Exhaust manifold and riser

[Uncle Dave]

I have a 140 Hp Mercruiser. 4 banger. '86 or 87<br /><br />It appears the exhaust manifold or riser have never been changed. They look excellent on the outside.<br /><br />Any way to "check" them out with out removing? Would slight tapping with a sharp tool be advisable? Thought being that if it nearly rusted through then the tool will easily break through. Better in the barn than 25 miles off shore.<br /><br />Put another way. Will a nearly rusted thru one show signs of seepage before the gusher comes?<br /><br />Thanks,

 

[tommays]

Re: Exhaust manifold and riser

dave<br />they rust from the inside and then leak into the exaust and other than the riser cloging dont really give much warning other than leaking and causeing engine damage<br /><br />it sounds like your in saltwater and if they have allways been used that way you have gotten a long time out of them<br /><br />tommays

 

[Bondo]

Re: Exhaust manifold and riser

Hi Uncle Dave,<br /><br />Welcome to the forums here at iboats........<br />

Any way to "check" them out with out removing?

No......<br />

Would slight tapping with a sharp tool be advisable? Thought being that if it nearly rusted through then the tool will easily break through.

Nope,...... It don't work that way......The Most Common rot out area is where the Manifold,+ Riser Meet.........<br />And, Most of the Rusting occurs on the Inner Exhaust passages, Not between the waterjacket,+ the Outside........<br />

Will a nearly rusted thru one show signs of seepage before the gusher comes?

Usually..... But Not Always......And,... If it Does, It'll be Internally.........<br /><br />Good Luck............

 

[Uncle Dave]

Re: Exhaust manifold and riser

Thanks for the prompt replys.<br />Actually I am not new. Just had some problems with Netscape browser. (a cookie thing). I tried a new handle and that didnt work either. I had to get the cookie thing resolved. Works fine now. Old handle Mr. Fitz. I'll just keep both.<br /><br />Back to the riser. Most failures give suttle hints of inpending doom. Will this manifold do that.<br />This boat (trailered) has spent most of its time in the barn. And is low hours.<br /><br />Uncle dave/ Mr. fitz

 

[tommays]

Re: Exhaust manifold and riser

dave<br />no one can say for sure but a big factor is if the motor was flushed with fresh water after ever salt trip<br /><br />but even for fresh water use there pretty old because even sitting in your barn the manifold had water in it unless you drained it after use<br /><br />tommays

 

[trog100]

Re: Exhaust manifold and riser

I am pretty much in the same "boat" dave.. 88 engine which i think has the original manifold and risers on it.. the boat has been in fresh water for the last four years.. everything looks okay on the outside and the engine runs perfectly..<br /><br />i do not intend spending several hundred UK pounds to replace the lot just in case.. i might be wrong but thats my way..<br /><br />sooo.. any hints as to what to keep an eye on would be usefull to me as well as u.. obviously looking for steam coming out the exhaust aint gonna work.. he he <br /><br />i would imagine quite a few others would be interested as well... they probably dare not ask or know the answer they are likely to get so dont bother.. <br /><br />it might be prudent to use helicopter methods of maintainance in some cases on boats but i aint overly keen on doing it.. my boat is only used on rivers mostly at low speed.. so it isnt a life or death situation for me.. if it was i might take a different view..<br /><br />so apart from this imminent doom stuff if u dont replace them immedately.. what symptoms/damage would we get when the things do actually start to leak..<br /><br />general misfires.. rusted valves.. rusted cylinder walls.. water in the engine oil.. all seem things that can be kept an eye open for.. assuming reasonable vigilance.. is without warning engine wrecking hydrolocking a real possibility... ???<br /><br />trog100

 

[Uncle Dave]

Re: Exhaust manifold and riser

I am not trying to de-rail my own thread ,but,<br /><br />I have had no experience with hydra-lock. But have heard from several who have.<br /><br />My question is rather theoretical I would guess.<br />If far off shore and hydro lock occurs. It could be from wave action while stopped or a rusted out manifold.<br />Whatever the cause would it be possible to remove the plugs, spin the engine and remove mostof the water. <br />Then get the engine restarted. If its a busted manifold would it run long enough to get in. Or would time be better spent trying something else. Such as saving the battery for bilge pump or electronics. Even an engine at idle is better than none.<br /> I like to think some of these things out prior to setting "sail".<br />Uncle dave/Mr. Fitz

 

[KaGee]

Re: Exhaust manifold and riser

I never hydro locked, but the motor ran crappy. Pulled the plugs... sho nuff... water! Checked the dipstick.... milky.<br /><br />Mine just went without warning.

 

[Dunaruna]

Re: Exhaust manifold and riser

Water doesn't compress, hydrolocking usually causes irreversible damage (bent valve, bent conrod etc). In a situation that you have described, pulling the plugs and trying to flush out the pots is definetly the first thing to do and then hopefully limp home - but usually the fat lady has sung.<br /><br />I never go 'far ofshore' without at least a companion boat, plenty of fresh water (enough for 2 weeks) and a well maintained kicker.<br /><br />Aldo

 

[trog100]

Re: Exhaust manifold and riser

"I never hydro locked, but the motor ran crappy. Pulled the plugs... sho nuff... water! Checked the dipstick.... milky."<br /><br />i can live with that kinda failure.. not so sure about that fat lady singing thow..<br /><br />"My question is rather theoretical I would guess."<br /><br />well dave.. it sounds pretty practical to me.. he he.. we now know u cant tell by what they look from the outside.. that leaves the other important question.. if they are an unknown quantity.. do u replace em before they fail or wait until they do fail.. ???<br /><br />kaygees answer tends to make me think wait until they do fail.. Dunarunas fat lady singing has me worried thow.. he he<br /><br />"I never go 'far ofshore' without at least a companion boat, plenty of fresh water (enough for 2 weeks) and a well maintained kicker."<br /><br />that one sounds a wise precaution as well.. my boat does have a kicker cos it used to be mainly used for sea fishing.. but its well and truely riverlocked now.. thow i will probably take it down to the coast next summer..<br /><br />trog100

 

[tommays]

Re: Exhaust manifold and riser

water from bad manifold/elbows kills more motors than allmost any other cause<br /><br />if your motor is in great shape the cost of new iron before it fails is far less than hopeing your going to get luckey enough to change and hour before it fails <br /><br />it sounds like you got 19 trouble free years how many does anybody really expect<br /><br />tommays

 

[Uncle Dave]

Re: Exhaust manifold and riser

if your motor is in great shape the cost of new iron before it fails is far less than hopeing your going to get luckey enough to change and hour before it fails<br /><br />it sounds like you got 19 trouble free years how many does anybody really expect<br /> <br />Now that seems to most logical<br />Any idea as to where to find after market iron?

 

[Uncle Dave]

Re: Exhaust manifold and riser

Thanks to all that have given me input on this thread!! <br /><br />And do continue on if you like

 

[Uncle Dave]

Re: Exhaust manifold and riser

Greetings all,<br /><br />I just "inspected" the prospect of manifold inspection/replacment.<br />It seems: remove the carb. remove 5 bolts. remove a hose and the manifold is off.<br />There appears to be a plate (about 4inches) on each end.<br />The question is can the manifold be adequately inspectd with it off and the plates and the riser removed?<br />Again 140 hp mercruiser 4 cy 1987

 

[Don S]

Re: Exhaust manifold and riser

Those end plates were basically used to cover the hole made by the core of the mold when the manifold was cast in the foundry. Had to have some way to get the sand out.<br />All you will see when you take the end cap off is the first half inch of the insides, then the rest is invisible. So to answer your question, NO, it will not provide for an adequate inspection.<br />You may be able to pull off the riser and manufacture a block off plate where you can pressurize the water passage, and that will tell you if there is presently a leak or not, but not how thin the wall are or anything else about it.<br />You could probably get the thing X-rayed for closer examination, used to do this to castings when I worked in a foundry. Should only cost around 1000 bucks.<br />In reallity, if you pressure check it and it's good, run it. Just be aware that it could go at any time. Then if the engine suddenly starts running rough, immediatly check for water on the plugs. The engine will not hydrolock when the leak first starts, and as long as you catch it early and don't let it turn into a massive leak you "MAY" be ok.

 

[trog100]

Re: Exhaust manifold and riser

that one is good enough for me Don.. my "old" engine that runs and looks okay will stay doing just that untill it shows signs of doing otherwise then it will get immediately investigated..<br /><br />immediate investigation.. is the key here i think.. lack of which is probably the thing that kills most things mechanical when it bottoms down to it..<br /><br />trog100

 

[Uncle Dave]

Re: Exhaust manifold and riser

Thanks Don,<br />Your input is highly regarded!!

 

[lakelivin]

Re: Exhaust manifold and riser

Originally posted by Don S:<br /> .....In reallity, if you pressure check it and it's good, run it. Just be aware that it could go at any time. Then if the engine suddenly starts running rough, immediatly check for water on the plugs. The engine will not hydrolock when the leak first starts, and as long as you catch it early and don't let it turn into a massive leak you "MAY" be ok.

Using the 'no question is stupid if you don't know the answer' principle, here goes: <br />I know the earlier the better, but do you mean 'stop the boat in the water & get a tow home' immediately (like if oil pressure drops severely) or 'you're probably ok driving 3 or 4 miles home and then replacing it before you take it out again' immediately?

 

[Don S]

Re: Exhaust manifold and riser

You're trying to get me to put a hard fast rule on something that doesn't follow the rules. <br /><br />If you notice the engine is starting to misfire at idle, when you get parked/anchored, check it out. If you can't hardly keep it running at 2000 rpm, shut it off and call for a tow. You have to make a common sense call on this one.<br />It could be bad spark plugs, bad points, bad plug wires or....who knows, maybe even water getting into the cylinders. What I'm trying to say is if you notice something going wrong with the way the engine is running, find out what the problem is. Don't wait for 3 more months till you pull the boat out of the water for a scheduled inspection, or next spring when you have the money. Find and fix the problem, (What ever it is) before it damages something else.

 

[TwoBallScrewBall]

Re: Exhaust manifold and riser

Listen. Drop the $400 on the new manifold and riser and be done with it. The warm fuzzy feeling you'll have KNOWING the condition of your new manifold, and the fact that it will likely save you lots of $$ in engine repair, are worth it. $400 is a lot of cash but nobody ever said boats were a cheap hobby. <br /><br />I had an 88 3.0. I know what it costs and how much work it is to replace the engine. Replace the manifold. You're worried about it and asking about it here for a reason, right???<br /><br /> <br /><br />Good luck!