SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: damstarr on June 28, 2012, 07:10:56 PM
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Ok first off it's an I/O so go easy on me guys lol. Bought a 21ft 1978 centurion with a mercruiser 260 which is a 350 small block 260hp. So previous owner says it's lake ready including the impeller in the water pump. So I take it to the lake and run it 1/2 to 3/4 throttle for a couple mins watching all my gauges. All looks good. Make another lap little longer looks good. Stop at shore look for leaks and what not. Looks good. Boat is running like a bat. Surprising fast. So go out for another lap. Running around 3000 rpm (WOT RPM is claimed to be 4600) temp starts climbing hits 200 keep a close eye start heading for shore. Climbs to 220 I idle down and shut it off. Coast to the dock ( with a little swim) and call it a day. Next day I install a new impeller old one was shot. Take it back to the lake the next day and it won't start. Sounds like dead battery or starter dragging. Make a few phone calls and was advised to get it home and pull the plugs. 2 CYLINDERS WITH WATER. So I attempt to run a compression check but after checking first cylinder I notice after I let go of key about 3 seconds later starter disengages. So I look at the starter and the whole front piece is cracked. So it's pulled. Waiting to get another tomorrow. Oil Is still fresh and semi clean. No milkshake or obvious water mix. What do you guys think. Blown head gasket? Can't be sure till I run a compression check this I know. Just trying to get an idea of what's going on???? Any help or ideas will be appreciated
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Leaky exhaust risers?
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If you were moving even a little fast as you shut it down and don't have exhaust flaps to stop the back wash water can rush in and go in the open exhaust valves. Did this once. No big deal. Change oil and run it. Continue on your path and run compression check. At this point water has seeped past the rings into the pan. If it's alot of water I had an old race guy tell me when they flipped and sank a race boat they would put a quart of diesel fuel in place of 1 quart of oil and run it a few minutes, then do another complete oil and filter change. Diesel absorbs the residual water. Heat will also help evaporate what's left.
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i know my exhaust manifolds are hairline cracked on the outside but that should allow the water to go in right? Not sure about the inside of those things. Yah i have my fingers crossed my compression check will look good since my oil is still looking good. Been pulling my dipstick about 10-15 times a day for two days now. (yah im sure somebody has somthing to say about that lol)
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Here's how she looks on the water
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Watch for a milky froth in the oil when you run it. If you have it change it :banghead:
Been there done that a few times
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just so you know just cause water can get into the cylinders does not mean it will go into the oil, with a blown head gasket.there is a slim chance you dont need a head gasket. its not really a big deal, to do one. well good luck.
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Thanks for any advice. I'll run a compression check in the morning and go from there.
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You want the good news, or the bad?
Be willing to bet a matching set of cold ones the manifolds are cracked internally... :thumbdown: :thumbdown: :thumbdown: :thumbdown:
Here is the lowdown.
Remove the hoses to the manifolds off the engine, there is a potential that there will be three depending on the year (you may have told me but I have the memory of a deer tick).
Now take the hoses and Chris Cross them to create a closed vessel. Now remove the hose that comes from the transom assembly and devise a fitting to pressurize the block with air (go to about 15PSI) it should hold pressure for near forever... :sly:
If you pass that test, buy some manifolds.....I am still digging to find you a descent set for "on the cheap"... 8)
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4 cranks on every cylinder gave me 150psi. Even the 2 that had water. Good right
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Oh and I did forget to mention that after I installed the water pump impeller I ran it in the drive way on a hose. Could my problem be self inflicted? Lol. I ran the hose for about 5 second then started it like I was told.
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When you say water what exactly do you mean. Remove plug, crank and water shoots out or water droplets on face of plug?
I still think water went up the exhaust when you shut down. 2 exhaust valves being open makes perfect sense to me. This would cause the engine not to crank over and when it happened to me I smoked the starter cause it was trying to hard. Who would have thought water doesn't compress :banghead:
Do you have logs and do you have working flaps in the exhaust?
The way you ran it in the drive way is correct.
All the cylinders being the same is good and 150psi is fine. IMHO you are in good shape, you simply have to experience this kind of crap to understand your boat. I have a BBC468 that has 125psi on all cylinders when fresh from build. Low compression, high boost O0
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Was the old impeller coming apart and if so did you clean all of the debris out.