Sea Trial-melted raw water impeller and tube?

WaterKrafter

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Jun 12, 2017
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Ahoy, ok, so I finally launched the '83 Marlin 20 with Mercruiser 470 after rebuilding the carb and getting the fuel pump to work after bad fuel, etc. Anyway, she idles, accelerates, gets on plain then after about 40 seconds of what seemed to me as success finally...smoke everywhere! I shut her off and drifted to my slip.
Ok, it was rubber melting apparently from a stuck impeller and water guide tube. I also noticed the exhaust bellows was cracked on the underside.
what I don't know is if the exhaust or cooling system was plugged up from silt/sand that may have entered the system upon my reversing off my trailer in really shallow wated for about 20 feet. I didn't recoqnise it as too shallow but my prop was pretty much submerged about half way into it although I had trimmed up part way.
Meanwhile the impeller was new now it the worst case of a water pump gone bad I have ever seen.
I can't tell what or where the meltdown started or why...
Thanks for reading. If anyone can help me fiqure this out I would be extremely grateful as I hope I didn't break the boat now that she is finally running. I can start her up. She idles 650 rpm but when I pur her in gear...she just stops immediately.
 

Scott Danforth

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on this new to you boat, I assume you didnt replace the bellows when you got it

you said the impeller was new, did you make sure you had water flow?

did you pull the drive to inspect the impeller? how do you know it was stuck and simply not toast from day one

if you melted rubber, you did a pretty significant over-heat

pull the outdrive and check to see what else is damaged.
 

Rick Stephens

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Aug 13, 2013
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Test everything while running on muffs before putting in again. You must have water flow through engine. A plugged up cooling system won't have water pass through the motor into the exhaust and out the back even on the muffs. Easy to test before you go back in.
 

Grub54891

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The impeller housing and water tube are the last in line to melt when there is no water flow. I'd say the flappers are gone, and the boots on the riser are compromised also. Time to go through all of it and hope ya didn't hurt the motor.
 

WaterKrafter

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Geez, Gentleman, I wouldn't even know where to begin to "go through everything"...meanwhile, I dropped the lower unit...I'll need a torch to get the impellar off the shaft. Even the plastic ling from inside the housing has fussed itself upon the rubber fins...I had just replaced it a few months for good measure while working on the carb, pump, and fuel supply challanges.
However, I am anxious as to pulling that impellar off to inspect it furthur. It's rather ironic that just prior to my immediate blunder, I found myself looking down into my hand wondering what I had been fondling carelessly on my desk? It was a KEYWAY! Now unless it was the duplicate from another drive I have for parts, then I reckon It may be that in my haste...I may have forgotton to lock it onto the shaft with the impellar upon installation a couple of months back!?! I can't tell yet for sure until I get it off! I'll try again tomorrow. I'll try to post some fotos...
Yes, my belows is cracked. So now I have that to do as well..
I keep you posted.

Thanks for listening 😵
 

stonyloam

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Dang, that is tough. Yeah leaving the key way out will do it. You had no water flow to cool the exhaust. So for sure your shutters are gone. Pretty easy to replace when you do your engine bellows. 470’s are pretty sensitive to overheating which can cause head gasket failure. If you only ran it for 40 sec or so then you are probably OK because you started burning rubber before the engine had a chance to overheat, but it would be a good idea to do a compression check when you get it running. When you get it apart you will want to look up inside to see if the plastic water pocket cover has melted. They can be a little tricky to replace because the screws can strip or break off, so if it looks OK leave it. Good luck.
 

kenny nunez

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Just like Stony said about the plastic cover in the upper housing. With the copper pipe in the plastic cover get a length of 5/8” auto heater hose connected to a garden hose, this will show if the plastic cover has to be replaced. This is also a test to check if the raw water side has any restrictions. If there are no leaks from under the cover then leave it alone. The chances of breaking those bolts are pretty high.
 

Rick Stephens

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Pictures are really helpful to see how melted stuff is. Hard to have an opinion without.
 

QBhoy

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You sure this isn’t an internal FW cooling caused overheat ? Caused by the usual well known 470 issues.
 

stonyloam

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Don’t think so, the symptoms indicate a lack of raw water flow through the exchanger into the exhaust.
 

WaterKrafter

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Jun 12, 2017
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Update! Final analysis...exhaust belows was cracked in half and as such went unnoticed by me when I launchen her before melt down...I backed her into the drink with a firm yank off my trialer. In addition it was rather shallow so she scooped up all that sand and mud right up through the bellows into the motor while in reverse! Almost really put her down.
However, I pulled off upper and lower, replaced exhaust bellows, upper plasic water tube reciever (without breaking those mounting screws), cleaned it up. Then replaced lower water pump housing and seals, tube, and impellar. Cleaned out passage ways, replaced upper water pump housing and all gaskets and centrifical slinger, etc. In addition to which I back flushed all cooling passages throughout motor and heat exchanger (lots of silt and sand needless to say untill clear).
Went to fire her up...and now I am cranking with no start? So I am hoping all the steam and moisture just corroded some wire connections. I have power and spark to the points, but no spark at the plugs...any suggestion would be great otherwise I guess I'll replace wires, points, condenser, cap, rotor and whatevas eventually, although keep in mind everything is basically brand new! Only 31 original hours on her!
Thanks everyone for your support thus far!
 

Scott Danforth

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have you verified compression?

if your ground to the points is good, and the points are set right, make sure they are clean, and re-set if needed (fold a match book cover in half if you dont have feeler gauges)

from there, +12 volts to the coil while cranking or 9 volts while running and you should have the coil firing

then between the coil and the spark plugs is the cap, rotor and wires
 

WaterKrafter

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Jun 12, 2017
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Thanks Scott...I'll verify today and post back. I did find the insulating plastic coating of the primary contact wire under the cap was or looked like it had melted away exposing the strands of wire within right where it exits the distributer body through and out the little cut away. Being exposed like that I am thing it possibly is shorting everything out? I coated it in liquid electrical tape and will test this morning.
PS. Which post on the coil does this connect to, + or - ?
 

thumpar

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You don't even need the exhaust bellows so a crack in them is not a real problem. Did you make sure the key was in place on the shaft that drives the impeller?
 

Bondo

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Being exposed like that I am thing it possibly is shorting everything out? I coated it in liquid electrical tape and will test this morning.
PS. Which post on the coil does this connect to, + or - ?

Ayuh,.... The points open, 'n close the coil's Ground path,.....

Which causes the coil to fire,....
 

WaterKrafter

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Jun 12, 2017
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Yes, the key on shaft is in place...I already installed exahust belows...successfully...first attempt. Week and a half later it is still holding strong!
more in a bit...
 

WaterKrafter

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Jun 12, 2017
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Well, with all the support here It was successfull in starting like a top after isolating the primary distributor wire with a hot glue gun & dab upon finding it was bare and shorting it out where it come out under the cap before making its way around to the coil. Then having Emory clothed all the battery connections and dual battery switch connects, she fired right and warmed up to idle at 700rpms @ 140-150' degrees steady... It's just that when I shift into gear...she just shuts down. Immediately...No grind or squeal, just off. Right now.
I am pretty depressed. After all of my learning curve and time and efforts. I assumed I had this project conquered...
Anyway, I haven't ever experienced such a malfunction...nor have I any clue or instinct as to what this is about.

Thanks for the guidance and direction herein as this forum and all gentlemen who have seen myself and each other through such incredible feats my hat is off to you! Very compensable contributions and makes it a better world to live in frankly...

Sincerely & Respectfully
Scott (WaterKrafter)
 

Grub54891

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Either the lower shift cable is out of adjustment, or the overheat melted the cable where it passes by the exhaust manifold. It'll hang up and the cutout will kill the motor.
 

WaterKrafter

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Jun 12, 2017
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Captain! Thank you...I read some about just that after posting my armagedon speech. Well, I better get busy!

Too be continued...
 

thumpar

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Like Grub posted. The shift interrupt is probably kicking in. It should only activate when coming out of gear so out of adjustment most likely. Sounds like you are close.
 
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