Flexplate Woes... (Page 1/3)
eti engineer NOV 22, 07:45 PM
OK Gents, help me out on this one...

I have a new long block engine coming from Accurate engines. It will be an LA1-based build. I just pulled the old 2.8 liter engine and the bay is empty, awaiting the arrival of the new 3.4. The issue I am facing is whether or not to get a new flexplate (I understand that this may be a necessity) and if so, which flexplate, by part number (like from the Fiero Store, or elsewhere) should I get. I have been told that I cannot use the old flexplate, but don't know which flexplate I should order. I am sure someone in here has done this mod before. Can you please help me out? Thanks in advance....
Raydar NOV 23, 10:14 AM
If it's an 88, your old flexplate should work.
Otherwise, you'll need one for a 60 degree V6 (3.1, 3.4 or 3.5) from a FWD application.
I wouldn't be surprised if most all of them are the same part #.
Make sure it is drilled to accommodate whatever torque converter your trans uses.
eti engineer NOV 23, 09:34 PM
Raydar,

Thanks for the information. I have heard, possibly mistakenly, that there can be spacing issues with the transmission. The old flexplate looks good. The ring gear teeth are in excellent condition and a visual reveals no defects. I guess I will give it a shot and see. I see no reason it shouldn't work, but I am a neophyte when it comes to swapping out anything in a Fiero. I once put a mildly massaged Datsun 280Z engine and 5-speed manual transmission in a 530! BMW that had a floor shifter automatic in it. That was not too hard, but I was using intact units to do it. I didn't have to get down to the component level. I am in no rush to get this done, so I will take my time and get it right and let others know what I learn. We all benefit from the knowledge in here, and there is a lot of it.

Have a great Thanksgiving Day, especially under the circumstances in which we find ourselves.

c.
olejoedad NOV 24, 06:28 AM
The early 2.8 v6 was externally balanced.

In 88, the 2.8 was changed to an internally balanced design, as were all later 60° V6's.

The two designs use different flex plates - due to the balancing issue.

You must use a neutrally balanced flex plate with your swap.
eti engineer NOV 25, 06:15 PM
Olejoedad,

Thanks for the comeback. I will look for the proper replacement. Just out of curiosity, what would have happened if I used the original flexplate?
eti engineer NOV 25, 06:30 PM
Olejoedad,

Thanks for the comeback. I will look for the proper replacement. Just out of curiosity, what would have happened if I used the original flexplate? Vibration???

[This message has been edited by eti engineer (edited 11-25-2020).]

Gall757 NOV 25, 08:56 PM
Yes.....vibration.
eti engineer NOV 26, 11:05 AM
Thanks. I did some reading on this and now I understand the issue. I used to teach vibration analysis and fully understand how just a little bit of imbalance can create a fairly large amount of vibration when rotated. As I recall, if one puts a 2-ounce weight at a radius of 3 feet on a perfectly balanced disc and spins it at 3600 rpm, it will exert a tangential force of over a ton. Tough on bearings and I am sure one would feel it throughout the car. I have located a source for the flywheel I need. Have a great Thanksgiving!!!
Raydar NOV 26, 02:08 PM

quote
Originally posted by eti engineer:

Thanks. I did some reading on this and now I understand the issue. I used to teach vibration analysis and fully understand how just a little bit of imbalance can create a fairly large amount of vibration when rotated. ...
Tough on bearings and I am sure one would feel it throughout the car.



I had a friend who had an old Chevy Nova. Had a 350 and a 4 speed. Engine ended up breaking, and he replaced it with a 400 and an automatic.
The 400 was (supposed to be) externally balanced, but he ended up using a 350 flex plate. It vibrated like a Home Depot paint shaker. I'm amazed it stayed together.
eti engineer NOV 26, 08:15 PM
Raydar,

I am sure that it would be a bad vibration. It really doesn't take much to produce it . This is why when you lose a balance weight on a wheel, it feels like hell, and your wheel is not spinning at a high rpm when compared to the spin of the crankshaft. I was not aware of the issue with external and internal balancing. I found out about it through you and others in here. Thanks for looking out for my best interests. I would hate to have gotten the whole thing back together, just to find that I had to pull the whole engine and drivetrain cradle again!!! I am retired and in no big hurry to get this thing back together. I just want to take my time and do it right. For anyone who has been through this and who might be aware of any pitfalls I should avoid, please speak up. The Fiero configuration is one I have not dealt with before now.

Hope you had a great Thanksgiving!! Leftovers forever at or house now. It's just my wife and me, and it takes a while to eat what's left.

Later...