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possibly cracked block..


machzrcr

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i have read quit a few threads on this already. But i am pretty sure i have a cracked block. I have replaced the heads and put all new gaskets in the upper end of the motor. and while we had it apart we inspected for any cracks and turned the motor over and could not see any cracks in cylinder walls, valley, or cylinder heads. where else would the block crack from that would be causing this? would it be a crack in the cylinder wall below the lowest point of the piston? or i have heard of freeze plugs breaking, if one of those broke would it be leaking outside the motor? or are there freeze plugs in the motor that you cannot see without for say taking the oil pan off?

going to be pulling the motor unless for some reason we find something really obviouslly that we dont but its not looking good. so any help would be appreciated!

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Look at exhaust manifold. Don't know if your engine is set up the way my old one was but the exhaust manifold had an aluminum plate separating water jacket from exhaust. exhaust ate a hiole in it. 1 of the reasons I got rid of it.

Tom B.

(LongLine)

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if the exhaust manifolds were cracked how would water get into the oil? I do know when we had them off they were not cracked around the flanges where they enter the heads at all.

msnifolds look like these.

x200_Volvo_Penta_V8_305_350_Exhaust_Manifold_001.jpg

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I have a 1982 mercruiser 350, and just went through all this BS. If the exhaust manifold is cracked or rusted through it will put water into the cylinder via the exhaust valve, then in to the piston, while the engine sits all the water in the cylinder runs past the first ring then the same for the second ring as the ring gaps are opposite the other then it sits on top of the oil ring and if the oil ring is wore, into the oil pan the water goes, with all this said, to do a quick check pull the plugs and spin the motor over and see if water flies out of a cylinder do one side then the other, if all this is happening the motor should run like sh#@$t to start with. With my motor I had water in the cylinders, fresh reman well known engine builder, bored .30 over new heads cam lifters rods you name it, it's new, then why the water in the holes? well the new heads where warped it took 10tous, to clean them up, they actually rocked when we set them on the block, who would think to check a pair of high performance heads brand NEW? SO what I'm saying is if your heads are warped you wouldn't have water in the oil. If your exhaust shutters are bad or even there, it is a good possibility you might be getting water in that way also, my riser gasket system is 1 fiber gasket 1 stainless steel plate with a small vent hole then a fiber gasket, if you back your boat in to fast or you are in rolling seas the water will go over the riser into #8 or #7 cylinder, the water will seep through the little vent hole in the steel plate and if you have the old log style exhaust manifold #8 cylinders are a strait shot into the head. Hope this helps as I had to learn the old way with my WALLET!!!!PAP.

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Well i have had the engine running and its runs mint i even took it out on the water with fresh oil to see if it would act different and fished for 6 hours with doing one oil change and it changed colors the same as when we were running it in the driveway. an hour an a half total from putting on new heads and all oil changes. ( ive changed oil 5 times hoping it was flushing out old crap) and we checked the new heads for flatness using a bar i had ground down to within 5 microns run out over 20 inches. and the heads were nice and flat. but with it still changing color in the driveway would that rule out water coming back in from the exhaust? but it would b a lot easier to only replace the manifolds! but gotta pull them before the motor so what method do you guys suggest to pressure test them off the motor?

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What I did to pressure check my manifolds is take a gasket and a piece of 2"x 5/16 inch steel and trace the out line of the gasket & the 4 bolt holes, drill the bolt holes out then use formagasket sealant on both sides of the gasket then bolt the steel over the gasket, I needed longer bolts and nuts to draw the steel tight against the exhaust ports let set till the sealant is cured, mean while make a plate for over where the riser bolts on useing a gasket and sealant 4 nuts& washers and put a c clamp in the center of the plate and tighten down in the center a little, let cure know drill a hole in the center of a exhaust port and tap threads into the steel to accept a air fitting screw the fitting into the port put 2 ballons on the end of the manifold where your water line goes on ad a little air, I used a gauge with a valve so I could see how much air pressure I was puttig to the manifold, and watch for the ballons to blow up if they blow up the manifold is cracked inside the box looking manifold is a header type exhaust chamber that is sealed from the water that surrounds the exhaust part and the water cools the manifold so it can be under cover and not get hot enough to catch the boat on fire, exhaust temp. out of the head is over 600 degrees exhaust temp!! so this is to cool down the exhaust manifold it's self I paid 350.00 per side for exhaust!! OUCH ;( hope this helps PAP

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You may want to just pour some laquer thinner in the water jacket and see if it weeps through. Its thinnner than water and will run quickly threw a small crack, save you alot of time and construction. If it leaks though its bad dont matter how much it leaks just if it dose.

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I tried the the thinner trick with no luck, manifolds back on same problem, took them back off put air to them and they leaked, when the manifolds where cold they wouldn't leak when they where hot they leaked, air pressure will go where no liquid will go, so manifolds cold, air pressure is the way to go. When they pressure check heads they dont pour thinner in them. PAP

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  • 2 weeks later...

just a consideration.....

The older gm heads also develop a small water leak in the head between the water port and the exhaust port. the distance between the two is small and in time rust causes a small hole so water transfers from the water port to the exhaust port and then into the cylinder when the engine is off. Farmer automotive will confirm this failure, Dan gets 10 - 20 a year and we get a hand full each year. The new heads have more material between the ports. Also dont buy salvaged 1980's heads to fix your problem, it will be back soon if they were used only one year (the rusting process has started)

You wont know by a compression test only a leak down test.......

Usually the engine will run poor at low rpm though...

Tim Habecker

Krenzer Marine.

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well an update. X-jet boat bill came over we tore the engine down to a bare block.. and it definitely was a cracked block, a crack about 2 inches long on the bottom cylinder wall of cylinder 7! So i get to join the bad winterization club... deffinitely will take more time this year winterizing it!

thanks for the help bill!

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well an update. X-jet boat bill came over we tore the engine down to a bare block.. and it definitely was a cracked block, a crack about 2 inches long on the bottom cylinder wall of cylinder 7! So i get to join the bad winterization club... deffinitely will take more time this year winterizing it!

thanks for the help bill!

Sucks about the block but glad you found the problem.

Jet boat Bill is a great guy!!!

Glen

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Sorry to hear the bad news but I'm sure with x boat and yourself you will find a good 4 bolt main block and go from there Good luck guy's PAP

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