6.9L vs. 7.3L IDI piston weight ? - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 2 (permalink) Old 06-17-2011, 03:36 PM Thread Starter
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6.9L vs. 7.3L IDI piston weight ?

I am new here so Hello to everyone ! I am in the process of changing over an early 6.9L with 4 speed manual trans. to early 7.3 L. I would like to use the flywheel from the 6.9L to make things easy and cost effective.
The 7.3 L was removed from a running vehicle so the engine is assembled.
I am told that there is a balance issue if I do this ? I will rebalance the flywheel but in order to do this I need the difference in the weight of the pistons from the 6.9 L to the 7.3 L.
Any help would be greatly appreaciated. Thank you in advance, TBolt
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post #2 of 2 (permalink) Old 06-17-2011, 04:52 PM
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A little advice from an engine builder's perspective:

See if there is an aftermarket flywheel from South Bend or another reputable source like Centerforce that offers the correct balance, has the same ring gear spec, and offers the clutch pattern you need. Any time you change the balance on a flywheel without it being balanced with the crankshaft, you create a potential problem with vibration. That vibration may not be super evident in your application, but if it's there and goes unnoticed, you could wipe out the bearings or even break the crankshaft in that 7.3. An aftermarket flywheel will have the right balance (offset weight) to be within the oem range and let your project proceed without worry.

I've seen this kind of situation with gas engines literally hundreds of times, where the original engine is a different balance than the later engine and the guy gets the wrong flywheel or flexplate. Happens with small and big Chevrolet and Ford regularly these days. All it takes is a little research to know what the have and the issue is an easy fix, yours is potentially no different.

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