Reusing rods

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gumper

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So my engine is at the machine shop, and the guy there told me I should buy new rods for my 408 rebuild. Said that by the time I spend the money on new bolts (proprietary to Scat) and have the rods resized I could just buy a new set of rods. First I wondered if I truly need new bolts to begin with. They ran in my engine for 13 years, but that engine did only make about 475 horsepower. They are forged Scat I-beams that came with my stroker kit with their ARP bolts. Second I wondered if this guy knows what he’s doing. Said he wants my flexplate to balance new rods and pistons, but it’s internally balanced. Should I just get the new rods, and go with what he says? Or get my parts back from him, and find someone else? I’m also to the point that I’m regretting tearing the engine down at all. Should have keep running it as is, and turned it back into a street car.
 
New rods usually cost close to "recondition with new bolt" price. Yes, you will need the flex plate, balancer, pistons, pins, retainers, a ring set, a rod bearing set to balance and of course the crank. Basically everything (or parts of everything) that rotates. They weigh it all to calculate the bob weight so they know how much to add or remove to balance the assembly. He is right on.
 
I thought you didn’t need to bring the balancer and flexplate to the machine shop if the engine was internally balanced only if it was externally balanced?
 
This one is kinda interesting......at first glance by the title "Reusing rods" thought that it was a case of reusing stock rods in a build vrs something new. Turns out you already have an aftermarket rod; in this case a Scat I-beam; one of the preferred upgrades from the stockers. If it were me, I would have the big end checked for size and if in spec I would not do anything else with them except clean them and make them ready for assembly. Yes you can argue that they are 13 years old, yet that does not mandate that they need to be rebuilt, they have not gone thru multiple torque cycles, the bolts; ARP's by the way; are fine. The advantage of the aftermarket rod is that they are dimensionally stable, better material, that's why you bought them in the first place.

I don't understand why, if you are having your rotating assembly balanced internally, he needs the flex plate; IT (the flex plate) should be neutral, it will neither add nor subtract to the rotating assembly, by including it you are adding an EXTERNAL weight to the calculations, it defeats the notion of internal balance.
 
I thought you didn’t need to bring the balancer and flexplate to the machine shop if the engine was internally balanced only if it was externally balanced?
Here's a fairly short video. At about 7.25 it shows the crank, flywheel and balancer with the bob weights attached to the crank throws. Notice they even added the lower crank gear.
 
Here's a fairly short video. At about 7.25 it shows the crank, flywheel and balancer with the bob weights attached to the crank throws. Notice they even added the lower crank gear.


454 Chevy is an externally balanced engine; look at the still before hitting the "play" button and you can see a big old weight welded to the flex plate
 
That is an external balance rotating assembly.
 
If I change any internal components except rod bolts, I re-balance the assembly. If it's internal or external balance I send everything that spins to the balance shop. I do this for two reasons. One is I don't want to make a second trip and two overtime a balancer can be out of balance itself. ATI rebuilds balancers all the time because they do change over time.
I had a guy assemble his own small block Chevy engine after I did the machine work. It had a bad vibration between 2500-3800 RPM's even thought I had everything balanced. I tore the engine down looking for the problem. Come to find out the new ATI balancer had been dropped on the floor and it was damaged.
Had the balancer checked at ATI. They repaired it for 40.00 and everything was good.
Just my way of doing things.
 
I measure the big end of the rod before I think of replacing bolts or rods. Especially ARP rod bolts. You are probably good to go.
 
I’d reuse the rods. Not sure why if it's an ARP bolt it might be proprietary. But I’d rather reuse than buy again.

If he wants all that extra stuff to balance all it means is that stuff has to stay with that assembly forever. Personally I don’t do that because most people will change something that bolts into an engine at some point. I’ve never had an issue just doing the crank either.
 
Flex plate is neutral balanced, sending that in wont change the bobweight. I dont think you can even balance a fluiddamper style damper, or a convertor without a special jig to hold the stator. All the 318 dampers are neutral balanced....a bunch of zeros add up to zero.
 
The 1 builder I know changes the fastners every time a motor comes apart. Doesn’t matter what rods or rod bolts are in it. Kim
 
Flex plate is neutral balanced, sending that in wont change the bobweight. I dont think you can even balance a fluiddamper style damper, or a convertor without a special jig to hold the stator. All the 318 dampers are neutral balanced....a bunch of zeros add up to zero.


If it’s a Chrysler style flex plate, it doesn’t make much difference. If it’s a GM/Ford style you’d better damn well bolt it on because it will change the balance of the crank.

Any shop that doesn’t balance the whole assembly should either learn to do it correctly or quit doing balance jobs. Everything needs to go on the crank when balancing, with the exception of quality dampers like the FD, Innovaters West and the ATI stuff.

If it looks like an OE damper in needs to be on the crank because it will change the balance of the crank.
 
Stock rod bolts were supposed to have 3 torque cycles, and 2 were used up at the assembly line! I'm not sure ARP or 180,000 psi bolts (Pioneer, Milodon, etc) are that fragile.
 
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