I first searched the archives for an answer but couldn't find an exact.
Being new to SBC engines, I have an '87 one piece RMS 350 short block that may be going back to the machine shop to have done for a second time. (a story for another thread)
It was just a hone & ring job using the same pistons,etc so no re-balancing was done.

My question is if this block ends up going .030 over it obviously will then need to be re-balanced. Will I have to give them the flywheel for balancing? (manual trans car)
I have read these one piece RMS engines are kind of a hybrid when it comes to being an internal or external balance engine. They are an internal balance but use a weighted flywheel/flexplate and the typical neutral balance harmonic balancer.
Since the flexplate/flywheels for these particular one piece RMS engines are weighted (because of no external counterweight on back of crank) are they pretty much interchangeable so it wouldn't matter if I give them my flywheel or not? Am i understanding this wrong?

The engine was originally in an auto trans car and it will be now going into a manual. Is it a good idea to supply the machine shop with my flywheel for balancing?

 

DO NOT UNDER ANY CIRCUMSTANCES
let your flywheel / flex plate exist in the same shop when doing ANY "balancing"!!!!!

Have the shop balance the crank rods & pistons to the STOCK spec. The operative word here is STOCK. Have the flywheel balanced elsewhere/elsewhen to the STOCK spec. That way, you have a motor that you can bolt ANY flywheel to whenever whyever you need to, and a flywheel that you can bolt to ANY motor it might need to. (such as for example if this current project goes south for whatever reason) Or, if you put it in another car, with a different transmission.

The late-model 305/350 setup is NOT "externally balanced", no matter what the catalogs say. It is still INTERNALLY balanced. "Internal" vs "external" does NOT depend on which side of the crank/flywheel split the weight is on. Because of the MASSIVE confusion that exists in the minds (I use the word loosely) of "customers", many people who should know better, have GIVEN UP on enforcing the CORRECT use of the words. Regardless, it's best to stick with the words "STOCK spec"; and MAKE DAMN SURE that there's NO WAY IN HELL that either your motor or your flywheel will get "balanced" to ANYTHING BUT that.

 

I get what you are saying about if the new flywheel was balanced with this engine they'd then have to stay "married" but wouldn't the new flywheel already be balanced by the manufacturer since it's being sold as a replacement part to fit this particular engine family? In this case a later 350 engine that uses/needs a balanced flywheel?

 

Like Sofa said, have the shop balance the internals to stock specs. A new flywheel comes balanced already, no need to send it anywhere.

 

Generally yes; butt its perfection can often, in fact nearly always, be improved.

Not sure where you're going with this. ALL engines benefit from a properly "balanced" flywheel, whatever their specs may be.

In the case of the 86-up 305/350, they made the flywheel flange on the crank absolutely round, so the seal could go over it.

All 85-back SBCs except the 400 used neutral-balanced crank dampers and flywheels/flex plates. That made things pretty easy and straightforward, without confusion. All balance weights were part of the crank except 400. All of these earlier SBCs with stroke greater than 3" (which would be, all of them including the 400 except the 265 & 283) required that flange to be asymmetrical, to create a balance weight for the rearmost journal.



When that feature was forced to be abandoned by the 1-piece rear main seal, they moved that last little bit of INTERNAL balance weight to the flex plate / flywheel, which to the untrained eye, makes it look "external". IT IS NOT. Those cranks are still INTERNALLY balanced, since all the balance weights are right where they need to be, which is to say, each individual crank throw has the correct amount of balance weight properly distributed right next to it on either side of it. This is unlike SOME motors, where there isn't enough space to put that much counterweight in the correct INTERNAL (between the journals) locations, so the required weight to STATICALLY balance the assembly is mounted EXTERNALLY (NOT between the journals), which more often than not, means that it is also on a separate piece, although it doesn't absolutely have to be. Motors like that are not DYNAMICALLY balanced however, since each crank throw no longer has the right counterweights right next to it, making it inferior to internal balance. A part that isn't dynamically balanced will still vibrate, even if statically balanced, because different parts of it are trying to fly off in different directions, which tries to make the whole thing "wobble". This is why internal balance is always preferred for high-RPM applications wherever possible.

The whole "appearance" thing looking like the weight is external even though IT'S NOT, is the reason for the confusion about THAT PARTICULAR CONFIGURATION (86-up 305/350), and the ambiguity and lack of rigor in the "naming" of its balance.

The one thing you DO NOT WANT, EVER, is a rotating assy that's set up for ONE SPECIFIC flywheel, or a flywheel that will only work with ONE SPECIFIC rotating assy. That's the reason for specifying STOCK balance specs on both, and for NEVER EVER AT ANY TIME FOR ANY REASON allowing those 2 parts to exist in the same shop at the same time. The temptation to take the easy way out is often TOO GREAT TO RESIST for the balance tech, and they end up balancing ALL the parts together, in which case you end up with the unmaintainable and DEAD FUTURE situation where there is ONLY ONE flywheel in the entire known universe that will work on that rot assy and/or ONLY ONE rot assy in the entire known universe that will work on that flywheel, and you have NO WAY TO KNOW what if anything is compatible with anything else. DO NOT LET that happen to you!!!! It REALY SUCKS when something has to be changed on down the road, and you discover that NOTHING you have will interchange with ANYTHING ELSE, until/unless you disassemble it COMPLETELY and re-balance it ALL.