If you have a TC and you want to go gear driven cams the crank can have no more than .003" runout or you have to get it trued and welded (at least that is what they say in the other forums). Since Sportsters have the geared cams does that mean that their cranks are held to the same tolerance from the factory or are these totally different animals and the crank runout on a Sportster is not so important. Just curious!

 

Harley went to chain cam drive on the twincams, but only after a few years of production realised they don't need to maintain the tight tolerances they had used since the dawn of time on crankshaft runout! So they relaxed them. They continue to build Sporty cranks to the same older tolerances, otherwise the cam gears wouldn't run. Spec for runout at the shafts in my factory service manual is zero to .002".

 

Never occurred to me to check my factory manual.

 

Table 3-12 in mine!

 

Thanks, you made it easy to find that spec. Lots of other tables in that section with mucho information. Funny, the FSM was the first accessory that I bought for the bike though I find the body of knowledge in this forum to be invaluable and have learned that sometimes you need both.

 

Just a note: The true specs on the twin cam have not been changed. What has changed is that they must be checked on V blocks. The two machined and ground bearing surfaces are finished together within tight specs.

Using the center points on each end that where machined separately is not the way to check correctly. The splines on the end were machined prior to the two sides being matted and run out doesn't mean crap between them. Most HD dealers and indy's are clueless to the proper testing of the crank.

A crank that shows 10 to 12 thousandth on the spline end with show .001 when the crank is on a test bench resting on V blocks with dial indicators on the ground bearing surfaces. This is the biggest myth that exists with the TC's.

There is a large cottage industry truing TC cranks that there is nothing wrong with. However any power build should weld that sucker.

There is a great Utube video showing a HD dealer identifying the correct procedure and showing the results of both methods.

 

My pleasure ntg433! You'll find that book a real page turner - better than counting sheep on those sleepless nights!

lh44, thanks for underlining my long held opinion that scissoring is over-played. I now understand how that has come about!