Just rebuilt my 454 using stock bottom end. Factory crank, rods, and flat tops. I had re used my cam. 049 heads. Last year I had to have the block sleeved. After that I bent a rod. This rebuild is from that. I have another set of stock rods and was told by a machine shop all the rods from the big block chevs were around the same weight and to just throw it in. I get it all together and fired up for last weekend. Sounds great.  Idles perfect. Vacuum is at 17lbs and steady. Timing marks dont line up so I set it at 3000 rpm by ear. Runs beautifully except for a crazy vibration. I thought it may have been the driveline so I disconnected it and its the same. New B&M flywheel so they weights are not missing. Dampener is newish and the rubber is not expanded nor missing chunks. No water in oil. Everything is fine except for the vibration. I can't figure it out. Maybe the ring on the dampener moved? But I closely inspected it and it is not shifted and as said the rubber is near perfect. Timing marks are not even close though. The vibration is so bad it broke off my 6 inch brass fitting from the jet pump and nearly sank the boat. Any suggestions? Could a bad cam cause this? Spark plugs look perfect. As said I replaced the stock number one rod with another stock one. Could it have cause the bottom end to be that unbalanced? No vibe at idle, but happens above 1800. 3200 especially. Gets better but not gone over 3600.

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Just rebuilt my 454 using stock bottom end. Factory crank, rods, and flat tops. I had re used my cam. 049 heads. Last year I had to have the block sleeved. After that I bent a rod. This rebuild is from that. I have another set of stock rods and was told by a machine shop all the rods from the big block chevs were around the same weight and to just throw it in. I get it all together and fired up for last weekend. Sounds great.  Idles perfect. Vacuum is at 17lbs and steady. Timing marks dont line up so I set it at 3000 rpm by ear. Runs beautifully except for a crazy vibration. I thought it may have been the driveline so I disconnected it and its the same. New B&M flywheel so they weights are not missing. Dampener is newish and the rubber is not expanded nor missing chunks. No water in oil. Everything is fine except for the vibration. I can't figure it out. Maybe the ring on the dampener moved? But I closely inspected it and it is not shifted and as said the rubber is near perfect. Timing marks are not even close though. The vibration is so bad it broke off my 6 inch brass fitting from the jet pump and nearly sank the boat. Any suggestions? Could a bad cam cause this? Spark plugs look perfect. As said I replaced the stock number one rod with another stock one. Could it have cause the bottom end to be that unbalanced? No vibe at idle, but happens above 1800. 3200 especially. Gets better but not gone over 3600.

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Either wrong balancer or it spun due to a failed Woodruff key

Also, anyone who says "all the rods from the big block chevs were around the same weight and to just throw it in." is not a machinist, but rather a shade tree mechanic.

When we build a high performance engine, I normally order 10 rods and 10 pistons. Somewhat to have spares, but more to be able to have more choices when balancing.

Dimple rods are heavier that pass car rods, the rod bolt weight always comes into play as well..

How sure are you that you did not bend a crank? Seen it, done it and still don't believe it is possible, but it is.

GT

Either wrong balancer or it spun due to a failed Woodruff key

Also, anyone who says "all the rods from the big block chevs were around the same weight and to just throw it in." is not a machinist, but rather a shade tree mechanic.

When we build a high performance engine, I normally order 10 rods and 10 pistons. Somewhat to have spares, but more to be able to have more choices when balancing.

Dimple rods are heavier that pass car rods, the rod bolt weight always comes into play as well..

How sure are you that you did not bend a crank? Seen it, done it and still don't believe it is possible, but it is.

GT

Thanks

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Real quick. When I installed the crank it turned by hand. Installed pistons without heads it got stuck pretty bad. I had to free it up with a breaker bar. I forgot to oil two of the cylinders before putting the pistons in. Did it after upper and lower. Got better but it still was hard to turn. Maybe another slightly bent rod that I missed? Compression check should show correct? Sounds good though running.

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What is the amount of damage that could be done if I run it for the rest of the season? Stringers? Pump?

Catastrophic failure!

Real quick. When I installed the crank it turned by hand. Installed pistons without heads it got stuck pretty bad. I had to free it up with a breaker bar. I forgot to oil two of the cylinders before putting the pistons in. Did it after upper and lower. Got better but it still was hard to turn. Maybe another slightly bent rod that I missed? Compression check should show correct? Sounds good though running.

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How many rods did you replace?

V8 engines should ALWAYS have rods replaced in pairs...

The motor should have spun fairly easily as a short block. I always spin the motor over with a dial indicating torque wench after each rod. It should not take a properly assembled engine to require more than say 30ft/lbs to spin it.

This thing needs to come apart.

You can break the crank, the block, the pump, the hull, the motor mounts and the limit on your credit card if you let it rip...JMHO.

In most cases, it costs Les than $200 to balance a "stock" V8.. Custom engines are always a bit more simply because of how far out they can get. My last marathon motor used a whole bunch of Mallory metal to bring it in. You could have set a cup of coffee on the scoop with it running at idle all the way to red line.

GT




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Figured it out. Pretty embarassing actually since I've been building motors for 12 years now. Upon recent inspection of the rod I used to replace the bent HD rod, I realized that the center is actually slightly thinner. So I HAD HD rods and I replaced the one with a weaker smaller rod. I good gentlemen of socal jet boats, am a fucking retard. Thank you for the support. I'm going to go cry now.

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Well... before you get too far into ripping into this thing... just check ONE thing more... as it would be a pretty good chance of being your problem. Take a look at the flex plate...there are the 6 bolt holes and 1 dowel pin hole... often times the dowel pin is missing in the crankshaft, and the flex plate can bolt on 6 different ways, but only 1 way is the correct one. The flex plate is still gonna need to be located properly... MAKE SURE that the flex plate is clocked correctly... if the dowel pin is missing, then the extra hole in the flex plate is gonna need to line up with the extra hole in the crank flange. Already, 2 times this season have seen people install their flex plates incorrectly and been the reason for their vibration issue... it happens more than you'd think.

Personally... I like to work from simple to complex in resolving an issue... but that's just me.

As for rods and crank balance... very possible... very likely as well... but food for thought: I have seen stock rods as much as 20g different and total balance be on stock engines as much as 60-70g and be factory stock, non-shakers. This is totally not right and in no way acceptable, but you'd have to be really far off on either for it to shake violently enough to break off brass fittings and loosen bolts after a short run.

No matter what you find... good luck... and hope you get back on the water soon enough.

Cool. I know about the dowel. Mine is there but ill dbl check. Thanks.

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