Harmonic Balancer Puller Bolt Size

[Hardway]

I already have the large 27mm bolt removed from the engine.  The balancer has two threaded holes that are to be utilized when using a puller per the FSM.  Unfortunately it does not state what size the holes are.  An M6x1.0 bolt is too big and a M5x0.8 bolt is too small.  I have spent about 20 minutes trying various bolts in my collection and so far no luck.  Does anyone know what size the holes are?  Thank you.

[Zed Head]

Found this in my 1976 FSM.  Weirdly, it doesn't show L28 as an application.  But it does imply the bolts are 1/4", non-metric,  also weird.

[Hardway]

Thank you Zed Head.  Unfortunately 1/4 inch is too big.  After some more trial and error I have determined they are SAE 12-24.  Now the hard part is finding a strong enough bolt in that size that will be long enough to work with the puller and not break.  The search continues.

[Namerow]

I discovered the SAE thread anomaly, too.  I can't remember what I used as the puller cross-piece (maybe my generic steering wheel puller), but my recollection is that it really didn't take much force to make the harmonic balancer free up.  I'm pretty sure I just used hardware-store grade bolts.  Why not give it a try before you get too worked up about trying to find high-strength bolts?  The balancer is a tight sliding fit, but not an interference fit...

... unless there's been corrosion at work.

[Captain Obvious]

12-24? Seriously? That's evil. Sure it exists, but nobody ever uses that size!

Honestly, I suspect they are really M6-1.0 but there is rust in the threads that make it seem as though the M6 is too big. For the record... M6-1.0 (converted to inches) is .236 x 25.4 TPI

And (according to a quick web search) 12-24 has a major diameter of .216 in. So 12-24 would be .216 x 24. So 12-24 (converted to metric) is M5.5  x  1.06

I bet you could run a M6x1.0 tap in there and clean up the threads. Or maybe you could give a M6 x 1.0 bolt a quick hit with a file and knock the crests off the threads and it might fit?

I'm certainly not saying it's impossible, but I'm just very skeptical they did that!

[Hardway]

Good news, I got it off.  Just as Namerow predicted, once it was started it came off with just some medium effort.  I used a pry bar to gently push on it and I could see the shininess of the crank in the gap between the balancer and the timing cover widen.  Once it was 1/3 away from the timing cover I was able to work it off by hand.

I tried a M6x1.0 bolt and tap and it would be quite a bit of material to overcome.  I was happy to get it off as everything else came apart as planned with no surprises.

Edited August 10, 2018 by Hardway