled application. A block-off plate is used on full systems with cast iron elbows. The raw water exits the elbow at top on the stainless elbows, then enters the elbow

Bravo II drives are for pushing barges and trawlers

 

[demaris]

350 express thundercraft, 94. yes a bit of a barge. it'll get up and go but i suspect it tips the scales at 18k or so. even at idle the other boaters are shaking their fists at me. meant brands of manifolds.

 

[achris]

Hey demaris How about you let us know what you are working on in the first post of any new threads. Makes it very difficult to answer a question when we have to search through 15 posts to find out what you have.

Remember:- Model, year, serial number... We have no interest in what boat it/they are in, that isn't important...

Yes, you may have put that information in another thread, but the people answering you are looking a DOZENS of different threads from different people. There is no way we can keep track of what everybody has. Heck, I have trouble remembering the serial number of my own engine, let alone someone thousands of miles away.

Cheers,

Chris......

 

[demaris]

well this is the second writing. site decided to dump previous before posting. probably too fast with the fingers.
numbers;
engine 0F159255
transom 0F210560
drive 0F185301
1994 mercruiser 7.4l, Bravo II



using the factory merc manuals and the others

 

[tank1949]

question is, can the manifold surfaces that mate to the heads be resurfaced or do they need to be replaced?

Usually, with a lot of elbow grease and file or better yet have buddy with a roller type sander, you should be able to sand a couple of thousands so that the exhaust manifold gasket takes up any imperfections. Depending on the manifold's age, most V8s are around a hundred bucks each or a little more. It might be worth it to buy new ones. Just saying...