4.1 Flexplate

[79bird]

Is there a difference between the 4.1 and 3.8 flexplates or are they interchangeable?

 

[Mease Performance]

flexplates

I believe they are different, not positive but the 4.1s we have here had different flexplates, if you rebalance the rotating assy you can use a 4.1 FP in a 3.8

can someone verify this?

 

[turbofish38]

Thats a tricky one. First turbos(both carb and SFI) use a different FW than 4.1 and 3.8NA. Depending on the year, 4.1 and NA FWs are the same but you have to have the balancer to determine. All years of 4.1 used the same FW. If your 3.8 has a solid(no rubber band joining two seperate pieces)balancer than the 4.1 is the same. The general rule of thumb is the flywheels are balanced to a particular set of pistons so if you have to put a FW on your motor its best to have everything rebalanced. Everytime I have a shortblock rebuilt I always send and extra FW along so I have a spare for those emergencies that never happen.

Eric Fisher

 

[79bird]

The motor that I'm inquiring for is a 4.1, NA, with an auto trans.

 

[turbojack]

4.1L flexplates----

I`m using a 4.1L out of a cadillac,1981, flexplate on that one is too small (less teeth) than the one that came on my orig 84TT,,by the way,that cadillac was a FWD,hope that helps--Jack

 

[cool 84]

I asked my engine builder the same question. The answer didn't matter because I have a few of both types of FWs. He said since we're balancing it anyway it didn't matter at all. I went with the 4.1 since it came with the motor. The turbo pistons are heavier, that's probably the difference in the FWs.

 

[turbojack]

4.1L flexplate

I also notd that when I got my 3.8L flex plate back from the balancer shop,It had been drilled in a few places to balance it to the 4.1L setup.Also the shop drilled a lot of holes in my damper up front,like about 6 holes,maybe I shoulda kept with my 4.1L flex and stuff ??

 

[87 turbo buggy]

Thats a tricky one. First turbos(both carb and SFI) use a different FW than 4.1 and 3.8NA. Depending on the year, 4.1 and NA FWs are the same but you have to have the balancer to determine. All years of 4.1 used the same FW. If your 3.8 has a solid(no rubber band joining two seperate pieces)balancer than the 4.1 is the same. The general rule of thumb is the flywheels are balanced to a particular set of pistons so if you have to put a FW on your motor its best to have everything rebalanced. Everytime I have a shortblock rebuilt I always send and extra FW along so I have a spare for those emergencies that never happen.

Eric Fisher

[WRONG].........!!!!% the flywheel/ flex plate has a commom static, common balance, as used in the even fire skyhawk, along with all others of the LB4 series motor. if what you said was true... ALL motores would need the motor pulled from the car and rebalance the flywheel\flex plate. the clutch cover would be indexed so as not to install it in the 3 possable bolt holes, and 6 different possible mounting holes for the flywheel the 4.1 and the 3.8 balancers from mid 77 to 86 may have looked the same from the front. in the rear now you will see the counter weight look quite different. also the outter cast iron ring on the 3.8, early year 4.1 [79.1/2 80] is drilled for weight pins, so the dealer could fine balance the motor's that had the shakes, that most... people did not like or recive well. use a brand new 4.1 rear flex plate. if running any thing for a harmonic balancer. Matt can install a interupter wheel on the rear of H\B, isen't that just great for replacement. if a H\B and the F\P has been balanced to a motor. i can rotate it 180* degeres and come up with a replacement with-in a few static grams at the center of each. Also have access to custom building and reinstalling new rubber on all haromic balancers, then heat curing the rubber. all the problems are gone.. while your at it up grade to the rotor oil pump.

matt

[extremeperformanceproducts@yahoo.com]

web of extremeperformanceproduct.com will be back up soon, must find why it keeps crashes, crashing,freeze out. someone sayes it has to do with .htl and html, dirt to me, must look it up. work in the machine shop is down, good for me want to get back to work on my 1918 5 toudor Ford.

ASE Master Mechanic,

Jourmey machinest, certified welder of all matels.

Master of much.

 

[turbofish38]

[WRONG].........!!!!% the flywheel/ flex plate has a commom static, common balance, as used in the even fire skyhawk, along with all others of the LB4 series motor. if what you said was true... ALL motores would need the motor pulled from the car and rebalance the flywheel\flex plate. the clutch cover would be indexed so as not to install it in the 3 possable bolt holes, and 6 different possible mounting holes for the flywheel the 4.1 and the 3.8 balancers from mid 77 to 86 may have looked the same from the front. in the rear now you will see the counter weight look quite different. also the outter cast iron ring on the 3.8, early year 4.1 [79.1/2 80] is drilled for weight pins, so the dealer could fine balance the motor's that had the shakes, that most... people did not like or recive well. use a brand new 4.1 rear flex plate. if running any thing for a harmonic balancer. Matt can install a interupter wheel on the rear of H\B, isen't that just great for replacement. if a H\B and the F\P has been balanced to a motor. i can rotate it 180* degeres and come up with a replacement with-in a few static grams at the center of each. Also have access to custom building and reinstalling new rubber on all haromic balancers, then heat curing the rubber. all the problems are gone.. while your at it up grade to the rotor oil pump.

matt

[extremeperformanceproducts@yahoo.com]

web of extremeperformanceproduct.com will be back up soon, must find why it keeps crashes, crashing,freeze out. someone sayes it has to do with .htl and html, dirt to me, must look it up. work in the machine shop is down, good for me want to get back to work on my 1918 5 toudor Ford.

ASE Master Mechanic,

Jourmey machinest, certified welder of all matels.

Master of much.

3 years later and my post answered the question.

Is there a difference between a 3.8 and a 4.1 flywheel? Yes.A physical difference. Reread what the thread starter asked.

And I do believe if you read my reply again you'll see Matt just repeated what I said. You can interchange 3.8 and 4.1 flywheels.

Now what was the purpose of your reply?