6.9 7.3 flywheel the same?

[IDIBRONCO]

Maybe they thought you're cute and were hoping for a kiss afterward?

 

[austin92]

Maybe they thought you're cute and were hoping for a kiss afterward?

Maybe, but I don't know how they'd see me over the phone.


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[tjsea]

The 6.9 flywheel will need machining to fit a single mass 5sp clutch kit. I know because I've done it. If you look closely the center around the crank bolts isn't nearly as big as a zf5 single mass flywheel is. You can redrill the flywheel for the pressure plate, but the springs in the center of the disc rub the flywheel. All that needs to be done is throw it on a lathe and cut the center out wider to clear the springs. It only needs to be about 1/4in deep though. Don't cut it to the full depth of the center as the flywheel gets thin out twords the edge then. I did this 10 yrs ago and redrilled it for a luk single mass clutch kit and it has been working great with no issues at all.

 

[austin92]

Any reason to order a 6.9 over a 7.3 flywheel? There's about a 40$ price difference on parts geek


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[austin92]

This thread kinda died and I still haven't ordered my flywheel. What makes the price difference between the 6.9/7.3 smf? Should I order one over the other?


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[Macrobb]

If you have a 6.9 infront of a ZF5, you can totally use a 7.3 SMF clutch kit for the 88-94 non-turbo specification.
I ended up with a Valeo 12" one because it came up cheap, but otherwise I'd go for the LuK 07-225.

Check RockAuto and Ebay to see what's cheapest. Or go with somebody like Autozone which will be a little more expensive, but will take returns easily.

 

[austin92]

I was just wondering if there was a benefit to one over the other and what made them different prices


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[Macrobb]

I was just wondering if there was a benefit to one over the other and what made them different prices


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I don't know.

What I know is:
In theory the SMF flywheels between 6.9 and 7.3 have different balancing masses... but in practice, the difference doesn't seem to be big enough to matter.

Heck, the 7.3 turbo flywheels /definitely/ have a different balancing mass... but it's totally possible to run the wrong one despite all the warnings.
Justin @ R&D ran a turbo-flywheel on a non-turbo 7.3 engine for a while - this was the motor that made over 400HP before the connecting rods failed.
Mind that the imbalance did not snap the crank or shear the block or anything.
It's not recommended as you can get the right part cheaply enough, but I thought I'd point that out.

In my case, I got my flywheel expecting to have a 7.3 motor(it's a 92 truck!), but it turns out that some previous owner had swapped in a 6.9.
Didn't want to buy *another* set and have to wait around for parts, so the 7.3 setup went in.

When looking at parts, remember that:
1983-86 had 6.9s with 4-speed transmissions. These have a 1 1/16" spline and are all SMF flywheels.
1987 had 6.9s with either a 4-speed the same as the 86, or a 5-speed with a DMF flywheel. The 5-speed spline is 1 1/4"
1988-1992 are all 7.3 non-turbo blocks with 5-speeds, DMF and 1 1/4" spline.
1993 and 1994 are either 7.3 non turbo or 7.3 turbo block with different DMF(1994 also has the PS motors, "direct injection turbo")

If you've got a 6.9 and 5-speed then either:
1. 1987 stock DMF
2. 1987 smf replacement kit
3. 1988-92 SMF replacement, which might have a slight imbalance.

The SMF flywheels are going to be the same diameter, size, bolt pattern etc. with different imbalance.
I'm sure that you could take a SMF or DMF from a 6.9 and re-drill it for a 12" clutch plate and disk, because that's all that's different.

You just need to make sure that your disk has a 1 1/4" spline on it, and the disk type(smf/dmf) matches your flywheel. Pressure plate is going to be basically the same, though a stock 6.9 DMF plate uses 6 bolts and an 11" disk; 7.3 came with 8 bolts and either a 11 or 12" disk.

Confusing enough for you?

 

[austin92]

I don't know.

What I know is:
In theory the SMF flywheels between 6.9 and 7.3 have different balancing masses... but in practice, the difference doesn't seem to be big enough to matter.

Heck, the 7.3 turbo flywheels /definitely/ have a different balancing mass... but it's totally possible to run the wrong one despite all the warnings.
Justin @ R&D ran a turbo-flywheel on a non-turbo 7.3 engine for a while - this was the motor that made over 400HP before the connecting rods failed.
Mind that the imbalance did not snap the crank or shear the block or anything.
It's not recommended as you can get the right part cheaply enough, but I thought I'd point that out.

In my case, I got my flywheel expecting to have a 7.3 motor(it's a 92 truck!), but it turns out that some previous owner had swapped in a 6.9.
Didn't want to buy *another* set and have to wait around for parts, so the 7.3 setup went in.

When looking at parts, remember that:
1983-86 had 6.9s with 4-speed transmissions. These have a 1 1/16" spline and are all SMF flywheels.
1987 had 6.9s with either a 4-speed the same as the 86, or a 5-speed with a DMF flywheel. The 5-speed spline is 1 1/4"
1988-1992 are all 7.3 non-turbo blocks with 5-speeds, DMF and 1 1/4" spline.
1993 and 1994 are either 7.3 non turbo or 7.3 turbo block with different DMF(1994 also has the PS motors, "direct injection turbo")

If you've got a 6.9 and 5-speed then either:
1. 1987 stock DMF
2. 1987 smf replacement kit
3. 1988-92 SMF replacement, which might have a slight imbalance.

The SMF flywheels are going to be the same diameter, size, bolt pattern etc. with different imbalance.
I'm sure that you could take a SMF or DMF from a 6.9 and re-drill it for a 12" clutch plate and disk, because that's all that's different.

You just need to make sure that your disk has a 1 1/4" spline on it, and the disk type(smf/dmf) matches your flywheel. Pressure plate is going to be basically the same, though a stock 6.9 DMF plate uses 6 bolts and an 11" disk; 7.3 came with 8 bolts and either a 11 or 12" disk.

Confusing enough for you?

This post actually took all the information I've read that was confusing the hell out of me and made sense of it so thanks man


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[junk]

Macrobb summed it all up very well.