200 hp merc, new power head

[lowercase_j]

just had a new power head installed on my 98 merc efi, it runs good but it is very cold natured and it never was before. it also sounds a little [hard] if that is a good word? just wondering if this is common for break in, or if i should have this checked out.

 

[Texasmark]

Re: 200 hp merc, new power head

What was replaced? Just the metallic block and inner components, or other things too? If so, what things.

Mark

 

[lowercase_j]

Re: 200 hp merc, new power head

the powerhead was replaced with a new one from mercury, all moving parts from my understanding. also a new stator was installed cuz one side of mine was burned, thanks for your response.

 

[Texasmark]

Re: 200 hp merc, new power head

When I troubleshoot I usually try to go from there to here. In short, what were things like before I touched something, and what are they like now. In the process what changed and in that start the process of evaluation.

I just put a new CDI (trigger) module (have one per cylinder in a 3 cyl Merc) in my engine because it fouled out at low speeds when first operated. Like I start it and go park the trailer and come back and motor out to the end of the no wake zone and hammer it. It would stutter and shudder, get on plane, cough some more and in a minute or two all was well and was that way the rest of the day.

So, on a cold (didn't feel like fighting the weather) day I trouble shot the ignition and found that 2 cyl fired just fine on the cold engine, but one didn't fire at all. I got a heat gun and heated the non-firing module and tried again. Wala, had spark. The new module is in and I haven't had it out yet for the test run. The DC resistance of the secondary of the bad module did measure slightly lower (20 ohms) in resistance than the other two (which read exactly the same) and the new one which measured slightly less (8 ohms) than the other two, but the new one was a later dash number part which could have affected the reading.

There has to be a certain amount of noise associated with a new engine, but I wouldn't think all that much. I have bought several new outboard engines over the years and broke them in and there wasn't much noise at all.

Only thing that comes to mind on your thermal mention is that maybe there is some (physical interface-something touching) problem with the new stator and the flywheel that may correct it'self with temp changes. Since the stator is just a potted soft iron core with a bunch of wire wrapped around it, I would think that it wouldn't necessarily be the cause of your concern (internally). But, who knows. Anything new can have defects.

Or, you man have had trigger problems prior to the swap-out and didn't know it.....or something could have just decided to get finiky.

Best I can do,

Mark

 

[lowercase_j]

Re: 200 hp merc, new power head

thanks mark, your info is much appreciated. my mechanic is the best around and he is very busy, it would probably take two weeks just to have him look at it, so i didn't want to be without a boat just being picky. thanks again.

 

[achris]

Re: 200 hp merc, new power head

very first question..... Why was the powerhead replaced?

Chris.............

 

[lowercase_j]

Re: 200 hp merc, new power head

i poped the #6 piston. don't know why, but the motor was rebuilt about two years ago by the previouse owner, maybe something happind to it then.

 

[achris]

Re: 200 hp merc, new power head

i poped the #6 piston. don't know why, but the motor was rebuilt about two years ago by the previouse owner, maybe something happind to it then.

Or maybe the first re-build didn't fix the root cause.

Unless you find out why the previous power-head(s) failed, there is a good chance it will do the same thing again...

Define "popped"... tore up the ring grooves, blew a hole in the middle, detonated???

Chris...........

 

[lowercase_j]

Re: 200 hp merc, new power head

detonated, that's the word my mechanic used. he said the corner of the piston was gone.

 

[achris]

Re: 200 hp merc, new power head

Detonation can be caused by a few things including over-advanced ignition timing, low grade fuel, over propping, lean mixture just to name a few. Find the cause of the detonation or, I guarantee, you'll kill the new one too. Check the triggers for correct timing on ALL cylinders, not just #1. Have the carbs over hauled and fit a new diaphram kit to the fuel pump. Also check the fuel pump hoses (the ones that run to the block), if one is cracked it could let air into the engine and cause that cylinder to run lean. I can't remember which cylinder runs the fuel pump on those engines.

What boat and prop are you running? and what was WOT before #6 'took leave'?

Chris..............

 

[lowercase_j]

Re: 200 hp merc, new power head

I'm running a ranger r91 with a tempest 26 pitch prop, when #6 took a crap on me i was running a tempest 25 pitch @ 6200 wot. my mechanic replaced all fuel lines and hoses, he also seamed to think that low grade fuel could have been a factor.

 

[achris]

Re: 200 hp merc, new power head

Don't forget those 'drive' hoses for the fuel pump. They get overlooking very frequently....