Replacing manifolds/risers 7.4 MPI's

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Cruisers4ever

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Apr 13, 2012
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32942
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I have twin Mercruiser 7.4 MPI's. Time to replace the manifolds/risers. I have a good quote for the parts. My question is: does anybody have an idea about how many hours labor I should expect to pay somebody for? also, any miscellaneous parts beyond manifolds/risers, bolts,screws, gaskets that would be usually replaced?
Thanks,
Bobby
 
If those engines are a full FWC, probably no need to replace manifolds.
 
saltwater and age also determine when to change them. When you post a question include details like raw water or closed cooling, age of the engines and how long since they were last changed.
 
quote:
Originally posted by Cruisers4ever

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It all depends how hard, or easy, they are to get to in your particular boat.
It's all about access.
Removing, and replacing them on two motors shouldn't take more than about an hour if they were on a stand, or it could take a whole day or more if they are buried in the boat.
 
If you have a choice between two different kinds of riser gaskets and they're under $10, just get them both. When I did mine I got the wrong ones and it delayed the job by a week waiting on the right ones. Also not having an order over x dollars meant that I had to pay shipping on top of the gaskets. Also assume that the hot water knock outs from the old ones won't cooperate and just buy new ones up front.
 
You might want to consider changing the hose fittings also, or at least have them available at the time of install. I would count on a full day. And not sure if you have them, but the exhaust manifold to engine studs.......D..........
 
quote:
Originally posted by Cruisers4ever

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the amount of reasonable time will vary significantly depending on access and if the studs/nuts come off freely. any that have to be cut of/stripped are going to add significantly. as others have noted with easy access and no nut/stud issues its a pretty easy job. its unlikely you will get a fixed price that is reasonable as its typically an hourly rate for something that can vary so much.

if access is not too bad, i suggest removing them yourself after you drain the coolant from the block. you will know if there are issues right up front and have a much better idea how much time it should take to put it back correctly.
 
I spent an entire weekend replacing risers and elbows and exhaust hose on both FWC 7.4 Crusaders. But, I'm no mechanic either.
 
I find the hardest part on my FWC engines' exhaust is getting the exhaust hose to release from the cast iron elbow outlet .It takes a long time. There is almost no give on that big thick reinforced rubber hose, and no way to remove the short hose from the muffler end 1st.

I have special pry tools I made by heating big and small screwdrivers with a propane torch and bending the shaft so the tip is angled back almost toward the handle, so I can pull on it to work the tip under the lip of the hose and all around, verrrry reluctantly.
But it still won't break loose until I get the riser/elbow disconnected and raised up & freed off the manifold studs so I can twist the cast elbow very hard and the hose will very reluctantly eventually release if I have prepped it well enough .

However, if replacing the hose, then it could just take minutes to cut the hose off and remove the riser/elbow.

I'm hoping next time when I have switched to blue silicone exhaust hose the hose may release more cooperatively.

Don't forget to deck (or have the mechanic do it) the cast iron gasket mating surfaces. If you use a magic marker or similar to color that surface , then take a nice sharp (new) flat mill file on the surface, you will immediately see what looks and feels really flat, is not at all. File flat until all marking is gone and all is equally shiny metal. My Crusader replacement elbows always come with a note pointing out that "decking" is required for best seal.

On very rare occasions I've done mine (1 engine, & boat in the water) in a couple+ hours and other times it has taken most of 2 full frustrating days, so mechanic hours are tough to estimate.

And you want him to take time to "deck" ( though most won't unless that is requested- you could do it to save billed hours) and keep water out of cylinders and remove all old gasket material, purge trapped air and maybe paint any scraped metal before it rusts. And clean up afterwards.

Once you get the new stuff installed , I suggest you retorque the fasteners to spec after a few runs and heat/cooling cycles.
 
Next time anyone removes water and exhaust hoses, apply silicone dielectric grease. Does not 'melt' or evaporate. The hoses will come off really easy. It's better than anti-seize for bolt threads or electrical connections, too.
 
It would be nice if we heard back from the OP on this or is he another one hit wonder?
 
quote:
Originally posted by jtybt15

Next time anyone removes water and exhaust hoses, apply silicone dielectric grease. Does not 'melt' or evaporate. The hoses will come off really easy. It's better than anti-seize for bolt threads or electrical connections, too.

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I always do that on the hoses & barbs after cleaning off any corrosion . I think it helps but exhaust hoses are always very reluctant for me. I'm about to change to blue silicone high-heat resistant hoses and it will be interesting to see if they give up easier.
 
quote:
Originally posted by Bruce Herrington

Removing the 4" exhaust hoses was my biggest problem also.

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use a heat gun to warm the hose, I found a thin metal cake icing spatula along with a few shots of de-bonding spray worked pretty well on some very well attached 6" hose.

If its a short length of exhaust hose and your time is valuable, its way faster to cut it off with a razor/sawzal and replace the hose.
 
quote:
Originally posted by vic33004

quote:
Originally posted by Bruce Herrington

Removing the 4" exhaust hoses was my biggest problem also.

Click to expand...


use a heat gun to warm the hose, I found a thin metal cake icing spatula along with a few shots of de-bonding spray worked pretty well on some very well attached 6" hose.

If its a short length of exhaust hose and your time is valuable, its way faster to cut it off with a razor/sawzal and replace the hose.

Click to expand...


The heat gun never seemed to make any difference in my removal of the heavily-reinforced thick exhaust hose.

The sawzall ( replace hose) approach may work fine with boats out of water or whose whole exhaust systems are above the W/L. But if like mine in the water , cutting the hose would likely sink the boat.... unless the transom exhaust port was securely sealed with a plumbing rubber pressure-test cap and clamp. .
 
I made a tool very similar to the cotter Pin extractor. Took an old narrow blade screw driver bent it to 90°. Rounded off edges & ground to a thinner blade. Worked great.

BOB J
 
That's what I did but with even more-acute angle to make it easer to pull back toward me along the hose. It is surprisingly very easy to bend screwdrivers or similar steel pieces held in a vise after a propane or Mapp torch heats it red hot. I bend (and thin-out) wrenches to hold hex bases on marine battery studs under the cables, and other more convoluted ones for turning distributor base hold-down bolts and similar tasks. Customized tools like this can be big time savers and handier than a lot of specialized production tools.
 
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