Replace 454 manifolds

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firstlight

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I have two 1993 454 f/w/c mercruiser engines. I noticed a lot of rust on manifolds and when I first start engines they smoke from where the mainfolds meets the head, then once engines warms up smoke stops. The bolts are pretty much rusted and rounded out. How difficult is it to remove and replace manifolds ? They are original do I need to replace? Thanks for the advise.
 
If the bolts are badly rusted it could be a real job. Soak several time with a good penetrating oil .. Sears carries some sockets that can help with rounded off bolts. Good Luck!!
 
Yes, I would replace them.

How difficult is often a function of workable space and how rusted the bolts are.

While you are at it, I would replace the risers too.

I would remove and replace as one unit each side (risers and manifolds). This combination will be HEAVY, but with proper planning and yankee ingenuity, it can be manageable. I lay a 4X4 post across my gunnels and use a line and pulley to raise/lower the manifolds to the engines.

If the bolt heads are that rusted, I would actually spend very little time fussing with them and just cut them and slide the manifolds off, and then remove the bolts.

Make sure on your new manifolds you clean them out with air, as debris can be stuck in them when shipped (I have blasted out styrofoam popcorn things before that I never saw). Make sure there is no paint on the mounting surface and that it is flat and true.

Remember to replace the hose fittings as well, and remember to buy the gaskets.

Wjen re-mounting the manifolds, take two bolts that are longer than you need and cut the head off. Screw these into the block and mount your manifold. Now, put in two of the final mounting bolts and remove the two studs you created and finish mounting. (The studs make it much easier to align everything).

Overall this is a basic, bolt off, bolt on job, and is DIY friendly.
 
My '93, 37C has 454XL FWC engines. They "DO NOT" have risers but do have exhaust elbows. If the manifolds are FWC; they should last the life of the engine. Maybe you just have a bad gasket?? I replaced my elbows several years ago; didn't touch the manifolds.
 
quote:
Originally posted by Bob J

My '93, 37C has 454XL FWC engines. They "DO NOT" have risers but do have exhaust elbows. If the manifolds are FWC; they should last the life of the engine. Maybe you just have a bad gasket?? I replaced my elbows several years ago; didn't touch the manifolds.

Click to expand...


Its the same thing
 
Just for clarification, risers are what many people are now erroneously calling elbows and refer to risers as the spacers.

If you boat in salt water, your chances of the exhaust manifolds at the riser mating joint rusting/leaking increases 5 fold over fresh water run boats irrespective of raw or FWC systems.
 
Since they are Mercs, it's possible the "f/w/c/" system is only a 1/2 FWC setup, with A/F coolant only in the block & he/ex, not the manifold.
If... that's the case and they are original, the 17 yr old manifolds are perhaps 12 yrs past due for pre-emptive replacement.

If you are pretty sure they need replacing, and the mounting bolts are resisting normal effort, you may be able to take a maul & cold chisel and break the narrower flange casting around the bolt to remove the manifold and still have plenty of bolt to grab and hopefully turn out after several bouts of penetrating solvent application and patience. 1st try moderately banging straight on the bolt heads a few times to possibly help break corrosion bond at the threads and manifold flange to see if they will wrench out. As ITK notes , manifolds and "risers"/"elbows" are heavy , and can be awkward to lift. Personally, I'd prefer to separate pieces to minimize risk. (i.e., Paper beats rock, manifolds beat fiberglass hulls. :D )

Removing or replacing, the replacing of 2 bolts with temporary studs that ITK suggests is a very common, extremely handy trick to help keep things from dropping unexpectedly and afford easy reinstall alignment.
 
In the Know.........the part# CR 2098128 is a riser in my little world. The part# 2098126 is my exhaust elbow. My engine does not use part# 2098128.

Barr211.jpg
 
Bob:

CR 1 98243 = Manifold

CR 20 98126 = Riser

CR 20 98128 = 3" spacer block

"Just for clarification, risers are what many people are now erroneously calling elbows and refer to risers as the spacers."

Looks like Charlie was correct.
 
The terms riser and elbow may refer to different parts in the Mercruiser vs Crusader diagrams and parts lists. (In general, Mercruiser spacer = Crusader riser, Merc riser = Crusader elbow , and at least some older Crusaders and maybe other mfgrs had another simple cast "elbow" (w/o RW injection) between 2 sections of exhaust hose. And many parts supplier list the same part just for Mercs as either riser or elbow ( where RW is injected into exhaust stream.) And there seems to be no distinction with those terms as to whether exhaust mix exit is directed more aft or downward, so elbow doesn't denote more curve.

It certainly can be confusing. That's why I put "riser"/"elbow" above in quotation marks .
 
Promise, I'll drop it after this. In Crusader parts catalog for 454XL engine. On page 36; part# 98128 is called Exhaust Riser. Same page, part# 98126 is called Exhaust Elbow. Page 56 in same parts catalog show Elbow with Riser on starboard side & Elbow w/o Riser on port side for demonstration purposes. I'm done! NO MAS !
 
Thanks for the response. The manifolds are NOT saltwater cooled however they show rust and are 17 yrs. old. Not sure if I should attempt to change or follow rule, if it's not brokwn leave it alone. I am aware of the risers and required replacement. Thanks
 
" if it's not brokwn leave it alone"

If the manifolds are infact 17 years old that rule can lead to VERY expensive repairs!!
 
If manifolds are part of a "full" FWC system; meaning the manifolds are cooled by an enclosed system using antifreeze, they should last the life of the engine. Same as on a car. If you see rust; determine where it is coming from. It c/b nothing more than a gasket needing replacement.
 
That smoke may be just oil from valve covers burning off. If it were an exhausrt leak it would give a clacking noise.
 
OK so now I have two logical opinions, one change them two they last the life of engine
If it was a simple job I would just do it but it is tight and the bolts are rusted and rounded out. What to do!
 
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