Considering the weight of the rotating mass and the relatively low speed of the engine i wouldn't hesitate to use the new one within 10 grams of the original ones

well making slow progress on the clutch it's almost ready to go back in. I am just trying to wrap my head around the clutch ailment as the book shows the motor was changed at some point in its life. so I did some checking and not overly happy with what I found. the flywheel is out  0.085 from 6 to 12 o clock in face run out plus I have 0.014 backlash in the flywheel itself.  clutch spec said 0.010 max runout I still have to find the end play spec for the flywheel to see if I need to be doing thrust bearings in the motor to tightening things back up 14 seems a lot to me but I know it's a slow running motor. well, I made new fold-over locks ready for the reinstall and pressed in a new bushing into the clutch housing.     

Hi mog5858,
maximum permissible end clearance is 0.025" and the Specification is 0.009" to 0.015" for the D318 engine.
Cheers,
Eddie B.

thanks for the information edb. that help's to put my mind at ease.

with the weather being cold out progress has slow all but to a crawl on the clutch.  I went ahead a pulled the flywheel bolts as I was not happy with the way it was running out. when removing the bolts I seemed to have pulled up some of the cast iron up is that normal for them to pull like that I know there a tight-fitting bolt but that surprised me a little.  I hoping to take off and inspected the crankshaft to flywheel matting surfaces today. Does anyone have to torque spec for the flywheel bolts I guess I will need them before going back together.
   

Hi Mogg,
it could be possible some in the past has fitted the flywheel and bolts dry on the bolt shank and one bolt at a time and tightened them as they went--it is preferable and best practice to install all bolts loosely so the dowel effect of the ground finish and neat fit of the bolts in the bolt bores of the flywheel can center the flywheel correctly.
I tighten said bolts in small increments and in a criss-cross torque sequence pattern as you would for vehicular wheel nuts etc.

The galling on the bolt shank and bore will need cleaning up. If the galling on the bolt is severe enough it can be a stress raising point and so be a fatigue failure site for the bolt in future.
Cheers,
Eddie B.

thanks for the info on my flywheel bolts they have no galling on the bolt shank and would say they were oiled before they were installed. everything looks good just a little razed edge at the face of the flywheel as shown. I will install the bolts oiled and go with torque spec for the bolt size and fold-over locks. when cleaning up the clutch housing I found my missing parts to put the clutch back together part # 16 and the broken off Cat bolts that were tie wired together rather than the use of a fold overlock as showing in the parts book I also found 4 sims that were living under #16   for a total of .100 shim but I can't find any info on shining the end of the shaft in either the parts book or the serviceman reference.  3 shims look to be factory make and one is homemade. shimming the end of the shaft would take adjustment away from the clutch so I see no need for them to be in there? input or thoughts about the sims would be nice. 
       

Hi Mogg,
there are indeed factory shims under the retainer plate as per the Service Magazine Feb. 20-1951 for both the D6 and D7 of the day as per the Serial Numbers given to limit the crush/draw on the retainer to 0.005".
Hope this helps,
Cheers,
Eddie B.

thanks for the information edb your a lifesaver now I understand why there are shims I going to do a dry assembly and see if I need them as my tractor does not fall in that range of the update
it's a D6-8U 2337. witch is about 2000 units newer as it does not start till 8U3965. without your help, I would never get this right thanks again Martin.