Flexplate Balance Matching Ext. Bal,

I have an externally balanced (hatchet) stroker rotating assembly, however I am not going to use the flexplate used for balancing can I upgrade to an aftermarket SFI flexplate and have it matched to the balanced flexplate or do I need to rebalance the rotating assembly for the SFI flexplate?.

The balance shop I use here in So Cal has done it several times for me.

From what I understand most cast crank stroker kits are made for the external balance parts to be used so that the crank will not need mallory. This reduces the balance cost because material will be removed from the cast crank. The cost difference on the balance is roughly $170. Both weighted and non-weighted flex plates are available with SFI certs.
There is nothing wrong with using external weighted parts to help balance.
If you have an SFI weighted flex plate you could cut the welds/weight off to make it same as a non-weighted plate.

Dave De wrote:From what I understand most cast crank stroker kits are made for the external balance parts to be used so that the crank will not need mallory. This reduces the balance cost because material will be removed from the cast crank. The cost difference on the balance is roughly $170. Both weighted and non-weighted flex plates are available with SFI certs.
There is nothing wrong with using external weighted parts to help balance.
If you have an SFI weighted flex plate you could cut the welds/weight off to make it same as a non-weighted plate.

It is an FRPP 521 that was balanced with a non sfi external balance flexplate, the tick is getting a Meziere neutral balance SFI flexplate to balance with the externally balanced one, the externally balanced one had drilling on the factory weight and weight added, overall weight not the issue the placement of the balancing offset weight is in order to keep the overall assembly balanced, I have had it done on 351C in the past but if I am going to do it I need a double check to know it is correct.

So you want to re-establish the flex plates weight before it was modified. The weight is steel and it has an overall size still identifiable? If yes then weld up the hole. You can also cut off a bolt and thread it into the hole to fill it. There shouldnt be a need to balance the plate or check it.

rmcomprandy wrote:

FalconEh wrote:

Dave De wrote:From what I understand most cast crank stroker kits are made for the external balance parts to be used so that the crank will not need mallory. This reduces the balance cost because material will be removed from the cast crank. The cost difference on the balance is roughly $170. Both weighted and non-weighted flex plates are available with SFI certs.
There is nothing wrong with using external weighted parts to help balance.
If you have an SFI weighted flex plate you could cut the welds/weight off to make it same as a non-weighted plate.

It is an FRPP 521 that was balanced with a non sfi external balance flexplate, the tick is getting a Meziere neutral balance SFI flexplate to balance with the externally balanced one, the externally balanced one had drilling on the factory weight and weight added, overall weight not the issue the placement of the balancing offset weight is in order to keep the overall assembly balanced, I have had it done on 351C in the past but if I am going to do it I need a double check to know it is correct.

IF it is a Ford Racing engine directly from Ford Racing it will have a factory O.E.O. external balance flexplate.
Any holes drilled in it or the weight were done at the Ford factory to get that flexplate to meet factory external specifications.
Some of those 521 crate motor have mallory AND external balance.

So each flex plate is specially balanced to the rotating assembly. Then Falcon needs to have the old flex plate checked for balance and recreate the same imbalance and angle on the new plate.

I used a NOS Ford Racing 514 crank and had to have a piece of Mallory even with "truck" rods and lighter aftermarket pistons. $275 balance job. I used a NOS D9TZ flex plate ( counter weighted)

gt350hr wrote:    The balance shop I use here in So Cal has done it several times for me.

rmcomprandy wrote:

Dave De wrote:

So each flex plate  is specially balanced to the rotating assembly. Then Falcon needs to have the old flex plate checked for balance and recreate the same imbalance and angle on the new plate.

NO ... each flexplate from Ford Motor Company is balanced to a pre-determined counterweight spec for production engines.
ALL 460 external balance flexplate/flywheels for a O.E.M. external balance 460 production engine are balanced to a 24.2 in/oz counterweight spec.

Actually you are all correct, I did not explain myself well enough the rotating assembly is new but the assembly has been sent out and balanced including the flexplate(no longer stock), which is why it needs to be duplicated. I have an avenue now to get it done, so I believe I can get it done semi locally.

Thanks for the replies

I bought a cast Scat 4.3" rotating assembly a few years ago and last year knocked a few teeth off the flexplate. My rotating assembly had been balanced when new. When I pulled the old flexplate, it appeared that the external balance weight had been drilled in 2 spots. I thought to myself, "oh crap! How will this ever be perfectly duplicated now that the flexplate has teeth missing?" I called the balance shop and they said the flexplate had not been touched. We actually got in a pretty heated argument over it because I definitely saw a hole drilled in the small weight welded onto the flexplate. So, regardless I needed a new flexplate. I got on the net and ordered a new Scat plate. Low and behold the same holes were drilled in the new plate's weight. I called the balance shop back and apologized.

Long story short ---- I believe the holes you are talking about can be stock on the external balance flexplate.

Jon

That's true. Plus the holes can vary a bit due to the amount of weld used to attach the weight and sometimes the weight itself is a little heavy. Drilling holes is easy, adding weight is usually more expensive. Ford parts are usually right on spec.