When to replace risers and manifolds? or check? - The Hull Truth

rpbolling · 10-23-2005, 06:43 PM

I have had several posts in the last few weeks looking at several boats. The particular boat I'm talking about is RWC and has Mercruiser 454's. One of my main concerns is from a recent survey. If I wasnt reading very carefully, there is one line that says "during seatrial, active water leaks at inboard and outboard exhaust risers/manifolds". Thats it. Nothing else about this. These engines are supposedly new and replaced Crusaders in 2000. They are pretty low hours and really only been used in fresh and brackish water with some in gulf. Anyway, I have been on the boat a couple times since then with the motors running for 15-20 mins each time. Now we weren't underway..just at idle, but I did not notice any water coming out of them. Also, I took my mechanic (an "old salt" who makes his living free lancing working on boats) and he said they looked good to him..and he felt them while idling and said they felt "good" and even heat with no 'hot spots' So, how do you tell if they need to be replaced?

Can you do anything besides removing them? How much work is it to remove them to inspect them....especially when its not your boat? What gaskets do you buy to replace?? Yea.. I know...get an engine survey. The problem is...with Katrina and Rita, It will be months before I can get someone to come look at it. I contacted half a dozen people. If anyone knows of someone in the Mobile, Biloxi area please let me know.

Any suggestions are appreciated.

Thanks.

a7ewizard · 10-23-2005, 08:37 PM

I was told to replace mans and risers at about 500 hours (5-7 years for the average boater who runs 50-100 hours a year).

You can separate the riser and have a peak down into the manifold to look at the extent of rust and scale and to inspect the mating surfaces. Since the guy was to cheap to install FWC, you can assume the engine water jackets are in about the same condition as the manifolds.

Furthermore, if water is seen leaking at the riser joint, those engine(s) may have some internal damage from hydraulic locking...a compression test is needed.

Good luck!

richinct · 10-23-2005, 10:28 PM

I agree, 5-7 years is about right for manifold/riser replacemant in salt water, it is a part of routine maintence with inboard engines. If the are leaking out at the riser to manifold joint then they are probably leaking in also, not enough to hydro lock the motor if just seeping. You can take them off and look inside for traces of rust in the exaust ports, they can also be pressure tested with the right block off plates. No test is reliable though, you just don't know how thin the walls have become. Since these are 5 years old I would try to negociate the price to replace them in the selling price. You will have peace of mind for at least the next 5 years or so. Engine hours are not a good indicater of the manifold condition, once the salt is in there it continues to do damage even just sitting.

rpbolling · 10-23-2005, 11:56 PM

Thanks....I'm glad I asked. I hope to find a surveyor to give me some good information.

rpbolling · 10-24-2005, 12:13 AM

Would I be able to tell about the engines from just starting them and running them at idle?

So how much to replace them? What should I want knocked off the selling price? Thanks.

surfnfish · 10-24-2005, 12:53 AM

a7ewizard's suggestion of separating the riser from manifold is relatively easy. Gaskets for this interface should be replaced if you pull this apart. They're easy to get. Use a small mirror and high intensity penlight to check the typical wear point at the turn in the riser. Check prices at OSCO for superior aftermarket replacements. To be safe, assume that all needs to be repalced. I pull off risers and manifolds every 4 years and have them cleaned at a radiator shop. (Chrysler 360 FWC). Also be certain that in the design of this vessel, the high point in the riser is sufficently above water level to prevent seawater from backing down the exhaust. Good luck.

richinct · 10-24-2005, 05:20 AM

Osco are good manifolds, goggle Osco and you should be able to find prices. About 7 to 8 hundred per engine, plus probably 8 hours labor
Try this link http://bpi.ebasicpower.com/Merchant2...ode=CRUEXHKITS

mb_24 · 10-24-2005, 08:03 AM

Quote:

rpbolling - 10/23/2005 11:13 PM

Would I be able to tell about the engines from just starting them and running them at idle?

So how much to replace them? What should I want knocked off the selling price? Thanks.

As far as engines telling a story at idle, they don't. You have to have an engine under load to see what the effects are. And that doesn't mean just revving them to 3400 rpm and observing.

Case in point, recently surveyed a boat. Everything looked fine, normal wear and tear. Sea-trialed and a weld on heat exchanger popped and was spraying salt water in the engine compartment. Surveyor saw it, not me since I was running the boat.

Got back to the dock and the surveyor tried to show me the condition. Couldn't replicate it since the engines weren't truly under load.

When negotiating around a pre-existing condition, just beware the comeback that you're buying a used boat, and everything is got wear. That's why it doesn't cost list price.

Good luck

rpbolling · 10-24-2005, 01:34 PM

The question I have to all you guys, it how do I know if it's done any damage to the motors if they are bad. At survey, starboard engine was about 400 rpms lower than the port (4400 port...4000 starboard) at WOT. The props were reported to be ok so this shouldn't have been observed. Would a compression test solve this? Thanks.

hlights2 · 10-24-2005, 02:18 PM

A compresion test and check the oil - if water is getting in, it'll have a milkly look to it.

djcxxx · 10-24-2005, 02:56 PM

I just changed the risers out of my 01 7.4MPI Crusaders and they were definitely ready for a change. The FWC on the Crusader includes the mainfolds and they looked practically new on my engines. I would have a mechanic break down the risers and mainfolds for an inspection before I bought the boat. Remember the block is RWC as well. I would get a separate engine survey before I bought RWC Mercruisers. But I wouldn't choose to repower an inboard boat living in salt with a RWC system, and I wouldn't replace any Crusader with a Mercruiser but that's just my opinion.

rpbolling · 10-24-2005, 04:57 PM

I agree with you dj, and thanks for the info on the Crusaders as well. The boat was basically in fresh water all its life until the present owner bought the boat about a year and a half ago. It was repowered when it was in freshwater. And I"m looking for an engine surveyor....but can you believe they are very few in AL and MS? Thanks.

richinct · 10-24-2005, 05:19 PM

A compression test should be done no matter what, it won't 'solve' any problem, only tell you if a problem exists. You didn't give any info on the boat but I assume with twin 454s you are paying more than a few dollars for it. I would be a little concerned about the difference in RPMs. You said the props were ok. Don't let the seller tell you something like 'it's probably something simple like a tune up' ... A compression test will tell you a lot, you already had the boat surveyed so all you need is a marine mechanic to do the compression test. The seller will probably require that he be licensed and insured which is understandable.

rpbolling · 10-24-2005, 05:58 PM

I am trying to attach pictures of the engines...what do you think?

rpbolling · 10-24-2005, 06:20 PM

Didnt work on here...what they show is rust at the joints to the manifold to riser and riser to elbow.

richinct · 10-24-2005, 06:33 PM

Quote:

rpbolling - 10/24/2005 5:20 PM

Didnt work on here...what they show is rust at the joints to the manifold to riser and riser to elbow.

Doesn't matter, no one could give you an accurate assessment from a pic

rpbolling · 10-26-2005, 05:39 PM

The owner is still telling me that they are not in need of "immediate" replacement if they leak at the joints. He says I could get another season out of them. I don't buy this.

richinct · 10-26-2005, 06:01 PM

With new gaskets, you might get another season, you might get 5 more...the problem with diagnosing manifolds is that the deterioration takes place on the inside...it is really a roll of the dice...the average life in salt water is 5-7 years, that is the bottom line, maybe you can negociate for 1/2 the replacement cost...I don't know what kind of boat this is or what the asking price is but if the cost of manifolds is gonna be a deal breaker the walk on it.

I believe this horse has assumed room teiperature