Background:

A few months ago in the process of installing cams I was installing the rocker arm plate back in the front cylinder, when torquing down the holder bolts as per the manual specs and with a torque wrench set in the middle of the torque range, the left bolt on the pushrod side snapped, it broke in half, a grade 8? bolt snapped, well, ordered a new one on the HD dealer (3 weeks for a goddamm bolt), got the broken one out (was easy since it didn't snap inside the threaded hole), to check if the thread was in good condition I inserted one of the old bolts with the threads chased with a thread chaser, it bolted on right and without effort with hand force, well, continued to install the plate, started to torque the bolts in a cross pattern increasing the torque each step, all of the bolts were to torque spec but the one in question, which snapped far too easily, maybe it could have been from the broken bolt (its weird since the broken one screwed out really easy with some wd 40 and a plier).

I was really angry since this issue in USA isn't a big one whereas in Europe it is since its hard to find helicoil inserts for bolts in inches, got a helicoil set from a UK store and got it fixed.

Today:

I'm finishing the install of the FM 107 kit at my bike, got the heads up and torqued and proceeded to finish the top end of the front cylinder, started to torque down the rocker arm plate, same procedure as before, and guess.. THE RIGHT BOLT HEAD THREADS SNAPPED, the brother of the previously snapped bolt also snapped, but this time instead of breaking it down in two pieces the head threads were screwed, seriously.

Either I've got a bad head casting or I'm doing something wrong, the holes were all clean (blowed with compressed air) and the screw was clean, just like the bolt threads, yet that damm betch snapped.

Tomorrow i'll helicoil it too (thank god that its a the pushrod side and I've got enough clearance to use my drill without removing the head) but honestly, this is starting to become funny.

I am doomed or as I said, am I doing something wrong?

 

They are only 18-22 ft lbs (24.4-29.8Nm) but before you get to torque, 1/4 turn only on each in proper order till they bottom ...You doing that?

 

Yup, I followed the manual line per line (I usually do to avoid this kind of things, meh)

 

Might want to get you another or have your torque wrench checked. I seldom use a torque wrench on maintenance cover since I think repeatedly torquing in aluminum threads will take the thread out but on engine assembly, like you I do for sure.. Also, at the level of 22 lbs, you need a 3/8 torque wrench in the lower range but most are then inch lbs. They must have stretched the original bolts and they all need replaced or your wrench is defective. A little tug is 22 ft lbs for me or 264 in lbs. It took a whole lot more then 22 ft lbs to pull the aluminum threads out if the were OK to start.

 

I have other two torque wrenches and just to be sure I did several torque checks with the one I use the most and they all were aprox in the same range, so the wrench is okay.

This one snapped before I could even apply 12 Nm to it, def the threads were damaged, maybe on dissasembly

 

you broke a 5/16 bolt or a 1/4 bolt? if you torqued a 1/4 bolt to 22 #`s,no wonder why it broke.their torqued to INCH #`s,not foot pounds.if you broke a 5/16 bolt,jeez,you should have thought something wasn't right (surprised you didn't pull the threads out of the head)

 

5/16, the four bolts that holds the plate, not the smaller that holds the breather.

Usually i don't follow ft lbs or in lbs numbers but Nm numbers, so no confusión on that side.

This is not the first time i've wrenching, i've assembled and dissasembled other bikes in the past without problems, is just that this thing is too weird to me.

 

Are you by any chance using an adapter on the torque wrench? If so it has to be at 90 degrees to the wrench, not inline with it. Using one incorrectly caused another member here to snap his bolts also.

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surprised it didn't pull the threads before it broke,

 

Nope, I can torque all the plate bolts just fine without the need for an adapter, besides, i was already aware of the 90 degree trick.

BTW: Related with your rockouts, since I was pulling the plates out I installed also your rockout lockers, on a rocker plate they fit just fine however in the other one i stripped one of them, something interesting is that the plate where they did fit just fine is a new plate whereas the plate where they didn't was an old plate, something I noticed when I changed the plate to the new one was that the tolerances were bigger, you can't move the rocker arm shaft easily on the old one while in the new one is really easy to rotate it, maybe you designed them for the newer plate tolerances?

Yeah, same, probably the bolt was shot.

Anyway, i helicoil'd the thread today and installed the plate just fine, did the same in the rear head without any threads stripping.

Im pretty sure that the casting was weak on that side, I don't see any other explanation for it.