1973 18 ft crestflite inline six gmc 250 cid

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1973 18 ft crestflite inline six gmc 250 cid

Postby chefjp » Wed Jul 29, 2009 7:07 am

Ok guys need help 1973 gmc inline six 165 hp.In a 18 ft crestflite. Have had my problems with water getting in the oil.Replaced the exhaust gasket nice a tight with gasket sealant,rebulit carb ,clean gas tank,new thermostat,changed oil 3 to 4 times. Could this be a blown head gasket,shes running fine rpms very good just need to figure this water in the oil?????Please help. Also if anyone has any pics of the stringer layout of the 18ft crestflite that would help ,i have a few soft spots i need to repair.After this need help with forward and reverse cables adjusting them there driving me nutssssssssssssssss. thanks so much
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Re: 1973 18 ft crestflite inline six gmc 250 cid

Postby Rich_V174SS » Wed Jul 29, 2009 7:21 am

Welcome! See my rebuild in the Projects In Progress section under "1967 V174 Stringer and Floor Reconstruction". The stringer layout may not be exactly the same as yours but it should give you a good idea. As for the water in the engine problem it could be a bad head gasket. After running the boat take out the spark plugs one at a time and note their condition. Drops of water or a clean unburned end could indicate which cylinder might contain water. A compression check of each cylinder could also indicate a bad head gasket or problem cylinder. If they're all burning normal tan/brown with dry light soot deposit then you could have a crack in the block or head from an improper winterizing.
1967 V174 Crestflite SuperSport Modified
1986 Mercruiser 190 3.7LX / Alpha One
Rebuild Thread: http://www.classicglastron.com/phpbb/viewtopic.php?f=75&t=147

1970 V176 Swinger
1983 Mercury 115
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Re: 1973 18 ft crestflite inline six gmc 250 cid

Postby JimAndros » Wed Jul 29, 2009 8:05 am

Bad manifold or riser is my guess. Take the 4 bolts & 2 nuts off. Slide the manifold away from the head leaving it on the studs. Fill the manifold thru the water hose at the front & look for water appearing at one of the ports.
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Re: 1973 18 ft crestflite inline six gmc 250 cid

Postby chefjp » Wed Jul 29, 2009 10:23 am

Well i pulled the plugs they looked good burning good,Motor runs strong sounds good. Just water in the oil. The exhaust manifold is there bellows in it to keep water out of the motor???????? took the riser off of the manifold looked clean???? Let me know guys ,thing is driving me nuts,This is worst then a drug habit. I always say thats it iam quitting no more no more. But it keeps sucking me in.HELPPPPPPPPPPPP
chefjp
 
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Re: 1973 18 ft crestflite inline six gmc 250 cid

Postby JimAndros » Wed Jul 29, 2009 11:01 am

The manifold is water cooled. Any internal crack or corrosion & water will then seep into either the intake or exhaust and into the cylinder. If everything is OK while the engine is running, then I will guess it is going into the exhaust side.

If the riser is bad or if the gasket is leaking, water will find its way into the exhaust too.

Jim
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Re: 1973 18 ft crestflite inline six gmc 250 cid

Postby chefjp » Wed Jul 29, 2009 11:17 am

Well Jim i dont know i clean both sides of engine and manafold real good they where nice and smooth,order the new ,look like a lead gasket ,goop up both sides motor and exhaust manfold, Bolted it down squeese out good looks like a good seal. Now the crack iam looking for are you saying in manifold or engine area??? Sorry just trying to figure it out with out paying A FORTUNE TO GET IT FIXED. Thanks for your time and info
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Re: 1973 18 ft crestflite inline six gmc 250 cid

Postby JimAndros » Wed Jul 29, 2009 12:06 pm

A few things:

No sealant on the head or manifold gaskets. I do however use sealant on the riser gasket. If you have already used sealant, oh well.

The manifold to head gasket will not cause a water leak. Head or riser gasket will.

If the manifold (or riser) is cracked or correded thru, water will leak into the exhaust or intake passages and then down into the cylinder when the engine is turned off. The water will leak past the rings and into the crankcase.

I believe that either end cap on the manifold may also allow water to leak into the exhaust side. This is from memory only & I don't have one handy to compare.
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Re: 1973 18 ft crestflite inline six gmc 250 cid

Postby chefjp » Wed Jul 29, 2009 4:10 pm

Thanks Jim i will take any info i can get
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Re: 1973 18 ft crestflite inline six gmc 250 cid

Postby chefjp » Sat Aug 01, 2009 7:16 am

Ok Mr Jim got a bug up my butt took the manifold off,It checked out ,Pulled the head sure enough the head gasket was broken towards the back of the motor where the water inlets are ,new gasket, New vaule cover gasket ,new manifold gasket.Will be putting it back together next few days.The pistons and all looked good. I did rod out the water passages they where pretty well cloged up.Should work good,If it doesnt i gave it a try.WOuld you know the torque spes on the head bolts?????.let me know if you do...Jp
chefjp
 
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Re: 1973 18 ft crestflite inline six gmc 250 cid

Postby Rich_V174SS » Sat Aug 01, 2009 7:24 am

I have a manual that has torque specs for a 140 4 cylinder handy because I just got done doing a head gasket on one of those. They say 90-100 ft pounds but you have to tighten them in steps up to that amount and follow a spiral pattern working from the center bolts out to the ends.
1967 V174 Crestflite SuperSport Modified
1986 Mercruiser 190 3.7LX / Alpha One
Rebuild Thread: http://www.classicglastron.com/phpbb/viewtopic.php?f=75&t=147

1970 V176 Swinger
1983 Mercury 115
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