Fly wheel help

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Jul 6, 2011 | 07:48 PM

josephpaar

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Fly wheel help

I’ve got an 86 f350 4x4 that has a 6.9 with a manual trans. I recently got a 90 7.3 that was bolted to an automatic that I’d like to put in. Can I use the 6.9 single mass fly wheels on the 7.3? I keep getting conflicting stories on the whole deal. Some help would be great. Thanks.ffice

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Jul 6, 2011 | 09:52 PM

farmert

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From: western SD

When I put the 5 speed in my 85, I used a single mass conversion ment for the 7.3, and have had no issues with it. I would say you would be fine with the 6.9 flywheel on the 7.3.

Jul 6, 2011 | 11:07 PM

84-6.9L

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From: Princeton MN

They are different and should not be interchanged, as stated abouve it can be done but I did hear somehwere it may work better by swaping balancers also. I hope someone can chime in on that. Oh and by the way whats worng with the 6.9? It's a better block and if they are both NA I don't think the 5 to 10 hp gain is worth it.

Jul 7, 2011 | 10:50 AM

Phy

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From: 8600 ft in Colo

These motors are externally balanced by the flywheel & harmonic dampener. The 6.9 and the 7.3 flywheels & dampeners are different due to the difference in rotating mass of the two engines. 6.9 and 7.3 flywheels & dampeners shouldn't be interchanged. Many people have done it, but the balance isn't right. It may not be a big issue due to the low rpm these engines run, but it might...
If it were me, I'd get a new flywheel for the 7.3...

Jul 9, 2011 | 03:16 PM

josephpaar

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The only reason for the swap is because the 6.9 that’s in the truck needs to be rebuilt, and I don’t have the funding for that right now. I understand that a LuK clutch kit would solve the dilemma. If anyone has any experience with Luk id like the input. I pretty sure the kit comes with the SM fly wheel. Thanks! Oh, love the site, lots of good info. Thanks again.

Jul 9, 2011 | 04:34 PM

starmilt

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From: Faibanks Ak.

I put a 91 7.3 in my 84 in place of the 6.9 and used the 6.9 single mass flywheel with no problems for over 100,000 miles. I have since read that ford recommends changing the flywheel and the balancer, but I had no problems and no vibrations.

Jul 9, 2011 | 08:56 PM

540milotalon

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From: Near Shenandoah Valley

Your 6.9 will have a small spline ( 4 speed ) in it. The 7.3 came with a large spline (5 speed ) didn't it? Of course this one is auto trans. I really think there is not a problem. If I change a flywheel on the 6.9 to go to a 5 speed, it will most likely be a 7.3 complete kit. Instead of that I'm swapping out the disc only. Unless someone has a very convincing argument I'd say it all swaps.