Replace Exhaust Manifolds

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  #1  
Old 06-30-08, 07:32 PM
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Question Replace Exhaust Manifolds

I have a 1987 Four Winns 190 Horizon with a 4.3L Mercruiser 175 hp engine. Exhaust manifolds cracked and need to be replaced. I found two different types of manifolds one is ceramic/ edp coated and the other is non-ceramic but painted manifold. Any real difference that should be noted? Also, I was told that replacing the manifolds is something one can do on their own rather than taking it somewhere and paying all the labor fees. I do not know too much when it comes to boat engines but can maybe fool around and try to figure it out with a few friends... just need to know exactly where I am looking on the engine for this part to take off and replace???? Any help to start this project would be greatly appreciated... thanks in advance.
 
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  #2  
Old 07-01-08, 05:37 AM
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Replacing the manifolds is pretty straightforward. Heavy/dirty, but not technically difficult. I just replaced mine last weekend. Typically, when you replace the manifolds, you also replace the exhaust risers that are situated on top of the manifolds.

For the most part, and this is simplified, the old manifolds are disconnected from the cooling system (hoses), unbolted from the block (2 bolts at each exhaust port, usually rusted and hard to remove at that age, and removed. This is a good time to clean up around the valve covers (replacing those gaskets is a good idea at this time) and block. Replacing the spark plugs is a breeze also with the manifolds removed.

Clean the block exhaust ports (remove old gasket), and install the new manfolds - followed by the new risers - reconnect the hoses - and go to the lake.
 
  #3  
Old 07-01-08, 06:59 AM
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Thanks for the quick response. How long did it take? Did you follow some instructions or just general knowledge of boat engines? Where did you order your manifolds from? I think I have pin-pointed the correct replacement manifolds for my engine but am not 100% sure. I found I can buy two manifolds for $300 online and then just try to install myself. I am in college and already put a good chunk of money into the boat last summer because I had no idea what was wrong with it so I am trying to save money this summer and do it myself. I just want to get the boat in the water... half the summer is already gone. Thanks again.
 
  #4  
Old 07-01-08, 07:53 AM
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Been doing engines forever.. hence, just know how to do it... though, I must say - it's pretty straightforward - take one off, put new one on..

Why do you think you need to replace them? Are they leaking, or what? Though, at the age of your boat, it's probably a good idea to spend a few hundred now rather than a few thousand to replace the engine when the manifolds fail due to water intrusion from a leaky manifold.

Takes about a half hour/side when you know what you're doing... There are no instructions with your new manifolds.

I'll be happy to work with you on your project - PM me and we'll go through the specifics including which ones are the proper manifolds to purchase. We'll need model numbers/year/etc., to make sure you're on the right track. though - again - why do you think you need to replace them - to begin with.

Not familiar with your 4.3 - but assume it's a v-8 rather than a 6 cylinder.. let me know. Easy enough to find out - but I've got to run for now...
 
  #5  
Old 07-01-08, 06:14 PM
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Do two or three soaks with penetrating oil, way before the job.
Sometimes nuts that won't come off can be freed by tightening them 1/8 turn or so, first.
 
  #6  
Old 07-01-08, 08:05 PM
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Actually I, myself am not sure it is the manifolds; the marina I took it to last fall to get winterized said the manifolds were cracked and needed to be replaced before I put it in the water in the spring. Is there a way for me to actually tell/ see for myself if the manifolds are cracked?

I went out and wrote down all this information from the engine tonight
Mercruiser Alpha One
175/ V6
4.3L
Model: MCM 175

I also found two numbers stacked on the side of the manifold:
89745
20347

How would I go about finding replacement parts? I don't need top of the line parts. Also, I do not know how to private message yet; just signed up the other day and still trying to figure things out.


Thanks again for all your help.
 
  #7  
Old 07-02-08, 09:09 AM
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See your PM for specifics...

As a generality, the exhaust manifold is more or less a "tube inside a tube" with the inner tube carrying red hot exhaust gasses and the outer tube carrying water to cool the exhaust system. If it cracks, especially inside the first tube, then you are prone to having water leak into your cylinder heads, which means a major rebuild when the engine blows a head/piston/ring/rod. A little $$ spent now can save you a lot of $$ later. The riser, which is on top of the manifold, keeps water from the lake from backing up in to the system also (It's at a level above water level) as well as being part of the tube in tube system. Typical life of those parts is "ballpark" 10 years, depending on fresh or salt water use....
 
  #8  
Old 07-02-08, 09:36 AM
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So is there a way to check and see if the exhaust manifold is cracked... how do mechanics do it?
 
  #9  
Old 07-02-08, 10:08 AM
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You can do a visual inspection with a flashlight and body contortions.... Look thoroughly around/under/over/behind each unit - and look for rust streaks that tend to accumulate around cracks. Unfortunately, that will show cracks in the outer tube - but the inner is impossible to check (simply cannot be done, by you nor your mechanic). One of two things happened, he saw cracks/rust marks - or simply warned you based on the age of the boat.

I know you want to save $$ - but I promise, at the age of your boat - you really want to replace them... especially if the boat is/was ever in salt water - which reduces the life of a manifold in half.
 
  #10  
Old 07-02-08, 11:59 AM
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a way to check

I don't do marine stuff, but how 'bout painting the manifold with a soapy water solution with the engine running?
The exhaust gas will make bubbles, and even better bubbles if the exhaust is slightly restricted.

Depending on temp and humidity, like in the winter, the exhaust gas might be visible.

Or scan the whole surface with the open end of a garden hose, with someone at the other end. He might hear the escaping gas.

Can you safely submerge the manifold, like checking an inner tube for leaks?

How 'bout wrapping it with a plastic sheet before it gets hot, and look for bulges due to pressure while the engine is running?

I've never used an IR meter, but if it can detect heated air rather than just heated surfaces, you might see "a plume" coming out of the surface of the manifold where there is a crack.
I think you can rent these meters.
 
  #11  
Old 07-02-08, 12:39 PM
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As the outer jacket is filled with water - and runs at very hot temps, even with the water - then soapy water will evaporate almost instantly - and any water leakage will not form bubbles, but rather rinse away any coating that might remain. Not a bad thought - but doubt you would be successful in this instance... Whatever you do, don't try wrapping with plastic - it will melt instantly close to the exhaust ports - making a nasty, not to mention smelly, mess.

Not to be a PITA - but at 21 years old - those manifolds need to be replaced...
 
  #12  
Old 07-02-08, 01:05 PM
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Thanks for throwing around numerous ideas. I cannot actually say if these are original manifolds on the boat. I just boat the boat last summer and like I said when I went to get it winterized, the mechanics said the manifolds are both cracked and needed to be replaced.

What is the harm in starting the boat right now say if the manifolds are in fact cracked? Will it not even turn over or will it damage anything?

I'm just saying because they may be fine... the mechanics might just be saying that to get some work out of me..? The quoted me somewhere around 700-800 last winter for the labor and parts to fix this problem if I wanted at the time but I waited until the spring so I could take a look myself and ask around.

I can take a picture of the manifolds and email them to you if that would help at all.
 
  #13  
Old 07-02-08, 01:23 PM
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Originally Posted by thezster View Post
You can do a visual inspection with a flashlight and body contortions.... Look thoroughly around/under/over/behind each unit - and look for rust streaks that tend to accumulate around cracks. Unfortunately, that will show cracks in the outer tube - but the inner is impossible to check (simply cannot be done, by you nor your mechanic). One of two things happened, he saw cracks/rust marks - or simply warned you based on the age of the boat.

I know you want to save $$ - but I promise, at the age of your boat - you really want to replace them... especially if the boat is/was ever in salt water - which reduces the life of a manifold in half.
Do the visual - find the cracks... or ask the mechanic to show you his reasoning for suggesting replacement.
 
  #14  
Old 07-02-08, 06:22 PM
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Forgot

Magna Flux to detect cracks,
a candle flame (?) to detect airflow from those cracks.
. . .Dunno'.
 
  #15  
Old 07-05-08, 05:20 AM
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If the manifolds are shot u will often have water in the oil, it will look milky. Don't run the boat with cracked manifolds or u will fry the engine. They probably cracked because the engine wasen't properly winterized. I would not buy used manifolds, it ain't worth it. You need to tear into the engine to see if the intake manifold is also cracked. I will bet $$$ that it is. Try ebacicpower.com for the manifolds. The prices are reasonable & they use to offer free shipping. Don't know if they still do. And get yourself a shop manuel for your setup. Once again, do not run the engine until you fix the problem or u will end up with thousands of $$$ in engine damage. Here's a forum that is an excellent resource, iboats.com.
 
  #16  
Old 07-06-08, 11:19 AM
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I'm sorry dude... but the last post is not necessarily true. If the manifolds are cracked in the outer shell, there will be no water in the oil. Before you get water in the oil, you will get a seized piston due to hydrostatic pressure/failure in the cylinder when water leaks into them on the compression stroke (water does not compress). The manifolds are probably cracked because they're 20 years old and were not intended to last that long. The exhaust manifolds have nothing to do with the intake manifold - which could be/should be just fine regardless of the condition of the exhaust manifolds.
 
  #17  
Old 07-07-08, 10:03 AM
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Smile

Found the part:

http://bpi.ebasicpower.com/p/glm51220/

This was the cheapest place I could find online and it has free ground shipping which will only take 2 days. I will be ordering the part tonight and hopefully fixing by the end of the week. I hope this solves the problem and I can finally put the boat in the water for the first time this season. Thanks everyone for all the help... we still may be in touch though.
 
  #18  
Old 07-07-08, 10:37 AM
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I think you made the right move... many aftermarket suppliers offer better warranties than factory parts - as I found out last week when I got a one year warranty on factory manifolds compared to a 3 year warranty on aftermarket units.

The risers usually (usually) last longer than the manifolds - and could, maybe, kindasorta - still be in good condition - though, I wasn't willing to bet on it in my case - and replaced the entire assembly.

Hope you have fun replacing the nasty/dirty/heavy units... and are able to get the bolts in/out without too much trouble. (Replace the manifold bolts... DO NOT try to reuse them).
 
  #19  
Old 07-07-08, 10:38 AM
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I just ordered new manifolds & risers for my 86 OMC 5.7L.

Both manifolds have a 2" crack on the underside with quite a bit of rust. The startboard side leaks. The engine oil, fortunately, is clean with no evidence of water. I couldn't find evidence of any leaks anywhere else.

The kit should be delivered on Friday and if I can get them replaced that evening I'll be able to get out to the lake Saturday morning.

 
  #20  
Old 07-07-08, 10:43 AM
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Perfect!!!

Your new manifolds/risers will come painted black - with paint over the mating surfaces of the riser/manifold portion and the manifold/block portion. Take a scraper and remove the paint thoroughly - along with sandpaper to a smooth metal surface. It's a PITA - but will keep the gasket seal good over the long run.
 
  #21  
Old 07-07-08, 10:47 AM
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Originally Posted by thezster View Post
Perfect!!!

Your new manifolds/risers will come painted black - with paint over the mating surfaces of the riser/manifold portion and the manifold/block portion. Take a scraper and remove the paint thoroughly - along with sandpaper to a smooth metal surface. It's a PITA - but will keep the gasket seal good over the long run.
Good advice. I have never replaced manifolds before. I replaced a water pump many years ago that had a gasket and I used some red gasket sealer that came in a tube. Should I do that as well? Do you think the existing gaskets will come off clean or will they be stuck to the surfaces?
 
  #22  
Old 07-07-08, 11:44 AM
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Existing gaskets may, or may not come off clean and easy.... Make sure all mating surfaces are clean and dry - use no sealant - shiny side of gasket away from engine - try to find the proper torque specifications for your engine (try the manufacturer of the engine - ie ford/chevy - if you can't find the marine specs) to tighten down the manifolds. While the manifolds are off - this is the time to retorque your valve covers also - unless they're dry as a bone, in which case, don't touch the bolts... (they tend to leak over time, causing a troublesome smoking issue with the engine as the oil drips onto the manifolds/exhaust...
 
  #23  
Old 07-07-08, 11:44 AM
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Originally Posted by ForgottenName View Post
I just ordered new manifolds & risers for my 86 OMC 5.7L.

Where did you get your parts from?
 
  #24  
Old 07-07-08, 11:50 AM
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Originally Posted by thezster View Post
try to find the proper torque specifications for your engine (try the manufacturer of the engine - ie ford/chevy - if you can't find the marine specs) to tighten down the manifolds.
My buddy mentioned torque specs and said it is very important when replacing manifolds. How do you go about doing this? What type of tool/ reference do you use? Is the manual something that is found online for free or do I need to go out and buy my engine manual like I have been seeing online for around $25-30? I'd really rather not do that for a few numbers but if it is the only way and extremely important then I will have to so I know the job is done right. Thanks
 
  #25  
Old 07-07-08, 11:53 AM
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Originally Posted by michigan353 View Post
Where did you get your parts from?
http://www.boatequipmentsuperstore.com/

http://www.boatequipmentsuperstore.c...Manifold-Sets/
The manifold kit was $450 with free shipping.
 
  #26  
Old 07-11-08, 06:28 PM
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Just finished replacing the exhaust manifolds, gaskets, and spark plugs. Boat has power as the horn, bilge, lights, etc. work but when I try to start the engine it just keeps clicking a lot and really fast... it almost sounds like it wants to start but just isn't right now. Oh, also topped off the gas, it has oil, power steering fluid. Any suggestions on what is wrong? All I want to do it get it on the lake for the first time this weekend and its not going my way right now. Thanks in advance.
 
  #27  
Old 07-14-08, 08:01 AM
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Replaced exhaust manifolds and while I had those off, replaced spark plugs. Ended up going back and also replacing the spark plug wires after the manifolds were already back on which was a bad choice. Next time, replace spark plugs (make sure you gap them) and spark plug wires (wires are same as cars) all before putting the exhaust manifolds back on otherwise you will have a difficult time getting down and in there with a wrench to do it properly. Changed the idle because it was running rough... idle not set at black dot on RPM dial. Also tied a new sound system into an accessory port on the dash and replaced the battery with a better marine battery... the person I bought the boat from had a car battery in there. Runs better than it ever did now and can enjoy the rest of the summer on the many lakes around the state of Michigan. Thanks for all the help and assistance out there.
 
  #28  
Old 07-14-08, 09:01 AM
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Good for you... congrats on your new DIY skills
 
  #29  
Old 08-03-08, 02:46 PM
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Replacing Exhaust Risers

Can someone tell me how I should know that it's time to replace the exhaust risers on my Chevy 350? I replaced the exhaust manifolds because they were obviously cracked and couldn't be repaired. The issues I'm still dealing with are: excessive steam coming out of my exhaust, and loss of power at high RPM's. Also, I thought I was overheating but using an infrared scope indicated that I wasn't getting as hot as my old temp gauge was indicating.
Thanks for any input.
 
  #30  
Old 08-12-08, 07:15 PM
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Hi, sounds like you need to charge your battery, and always check and clean your battery clamps.
 
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