Questions about manifolds

[Animal223]

I have a 1990 Mercruiser 5.7L Alpha 1. I boat in salt water, but it's a trailer boat and I flush it out on the muffs after each time I go out. I've owned the boat now for 3 years, and never done anything to the exhaust manifolds and elbows. I do not know when the previous owner last replaced them (if at all).

My questions are 1) how do I know when to replace them (preferably before some catastophic failure), 2) how would I inspect them? Anyone got photos of OK versus not OK? 3) After inspecting, would I need new gaskets if the manifolds are in OK shape, or can I re-use? 4) is this a job a moderately mechanically inclined do-it-yourselfer can do, or should I save it for the pros?

Thanks for any help you can give. I want to do the proper maintenance, but I also don't want to replace (expensive) parts needlessly. For what it's worth, I don't overheat. Tops of elbows get fairly warm to the touch (not super hot, but hot enough I don't want to hold my hand on them for more than 4-5 seconds or so) - but they are both about the same temp. No indication of water getting into the cylinders but of course I don't want to get to that point!

 

[John_S]

Re: Questions about manifolds

I would say you are due to inspect them. Getting close to end of season, you might be able to hold off, if Murphy doesn't visit you as often as I.

http://forums.iboats.com/showthread.php?t=220340

Check this thread and the post from Don. It should answer 1 and 2. 3 and 4 are both yes.

 

[Rob454]

Re: Questions about manifolds

From what I understand the manifolds shoudl be replaced periodically. Id say every 5-6 years sooner if you go in salt water and dont use a salt dissolving product. I used to use my jet ski 98% of the time in salt water. i used salt away and when I sold it the guy asked to pop the head to look in the water passages. ( I had a o ring removable head) so i did it there was not a speck of rust corrosion or any foreign matter. the cylinders looked like they were factory fresh at the water passages. The ski did not have a trace of rust or corrosion. This was a ski that was used constantly in the ocean. About 180 hours when I sold it andf 160 or so were on the ocean.im a firm believer in a salt dissolver. I jsut got a good deal on some salt X so Im using that up.
As for the gaskets I personally wouldnt reuse them unless its a matter of life and death otherwise its not worth possibly damaging a motor for a set of 20$ gaskets.
I dont see why you couldnt do it yourself as long as youre somewhat mechanically inclined. if you dont know a open end wrench from a torque wrench then let someone who knows do it.

As for inspection just look at the water passages. they should be fairly clean with some build up of calcium salt etc. if the passages are full of crap and look clogged then it may be time for a new set.

 

[Don S]

Re: Questions about manifolds

From what I understand the manifolds shoudl be replaced periodically. Id say every 5-6 years sooner if you go in salt water and dont use a salt dissolving product.

A lot of this hearsay stuff is just a bunch of bull. 5 years is a good time to start pulling the risers yearly, clean the gasket surfaces, inspect the surface area of manifold and riser and check for clogging of the passages. I didn't say clean them, just inspect.
If you clean them, you lower the lifespan. Because all that corrosion is stopping some minor defects and potential leaks.
If they look like they are plugging up, and the temp has been fine, you may have a year or so to go.
My experience on plugged manifolds is that you start seeing the temp go up 5 degrees for a while, then 10..................... THEN you have an overheat.
Read the signs, if it starts running 5? warmer than normal, you have a problem.
Keep the impellers changed every other year so you don't compound your problem with clogged exhaust and old worn impeller.
Keep up with the maintenance and inspections, and you won't loose an engine

 

[Chris1956]

Re: Questions about manifolds

Animal, If you flush the engine with fresh water each time you use it, the manifolds and risers will last a long time(10 years +).

The first sign of riser/manifold failure is the part of the riser that is under the rubber tube. They get a rust hole in this area. It is easy to inspect, by sliding the rubber sleave back over the alunimum elbow. If it is intact, it it likely the manifold is OK.

 

[Animal223]

Re: Questions about manifolds

Thanks everyone for the help. I bought new gaskets and intended on inspecting the manifolds and elbows as Don S. suggested. I'm following the service manual for disassembly and I'm stuck at the step "Remove exhaust bellows."

Is there any trick to getting those rubber sleeves to move? I figured it should slide aft, over the mating exhaust tube, but I can't get it to move other than rotate. Won't slide off the lip on the elbow. I figure I must be doing something wrong because it doesn't look like it should be that hard.

Thanks and sorry if this is a dumb question.

Jared

 

[Bondo]

Re: Questions about manifolds

Ayuh,.......

As you remove the Riser,...... Things can Slip apart.......

It's not so much as removng part A, Then part B,.....

It's more like getting Everything Free,+ Disassembling it..........

 

[Animal223]

Re: Questions about manifolds

Thanks Bondo - came right apart once I unbolted the riser.

It looked to me like the riser was pretty rusty inside, although the manifold isn't bad, but seeing as how I don't know what normal is, I wanted to run some pictures by the experts for an opinion - replace or no?

Jared

 

[krisnowicki]

Re: Questions about manifolds

so other then clogging and leaking how do they go bad. I understand that the have to have a flat surface to meet flush with the block but other then leaking and clogging how would an exhuat maifold go bad

 

[rodbolt]

Re: Questions about manifolds

looking at the salt scale in the exhaust port, I would not reuse the riser.
10 + years in the salt pond? ya have a death wish or very deep pockets.
but it looks like the riser has been "bleeding". cast iron is very porous, once the salt is in the pores I dont care what snake oil is used, it rusts.
you have to remember, you have very corrosive hot gasses on oneside of a thin piece of cast iron and very corrosive hot saltwater on the ther. eventually the two will meet.

 

[Animal223]

Re: Questions about manifolds

Any thoughts on the manifold? No rust and salt in the exhaust passage, and it looks like minimal rust in the water passageway.

Are the riser and manifold typically replaced as a matched set, or would it be OK to leave the manifolds and replace the risers?

 

[Scaaty]

Re: Questions about manifolds

A 1990 in salt, flushed or not, is due. Less than $400, and ya be good to go 10 more if flushed, and using Saltaway...
You are on borrowed time. The problem is the salt is eating a away at the BOTTOM of the mans all these years, where ya can't see. ... and a little pinhole, ya got a cylinder/motor fulla salt water...