External Balance For Even Fire Buick 231

I am hoping one of you can help me. My CJ had an engine swap done by the previous owner to an odd fire Buick 231. I am now replacing that engine with an even fire 231. My new engine should be here on Friday, but I do not know how to correctly install the flex plate.

I do know that both the odd and even fire engines are externally balanced, and I have purchased the correct flex plate and harmonic balancer for the new even fire engine. The problem I am having is the bolt pattern on the flex plate is not (or does not appear to be) asymmetrical, and I am worried I will not have this installed correctly. Everything I have found talks about marking the old flex plate / flywheel and installing the new one in the same orientation. I still have the old odd fire engine and flex plate and I had marked them, but I am guessing that the orientation is different.

Does anyone know what the correct orientation is for the flex plate? I have emailed the vendor I ordered my engine through several times, but they have been unable to help with this.

The new even fire flex plate has several letters / numbers stamped around the outside edge. If I have it sitting with the number 3 (at the 12:00 position), the numbers going around are 5 at roughly 2:00, S at around 4:00 followed closely by a 7, 6 at 6:00, 11 at around 8:00, and 1 at around 10:00. I'm hoping that when you set the engine to TDC for the number 1 cylinder there is an identifiable way to correctly index this flex plate to the engine. If it helps the flex plate appears to be weighted heavier (less material removed) between the 6 and 11 at around 7:00 as I have it sitting. On my old odd fire engine it is that heavier portion between the 6 and 11 that is at the 12:00 position when installed on the engine with the number 1 cylinder at TDC.

 

Flex plate or flywheel? Flex plates are for automatics. Flywheels are for manual transmissions.

If the engine is external balanced, the flywheel/flexplate will only mount one way. The bolt holes will be asymmetric and only fit the bolt holes one way. If neutral balance (aka internal balance), the rotating assembly (crank, rods, pistons) does not need the flexplate/flywheel for balance, thus it can mount in any orientation.

I suspect the even-fire engine is neutral balance, and the odd-fire engine is external balance.

 

I am using a flex plate for use with my TH350. I just figured I could apply the same logic if someone knew the answer for a flywheel as they are being used to balance the same internal components, so the heavy section would be in the same location in relation to the crank. I thought both the odd and even fire Buicks were externally balanced, but I am new to these old Buicks. My past experience had shown that externally balanced engines should have asymmetrical bolt patterns or a locating pin to prevent the flywheel / flex plate from being installed incorrectly as you had noted. Can you see the picture in my initial post? That picture is of the new flex plate and just the shape and location of the circle and half circle cutouts makes it look like it is not neutrally balanced, but the bolt pattern is not asymmetrical. I have attached the photo of my old flex plate from the odd fire engine to this post for comparison.

To me they both look to be weighted with the heavier portion being between the number 6 and 11 markings where the large half circle cutouts are. I could be wrong on that and I guess it is possible that my odd fire engine had been rebuilt internally balanced, and if the even fire is internally balanced like you suggested that would explain my confusion.

 

All Buick V6 engines come from the factory as externally balanced. However, if the Internals have been modified , on that engine, then all bet's are off. Don't worry , If you have a stock 231 , the flywheel /flex plate will only mount one way . Same goes for the Harmonic Balancer.

 

okay so I should have measured the bold pattern rather than just eyeballing it. I just pulled my calipers out and measured, and the pattern is asymmetrical just not by much. This would have become obvious if I had the new engine here and was trying to line up the holes and not just worry about making sure we are ready with all the parts and ready to get this thing back running.

 

Oh ..... I just reread that you do not have your new engine there yet ? Anyway, You'll have no problem's with what you were sent. They'll go on the same way as your Odd Fire , 'cuz both Buick engines are externally Balanced , at the Factory.