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rebuilt 454 seems to run very rough

The GEN V's do NOT have the mechanical fuel pump mounting provisions; I'm pretty sure the GEN VI's DO HAVE the mechanical fuel pump mounts. As far as ascertaining what IS bolted to the stringers, I'd suggest two parallel paths. First, get the block/casting numbers as suggested in an earlier post. Second, contact the rebuilder/reseller and ask them what they provided. As far as figuring out what you started with...if its gone, it'd be hard to verify. Maybe the title or documentation paperwork can help here.

Most of the older Mark IV "bolt ons" will work with the newer style blocks. There are several areas to be careful with...best to use a trusted source when dealing with these.
 
I have the person that I purchased the motor from coming to the boat today. he is going to get the casting numbers off it and contact his supplier directly. then we can try to figure out the next step. just hope that there is a end in this sometime in the near future! and hopfully no damage occurred to the motor from the vibration.
 
Let just hope its the MArk IV flywheel on a GEN VI short block...if it is, don't be surprised if they recommend you change the harmonic balancer, too. From the little i found, the newer assemlies require a different balancing procedure (& parts, too).
 
Now I am getting worried there is another issue maybe inside the motor. the person that I bought it from went down and reinstalled the valve covers....now I start it and there is no oil pressure. I had noted that the more I ran the motor the less pressure I would see on the gauge. Really hoping that the inside of the motor didnt get damaged.....
 
Well I got the trans out and checked the flywheel, it was off a little bit. I lined it up properly but the shake didnt seem to change any. it will feel smother at some rpm's now but really bad at others. Hte oil pressure is good when the motor is first started but then seems to drop down after warmed up. When warm it is around 10 at idle and about 25 1500 and above. much lower than the other motor. not sure what to check next....starting to think it is a internal balance issue?
 
The flywheel was "off a little bit". Huh? Explain, please. Also, what oil are you running? Sounds like a worn out engine right now, not a new one; when you tell us the oil pressure drops after warm up.
 
the empty dowel mark was off by one bolt. instead of being lined up it was one bolt hole off. for oil I am using rotella 15w40
 
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sounds like the crank may be missing the alignment pin. Did you see the provisions for one? Anyway, the low oil pressure is equally concerning. You need to get 40psi at 3000 rpm, even when warm. Did you verify the reading with a mechanical gauge? If so, that engine needs to go back to the rebuilder.
 
I have not yet checked the pressure at the block. I am planning to hook a gauge right to that to confirm the pressure. I am very concerned that there is a internal issue with the crank. It very much feels like a rotational issue.
 
Did you ever find a resolution to this vibration problem? I'm having the same issue on a Rebuilt 454. RPM changes the vibration (shake) I've replaced the wires, plugs, coil, cap, rotor , harmonic balancer...
 
I did finally get to the bottom of it. it turned out to be the motor that I bought for the boat had a defective crank shaft. the builder claimed that they had installed a new one but I have a feeling that they just tried to use an old one and it was no good. I sent the motor to them and they had to rebuild it again. after that it was much better. the new motor still does have a slight vibration but not bad at all. as it sits I am just planning to run it
 
Thanks for the quick reply! Sorry to hear that it was the crank shaft. Mine is noticable at idol, goes away between 1000 and 1600 than shakes from 1700-2500 then goes away (kind of.) I'm going to try playing with the timeing next. As far as oil pressure goes, both motors sit at 60 when I'm running.
 
mine at idle seems nice and smooth. around 1100 to maybe 1900 there is a slight vibration. over 1900 it is again nice and smooth. we will see.....Oil pressure is a little on the low side with the new motor which i am not happy about. I have not hooked up a gauge right to the block yet to confirm the reading is correct though. we will see. good luck with yours!
 
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