1974 455 Oldsmobile jetboat engine

[Tdela55]

Hey all,
I was just wondering if anyone can assist me on this issue i have been having. I have a 1974 455 olds engine in my 74 jet boat and it appears that i have some water in the oil-pan. I know it's not a cracked head since I just had the engine re-done. I had called several engine repair shops and told them of the issue I have. They told me that it's typical for old Oldsmobile engines back in the day for water leaking into the oil-pan. What happens is that when the engine is steadily reved, water presure builds and leaks into the oil-pan. I am not savy with old engines but was wondering if this is true. Could somebody let me know what the problem might be? I would be highly greatful....Thanks!

[cyclops]

Do a search for the jet boat sites. My first common sense answer to water being normal is, BULL. Find why it is leaking and from where. ----------------------------If I told you my boat has a normal water leak always into the oil pan. What would you think of me?

[gonzo]

You should never get water in the oil pan. What those shops told you is BS. Check the manifolds and risers for corrosion. Another source of water intrusion is a burnt or warped exhaust valve. It allows water from the manifold to be sucked into the cylinder. Water pressure in a marine engine may build up to 3 PSI; on a car to 15PSI. Are they claiming all Olds had crankcases full of antifreeze? The head gasket and the bypass in the intake may leak too. Pressure test the block to see if it is one of them.

[Tdela55]

thanks cyclops and gonzo for your suggestions. Would you know any trust worthy mechanics in the Los Angeles or San Bernadino Ca area if you are from California. I'll let you know after inspection

[cyclops]

Do a web search for------------jetboat forums--------------They will get it and you running right. You have bad mechanics and machine shops to have that problem still happening. To the forums.

[FAST FRED]

OLDS is still used in a large variety of fun things that need a 455's power and cant be bothered with the bigger less reliable & really fulish RAT motors.

If this has been a problem since last wrenching session , I would suspect an auto gasket set was used , rather than a marine head & exhaust gasket set.

FAST FRED

[Tahorover]

non marine High performance camshafts with to much overlap can suck water in the motor.

[gonzo]

Yes, unless you use a high performance marine wet header.

[Tahorover]

Originally Posted by gonzo

Yes, unless you use a high performance marine wet header.

With a high amount of overlap ,during closed thottle high manifold vaccum you can still pull water in. Over transom, thru-trasmon headers, manifolds with risers it doesn't matter.

[gonzo]

That's true. However, headers help because of their long runs. As you say, the problem may be that they tried to hot rod the motor.

[pweaver]

When a jetboat is under power the jet can produce more pressure than a common auto cooling system does. Try to back off on the pressure by closing off the valve a little. Or you can go to
http://hi-techperformance.com/Parts.HTM
and buy their pressure regulator made for this very problem.

[myoung]

It's more than likely leaking at the intake into the lifter valley due to too much water pressure. I've been seeking out info on Olds engines since I have one in my boat and have come accross this a few times. Apparently it's a problem with the Olds, especially with older manifolds and heads that may have some corrosion around the water cross-over ports. I guess there just isn't enough sealing surface area for the pressure that can build up. I'll be looking into one of those pressure regulators for mine if it becomes a problem.

[pweaver]

Wherever they are, minor leaks can be sealed with modern sealants if you prep the surfaces right (and the pressure isn't excessive.) Clean off stubborn corrosion with a wire brush. Once the Oxydation is removed, clean the surface with an oil degreaser and then alcohol. If the pitting is deep, fill it with JB Weld. Once the JB is set, use a good sealer. If you use RTV, spread it on evenly and give it a couple minutes to soak up the air before you assemble. If the sealer requires an activator use it or you are wasting your time.

ps if anyone knows where I can get a pair of good wet log exhaust manifolds for a 455, please let me know.

[myoung]

Originally Posted by pweaver

ps if anyone knows where I can get a pair of good wet log exhaust manifolds for a 455, please let me know.

Ebay has a lot of 'em and sometimes on hotboat.com in the forums, not so much in the classifieds.

[pazc23]

I was reading the problem you have and I have the same engine for my 72 jet boat. Did you ever figure out the problem you were having? If so, would you be kind enough to email me back and share the info. with me. Thanks!