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d36yzrider 04-15-2013 01:26 PM

84 S&S 351 rebuild or crate motor
so the motor on my 84 Mastercraft is very tight thinking its has a bent rod or something bent on the valvetrain anyways im about to pull the motor and tear it down at the moment a rebuild kit seems alot cheaper than a crate motor I can get a kit with just about everything for around 300 bucks as where a short block is around 700. any advice

1redTA 04-15-2013 02:24 PM

I'd tear it down to see what went wrong and rebuild it if you have the means, it's what I'd do

MikeyOrange88 04-15-2013 04:58 PM

my cheap advice
Before you start tearing into it, could you elaborate a bit on the 'very tight' aspect you're having with the (assuming 351W) motor, number of hours, etc., and maybe what you've already done to it. Lots of smart, helpful engine people on this forum that could probably help diagnose. I'd at least like to kinda know what you're looking for, if it's indeed tear down time. :D

d36yzrider 04-15-2013 05:43 PM

we bought the boat a few years ago with 185hrs as a replacement for my dads 85 S&S that was totaled due to some shallow rocks. It now has close to 400 on it and for the last 2 years it doesnt crank over when its warm would fire right up when it was cold and run fine but as soon as you kill the motor it cranks very slow you would have to wait several hrs for the motor to cool down then it would fire back up. just about every electrical part has been tested or replaced. after sitting for the winter it hardly turns over. I have put a breaker bar on the crank and turned it by hand with the plugs out and it has 2 hard spots in the motor im thinking something is bent. This boat has low hours but at one time I believe it has been on fire or overheated when I bought it anything plastic was melted or distorted and the engine paint is melted on the block. not sure what it is but im just sick of being the guy with the boat that always breaks down so a total overhaul is what im trying now

03geetee 04-17-2013 05:08 PM

Ok hopefully this will help lift your spirits, so take it with a grain of salt. Based on what you have told us and what I would consider a "fair" description of the problems here goes.

#1 do a compression and leak down test to see how the rings and or valves are holding up. If the motor was over heated due to a variety of issues and it fried the rings or worse this will get you closer to the truth without tearing it down.

#2 if the compression and leak down tests come back with normal results (which I feel they will) here is what I would recommend. What you described at (hard spots) could just be the natural feel of the motor when turning by hand, if it spins with relative ease I think you are fine.

#3 if the boat has an old battery, stock starter, original battery to starter/block positive and negative cables, and the original starter toss each of these items in the garbage and replace them with an Interstate 1000CCA marine Cranking battery, new battery cables, new Arco gear reduction starter.

#4 if the boat has point style ignition replace it with a pertronix electronic ignition and matching coil. Also make sure the timing is adjusted to between 8-10 degrees BTDC as this will effect hot and cold starting a TON!!!!!!!!!!!!!

These boats have been prone to a hard start issue when hot with the starter not getting much airflow being so close to the motor. Over time these will fail and draw too much amperage from the battery and if you have old crappy connections the problem intensifies even with a good battery. Replace these parts, check your timing after installing a new ignition, and enjoy happy boating. That boat with only 400 hrs on it should have a nice motor with plenty of life left. If you dont believe me I have almost 3000 hrs, that is not a typo, on my 83s original long block. I replaced the items above and she starts like a dream in 90 degree summer air after running all day long.

Let me know what you find out, and all these parts will cost you the following....

Cables 50-80 bucks
Battery 110 bucks
Starter 118 bucks
Ignition modules 150 bucks

Cheaper then a rebuild, way less labor too.


Spork 04-17-2013 07:22 PM

^ 03gt is right on the money with his diagnosis, replace or check the basic electrical stuff and she should start very easily warm. Definatly sounds like your elec. system is really drawing down causing the hard warm starts.

CruisinGA 04-17-2013 07:47 PM

I'm with 03geetee

If it runs well when it does start, I think you are barking up the wrong tree.

MikeyOrange88 04-17-2013 09:43 PM

My slow crank/hard to start hot issue on my '88 turned out to be the starter. New Arco gear reduction starter solved that problem. Heck, it was 25 years old.

jakethebt 04-17-2013 10:51 PM

Wow. Great trouble shooting and advice. This forum is one of the best reasons to own a Mastercraft!

d36yzrider 04-18-2013 02:51 PM

I guess ill take another run at the electrical issues just about all of the above has been replaced I do have a cheap autozone lifetime starter in it so thats possibly the issue. as for low hours I know the 85 we had was around 1500hrs and ran like a top

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