RedDog382

Mike,

Sorry to hear you have a problem again. I don't think this is from the internal flappers ... they were burnt out in my 311 and I never had this kind of problem with my stock motors.

Were these your original heads and were they magnafluxed before re-installation?

What material were the valves and were they new? You should be using severe duty stainless for the intake side and Inconel for the exhaust. Doesn't really sound like you ran it hard enough to hurt them, even if they weren't severe duty.

Were the valve guides new or reconditioned (knurled)?

I have two complete sets of aluminum roller rockers with only two hours on them. Let me know if you are interested in them.

Wish I could be more help to you on this! Good luck and please post your findings when you get this sorted out.

Chris

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iTrader: (1)

I believe the Jasper motors are long blocks ...boat was new to me in April ...this motor was installed June of 03 ... I agree on the internal Flap but really dont know for sure ...usually try to not slam on the brakes ..the only one time was when the port motor got hot 1st time out ...shut it down as soon as I saw the temp peg ....

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iTrader: (1)

one bent Valve ..one with some rust 2 valve seats need replacing but going to replace them all with a different type .......everything else is ok ....

cig1988

Could it have been reversion? What's the cam specs with centerline?
Are you running OEM merc risers or aftermarket risers?
Any water in the oil?

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iTrader: (1)

I am not sure of cam specs but would assume 454mag specs would be pretty mild ....I think the manifolds and risers are Siera's ...and yea there was some water in the oil ....

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iTrader: (1)

The motor was put back together and ran it for almost 2 hours on the stand with no problems ...Put the motor in the boat and my mechanic ran it for another 2 hours in the river with no problems ...65 mph at 4500 rpm ...( gota get those props tuned) ..I picked up the boat ..ran 5 miles to the house ....came off a plane and Same motor Stalled (star) ..cranked it up was running on like 3 cylinders ...shut it down and Idled back to shop ...talk about frustration .....

cig1988

I had a water in the oil issue recently. When I re-did the heads springtime,I put aftermarket risers (sierra) on just as a precaution. Boat ran fine but spun a brg later in the season. Replaced the cam upon rebuild. Ran the engine @ high idle to break in the cam and everything was fine. Idles it the next day and had milk. Had the bore scope in the cyl and h20 around the valves etc. Long story very short...took the exhaust off one side to the other and no more milk. It turned out to be the design of the riser on the aftermarket riser. Take a merc riser and compare, you'll notice the differance.

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iTrader: (1)

shop just called .....no compression in one cylinder again ...dont know if its the same one ........now they want to repull the motor and gon into the bottom end .... If we have piston/valve contact again ....what in the bottom end would cause that ?

wannabe

Dollars to doughnuts the previous owner went "cheap" and did not spec marine grade.... hence the rust meaning NOT SS valves. That is why the valves hung up.

I suggest you have the heads on both engines redone.

Wannabe

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iTrader: (1)

Jasper Reman motors ....Stainless Valves ... I would think a spun bearing would let the piston contact the head and would let you know it ...the first time was just a slight ring where Exhaust Valve tapped the piston ....might know this afternoon if it same symtoms