The Head nuts on a Twin Cam were never and issue, the M8's are junk. Use one time and toss them. They break in half just above the threaded area. Several engine builders have tried to reuse them and have had issues and SE added them into there Stage IV kits but may not have updated the parts list. As I recall the last ones I bought were pretty cheap from HD. The ARP replacement nuts are big bucks but if you plan to tear it apart many times well worth the money.

 

Right! This is all I was saying. It is not news to some of you like Steve and a couple of others.
I am just sharing the info that I have found from personal experience.
We have built MANY, big power M8s and we have had a few head bolts snap in half....during assembly, or worse in the field

 

So from what I am discerning, the ones that you have had break are ones that were reused, not brand new HD flange nuts. The new ones that have only been torqued once are holding up fine, correct?

 

From what I observed when I built my 120, the cylinder studs on the M8 are larger diameter than the twin cam, but the walls of the flange nuts are not any thicker than the twin cam, so they are weaker. I used new flange nuts.

 

I asked FM if they used new flange nuts on their M8 builds, and the answer was no. I reused mine, but since I've torqued them a few times (wrong cylinder, now decided to install the level B heads), I will be using new nuts on the final assembly. I asked the local shop who will be doing my dyno tune what they do on these engines, and they said they've always reused them also with no issue. I guess it's a crap shoot.

 

In November of 2016 My new Road Glide got a stage III done that included new Flange Nuts. The Installation sheet states "Install cylinder heads using NEW flange nuts included in kit" This kit was early on, instruction sheet is dated 2016-10-07

 

The PN: 10200303

 

That's the same number as the stock flange nuts, so there is apparently no SE version as Peter was inferring. If the stock ones are fine for a single use then that is what I will go with. The Fueling's are close to $30 each, compared with $5 each for the HD's.

 

You can reuse the nuts, as many times as you want to.
My tip is to buy new ones, just like head gaskets.
It is not a MUST DO, but I wont reuse them again.
Only because we had two different M8 jobs snap nuts after we built the engine...
Of course it blows the head gasket and it is an all day fix.
Out of 25 more engines, with new nuts, no engines have broke head nuts...
I am ONLY sharing my experience.

 

I heard HD went to a 7/16-NC thread on the head bolts. Aftermarket doing anything?