86ComancheXNate Posted January 25, 2012 Share Posted January 25, 2012 I've done some research on this and am now in the middle of this swap. From the research I have read I have found that I can re-use the flywheel from the 2.8 if I get some of the excess weight machined off and get it neutrally balanced. I called a local machine shop in town and ask for an estimate on the machine work and they told me that all they could do is resurface it without knowing the "bob" weight. Does anyone know what they meant by this and how I would figure this out? Link to comment Share on other sites More sharing options...
JeepcoMJ Posted January 25, 2012 Share Posted January 25, 2012 I've done some research on this and am now in the middle of this swap. From the research I have read I have found that I can re-use the flywheel from the 2.8 if I get some of the excess weight machined off and get it neutrally balanced. I called a local machine shop in town and ask for an estimate on the machine work and they told me that all they could do is resurface it without knowing the "bob" weight. Does anyone know what they meant by this and how I would figure this out? try a shop that builds driveshafts. they have lathes, and understand what it is to balance something out. Link to comment Share on other sites More sharing options...
86FUBAR Posted January 25, 2012 Share Posted January 25, 2012 you can also purchase a new flywheel for a early 90's chevy s10 2.8 flywheel as the later 2.8 were internaly balanced . Here is some good info on swaping the engines . http://60degreev6.com/forum/showthread. ... -questions page 12 post #116 has the flywheel info . Link to comment Share on other sites More sharing options...
hamilton Posted January 26, 2012 Share Posted January 26, 2012 I did this swap on an '85 XJ 2.8. Didn't address the flywheel(manual tranny, flexplate automatic) at the time of the swap even though I was aware it needed to be changed. The vibration under acceleration was unbearable past 25000rpm. If you can't find a shop to neutrally balance yours, I think they are still available from GM Performance Parts. That's the way I went. I figured the extra expense was worth it if i was dropping the drive train again. Was like night and day driving it after replacement. Never had an issue with the crank damper. Eagle was active on the NAXJA.ORG forum back in the day when a few of us did this swap. He might have something to add, or perhaps he's staying out of this thread to encourage the use of an archive search. ;) Link to comment Share on other sites More sharing options...
Eagle Posted January 26, 2012 Share Posted January 26, 2012 I've done some research on this and am now in the middle of this swap. From the research I have read I have found that I can re-use the flywheel from the 2.8 if I get some of the excess weight machined off and get it neutrally balanced. I called a local machine shop in town and ask for an estimate on the machine work and they told me that all they could do is resurface it without knowing the "bob" weight. Does anyone know what they meant by this and how I would figure this out? What it means is that you need to find a machine shop that knows what they're doing. That one obviously does not. Here's the deal: The 2.8L V6 was a crappy engine. One of the problems was that the design was not sophisticated enough to be inherently balanced, so in order to make the complete rotating assembly balanced GM had to add a chunk of metal at one point on the perimeter of the flywheel. This is referred to as a "bobweight," and engines that require this type of flywheel are called "externally balanced." The old AMC 390 V8 also required an eccentrically balanced flywheel. The 3.4L V6, being a newer and more advanced design, does not have the same balance issues and is internally balanced. So the flywheel doesn't need a chunk of metal at one point on the perimeter -- it needs to be "neutral" balanced, which is just saying it needs to be in complete balance all the way around -- just like we hope our tires and wheels will be. All the machine shop has to do with the 2.8L flywheel is grind off the bobweight and balance the flywheel. They don't need to know the weight of the bobweight, because you're paying them to remove it. Link to comment Share on other sites More sharing options...
Jeep Driver Posted January 26, 2012 Share Posted January 26, 2012 http://unitedspeedworld.com/ Take a drive to Tampa. These guy DO know what they are doing. Link to comment Share on other sites More sharing options...
mpace6a Posted January 26, 2012 Share Posted January 26, 2012 don't mean to hijack your thread, but I'm (hopefully) about to do the same swap, and was wondering if anyone knew if the ax5 that was bolted up to my 2.8 will bolt up to the 3.4, and if an np242 will bolt up to the ax5? again sorry for hijacking, but i figured this would be better than making a new topic for questions on a similar topic. Link to comment Share on other sites More sharing options...
Pete M Posted January 26, 2012 Share Posted January 26, 2012 the AX-5 will bolt up fine, but the 242 will need to be the older (and rarer) 21 spline variety or converted to be that from the later 23 spline. Link to comment Share on other sites More sharing options...
mpace6a Posted January 26, 2012 Share Posted January 26, 2012 how will i know what spline it is? Link to comment Share on other sites More sharing options...
Jeep Driver Posted January 26, 2012 Share Posted January 26, 2012 89-90 XJ Wagoneers and Limited..............all have the 242. Also a source for non CAD axles. I don't want to speak out of line on spline count but I think that's what the other guy meant by 'older'. 89 to 90 seems to be a dime a dozen round here......just a matter of price. Link to comment Share on other sites More sharing options...
Jeep Driver Posted January 26, 2012 Share Posted January 26, 2012 http://charlottesville.craigslist.org/c ... 30897.html Link to comment Share on other sites More sharing options...
carnuck Posted March 7, 2012 Share Posted March 7, 2012 Jeep used to have 2 different flywheels because when they did a replacement motor, they had to use the internal balanced engine after '87 (GM ran out of the external balanced ones they pawned off on AMC) Don't assume your motor is externally balanced! Look at the plate for either massive drill outs on one side or a weight on the automatics. Link to comment Share on other sites More sharing options...
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