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Old 09-28-2015, 06:10 PM
93xs2003 93xs2003 is offline
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Boat: Mastercraft, Prostar 190, 1992, 351W
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351W rebuild, fresh heads or ignore?

92 prostar / 351W / GT40 heads / powerslot / ~1400 hrs

I bought the boat late last summer, with the expectation that it would eventually need a rebuild. There is evidence that the previous owner overheated.

Checked compression last weekend, all cyl's are within 6% of max of 133 psi. (warmed up, plugs out, but carb closed)

Engine weeps a little oil into the bildge. It burned less than half quart of oil over the season. Other than that it pulls strong and runs well.

During winterization, I found rusty spark plugs on sbd. bank. On closer inspection, rust starts above #1 head bolt. There is a hairline crack in the waterjacket of the head. (apparently not uncommon) Plugs were very rusty when purchased, this set was new this spring. So the leak has been there for a while, and while I haven't seen any water, rust on new plugs suggest it has been actively leaking this summer. No water in oil. No water on plugs tips.

--------------------

Option 1: Do nothing, keep driving. Keep an eye on gauges, bilge & rust stains.

Option 2: Clearwater or tristate GT40p remanufactured heads. I think I would be at ~$600 after gaskets, bolts, etc.

Option 3: Pull engine, strip down.
Send to machine shop; clean, inspect, measure, bore as needed.
New rings, seals, bearings, timing chain at minimum.
Roller cam conversion, likely.
GT40p heads. Stock intake. Stock exhaust manifolds.
New damper plate, likely.
Ignition upgrade, possibly

I'm guessing this would put me in the $2.5-3.5K range.


The objective would be a reliable engine, and to avoid any down time during the ski season. I expect the boat will spend the majority of it's time at <3000 rpm. If my kids take up barefooting it could spend some time at higher rpm, but I have no illusions about trying to go fast in a ski boat.

So, given all the above, any opinions?
Would it make sense to put new heads on a 23 year old motor? or is it time to refresh the whole thing?
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  #2  
Old 09-28-2015, 07:11 PM
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Kyle Kyle is offline
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Join Date: Jan 2007
Boat: 93 Prostar 190
Location: Fort Worth, TEXAS
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I would yank the engine with that many hours.

A quick fix with head replacement will more than likely stress the bottom end, spin a rod bearing, sending the rod through the block, destroying the valve train, breaking your cam into 8 sections, bending your distributor and destroying your ignition, along with demolishing your oil pan (extremely hard to find a replacement).

You see I have been in your shoes ^^^^ I speak from experience.


Pull the engine and strip the heads off. A bore, hone, piston, ring, balance, and bearing kit assembled will be $1,500. When you're at the machine shop ask for GT-40p heads. $400 is a good price for some reman freshened heads with new seats etc. (20 extra ponies over standard gt40). The machine shop can assemble everything for extra money. I had them assemble a rotating assembly and balance everything. I then put my block on a stand and installed the oil pump and oil pan. Then I put my heads and intake on. At this point I installed the engine and finished the rest.

Replace the POS heavy intake with an edlebrock performer -$200 and way worth it (15-20 extra ponies)

New oil pump and all new gaskets. A great winter project and you can be put the door for $2700-$3000 if you install it.

The oil leak is probably a rear main seal or gasket somewhere. 1/2 quart usage isn't all that bad. The engine has 1 gear and its forward at 3,000 to 4,000 rpm. You will float the valves if you run the 4500 rpm a lot. It's not uncommon. I guarantee that if everyone on the forum measured their oil in the oil change, they would not get 5 total quarts out. It will be 4-4.5 at a 50 hour change.

A cracked head eventually will cause bigger problems later. New heads on a tired bottom end will eventually grenade the entire power plant. I know unfortunately. I had to replace everything and the oil pan was a huge pita to locate. Took months to find one.
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  #3  
Old 09-28-2015, 07:16 PM
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Bouyhead Bouyhead is offline
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If you go the tear down route I would consider resealing the transmission.
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Old 09-28-2015, 07:17 PM
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Kyle Kyle is offline
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Quote:
Originally Posted by Bouyhead View Post
If you go the tear down route I would consider resealing the transmission.
Great advise. Totally agree



OP don't be this guy lol http://www.mastercraft.com/teamtalk/...ad.php?t=36324
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If you want bling like the big dawgs, ya gotta lift your leg a little higher.....
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  #5  
Old 09-29-2015, 06:38 AM
93xs2003 93xs2003 is offline
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Boat: Mastercraft, Prostar 190, 1992, 351W
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Thanks.

Yes - the transmission is likely going to be rebuilt while it's out. I need to get the engine rebuild figured out first though.
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  #6  
Old 09-29-2015, 10:38 AM
maxpower220 maxpower220 is offline
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I would either run it til it breaks or rebuild/replace everything at once. Why spend the time and effort on the heads when compression is already on the lower end of OK. No need to do it twice.
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  #7  
Old 09-29-2015, 10:56 AM
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thatsmrmastercraft thatsmrmastercraft is offline
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Kyle's advice is good about not doing this part way. There is certainly some life left in this engine, but there is no way to determine how long until it meets it's end. You have to determine what a mid-season failure would mean to you vs. doing the work in the off season and having a fresh engine for Spring.
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  #8  
Old 09-29-2015, 11:26 AM
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paco_06 paco_06 is offline
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I also say option three if you have the time and money, option one if not. Option two will only lead to trouble!
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  #9  
Old 09-29-2015, 02:39 PM
gweaver gweaver is offline
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How long are you planning on keeping the boat? How bad is your OCD? If you're planning on upgrading in the near future, I'd just run it as is. If you're going to keep it for a while, then yes, pull the engine and do it right.
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  #10  
Old 09-29-2015, 03:43 PM
93xs2003 93xs2003 is offline
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Boat: Mastercraft, Prostar 190, 1992, 351W
Location: Northeast
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No plans to sell. I'm sold on rebuild.

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