Originally Posted by 377MONTE
I am looking into a few of the different balanced rotating assemblies available for a 377/383 stroker build. need some help here..
Eagle sells a BALANCED external balance 383 rotating assembly that comes with a new flexplate and harmonic dampener. Will this pre-balanced kit be good enough to drop into the block and bolt up, or will i need to have my local machine shop check their work and rebalance it???
Sometimes Yes and sometimes No. We had them both ways and when they aren't right it's a costly fix as the engine has to be torn down, cleaned, the rotating parts sent to a balance shop or worse returned to the source which often became an argument over what was or not done to the parts. So we stopped using kits a looong time ago. They may be convient for engine assemblers but not what an engine builder needs. When you build an engine you check and inspect each part and the assemblies they make. Often, especially with strokers you find adjustments need to be made for fit checking purposes. This is not to mention that some balancers just think that getting the whole thing kind of close is good enough where I want specific balances in particular places along the crankshaft.
So we buy only pieces and build the combinations. This also gives me a chance to select the exact combination of parts from various manufacturers and sources that I prefer and trust or want to experiment with. Balance is one of the last operations we do, however, the engine will be assembled and checked for timing between cam and crank and clearances of bearings and parts at least once for a standard build and several times for custom/competition builds even when using common off the shelf parts as often you get unpleasant dimensional surprises that are a lot easier to deal with before fire is put in the cylinders. Balance quality will vary between street and competition builds with that varience is cost. There is little sense in putting the effort (thus cost) into a mild performance street build up as goes into a high level competition engine and the type of balance between simple straight up versus games with under or over balance as this gets esoteric and costly and is not necessary for engines that don't see RPMs in the 6000 up range. That's not to say that a hot street engine isn't balanced well and correctly but I'll accept a bit wider tolerance in the intrest of cost. That is unless the customer wants it to the knats and is willing to pay for it even if it will never be used nor felt, if the customer want to spend money on an overbuild I'm willing to take it and we have several that do just that.
So the summary is that prebalanced kits may or not be correct and may or not be correctly done. Then there is aways the issue that assembly may require changes that upset the balance requiring it be done again. Lastly, if the balance isn't correct it takes engine removal and disassembly to correct which is a lot of effort and cost that is most likely not going to be covered by the manufacturer or seller.