Ok ...Some of are familure some or not ..briefly I bent an exhaust valve pulled it apart could not find anything wrong ..did the repairs and shop ran the motor about 1.5 hours ...I picked up the boat and it lasted 20 mins bent same valve ....this is a Jasper Reman. motor 454mag ...this motor was built in July 03 very little hours 20 or so ...It was out of warranty and I called them to get some help and they replaced the motor ... AND the labor if they could find somehting wrong with the motor ....they left a message today that everything checked out ok ....and the only thing that it could be is over reving the motor so they are not covering the Labor. I am ok with that because they have already stepped up in my opinon .. But .. other than the mechanic ...no one has been in this boat but me ...and I just reproped and its too tall and will not turn but about 4500 ...when I picked the boat up I KNOW I didnt go over 4K ....and it wont go more than 4500 ....It did turn 5000 with 23 Mirages but with Hydromotives (23's) I lost about 4-500 rpm .... My main question here is what would be overreving ...@ 4600-5000 redline ? I would think alot more ....
5000 is perfectly fine even with a standard 454. I would check the stem to guide clearance on the offending valve- this is very rarely done on a rebuild since it should be loose from wear. If it is tight to the touch, they leave it alone and replace or knurl the ones that are loose. I suspect yours is too tight and when the valve heats it siezes and hits the piston. This may be due to an improperly machined valve and/or guide. I am assuming that all other parts look good and valve adjustment was correctly done.
Another note-I have never seen an overrev bend just one valve-can't happen. They need to come up with something else.
Your motor should be able to go to 5000 with out problems. But, I have to ask you what kind of valve springs are in there? The valve train components are a major contributor of what dictates the max rpm of a motor.
The motors have roller cams but stock mag springs & rockers .... First time I had the heads inspected and Springs tested ..everything checked out fine ..In the message Jasper left I believe they said they checked valve guides ...Also said piston to deck clearance was ok ....I will talk to them Today ( friday) . I think I have seen psot on here about people running 5-5200 on mag motors all day without problems .....
I could run my 454mag with a bigger cam up to 5500 w/o any problems.
You say "stock mag springs and rockers" What is the lift on the cam??? Are the spring pressures matched to the cam??? Stamped steel rockers???
Stamped steel rockers ....the 1st time it happpned the head shop checked all the springs ..we thought maybe a weak spring ...I am not sure of cam spec but I am trying to find out ...whatever "stock" 454mag would be ...should be pretty mild ...
I would be keying in on leaking exhaust system. Is it a center cylinder that bends the valve? I can't put my finger on why this would cause a bent valve, just seems like the description fits that problem. Hydrolock is a violent event. And water dripping on a hot exhaust valve can cause all sorts of odd problems. Have you pressure tested this side on the exhaust? I would also consider changing the valves to all manley servere duty 3/8" diameter, non necked one piece before going again. I have never been able to keep valves from failing with any other brand valve. And new springs to match the cam. That is what I would do...
it was #4 cylinder both times ....and I am changing to different exhaust ...gil manifolds and Stainless marine pipes that dont water until the end of the pipes ..
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